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Biosynthesis, function and metabolic engineering of plant volatile organic compounds
New Phytologist
Abstract
1 I. 1 II. 7 III. 8 IV. 10 V. 12 13 References 13 SUMMARY: Plants synthesize an amazing diversity of volatile organic compounds (VOCs) that facilitate interactions with their environment, from attracting pollinators and seed dispersers to protecting themselves from pathogens, parasites and herbivores. Recent progress in -omics technologies resulted in the isolation of genes encoding enzymes responsible for the biosynthesis of many volatiles and contributed to our understanding of regulatory mechanisms involved in VOC formation. In this review, we largely focus on the biosynthesis and regulation of plant volatiles, the involvement of floral volatiles in plant reproduction as well as their contribution to plant biodiversity and applications in agriculture via crop-pollinator interactions. In addition, metabolic engineering approaches for both the improvement of plant defense and pollinator attraction are discussed in light of methodological constraints and ecological complications that limit the transition of crops with modified volatile profiles from research laboratories to real-world implementation.
... In the aroma of fruits, VOCs with specific qualitative and quantitative patterns act independently of each other and co-operate with each other to produce a broad range of aromas and confer different aroma characteristics on different types of fruits [9]. Studies have shown that tomatoes, watermelon, and lemon typically exhibit an 'herbaceous aroma', a unique odor formed by volatile compounds derived from alcohols, aldehydes, and carotenoids [10,11]. ...
... Plant aroma VOCs are diverse in nature and can be classified into terpenes (Figure 1a), benzene rings (Figure 1b), and fatty acid derivatives based on their structure [9]. Terpenes are the largest class of VOCs and consist of over 550 compounds [14] derived from two common C5 precursor compounds, isopentenyl diphosphate (IPP) and its allyl isomer dimethylallyl diphosphate (DMAPP) [15]. ...
... The current research is relatively clear on the first two stages. Terpenoids are produced in plants by two independent pathways, namely, the mevalonate (MVA) pathway and methylerythritol phosphate (MEP) pathway, both of which involve the C5 precursor IPP and its allyl isomer DMAPP [9]. The mevalonate pathway and the methylerythritol pathway are involved in this pathway but are not completely independent (Figure 2a). ...
Aroma, an important quality characteristic of plant fruits, is produced by volatile organic compounds (VOCs), mainly terpenes, aldehydes, alcohols, esters, ketones, and other secondary metabolites, in plant cells. There are significant differences in the VOC profile of various fruits. The main pathways involved in the synthesis of VOCs are the terpenoid, phenylalanine, and fatty acid biosynthesis pathways, which involve several key enzyme-encoding genes, transcription factors (TFs), and epigenetic factors. This paper reviews the main synthetic pathways of the main volatile components in fruit, summarizes studies on the regulation of aroma formation by key genes and TFs, summarizes the factors affecting the fruit aroma formation, describes relevant studies on the improvement of fruit flavor quality, and finally proposes potential challenges and prospects for future research directions. This study provides a theoretical basis for the further precise control of fruit aroma quality and variety improvement.
... hexanal), amino acid derivatives (e.g. indole) and carotenoid derivatives (Dudareva et al., 2013). The advancement in analytical techniques has made volatile compounds one of the most extensively studied classes of plant secondary metabolites (Pichersky & Gershenzon, 2002). ...
... In terms of biosynthesis, a total of 15 aroma compounds are plant volatiles: eight compounds could be originating from fatty acids (hexanal, octanal, nonanal, methyl acetate, methyl hexanoate, methyl octanoate, hexanoic acid, 1-octen-3-ol), five from carotenoids (β-cyclocitral, 6-methyl-5-hepten-2-one, isophorone, β-ionone epoxide, dihydroactinidiolide), and two from amino acids (methional and phenethyl alcohol) (Dudareva et al., 2013). The presence of 2-methylpropanal, methylbutanals, furfural, and 2-acetylpyrrrole suggested the Maillard reaction occurred at some stage in the treatment of the samples (Jousse et al., 2002). ...
... Five aroma-active compounds were found to be in common between the two species (as shown in Fig. 2): 2/3-methylbutanal, 1-octen-3-one, 1-octen-3-ol, methional and β-damascenone, and so it may be assumed that these aroma compounds are species-independent. As with GC-MS data previously, NIF-SNIF can also help to speculate that the Maillard reaction, lipid oxidation, beta-carotene degradation, and plant biosynthesis are pathways involved in Shihu flavour generation (Dudareva et al., 2013). In our case, there are reactions and therefore precursors (e. g. sugars, amino acids, pigments) in common between DO and DN. ...
Dendrobium orchid stems (Chinese name Shihu) are becoming popular ingredients in food and drinks such as wine, teas and desserts, however, its aroma chemistry is not currently understood. Gas Chromatography-Mass Spectrometry (GC-MS) and Gas Chromatography-Olfactometry (GC-O) were used to analyse two Dendrobium species. The Nasal Impact Frequency-Surface of Nasal Impact Frequency (NIF-SNIF) method was employed on thirteen untrained panellists using a newly built open-source software ("nif-simple"). An expert annotated odour descriptions and intensities of NIF-SNIF peaks. Twenty-four volatile aroma compounds were found using GC-MS, with 22 shared compounds and 17 reported for the first time. GC-O NIF-SNIF indicated nine aroma compounds were aroma-active in D. nobile and D. officinale. Five were found in both species suggesting that they are species-independent markers. Aroma-active compounds were characterised as brown, mushroom, metallic, nutty and potato aromas. Methional (NIF 83 %) and 1-octen-3-one (NIF 81 %) were most frequently detected in D. nobile and D. officinale respectively, and this study proposed aroma formation mechanisms in dried Dendrobium stems. Modified Frequencies demonstrated that NIF-SNIF is an effective GC-O method for identifying key aroma-active compounds. Understanding the flavour properties of Shihu could enhance its global appeal and encourage NIF-SNIF to be used in future studies.
... The realm of plant fragrances, a complex interplay of volatile organic compounds (VOCs), is dominated by terpenoids, notable for their structural diversity and significant contributions to floral aroma profiles (Dudareva et al. 2013). Curcuma alismatifolia, also known as the Siam Tulip or 'Shadow', is celebrated not just for its visually striking flowers but also for its unique fragrance, making it a subject of both commercial interest and scientific inquiry (Brown and Patel 2019). ...
... We found that the main volatile compounds released by 'Shadow' were monoterpenes and sesquiterpenes, mainly including linalool, caryophyllene, nerolidol, α-pinene, α-humulene, β-farnesene, and β-myrcene (Table 2), similar to the findings in other Zingiberaceae species, such as Hedychium coronarium (Yue et al. 2015) and C. alismatifolia 'Chiang Mai Pink' (Liao et al. 2022), with the main volatile components being monoterpenes and sesquiterpenes. In plants, the emission of volatile compounds is spatiotemporally regulated (Dudareva et al. 2013), a majority of floral scents usually occurs in a flower-specific, and the emission levels regulate with flower development. In H. coronarium, the flower is a source of floral volatile compounds, and floral scent emission increased as flower buds approach the full blooming stages (Yue et al. 2015). ...
Main conclusion
CaTPS2 and CaTPS3 were significantly expressed in flowers of Curcuma alismatifolia ‘Shadow’ and demonstrated bifunctional enzyme activity, CaTPS2 generated linalool and nerolidol as products, and CaTPS3 catalyzed β-myrcene and β-farnesene formation.
Abstractsss
This study presents the discovery and functional characterization of floral terpene synthase (TPS) genes in Curcuma alismatifolia ‘Shadow’, a cultivar renowned for its unique fragrance. Addressing the gap in understanding the genetic basis of floral scent in this species, we identified eight TPS genes through comprehensive transcriptome sequencing. Among these, CaTPS2 and CaTPS3 were significantly expressed in floral tissues and demonstrated bifunctional enzyme activity corresponding to the major volatile compounds detected in ‘Shadow’. Functional analyses, including in vitro assays complemented with rigorous controls and alternative identification methods, elucidated the roles of these TPS genes in terpenoid biosynthesis. In vitro studies were conducted via heterologous expression in E. coli, followed by purification of the recombinant protein using affinity chromatography, enzyme assays were performed with GPP/FPP as the substrate, and volatile products were inserted into the GC–MS for analysis. Partially purified recombinant protein of CaTPS2 catalyzed GPP and FPP to produce linalool and nerolidol, respectively, while partially purified recombinant protein of CaTPS3 generated β-myrcene and β-farnesene with GPP and FPP as substrates, respectively. Real-time quantitative PCR further validated the expression patterns of these genes, correlating with terpenoid accumulation in different plant tissues. Our findings illuminate the molecular mechanisms underpinning floral fragrance in C. alismatifolia and provide a foundation for future genetic enhancements of floral scent in ornamental plants. This study, therefore, contributes to the broader understanding of terpenoid biosynthesis in plant fragrances, paving the way for biotechnological applications in horticulture plant breeding.
... Terpenoids, phenylpropanoids/benzenoids, and fatty acid derivatives originate from divergent biosynthetic routes, and they largely constitute the floral scent of ornamental plants [1]. As the leading class of floral volatile compounds, terpenoids are derived from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), which are two common and interchangeable precursors [2]. ...
... Benzenoids/phenylpropanoids are the second most abundant family of plant volatile compounds [11]. Benzenoids/phenylpropanoids are exclusively derived from the aromatic amino acid phenylalanine (L-Phe), which is synthesized via either shikimate or arogenate plastidial pathways [12], a seven-and a three-multistep enzymatic process [1]. Phenylalanine ammonialyase (PAL) catalyzes L-Phe into cinnamic acid and represents the first committed step in benzenoid (C 6 -C 1 ) and phenylpropene (C 6 -C 3 ) biosynthesis [13]. ...
Floral scent is an essential and genetically complex trait in herbaceous peonies (Paeonia lactiflora Pall.); however, specific genes related to metabolic and regulatory networks remain scantily studied. Our study integrated metabolite profiling and RNA-sequencing to screen floral scent biosynthetic genes. Hence, the major molecules identified by headspace collection combined with cultivar-specific GC-MS analysis were geraniol, β-caryophyllene, 2-phenylethanol (2-PE), citronellol, and 1,8-cineole. Genes related to terpenoids and 2-PE biosynthesis were identified after the assembly and annotation of the P. lactiflora transcriptomes. Eight angiosperm-specific terpene synthases (TPSs) from the TPS-a and TPS-b clades, as well as enzymes linked to 2-PE synthesis such as aromatic amino acid decarboxylase (AADC), phenylacetaldehyde reductase (PAR), and geranial reductase (GER) were identified. The biochemical analysis of the enzymes encoded by PlPAR1 and PlGER1 generated 2-PE from phenylacetaldehyde (PAld). The pairwise alignment of AADC1 reveals a splice variant lacking a 124 bp fragment, thus highlighting the possible role of alternative splicing in modulating floral scent composition. This study offers insights into the molecular-level biosynthesis of terpenoids and 2-PE in Peonia taxa, and provides the basis for the functional characterization, breeding, and bioengineering of prospective candidate genes for the production of floral volatiles in the Paeonia genus.
... The enrichment of F6M and CGM DEGs from the Kyoto Encyclopedia of Genes and Genomes (KEGG) showed that the α-linolenic acid (ALA) metabolism pathway and plant hormone signal transduction play different roles in aroma accumulation regulation in different tea varieties ( Figure S4). ALA, one type of important plant phytohormone, is the main synthetic pathway of JAs, and can regulate the biosynthesis of volatiles and act as an upstream signal in plants like tea [30]. ...
... Horticulturae 2024, 10, x FOR PEER REVIEW 9 of 16 the main synthetic pathway of JAs, and can regulate the biosynthesis of volatiles and act as an upstream signal in plants like tea [30]. The contents of more than fifty important plant hormones have been investigated, including those of JAs, ABAs (abscisic acids), auxins, CKs (cytokinins), ETHs (ethylenes), GAs (gibberellins), and SAs (salicylic acids) (Table S4). ...
Aroma is an important factor in the measurement of the quality and market value of oolong tea. However, it is hard to develop an oolong tea with good aroma quality using unsuitable tea varieties. To explore the key factors of tea varieties in the formation of oolong tea aromas, the fresh leaves of the Chungui variety (CG, suitable for oolong tea, Camellia sinensis (L.) O. Kuntze) and the Fuyun No. 6 variety (F6, unsuitable for oolong tea, Camellia sinensis (L.) O. Kuntze) were harvested and treated by withering and mechanical stress in order. Then, aroma, transcriptome, and jasmonate (JA) contents, and weighted gene co-expression network analysis (WGCNA), of samples were investigated. The contents of characteristic oolong tea aromas, including indole, (E)-β-ocimene, (E)-nerolidol, α-farnesene, and jasmine lactone, were all accumulated in much higher quantities in the CG variety after withering and mechanical stress. Accordingly, the coding genes of aroma formation synthases TSB2, OCS, NES, AFS, and LOX1, and related genes in MVA, MEP, and ALA pathways, were all much more highly activated. These differential reactions are mainly caused by the higher accumulation of jasmonates, especially methyl jasmonate, a type of important plant signal chemical, in CG after mechanical stress. WGCNA analysis indicated 34 different transcription factors from different families are predicted to be involved in this jasmonate-responsive reaction.
... Although these substances are generally present, their concentration increases after an insect attack [17]. Several studies have also confirmed the induction of phenolic glycosides after an insect attack [15,[18][19][20]. The induction of phenolics in trees depends on several factors, including the specific tree species, its genotype, and the species of insect herbivore responsible for the attack [17]. ...
... Plants, and especially trees, are the largest source of volatile organic compounds (VOCs) worldwide, both in stressed and non-stressed conditions [19,21]. These compounds are important in plant-insect (including pollinators) or plant-plant communication [22][23][24][25][26][27][28]. ...
The main biochemical traits were estimated in poplar leaves under biotic attack (aphids and spongy moth infestation). Changes in the abundance of bioactive compounds in genetically uniform individuals of European aspen (Populus tremula), such as proline, polyphenolic compounds, chlorophylls a and b, and volatile compounds, were determined between leaves damaged by sucking insects (aphid—Chaitophorus nassonowi) and chewing insects (spongy moth—Lymantria dispar) compared to uninfected leaves. Among the nine analyzed phenolic compounds, only catechin and procyanidin showed significant differences between the control leaves and leaves affected by spongy moths or aphids. GC-TOF-MS volatile metabolome analysis showed the clear separation of the control versus aphids-infested and moth-infested leaves. In total, the compounds that proved to have the highest explanatory power for aphid-infested leaves were 3-hexenal and 5-methyl-2-furanone, and for moth-infested leaves, trans-α-farnesene and 4-cyanocyclohexane. The aphid-infested leaves contained around half the amount of chlorophylls and twice the amount of proline compared to uninfected leaves, and these results evidenced that aphids influence plant physiology more than chewing insects.
... TPS protein family members are capable of synthesizing monoterpenoids, sesquiterpenoids, diterpenoids, triterpenoids, tetraterpenoids, and their derivatives using products from the MVA and MEP pathways as substrates [35,45], while cytochrome P450 catalyzes the conversion of terpenes to resin acids [46,47]. In angiosperms, numerous studies in angiosperms have shown that TPS genes can be induced by biotic and abiotic stresses and promote terpenoid synthesis [48][49][50], including Arabidopsis [51], rice [52], and Gossypium barbadense [53]. Terpenoids produced under stress are mostly volatile organic compounds, which can act as pheromones against external organisms or transmit stress signals to the whole plant, thereby inducing other defense responses [48][49][50]. ...
... In angiosperms, numerous studies in angiosperms have shown that TPS genes can be induced by biotic and abiotic stresses and promote terpenoid synthesis [48][49][50], including Arabidopsis [51], rice [52], and Gossypium barbadense [53]. Terpenoids produced under stress are mostly volatile organic compounds, which can act as pheromones against external organisms or transmit stress signals to the whole plant, thereby inducing other defense responses [48][49][50]. Conifers have evolved specific defensive traits and strategies that have contributed to their evolutionary diversification and colonization success [54]. The defensive system of Pinaceae, a family that includes pines (Pinus) and spruces (Picea) among other tree species, relies heavily on resin, a mixture of diterpenes, sesquiterpenes, and monoterpenes that are toxic to herbivores and pathogens [55,56]. ...
Background
Drought stress severely impedes plant growth, and only a limited number of species exhibit long-term resistance to such conditions. Pinus sylvestris var. mongolica, a dominant tree species in arid and semi-arid regions of China, exhibits strong drought resistance and plays a crucial role in the local ecosystem. However, the molecular mechanisms underlying this resistance remain poorly understood.
Results
Here, we conducted transcriptome sequence and physiological indicators analysis of needle samples during drought treatment and rehydration stages. De-novo assembly yielded approximately 114,152 unigenes with an N50 length of 1,363 bp. We identified 6,506 differentially expressed genes (DEGs), with the majority being concentrated in the heavy drought stage (4,529 DEGs). Functional annotation revealed enrichment of drought-related GO terms such as response to water (GO:0009415: enriched 108 genes) and response to water deprivation (GO:0009414: enriched 106 genes), as well as KEGG categories including MAPK signaling pathway (K04733: enriched 35 genes) and monoterpenoid biosynthesis (K21374: enriched 27 genes). Multiple transcription factor families and functional protein families were differentially expressed during drought treatment. Co-expression network analysis identified a potential drought regulatory network between cytochrome P450 genes (Unigene4122_c1_g1) and a core regulatory transcription factor Unigene9098_c3_g1 (PsNAC1) with highly significant expression differences. We validated PsNAC1 overexpression in Arabidopsis and demonstrated enhanced drought resistance.
Conclusions
These findings provide insight into the molecular basis of drought resistance in P. sylvestris var. mongolica and lay the foundation for further exploration of its regulatory network.
... Terpenoids play important roles in plant physiology and biochemistry, such as photosynthesis, electron transfer, and developmental regulation [4]. The role of plant terpenes is crucial in luring insect pollinators, defending plants, facilitating plant-to-plant interactions, and mediating interactions across diverse ecological environments[ [5,6]]. Terpenoids are categorized into primary and secondary metabolites, depending on their roles in plants. ...
... The family is divided into eight subfamilies based on the phylogenetic relationships of the TPS gene family in plants: TPS-a, TPS-b, TPS-c, TPS-d (gymnosperm endemic), TPS-e, TPS-f, TPS-g, and TPS-h (Selaginella endemic) [ [19][20][21]]. To adapt to special ecological niches, such as attracting pollinators, spreading seeds, combating pathogens, and preventing consumption by herbivores[ [5,6,22,23]],terpenoids in plants have undergone lineage-specific evolution, with varying degrees of expansion and variation in various subfamilies[ [24,25]]. In dicotyledons and monocotyledons: TPS-a encodes sesquiterpene synthase; TPS-b, unique to angiosperms, produces a monoterpene synthase featuring the R (R)X8W motif, facilitating isomerization cyclization processes; TPS-c is a member of an ancient evolutionary branch and catalyzes cobaltyl pyrophosphate synthase; TPS-d, unique to gymnosperms, serves multiple roles, including the encoding of diterpene, monoterpene, and sesquiterpene synthases; TPS-e/f codes for cobaltyl pyrophosphate/kaurene synthase, which are key enzymes in the production of gibberellic acid; TPS-g possesses angiosperm-specific characteristics, yet it produces a monoterpene synthase devoid of the R (R)X8W motif; TPS-h is exclusively found in Selaginella. ...
Terpene synthases (TPSs) regulate plant growth, development, and stress response. TPS genes have been identified in Arabidopsis thaliana and Zea mays. Cannabis sativa TPS genes were identified and analyzed using bioinformatics. Genomic data were downloaded from Plant Transcription Factor Database and National Center for Biotechnology Information database, and TPS genes were predicted, analyzed, and visualized using ExPASy, PlantCare, and other online websites along with TBtools, MEGA software, and other software. To verify its role, quantitative real-time polymerase chain reaction (qRT-PCR) tests were conducted. The Cannabis sativa TPS family comprises 41 elements distributed over 8 chromosomes and a single scaffold segment. The isoelectric point varied between 4.96 and 7.03, while the molecular weight spanned from 20705.90 to 102324.64 Da. The majority of genes were found in the cytoplasm and chloroplasts, with the remainder situated in the peroxisome, nucleus, plasma membrane, and mitochondria. Several cis-acting components associated with stress response were present in the gene's upstream promoter region. Data from RNA sequencing and qRT-PCR revealed specific expression of TPS genes in all five organs of female Cannabis sativa plants. Collinearity analysis showed 4 homologous gene pairs between the Cannabis sativa and Arabidopsis thaliana, with many pairs of homologous genes in other species, which was consistent with the dicotyledons evolutionary relationship. Furthermore, some genes may participate in Cannabis sativa growth and development and play a role in secondary metabolite synthesis. Therefore, bioinformatics analysis of the Cannabis sativa TPS gene family provides a theoretical basis for future research on the volatile terpene compounds of Cannabis sativa.
... Based on their biosynthetic origin, all volatiles are divided into several classes, including terpenoids, phenylpropanoids/benzenoids, FA derivatives and amino acid derivatives in addition to a few species-/genus-specific compounds not represented in those major classes. Terpenoid volatiles are synthesized by the cytosolic MVA and the plastidial MEP/DoXP pathways, the former giving rise to sesquiterpenes, irregular terpenes and geranyllinalool, and the latter to monoterpenes, hemiterpenes, diterpenes and volatile carotenoid derivatives (apocarotenoids) [46]. ...
Limited research has been conducted on the metabolites present in the essential oils (EOs) of Phlomoides rotata (Benth. ex Hook. f.) Mathiesen (PR, syn. Lamiophlomis rotata (Benth.) Kudô), and their potential pharmacological activities, such as antioxidant properties, are often overlooked. We conducted a metabolomics-based screening to identify the characteristic metabolites (CMs) in the EOs extracted from PR. Meanwhile, we evaluated their in vitro antioxidant activities (AOAs). The EOs obtained through hydro-distillation are characterized by a light yellow color and a fresh, elegant fragrance. Cryoprecipitation was used to separate the crystals (Crs) from the EOs, resulting in the crystal-free EOs (CFs). A total of 121 components are identified and quantified in the EOs, Crs, and CFs. Among them, 84 were reported for the first time from such EOs. The major compounds include long-chain fatty acids (LCFAs) and their esters, such as palmitic acid (PA), myristic acid (MA), linoleic acid (LA), oleic acid (OA), stearic acid, and methyl palmitate (MP). Furthermore, 11 kinds of apocarotenoids (also called norisoprenoids) were first systematically investigated. Among them, eight C13-norisoprenoids, with trans-β-damascenone (DN) being particularly notable for its flavor, were identified. A sum of 11 CMs are screened , including PA, MA, LA, OA, MP, hexahydrofarnesyl acetone, phytol (PT), DN, stearic acid, linalool, and hexanal. These CMs are biosynthesized through FAs and 2-C-Methyl-D-erythritol 4-phosphate/1-Deoxy-D-xylulose 5-phosphate pathways. The in vitro AOAs of EOs, Crs, CFs, and seven selected CMs (PA, MA, LA, OA, MP, PT, and DN) were evaluated. Generally, PA and MA exhibited pro-oxidant activities (POAs) or weak AOAs. LA and OA demonstrated POAs or weak AOAs at lower concentrations, but at higher concentrations, they displayed medium to strong AOAs. Importantly, the CFs typically exhibited stronger AOAs compared to the corresponding EOs and Crs, potentially due to variations in their PA content. Overall, this study provides valuable insights into the potential utilization of EOs from PR.
... Notably, enzyme 182 promiscuity has led to regulatory considerations, such as those outlined in the Cannabis Act by 183 Health Canada and within the United States for classification of hemp cultivars (Cox, 2018). (Dudareva et al., 2013). 219 Terpenoids, among PVs, stand out as the most significant and abundant chemical group. ...
... ground defence against herbivores, the attraction of pollinators and seed dispersers, protection against pathogens, and plant-plant signalling (Dudareva et al., 2013). ...
Plants synthesise a vast array of volatile organic compounds (VOCs), which serve as chemical defence and communication agents in their interactions with insect herbivores. Although nitrogen (N) is a critical resource in the production of plant metabolites, its regulatory effects on defensive VOCs remain largely unknown. Here, we investigated the effect of N content in tomato ( Solanum lycopersicum ) on the tobacco cutworm ( Spodoptera litura ), a notorious agricultural pest, using biochemical and molecular experiments in combination with insect behavioural and performance analyses. We observed that on tomato leaves with different N contents, S. litura showed distinct feeding preference and growth and developmental performance. Particularly, metabolomics profiling revealed that limited N availability conferred resistance upon tomato plants to S. litura is likely associated with the biosynthesis and emission of the volatile metabolite α‐humulene as a repellent. Moreover, exogenous application of α‐humulene on tomato leaves elicited a significant repellent response against herbivores. Thus, our findings unravel the key factors involved in N‐mediated plant defence against insect herbivores and pave the way for innovation of N management to improve the plant defence responses to facilitate pest control strategies within agroecosystems.
... In plants, volatile bundles are formed on a few pathways: shikimate/phenylalanine, lipoxygenase (LOX), mevalonate (MVA), and 2-C-methyl-d-erythritol 4-phosphate (MEP) [32,33]. The influence of chemical compounds and phytohormones on the biosynthesis of volatile compounds in plants has previously been widely studied [34][35][36]. ...
Coleus scutellarioides (L.) Benth. is a globally spread species, known for its characteristic spectacularly colorful leaves of decorative value. Thanks to its rich chemical composition, the plant is used in ethnopharmacology, and it is also regarded as having high medicinal potential. The application of in vitro cultures enables the acquisition of homogeneous certified material of high quality. Additionally, excluding the effect of biotic and abiotic factors on the plants is a way to fully recognize the influence of phytohormones on the plant morphology and the biosynthetic pathways of compound production. The best way to grow C. scutellarioides “Electric Lime” under in vitro conditions is to use the basic MS medium (Murashige and Skoog medium), enriched with naphthyl-1-acetic acid at a concentration of 0.5 mg dm−3. The analysis of volatile compounds demonstrated that the content of volatile compounds in the plants cultivated under in vivo conditions was expressed at a level of 2848.59 µg g−1, whereas in the plants bred in vitro without supplementation with phytohormones, the level was 8191.47 µg g−1. The highest content was noted for copaene, α-pinene, 1-octene-3-ol, α-selinene, sabinen, γ- and δ-cadinene, 3-octanol, and β-pinene. Aroma profiling revealed a lack of boranyl acetate, 2-hexenal, and 2-hexen-1-ol in the plants cultivated under in vivo conditions. Differences were found in the volatile composition between plants bred in vivo and in vitro, with the most significant recorded for the contents of 1-octen-3-ol and 3-octanol. The addition of plant growth regulators into the basic medium under in vitro conditions affected the percentage ratio and contents of specific compounds in plant tissues. The most intense biosynthesis of volatile compounds took place in the plants cultivated on the medium enriched with NAA at 10,579.11 µg g−1, whereas the least intense was noted for plants cultivated on the medium supplemented with BA, where it was recorded at the level of 5610.02 µg g−1. So far, there has been no research published which would pertain to the profiling of volatile compounds performed using the SPME (solid-phase microextraction) technique. Moreover, the very few studies conducted on the chemical composition of these compounds do not mention the specific variety of C. scutellarioides under analysis.
... A unique smell of these plants is due the present of monoterpenes and other constituents of essential oils (Isman, 2000). In addition to attract pollinators and seed dispersers, they defend aromatic and herbal plants from biotic and abiotic stressors (Raguso, 2008;Dudareva et al., 2013). Although monoterpenes have been described as one of the most powerful botanical insecticides they considered as safe and biodegradable products with low risk to mammals and the ecosystem (Isman, 2006). ...
The insecticidal activity of ten monoterpenes against larvae of Musca domestica (Diptera: Muscidae) was evaluated. Monoterpenes were mixed with food-media at concentrations of 2.5, 5.0, 10.0, 25.0, 50.0, 75.0 and 100.0 mg/kg. Three monoterpenes, p-cymene, 1,8-cineole and cuminaldehyde displayed a durable larvicidal activity with LC50 values of 0.14, 1.59 and 1.90 mg/kg 3 days post treatment. The three monoterpenes were more toxic than deltamethrin (LC50 = 3.36 mg/kg). Likewise, monoterpenes induced a significant reduction in pupation and adult emergence. Cuminaldehyde at 25.0 mg/kg, and p-cymene, 1,8-cineole and citronellal at 50.0 mg/kg caused a complete inhibition of pupation and adult emergence. Also, p-cymene at 25.0 mg/kg reduced the activity of larval amylase and lipase, while 1,8-cineole and cuminaldehyde increased their activity. Cuminaldehyde and α-terpinene inhibited the activity of proteases whereas p-cymene enhanced their activity. In the case of acetylcholinesterase, general-esterase and adenosinetriphosphatase, p-cymene and 1,8-cineole induced enzyme inhibition and citronellal reduced enzyme activities. Finally, the tested monoterpenes caused histological changes on treated larvae, such as the basement membrane appeared and the epithelium cells deformed in some points and seen filled with scattered vacuoles. These findings indicate that the tested monoterpenes have a potential to be applied in IPM programs of M. domestica.
... It can be seen that withering affects RGT's quality, but the effect of green-making on RGT's quality is the most significant. Studies have shown that the biosynthesis and release of volatile organic compounds (VOCs) in plants are related to self-defense in the face of biotic and abiotic stresses [12]. Green-making causes the continuous mechanical injury and dehydration of the fresh tea leaves, which induces the transformation and release of volatile organic compounds under traumatic stress. ...
Rougui Tea (RGT) is a typical Wuyi Rock Tea (WRT) that is favored by consumers for its rich taste and varied aroma. The aroma of RGT is greatly affected by the process of green-making, but its mechanism is not clear. Therefore, in this study, fresh leaves of RGT in spring were picked, and green-making (including shaking and spreading) and spreading (unshaken) were, respectively, applied after sun withering. Then, they were analyzed by GC-TOF-MS, which showed that the abundance of volatile compounds with flowery and fruity aromas, such as nerolidol, jasmine lactone, jasmone, indole, hexyl hexanoate, (E)-3-hexenyl butyrate and 1-hexyl acetate, in green-making leaves, was significantly higher than that in spreading leaves. Transcriptomic and proteomic studies showed that long-term mechanical injury and dehydration could activate the upregulated expression of genes related to the formation pathways of the aroma, but the regulation of protein expression was not completely consistent. Mechanical injury in the process of green-making was more conducive to the positive regulation of the allene oxide synthase (AOS) branch of the α-linolenic acid metabolism pathway, followed by the mevalonate (MVA) pathway of terpenoid backbone biosynthesis, thus promoting the synthesis of jasmonic acid derivatives and sesquiterpene products. Protein interaction analysis revealed that the key proteins of the synthesis pathway of jasmonic acid derivatives were acyl-CoA oxidase (ACX), enoyl-CoA hydratase (MFP2), OPC-8:0 CoA ligase 1 (OPCL1) and so on. This study provides a theoretical basis for the further explanation of the formation mechanism of the aroma substances in WRT during the manufacturing process.
... The higher species richness of airborne bacterial communities in the library may be related to the large book collections and bacterial growth in books left standing for long periods of time (29). The low species richness in the meadow may be related to the bactericidal effect of plants (30,31), while the low species richness in classrooms may be related to their regular disinfection during the COVID-19 pandemic. ...
Given the dense population on university campuses, indoor and outdoor airborne bacterial contamination may lead to the rapid spread of diseases in a university environment. However, there are few studies of the characteristics of airborne and pathogenic bacterial communities in different sites on a university campus. In this study, we collected particulate matter samples from indoor and outdoor locations at a university in Bengbu City, Anhui Province, China, and analyzed the community characteristics of airborne and pathogenic bacteria using a high-throughput sequencing technique. The results showed that the composition of the dominant airborne and pathogenic bacterial communities was consistent among sites at the phylum and genus levels, with differences in their relative abundance. There were significant differences in the structure of the airborne and pathogenic bacterial communities between indoor and outdoor sites (p < 0.05). An analysis of similarities (ANOSIM) indicated that the structure of airborne bacterial communities in indoor sites was influenced by the room occupancy rate, ventilation conditions, and the extent of indoor furnishing (p < 0.05), while the structure of pathogenic bacterial communities was influenced by the number of individuals and spatial dimensions (p < 0.05). The impact of particle size on the structure of airborne and pathogenic bacterial communities was relatively minor. A total of 194 suspected pathogenic bacterial species were identified, accounting for 0.0001–1.3923% of the total airborne bacteria, all of which were conditional pathogens. Among them, Saccharopolyspora rectivirgula, Acinetobacter johnsonii, and Moraxella osloensis exhibited relatively high relative abundance, accounting for 24.40, 16.22, and 8.66% of the total pathogenic bacteria, respectively. Moreover, 18 emerging or re-emerging pathogenic bacterial species with significant implications for human health were identified, although their relative abundance was relatively low (0.5098%). The relative abundance of pathogenic bacteria in indoor environments was significantly higher than outdoors, with the laboratory and dormitory having the highest levels. The findings of this study provide valuable guidance for the prevention and control of airborne bacterial contamination and the associated health risks in both a campus environment and other public spaces with high occupancy rates.
... The biosynthetic pathways of cannabinoids and terpenoids share a common precursor, isopentenyl pyrophosphate (IPP). IPP is synthesized either via the mevalonic acid pathway in the cytosol (MVA) or the plastidial methylerythritol pathway (MEP) [72,73]. The MEP pathway is posited to play a crucial role in the synthesis of cannabinoid-terpenoid compounds [74]. ...
The global cannabis market is continuously expanding and as a result, the cannabis industry demands new and improved agronomic cultivation practices to increase production efficiency of cannabidiol (CBD), which is valued for its therapeutic benefits. This study investigates the influence of three rootstock types on the survival rate, morphological parameters, and biochemical composition of cannabis: potentially dwarfing rootstocks (PDR), potentially vigorous rootstocks (PVR), and seedlings-as-rootstocks (SAR). Rootstocks were used for grafting two scion genotypes: ‘ScionII’ = chemotype II of industrial hemp, and ‘ScionIII’ = chemotype III of high CBD accumulating variety. Contrary to expectations, PVR and SAR did not outperform PDR on most of the measured variables. SAR showed the highest survival rate of the grafted cannabis plants (40–70%). The rootstock type had a statistically significant influence only on the bud compactness index in ‘ScionII’, with PDR being particularly noticeable. A comparative analysis of the ‘rootstock/scion’ combinations with their controls (non-grafted scions) revealed grafting’s substantial improvement in most traits. Specifically, PDR increased CBD content by 27% in ‘ScionIII’, inflorescence yield and CBD yield per plant increased by 71% and 84%, respectively, when SAR was used in ‘ScionII’. SAR showed to be the most effective rootstock type for CBD production. Our findings suggest grafting as a promising technique for optimizing cannabis’s agronomic and medicinal potential, highlighting the necessity for further research on its underlying mechanisms to refine production efficiency and quality.
... Recently, empirical biochemical and transcriptomic data generated on tomato plants infested with T. absoluta revealed a decrease in the levels of total phenols, salicylic acid, amino acids, and jasmonic acid . Shikimic acid-derived phenylpropanoids are specialized metabolites produced from aromatic amino acids, phenylalanine (Phe) and tyrosine (Dudareva et al., 2013;Maeda & Dudareva, 2012). Recently, we have shown that plants can efficiently uptake and metabolize externally supplied Phe, and produce enhanced levels of specific Phe-derived phenylpropanoids in a variety of plants and plant organs (such as branches, leaves, flowers, and fruits) either intact or detached (Kumar et al., , 2021Oliva et al., 2020). ...
Tuta absoluta (“leafminer”), is a major pest of tomato crops worldwide. Controlling this insect is difficult due to its efficient infestation, rapid proliferation, and resilience to changing weather conditions. Furthermore, chemical pesticides have only a short‐term effect due to rapid development of T. absoluta strains. Here, we show that a variety of tomato cultivars, treated with external phenylalanine solutions exhibit high resistance to T. absoluta , under both greenhouse and open field conditions, at different locations. A large‐scale metabolomic study revealed that tomato leaves absorb and metabolize externally given Phe efficiently, resulting in a change in their volatile profile, and repellence of T. absoluta moths. The change in the volatile profile is due to an increase in three phenylalanine‐derived benzenoid phenylpropanoid volatiles (BPVs), benzaldehyde, phenylacetaldehyde, and 2‐phenylethanol. This treatment had no effect on terpenes and green leaf volatiles, known to contribute to the fight against insects. Phe‐treated plants also increased the resistance of neighboring non‐treated plants. RNAseq analysis of the neighboring non‐treated plants revealed an exclusive upregulation of genes, with enrichment of genes related to the plant immune response system. Exposure of tomato plants to either benzaldehyde, phenylacetaldehyde, or 2‐phenylethanol, resulted in induction of genes related to the plant immune system that were also induced due to neighboring Phe‐treated plants. We suggest a novel role of phenylalanine‐derived BPVs as mediators of plant–insect interactions, acting as inducers of the plant defense mechanisms.
... Sensory-focused studies are therefore now needed to define aroma transfer mechanisms from roasted beans to the coffee beverage and to establish the threshold perception levels for all coffee aroma compounds. Terpene synthesis is known to be under the control of both developmental and environmental cues [70]. In this study, transcriptome comparison between the yellow and red stages of ripening beans (last two stages of ripening) revealed few differentially expressed genes (DEGs). ...
Background
The fruity aromatic bouquet of coffee has attracted recent interest to differentiate high value market produce as specialty coffee. Although the volatile compounds present in green and roasted coffee beans have been extensively described, no study has yet linked varietal molecular differences to the greater abundance of specific substances and support the aroma specificity of specialty coffees.
Results
This study compared four Arabica genotypes including one, Geisha Especial, suggested to generate specialty coffee. Formal sensory evaluations of coffee beverages stressed the importance of coffee genotype in aroma perception and that Geisha Especial-made coffee stood out by having fine fruity, and floral, aromas and a more balanced acidity. Comparative SPME–GC–MS analyses of green and roasted bean volatile compounds indicated that those of Geisha Especial differed by having greater amounts of limonene and 3-methylbutanoic acid in agreement with the coffee cup aroma perception. A search for gene ontology differences of ripening beans transcriptomes of the four varieties revealed that they differed by metabolic processes linked to terpene biosynthesis due to the greater gene expression of prenyl-pyrophosphate biosynthetic genes and terpene synthases. Only one terpene synthase (CaTPS10-like) had an expression pattern that paralleled limonene loss during the final stage of berry ripening and limonene content in the studied four varieties beans. Its functional expression in tobacco leaves confirmed its functioning as a limonene synthase.
Conclusions
Taken together, these data indicate that coffee variety genotypic specificities may influence ripe berry chemotype and final coffee aroma unicity. For the specialty coffee variety Geisha Especial, greater expression of terpene biosynthetic genes including CaTPS10-like, a limonene synthase, resulted in the greater abundance of limonene in green beans, roasted beans and a unique citrus note of the coffee drink.
... Terpenoids are the most common and diverse class of secondary metabolites in plant volatiles; they can be produced by almost all plant organs, including roots, stems, leaves, flowers, fruits, and seeds [1], and they play important roles in the growth and development of plants themselves. Terpenoids have isoprene as their structural unit and mainly include monoterpenes, sesquiterpenes, diterpenes, and triterpenes [2,3]; monoterpenes and sesquiterpene compounds are the main volatile substance components produced by plants. ...
1-deoxy-D-xylulose-5-phosphate synthase (DXS) is a rate-limiting enzyme in terpene synthesis that can affect the accumulation of secondary metabolites in plants. In this study, three DXS gene family members were identified in the tomato genome-wide database. Using bioinformatics methods, we analyzed the gene structure, evolutionary affinities, and cis-acting elements of the SlDXS gene family members. Promoters of SlDXS genes contain plant hormone-responsive elements such as the CGTCA-motif, TGACG-motif, ABRE, TCA-element, TGA-element, ERE, CAT-box, and AACA-motif, which suggested that the SlDXS gene family may play an important role in hormone response. The RT-qPCR analysis showed that the tomato DXS2 gene was able to respond upon exposure to methyl jasmonate (MeJA). The construction of a virus-induced gene silencing (VIGS) vector for the SlDXS gene showed that the SlDXS2 gene was also able to respond to MeJA in silenced plants, but the induction level was lower relative to that of wild-type plants. The SlDXS1 gene is associated with the synthesis of photosynthetic pigments. This study provides a reference for the further elucidation of the DXS gene’s biological function in the terpenoid synthesis pathway in tomatoes.
... To account for 94% of the total identified fraction, benzyl nitrile and 2-nitroethyl benzene were added in almost equal percentages (6.2% and 6.0%, respectively) to the main constituent. The presence of p-dimethoxybenzene in significant amounts has previously been reported in the nectar of male flowers of C. pepo [94,95], and it has been identified as the most attractive compound to specialist squash bee pollinators [96]. Interestingly, the HS-GC-MS analysis of C. moschata fruit reported by [97] revealed 3-methyl butanal to be almost the only compound, with benzaldehyde also present in the flower (0.7%) sample. ...
The growing interest in functional foods is driven by the exploration of new foods with positive health effects. Pleasant sensory features are essential for consumer acceptance. In this work, we investigated the composition of the bioactive compounds, antioxidant activity, and aroma profiles of four edible flowers: Cucurbita moschata Duchesne, Dianthus chinensis L., Fuchsia regia (Vand. ex Vell.) Munz., and Viola cornuta L. For the first time, we quantified the water-soluble group of B vitamins. Significant variations in the content of soluble sugars, vitamins, and secondary metabolites were observed. V. cornuta showed the highest concentration of vitamin C and carotenoids, while C. moschata had the highest content of vitamin B and flavonoids. F. regia stood out for its exceptionally high content of total phenolics, while D. chinensis surpassed the other flowers in soluble sugar content. The aroma profile analysis revealed a diverse array of volatile organic compounds, with each species having its own unique composition. C. moschata was characterized by p-dimethoxybenzene and D. chinensis by non-terpene compounds; F. regia displayed high amounts of decanal and nonanal, while V. cornuta was rich in myrcene and α-farnesene. These findings provide valuable insights into the secondary metabolites and aroma profiles of these flowers, enhancing our understanding of their bioactive compounds and potential health benefits.
... Plants produce a diverse array of volatile organic compounds, which can be categorized into three major classes based on their structures: terpenoids, phenylpropanoids/benzenoids, and fatty acids [134]. Phenylpropanoids/benzenoids are essential components responsible for generating fragrance in plants [135]. ...
Background
Thymus mongolicus (family Lamiaceae) is a Thyme subshrub with strong aroma and remarkable environmental adaptability. Limited genomic information limits the use of this plant.
Results
Chromosome-level 605.2 Mb genome of T. mongolicus was generated, with 96.28% anchored to 12 pseudochromosomes. The repetitive sequences were dominant, accounting for 70.98%, and 32,593 protein-coding genes were predicted. Synteny analysis revealed that Lamiaceae species generally underwent two rounds of whole genome duplication; moreover, species-specific genome duplication was identified. A recent LTR retrotransposon burst and tandem duplication might play important roles in the formation of the Thymus genome. Using comparative genomic analysis, phylogenetic tree of seven Lamiaceae species was constructed, which revealed that Thyme plants evolved recently in the family. Under the phylogenetic framework, we performed functional enrichment analysis of the genes on nodes that contained the most gene duplication events (> 50% support) and of relevant significant expanded gene families. These genes were highly associated with environmental adaptation and biosynthesis of secondary metabolites. Combined transcriptome and metabolome analyses revealed that Peroxidases, Hydroxycinnamoyl-CoA shikimate/quinate hydroxycinnamoyl transferases, and 4-coumarate-CoA ligases genes were the essential regulators of the phenylpropanoid–flavonoid pathway. Their catalytic products (e.g., apigenin, naringenin chalcone, and several apigenin-related compounds) might be responsible for the environmental tolerance and aromatic properties of T. mongolicus.
Conclusion
This study enhanced the understanding of the genomic evolution of T. mongolicus, enabling further exploration of its unique traits and applications, and contributed to the understanding of Lamiaceae genomics and evolutionary biology.
... More than 400 organic volatiles have been detected in mature tomato fruits, but only a few significantly affect flavor quality [3,4]. Tomato organic volatiles can be divided into four categories: branched-chain amino acid derivatives, carotenoid derivatives, fatty acid derivatives, and phenylpropane derivatives [5]. The following key volatiles affect the nutritional quality of tomato fruits and have been associated with particular aromas favored by consumers: 2-phenylacetaldehyde (floral), 3-methylbutanol (malt), 6-methyl-5-hepten-2-one (fruity and floral), and hexanal (grassy). ...
Volatile accumulation during tomato ripening greatly affects the fruit flavor. In this study, four accessions from each of the three tomato subgroups (BIG, S. lycopersicum, CER, S. lycopersicumvar. Cerasiforme, and PIM, S. pimpinellifolium) were subjected to a sensory evaluation. The CER subgroup had the highest fruit-flavor score. Using a Headspace solid-phase microextraction/gas chromatography-mass spectrometer (HP-SPME/GC-MS), a volatile database containing 94 volatiles was created. Pentanal accumulated in green fruits and 1-pentanol in red fruits. 1-Octen-3-ol was discovered to underlie the bitterness of green tomatoes, and it was most abundant in PIM green fruits. Phenylethyl alcohol affected the acidity and sweetness of red tomatoes, and it was most abundant in CER red fruits. Branched-chain volatiles were most abundant in PIM and BIG red fruits, while apocarotenoids were most abundant in CER red fruits. These findings suggest that domestication and improvement have influenced volatile content, and apocarotenoids and branched-chain volatiles synergistically mediated aromatic flavors in red fruits. This study provides a metabolic basis for analyses of the molecular mechanisms of fruit-flavor formation.
... The increase in aroma compounds was mainly attributed to aldehydes in grape berries (Fig. 3A). Hexanal and (E)-2-hexenal, which are derived from the fatty acid pathway (Dudareva, et al., 2013), are the main contributors to increases in the content of aldehydes (Table 2). Changes in the content of amino acid-derived volatiles, such as benzaldehyde and benzeneacetaldehyde, differed from changes in hexanal and (E)-2-hexenal (Table S3). ...
L-Tryptophan (Trp) is a substrate for the biosynthesis of melatonin, and melatonin is a signal molecule that alters the secondary metabolite profile; whether Trp treatments promote the biosynthesis of melatonin to regulate aroma compounds in grape berries and wine remains unclear. Here, the content of melatonin was higher in Marselan grapes and wine than that in other grape cultivars. Marselan grapes were subjected to 30 different Trp treatments. The content of melatonin and aroma compounds in Marselan grapes was increased by several treatments. Increases in the content of volatiles were mainly driven by increases in aldehydes. Hexanal, the most abundant aldehyde compound, was the main contributor to increases in aldehydes following Trp treatment. The results of our study indicate that the root application of 250 mg/L L-tryptophan during the fruiting expansion stage and the spraying application of 50 mg/L L-tryptophan spray during the veraison stage were the optimal treatments because the content of melatonin and aroma compounds, as well as other basic quality parameters, were highest in Trp-treated grape berries and wine in these treatments. Overall, these two effective Trp treatments could be used to enhance the content of melatonin and aroma compounds in Marselan grapes, and this could increase the economic value of this cultivar.
... VOCs are a class of secondary metabolites that play important roles in protecting plants from pests and diseases, attracting pollinators, and increasing competitive advantages [15][16][17]. VOCs are reportedly closely associated with plant genotypes, environmental conditions, geographic variations, physiological factors, socio-political conditions, and harvest time [18]. VOCs emitted by different plant organs increase in response to abiotic stressors such as temperature, intense light, water, salt, and oxidative stress, as plants strive to swiftly recover, thereby enhancing their adaptability [19][20][21]. ...
Background
White standard Dendranthema grandiflorum (D. grandiflorum) is widely used for ornamental purposes. The volatile organic components (VOCs) of D. grandiflorum vary depending on the geographical origin and cultivar, which influence the market value. Here, we applied headspace extraction coupled with gas chromatography–mass spectrometry (HS–GC–MS) for the first time to determine the different origins (Korea, China, Vietnam) of D. grandiflorum in three genotypes (Baekgang, Jinba, Iwa-no-hakusen) based on volatile fingerprints and to assess the correlation among the metabolites identified in Korean and non-Korean D. grandiflorum.
Results
A total of 41 VOCs, mainly monoterpenoids, sesquiterpenoids, alcohols, and fatty acids, were identified. Principal component analysis showed that instead of geographical origin, genotype influences D. grandiflorum fingerprints. Cultivar discrimination was mainly affected by the metabolites associated with the alpha-terpinyl cation pathway. The orthogonal partial least squares discriminant analysis model achieved 100% and 93.3% accuracies in the calibration and validation sets, respectively. The results of volcano plots and clustering analysis, sesquiterpenoids were significantly more abundant in non-Korean than in Korean, whereas monoterpenoids were abundant in Korean samples.
Conclusions
41 makers confirmed robustness maintenance over two years. These findings can be useful for reliably identifying the geographical origin of D. grandiflorum and providing a comprehensive understanding of VOCs in D. grandiflorum cultivars grown in different countries of origins.
Graphical Abstract
... Terpenoids, the most abundant and diverse class of plant volatiles, are derived from two common isoprene precursors, namely, isopentenyl pyrophosphate (IPP) and dimethylallyl pyrophosphate (DMAPP). Terpenoids are pivotal in determining the rich diversity of floral aromas (Dudareva et al., 2005(Dudareva et al., , 2013Tholl, 2015). Plants synthesize these isoprene precursors through two distinct pathways: the mevalonic acid (MVA) pathway, located in the cytosol, primarily responsible for sesquiterpene production, and the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, situated in the plastids, primarily contributing to monoterpenes (Vranova et al., 2013;Tholl, 2015). ...
Herbaceous peony (Paeonia lactiflora) is a well-known ornamental plant in China, celebrated for its beautiful flowers that can emit fragrances. However, exact molecular mechanisms governing synthesis of floral volatiles within herbaceous peony remain unclear. To address this gap in knowledge, our study focused on analyzing the transcriptome and the levels of floral volatile compounds in P. lactiflora ‘Wu Hua Long Yu’ at different stages of flower development. Using gas chromatography-mass spectrometry (GC-MS), we obtained eighteen major volatile compounds, with monoterpenes being the dominant components among them. Our transcriptome analysis, based on pooled sequencing data, revealed the most differentially expressed genes (DEGs) existed between stages S1 and S3 of flower development. Among these DEGs, we identified 89 functional genes associated with the synthesis of volatile monoterpenes, with 28 of these genes showing a positive correlation with the release of monoterpenes. Specifically, key regulators of monoterpene synthesis in herbaceous peony appear to be 1-deoxy-D-xylulose 5-phosphate synthase (DXS), geranyl pyrophosphate synthase (GPPS), and terpene synthase (TPS). Additionally, our study identified some transcription factors (TFs) that may be involved in the biosynthesis of monoterpenes. These discoveries offer invaluable illumination into the intricate molecular underpinnings orchestrating the generation of floral fragrances in herbaceous peonies, and they offer a foundation for further research to identify and utilize candidate gene resources for this purpose.
... In plants under flooding, although there was an intermediate A net between drought and control, a reduction in the carboxylation efficiency of the Rubisco enzyme was observed, which could also lead to NADPH + H + accumulation and greater production of alkaloids; however, the investment in specialized metabolism was lower, with a particular increase in Liriodenine. The alkaloid biosynthesis depends on the availability of carbon and nitrogen and the energy provided by the primary metabolism, demonstrating a high degree of connectivity between primary and specialized metabolisms [60]. ...
Annona emarginata produces alkaloids of ecological and pharmacological interest and is tolerant to water and biotic stress, so it is used as rootstock for other Annonaceae fruits. There are few reports in the literature on how contrasting water stress impacts the production of specialized metabolites in Annonaceae and how primary metabolism adjusts to support such production. The objective of this investigation was to evaluate how drought and flooding stress affect alkaloid concentration and the primary metabolism of young A. emarginata plants. Three water levels (flooding, field capacity, and drought) were studied at two moments (stress and recovery). Variables analyzed were gas exchange levels, chlorophyll a fluorescence, leaf sugars, total alkaloid content, alkaloid profile, and Liriodenine concentration. The photosynthetic metabolism of A. emarginata was affected by water stress, with plants having a greater ability to adapt to drought conditions than to flooding. During the drought, a reduction in photosynthetic efficiency with subsequent recovery, higher starch and trehalose concentrations in leaves, and total alkaloids in roots (480 µg.g−1) were observed. Under flooding, there was a reduction in photochemical efficiency during stress, indicating damage to the photosynthetic apparatus, without reversal during the recovery period, as well as a higher concentration of total sugars, reducing sugars, sucrose, glucose, and fructose in leaves, and Liriodenine in roots (100 µg.g−1), with a lower concentration of total alkaloids (90 µg.g−1). It could be concluded that there is differential tolerance of A. emarginata to water stress, inducing the modulation of alkaloid production, while drought promotes a higher concentration of total alkaloids and flooding leads to an increase in the Liriodenine concentration.
... Third, contaminants (compounds released by the pot, polyethylene bag, aluminum foil, and other non-plant materials) and alkanes were eliminated. Although there was no blank collection in this experiment, most contaminants were easily identified, because plant volatiles generally include terpenoids, phenylpropanoids/benzenoids, fatty acid derivatives, and amino acid derivatives, in addition to a few species-and genus-specific compounds (Dudareva et al., 2013). Moreover, alkanes were excluded because they are generally ineffective in plant defences against herbivores (Turlings and Erb, 2018). ...
It is well-known that increasing crop biodiversity plays an essential role in achieving ecologically based pest management (EBPM); however, the mechanism is poorly understood. The Three Sisters (Maize/Bean/Squash polyculture [MBS]) is a traditional mixed cropping strategy that has been practiced for thousands of years in Mesoamerica; however, mechanistic evidence for its resistance to herbivores is still lacking. In the present study, using both greenhouse and field experiments, we investigated the effects of MBS on the direct and indirect defences of maize (Zea mays) against Asian corn borer (Ostrinia furnacalis) and fall armyworm (Spodoptera fru-giperda) caterpillars. MBS significantly improved the direct chemical defences of maize, especially against O. furnacalis, by increasing the content of primary metabolites, secondary metabolites (Benzoxazinoids), and phytohormones ((±)-Jasmonic acid-isoleucine, Jasmonic acid) in maize leaves, thus significantly reducing their survival and relative growth rates. MBS significantly improved the indirect chemical defences of maize by varying the species and content of volatile organic compounds (such as a mixture of nonanal, 1-dodecanol and 2-butyl-1-octanol), seemingly resulting in the avoidance of MBS plants by both herbivores in the Y-tube olfac-tometer tests. Field experiments further demonstrated that MBS significantly reduced damage to maize leaves by herbivores, enhanced maize yields, and increased the abundance of natural enemies. Therefore, we concluded that MBS improves the resistance of maize to major pests, and can be used as an effective and eco-friendly crop protection strategy in agroecosystems.
... Essential oils are plant natural products containing volatile organic compounds (VOCs) and phenolics (Gantner et al., 2019;Regnault-Roger et al., 2012). Of them, VOCs play an important role in directly repelling herbivores, indirectly attracting natural enemies of herbivores and plant-plant communication (Dudareva et al., 2013). Some compounds have been found to have strong repellent and fumigation effects against a wide range of SPPs (Caballero-Gallardo et al., 2011;Chaubey, 2007;Piesik et al., 2016;Piesik and Wenda-Piesik, 2015;Wang et al., 2006;Zhang et al., 2018;Zhu et al., 2003). ...
Rosa damascena Mill., commonly known as the King Flower, is a fragrant and important species of the Rosaceae family. It is widely used in the perfumery and pharmaceutical industries. The scent and color of the flowers are significant characteristics of this ornamental plant. This study aimed to investigate the relative expression of MYB1 , CCD1 , FLS , PAL , CER1 , GT1 , ANS and PAR genes under two growth stages (S1 and S2) in two accessions. The CCD1 gene pathway is highly correlated with the biosynthesis of volatile compounds. The results showed that the overexpression of MYB1 , one of the important transcription factors in the production of fragrance and color, in the pink accession of sample S2 increased the expression of PAR , PAL , FLS , RhGT1 , CCD1 , ANS , CER1 , and GGPPS . The methyl jasmonate stimulant had a positive and cumulative effect on gene expression in most genes, such as FLS in ACC.26 of the S2 sample, RhGT1 , MYB1 , CCD1 , PAR , ANS , CER1 , and PAL in ACC.1. To further study, a comprehensive analysis was performed to evaluate the relationship between the principal volatile compounds and colors. Our data suggest that the rose with pink flowers had a higher accumulation content of flavonoids and anthocyanin. To separate essential oil compounds, GC/MS analysis identified 26 compounds in four samples. The highest amount of geraniol, one of the main components of damask rose, was found in the dark-pink flower, 23.54%, under the influence of the methyl jasmonate hormone.
Floral scent emission of petunia flowers is regulated by light conditions, circadian rhythms, ambient temperature and the phytohormones GA and ethylene, but the mechanisms underlying sensitivity to these factors remain obscure. PHYTOCHROME INTERACTING FACTORs (PIFs) have been well studied as components of the regulatory machinery for numerous physiological processes. Acting redundantly, they serve as transmitters of light, circadian, metabolic, thermal and hormonal signals. Here we identified and characterized the phylogenetics of petunia PIF family members (PhPIFs). PhPIF4/5 was revealed as a positive regulator of floral scent: TRV-based transient suppression of PhPIF4/5 in petunia petals reduced emission of volatiles, whereas transient overexpression increased scent emission. The mechanism of PhPIF4/5-mediated regulation of volatile production includes activation of the expression of genes encoding biosynthetic enzymes and a key positive regulator of the pathway, EMISSION OF BENZENOIDS II (EOBII). The PIF-binding motif on the EOBII promoter (G-box) was shown to be needed for this activation. As PhPIF4/5 homologues are sensors of dawn and expression of EOBII also peaks at dawn, the prior is proposed to be part of the diurnal control of the volatile biosynthetic machinery. PhPIF4/5 was also found to transcriptionally activate PhDELLAs; a similar positive effect of PIFs on DELLA expression was further confirmed in Arabidopsis seedlings. The PhPIF4/5–PhDELLAs feedback is proposed to fine-tune GA signaling for regulation of floral scent production.
Supplementary Information
The online version contains supplementary material available at 10.1007/s11103-024-01455-8.
Plants adapt to balance growth-defense tradeoffs in response to both biotic and abiotic stresses. Green leaf volatiles (GLVs) are released after biotic and abiotic stresses and function as damage-associated signals in plants. Although, GLVs enter plants primarily through stomata, the role of stomatal regulation on the kinetics of GLVs uptake remain largely unknown. Here, we illustrate the effect of stomatal closure on the timing and magnitude of GLVs uptake. We closed stomata by either exposing plants to darkness or applying abscisic acid, a phytohormone that closes the stomata in light. Then, we exposed maize seedlings to Z-3-hexen-1-ol and compared the dynamic uptake of Z-3-hexen-1-ol under different stomatal conditions. Additionally, we used E-3-hexen-1-ol , an isomer of Z-3-hexen-1-ol not made by maize, to exclude the role of internal GLVs in our assays. We demonstrate closed stomata effectively prevent GLVs entry into exposed plants, even at high concentrations. Furthermore, our findings indicate that reduced GLV uptake impairs GLVs-driven induction of sesquiterpenes biosynthesis, a group of GLV-inducible secondary metabolites, with or without herbivory. These results elucidate how stomata regulate the perception of GLV signals, thereby dramatically changing the plant responses to herbivory, particularly under water stress or dark conditions.
We elucidate the role of stomata, small pores on plants’ leaf surface, in regulating the entry of green leaf volatiles, damage-associated signals, into plants, and thus influencing their signaling functions.
Plants adapt to balance growth-defense tradeoffs in response to both biotic and abiotic stresses. Green leaf volatiles (GLVs) are released after biotic and abiotic stresses and function as damage-associated signals in plants. Although GLVs enter plants primarily through stomata, the role of stomatal regulation on the kinetics of GLVs uptake remains largely unknown. Here, we illustrate the effect of stomatal closure on the timing and magnitude of GLVs uptake. We closed stomata by either exposing plants to darkness or applying abscisic acid, a phytohormone that closes the stomata in light. Then, we exposed maize seedlings to Z-3-hexen-1-ol and compared the dynamic uptake of Z-3-hexen-1-ol under different stomatal conditions. Additionally, we used E-3-hexen-1-ol, an isomer of Z-3-hexen-1-ol not made by maize, to exclude the role of internal GLVs in our assays. We demonstrate that closed stomata effectively prevent GLVs entry into exposed plants, even at high concentrations. Furthermore, our findings indicate that reduced GLV uptake impairs GLVs-driven induction of sesquiterpenes biosynthesis, a group of GLV-inducible secondary metabolites, with or without herbivory. These results elucidate how stomata regulate the perception of GLV signals, thereby dramatically changing the plant responses to herbivory, particularly under water stress or dark conditions.
The phytohormone jasmonate (JA) plays a central role in plant defenses against biotic stressors. However, our knowledge of the JA signaling pathway in rice (Oryza sativa) remains incomplete. Here, we integrated multi-omic data from three tissues to characterize the functional modules involved in organizing JA-responsive genes. In the core regulatory sector, MYC2 transcription factor transcriptional cascades are conserved. in different species but with distinct regulators (e.g. bHLH6 in rice)., in which genes are early expressed across all tissues. In the feedback sector, MYC2 also regulates the expression of JA repressor and catabolic genes, providing negative feedback that truncates the duration of JA responses. For example, the MYC2-regulated NAC (NAM, ATAF1/2 and CUC2) transcription factor genes NAC1, NAC3, and NAC4 encode proteins that repress JA signaling and herbivore resistance. In the tissue-specific sector, many late-expressed genes are associated with the biosynthesis of specialized metabolites that mediate particular defensive functions. For example, the terpene synthase gene TPS35 is specifically induced in the leaf sheath and TPS35 functions in defense against oviposition by brown planthoppers and the attraction of this herbivore’s natural enemies. Thus, by characterizing core, tissue-specific, and feedback sectors of JA-elicited defense responses, this work provides a valuable resource for future discoveries of key JA components in this important crop.
Plants emit biogenic volatile organic compounds (BVOCs) as signaling molecules, playing a crucial role in inducing resistance against herbivores. Neighboring plants that eavesdrop on BVOC signals can also increase defenses against herbivores or alter growth patterns to respond to potential risks of herbivore damage. Despite the significance of BVOC emissions, the evolutionary rationales behind their release and the factors contributing to the diversity in such emissions remain poorly understood. To unravel the conditions for the evolution of BVOC emission, we developed a spatially-explicit model that formalizes the evolutionary dynamics of BVOC emission and non-emission strategies. Our model considered two effects of BVOC signaling that impact the fitness of plants: intra-individual communication, which mitigates herbivore damage through the plant's own BVOC signaling incurring emission costs, and inter-individual communication, which alters the influence of herbivory based on BVOC signals from other individuals without incurring emission costs. Employing two mathematical models—the lattice model and the random distribution model—we investigated how intra-individual communication, inter-individual communication, and spatial structure influenced the evolution of BVOC emission strategies. Our analysis revealed that the increase in intra-individual communication promotes the evolution of the BVOC emission strategy. In contrast, the increase in inter-individual communication effect favors cheaters who benefit from the BVOCs released from neighboring plants without bearing the costs associated with BVOC emission. Our analysis also demonstrated that the narrower the spatial scale of BVOC signaling, the higher the likelihood of BVOC evolution. This research sheds light on the intricate dynamics governing the evolution of BVOC emissions and their implications for plant-plant communication.
The production of herbivore-induced plant volatiles (HIPVs) is a type of indirect defense used by plants to attract natural enemies and reduce herbivory by insect pests. In many crops little is known about genotypic variation in HIPV production or how this may affect natural enemy attraction. In this study, we identified and quantified HIPVs produced by 10 sorghum (Sorghum bicolor) cultivars infested with a prominent aphid pest, the sorghum aphid (Melanaphis sorghi Theobald). Volatiles were collected using dynamic headspace sampling techniques and identified and quantified using GC-MS. The total amounts of volatiles induced by the aphids did not differ among the 10 cultivars, but overall blends of volatiles differed significantly in composition. Most notably, aphid herbivory induced higher levels of methyl salicylate (MeSA) emission in two cultivars, whereas in four cultivars, the volatile emissions did not change in response to aphid infestation. Dual-choice olfactometer assays were used to determine preference of the aphid parasitoid, Aphelinus nigritus, and predator, Chrysoperla rufilabris, between plants of the same cultivar that were un-infested or infested with aphids. Two aphid-infested cultivars were preferred by natural enemies, while four other cultivars were more attractive to natural enemies when they were free of aphids. The remaining four cultivars elicited no response from parasitoids. Our work suggests that genetic variation in HIPV emissions greatly affects parasitoid and predator attraction to aphid-infested sorghum and that screening crop cultivars for specific predator and parasitoid attractants has the potential to improve the efficacy of biological control.
Nymphaea ‘Eldorado’, a valuable water lily, is a well-known fragrant plant in China. Studying the temporal and spatial characteristics of the floral components of this plant can provide a reference for the further development and utilization of water lily germplasm resources. In this study, headspace solid-phase microextraction (HS-SPME) combined with gas chromatography–mass spectrometry (GC-MS) was used to explore the types and relative contents of floral components at different flowering stages (S1: bud stage; S2: initial-flowering stage; S3: full-flowering stage; S4: end-flowering stage) and in different floral organs of N. ‘Elidorado’, combined with the observation of the microscopic structure of petals. A total of 60 volatile organic compounds (VOCs) were detected at different flowering stages, and there were significant differences in floral VOCs at different flowering stages and in different flower organs. The volatile compounds of N. ‘Eldorado’ can be divided into seven chemical classes,, namely, alkenes, alcohols, esters, aldehydes, ketones, alkanes, and others; the most common were alkenes and alkanes. A total of 39, 44, 47, and 42 volatile compounds were detected at S1, S2, S3, and S4. The VOCs present in high concentrations include benzaldehyde, benzyl alcohol, benzyl acetate, trans-α-bergamotene, α-curcumene, cis-α-farnesene, and so on. The types and total contents of volatiles at the full-flowering stage were higher than at other flowering stages. Comparing the VOCs in different parts of flower organs, it was found that the contents of alcohols, esters, and aldehydes were greatest in the petals, the alkenes in stamens were abundant with a relative content of up to 54.93%, and alkanes in the pistil were higher than in other parts. The types and total contents of volatiles in the stamens of N. ‘Eldorado’ were higher than those in other flower organs; they were the main part releasing fragrance. The observation of petal microstructure revealed that the size and quantity of the papillae on the epidermises of petals, the number of intracellular plastids, and the aggregates of floral components (osmophilic matrix granules) were significantly higher at the full-flowering stage than at the other flowering stages. This study suggested the main flowering stage and location at which the floral VOCs are released by N. ‘Eldorado’ and provided a reference for guiding the breeding of this water lily, exploring genetic patterns and developing related products.
Methyleugenol, a bioactive compound in the phenylpropene family, undergoes its final and crucial biosynthetic transformation when eugenol O-methyltransferase (EOMT) converts eugenol into methyleugenol. While Melaleuca bracteata essential oil is particularly rich in methyleugenol, it contains only trace amounts of its precursor, eugenol. This suggests that the EOMT enzyme in M. bracteata is highly efficient, although it has not yet been characterized. In this study, we isolated and identified an EOMT gene from M. bracteata, termed MbEOMT1, which is primarily expressed in the flowers and leaves and is inducible by methyl jasmonate (MeJA). Subcellular localization of MbEOMT1 in the cytoplasm was detected. Through transient overexpression experiments, we found that MbEOMT1 significantly elevates the concentration of methyleugenol in M. bracteata leaves. Conversely, silencing of MbEOMT1 via virus-induced gene silencing (VIGS) led to a marked reduction in methyleugenol levels. Our in vitro enzymatic assays further confirmed that MbEOMT1 specifically catalyzes the methylation of eugenol. Collectively, these findings establish that the MbEOMT1 gene is critical for methyleugenol biosynthesis in M. bracteata. This study enriches the understanding of phenylpropene biosynthesis and suggests that MbEOMT1 could serve as a valuable catalyst for generating bioactive compounds in the future.
Lipoxygenase enzymatic pathway is a widely studied mechanism in the plant kingdom. Combined actions of three enzymes: lipase, lipoxygenase (LOX) and hydroperoxide lyase (HPL) convert lipidic substrates such as C18:2 and C18:3 fatty acids into short chain volatiles. These reactions, triggered by cell membrane disruptions, produce compounds known as Green Leaf Volatiles (GLVs) which are C6 or C9-aldehydes and alcohols. These GLVs are commonly used as flavors to confer a fresh green odor of vegetable to food products. Therefore, competitive biocatalytic productions have been developed to meet the high demand in these natural flavors. Vegetable oils, chosen for their lipidic acid profile, are converted by soybean LOX and plant HPL into natural GLVs. However this second step of the bioconversion presents low yield due to the HPL instability and the inhibition by its substrate. This paper will shortly describe the different enzymes involved in this bioconversion with regards to their chemical and enzymatic properties. Biotechnological techniques to enhance their production potentialities will be discussed along with their implication in a complete bioprocess, from the lipid substrate to the corresponding aldehydic or alcoholic flavors.
In snapdragon flowers, the volatile ester methyl benzoate is the most abundant scent compound. It is synthesized by and emitted from only the upper and lower lobes of petals, where pollinators (bumblebees) come in contact with the flower. Emission of methyl benzoate occurs in a rhythmic manner, with maximum emission during the day, which correlates with pollinator activity. A novel S-adenosyl-l-methionine:benzoic acid carboxyl methyl transferase (BAMT), the final enzyme in the biosynthesis of methyl benzoate, and its corresponding cDNA have been isolated and characterized. The complete amino acid sequence of the BAMT protein has only low levels of sequence similarity to other previously characterized proteins, including plant O-methyl transferases. During the life span of the flower, the levels of methyl benzoate emission, BAMT activity, BAMT gene expression, and the amounts of BAMT protein and benzoic acid are developmentally and differentially regulated. Linear regression analysis revealed that production of methyl benzoate is regulated by the amount of benzoic acid and the amount of BAMT protein, which in turn is regulated at the transcriptional level.
Some basil varieties are able to convert the phenylpropenes chavicol and eugenol to methylchavicol and methyleugenol, respectively. Chavicol O-methyltransferase (CVOMT) and eugenol O-methyltransferase (EOMT) cDNAs were isolated from the sweet basil variety EMX-1 using a biochemical genomics approach. These cDNAs encode proteins that are 90% identical to each other and very similar to several isoflavone O-methyltransferases such as IOMT, which catalyzes the 4′-O-methylation of 2,7,4′-trihydroxyisoflavanone. On the other hand, CVOMT1 and EOMT1 are related only distantly to (iso)eugenol OMT from Clarkia breweri, indicating that the eugenol O-methylating enzymes in basil and C. breweri evolved independently. Transcripts for CVOMT1 and EOMT1 were highly expressed in the peltate glandular trichomes on the surface of the young basil leaves. The CVOMT1 and EOMT1 cDNAs were expressed in Escherichia coli, and active proteins were produced. CVOMT1 catalyzed the O-methylation of chavicol, and EOMT1 also catalyzed the O-methylation of chavicol with equal efficiency to that of CVOMT1, but it was much more efficient in O-methylating eugenol. Molecular modeling, based on the crystal structure of IOMT, suggested that a single amino acid difference was responsible for the difference in substrate discrimination between CVOMT1 and EOMT1. This prediction was confirmed by site-directed mutagenesis, in which the appropriate mutants of CVOMT1 (F260S) and EOMT1 (S261F) were produced that exhibited the opposite substrate preference relative to the respective native enzyme.
Upon herbivore attack plant react with a cascade of signals. Early events are represented by ion flux unbalances that eventually lead to plasma transmembrane potential (Vm) variations. These events are triggered by mechanical wounding implicated by chewing/piercing herbivores along with the injection of oral secretions containing plant response effectors and elicitors. Vm depolarization has been found to be a common event when plants interact with different biotrophs, and to vary depending on type and feeding habit of the biotroph. Here we shown recent advances of internal and external signal transduction in plant-insect interactions by analyzing the differential impact of mechanical and herbivore damage on plants. Vm variations, calcium signaling, and ROS production precede the late events represented by gene expression, proteomics and metabolomics. Transcriptomics allows to decipher genomic expression following Vm variations and signaling upon herbivory; proteomics helps to understand the biological function of expressed genes, whereas metabolomics gives feedbacks on the combined action of gene expression and protein synthesis, by showing the complexity of plant responses through synthesis of direct and indirect plant defense molecules. The practical application of modern methods starting from signal transduction to metabolic responses to insect herbivory are discussed and documented.
We determined the direct and indirect top-down forces in a tritrophic system composed of a guild of three parasitoid species (Necremnus tidius, N. folia, and Aprostocestus sp.), a single weevil seed-predator species (Ceutorhynchus sp. nov.), and the host plant, Holmathophylla spinosa, a woody crucifer of the high-mountain elevations of the Sierra Nevada (southeast Spain). By means of observational and experimental approaches, we focused on the possible regulatory effects of parasitoids on the weevil population as well as on the analysis of the sign and strength of the resulting indirect effects on plant fitness. Weevils attacked 21.7% of the fruit produced by H. spinosa during the study, selecting fruits having the most seeds. Seeds eaten by weevils were significantly bigger than uneaten ones. The number of seeds per fruit after being depredated by Ceutorhynchus was significantly smaller than for fruit not attacked. Thus, weevils affect the fitness of the host plant both by decreasing the number of seeds (quantitative effect) and by reducing the average size of surviving seeds per fruit (qualitative effect). When parasitoids were excluded experimentally, the percentage of attacked fruit (which corresponds to the number of weevil larvae) rose from 20 to 43%. We assume that the increase in the experimental weevil population may be because excluding parasitoids eliminates not only death by parasitoid oviposition for some Ceutorhynchus larvae, but also death by direct predation of parasitoids on weevil larvae. We have also experimentally verified that parasitoid activity benefits the entire plant, by way of parasitoids contributing to a higher average number of seeds dispersed per fruit in each plant, by influencing both the abundance of the weevils and the behavior of the weevil larvae.
SABATH MTs are found only in the plant kingdom, and they also do not display significant sequence similarity to other known plant MTs. However, they share several physical characteristics with some other families of plant MTs, such as forming homodimers and sharing similar SAM binding residues. The SABATH protein family appears to be unique among plant MT families in containing enzymes that transfer the methyl group to an oxygen while other members of the family transfer the methyl group to a nitrogen; previously described plant MT families contain members that appear to modify only one type of functionality.
Petunia hybrida W115 was transformed with a Clarkia breweri S-linalool synthase cDNA (lis). Lis was expressed in all tissues analysed, and linalool was detected in leaves, sepals, corolla, stem and ovary, but not in nectaries, roots, pollen and style. However, the S-linalool produced by the plant in the various tissues is not present as free linalool, but was efficiently converted to non-volatile S-linalyl-β-d-glucopyranoside by the action of endogenous glucosyltransferase. The results presented demonstrate that monoterpene production can be altered by genetic modification, and that the compounds produced can be converted by endogenous enzymatic activity.
Petals of 11 rose cultivars were analyzed by solvent extraction for the presence of key scent volatiles. Two different cultivars-'Fragrant Cloud', a very fragrant cultivar, and 'Golden Gate', a non-fragrant cultivar-were further analyzed by the headspace technique during flower opening. The 'Fragrant Cloud' headspace is composed of a variety of volatiles, including monoterpene alcohols, acetates, and terpene hydrocarbons, while the 'Golden Gate' headspace is composed mainly of orcinol dimethylether, a compound that is scentless to the human nose but that is perceived by honeybees, as judged by proboscis extension experiments. In both cultivars, the level of volatiles increased during flower development, while the ratio of different major volatiles remained constant.
Thiolases are ubiquitous enzymes involved in many essential biochemical processes. Biosynthetic thiolases, also known as acetoacetyl-CoA thiolases (AACT), catalyse a reversible Claisen-type condensation of two acetyl-CoA molecules to form acetoacetyl-CoA. Here, we report the characterisation of two genes from Arabidopsis thaliana L., ACT1 and ACT2, which encode two closely related AACT isoforms (AACT1 and AACT2, respectively). Transient expression of constructs encoding AACT1 and AACT2 fused to GFP revealed that the two proteins show a different subcellular localisation. While AACT1 is found in peroxisomes, AACT2 localises in the cytosol and the nucleus. The peroxisomal localisation of AACT1 depends on the presence of a C-terminal peroxisomal targeting sequence (PTS1) motif (Ser-Ala-Leu) not previously found in other organisms. ACT1 and ACT2 genes are also differentially expressed. Whereas ACT2 is expressed at relatively high level in all plant tissues, the expression of ACT1 is restricted to roots and inflorescences and its transcript is present at very low levels. The obtained results are in agreement with the involvement of AACT2 in catalysing the first step of the mevalonate pathway. The metabolic function of AACT1 is not clear at present, although its particular peroxisomal localisation might exclude a role in isoprenoid biosynthesis.
Greenhouse tomato (Lycopersicon esculentum Mill) production relies on pollination by
commercially-produced bumble bee (Bombus impatiens Cresson) colonies. Inadequate pollination by
bumble bees has been a problem for growers at certain times of year; however, its cause has yet to
be determined. Bumble bees have been shown to exit tomato greenhouses to forage on flowers of other
plants. This study investigates tomato's floral characteristics and their affect on bumble bee pollination
by 1) observing foraging preferences for bumble bees on greenhouse tomato, 2) determining if the
plant's floral advertisements could be used by the bees to estimate pollen availability,and 3) identifying
temporal changes in floral display which correspond to peak bumble bee activity. Flower size (petal
length, anther cone width, and anther cone length) and floral scent (release of
�-phellandrene,
2-carene,
alpha�-pinene, and p-cymene) were evaluated to identify the pollinator-important characteristics
of tomato flowers. Our results indicate that 1) bumble bees preferred to pollinate flowers which
produce less
�-phellandrene and 2-carene in comparison to flowers producing more of these volatiles,
2) flower size and floral scent are not likely used by the bees to estimate pollen availability, and 3)
cultivars are inconsistent in their production of floral volatiles during peak bumble bee activity.
�-phellandrene and 2-carene may be antiherbivory volatiles and reduced production during peak bee
activity may help to facilitate pollination of tomato. Pollinator-repellent volatiles may help to protect
flowers from damage caused by over-pollination.
Despite the importance of benzoic acid (BA) as a precursor for a wide array of primary and secondary metabolites, its biosynthesis in plants has not been fully elucidated. BA formation from phenylalanine requires shortening of the C(3) side chain by two carbon units, which can occur by a non-β-oxidative route and/or a β-oxidative pathway analogous to the catabolism of fatty acids. Enzymes responsible for the first and last reactions of the core BA β-oxidative pathway (cinnamic acid → cinnamoyl-CoA → 3-hydroxy-3-phenylpropanoyl-CoA → 3-oxo-3-phenylpropanoyl-CoA → BA-CoA) have previously been characterized in petunia, a plant with flowers rich in phenylpropanoid/benzenoid volatile compounds. Using a functional genomics approach, we have identified a petunia gene encoding cinnamoyl-CoA hydratase-dehydrogenase (PhCHD), a bifunctional peroxisomal enzyme responsible for two consecutively occurring unexplored intermediate steps in the core BA β-oxidative pathway. PhCHD spatially, developmentally, and temporally coexpresses with known genes in the BA β-oxidative pathway, and correlates with emission of benzenoid volatiles. Kinetic analysis of recombinant PhCHD revealed it most efficiently converts cinnamoyl-CoA to 3-oxo-3-phenylpropanoyl-CoA, thus forming the substrate for the final step in the pathway. Down-regulation of PhCHD expression in petunia flowers resulted in reduced CHD enzyme activity, as well as decreased formation of BA-CoA, BA and their derived volatiles. Moreover, transgenic lines accumulated the PhCHD substrate cinnamoyl-CoA and the upstream pathway intermediate cinnamic acid. Discovery of PhCHD completes the elucidation of the core BA β-oxidative route in plants, and together with the previously characterized CoA-ligase and thiolase enzymes, provides evidence that the whole pathway occurs in peroxisomes.
In plants, pollinator adaptation is considered to be a major driving force for floral diversification and speciation. However, the genetic basis of pollinator adaptation is poorly understood. The orchid genus Ophrys mimics its pollinators' mating signals and is pollinated by male insects during mating attempts. In many species of this genus, chemical mimicry of the pollinators' pheromones, especially of alkenes with different double-bond positions, plays a key role for specific pollinator attraction. Thus, different alkenes produced in different species are probably a consequence of pollinator adaptation. In this study, we identify genes that are likely involved in alkene biosynthesis, encoding stearoyl-acyl carrier protein (ACP) desaturases (SAD), in three closely related Ophrys species, O. garganica, O. sphegodes, and O. exaltata. Combining floral odor and gene expression analyses, two SAD homologs (SAD1/2) showed significant association with the production of (Z)-9- and (Z)-12-alkenes that were abundant in O. garganica and O. sphegodes, supporting previous biochemical data. In contrast, two other newly identified homologs (SAD5/6) were significantly associated with (Z)-7-alkenes that were highly abundant only in O. exaltata. Both molecular evolutionary analyses and pollinator preference tests suggest that the alkenes associated with SAD1/2 and SAD5/6 are under pollinator-mediated divergent selection among species. The expression patterns of these genes in F₁ hybrids indicate that species-specific expression differences in SAD1/2 are likely due to cis-regulation, while changes in SAD5/6 are likely due to trans-regulation. Taken together, we report a genetic mechanism for pollinator-mediated divergent selection that drives adaptive changes in floral alkene biosynthesis involved in reproductive isolation among Ophrys species.
The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple-choice four-arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.
Evolutionary and reproductive success of angiosperms, the most diverse group of land plants, relies on visual and olfactory cues for pollinator attraction. Previous work has focused on elucidating the developmental regulation of pathways leading to the formation of pollinator-attracting secondary metabolites such as scent compounds and flower pigments. However, to date little is known about how flowers control their entire metabolic network to achieve the highly regulated production of metabolites attracting pollinators. Integrative analysis of transcripts and metabolites in snapdragon sepals and petals over flower development performed in this study revealed a profound developmental remodeling of gene expression and metabolite profiles in petals, but not in sepals. Genes up-regulated during petal development were enriched in functions related to secondary metabolism, fatty acid catabolism, and amino acid transport, whereas down-regulated genes were enriched in processes involved in cell growth, cell wall formation, and fatty acid biosynthesis. The levels of transcripts and metabolites in pathways leading to scent formation were coordinately up-regulated during petal development, implying transcriptional induction of metabolic pathways preceding scent formation. Developmental gene expression patterns in the pathways involved in scent production were different from those of glycolysis and the pentose phosphate pathway, highlighting distinct developmental regulation of secondary metabolism and primary metabolic pathways feeding into it.
In response to insect attack, plants release complex blends of volatile compounds. These volatiles serve as foraging cues for herbivores, predators and parasitoids, leading to plant-mediated interactions within and between trophic levels. Hence, plant volatiles may be important determinants of insect community composition. To test this, we created rice lines that are impaired in the emission of two major signals, S-linalool and (E)-β-caryophyllene. We found that inducible S-linalool attracted predators and parasitoids as well as chewing herbivores, but repelled the rice brown planthopper Nilaparvata lugens, a major pest. The constitutively produced (E)-β-caryophyllene on the other hand attracted both parasitoids and planthoppers, resulting in an increased herbivore load. Thus, silencing either signal resulted in specific insect assemblages in the field, highlighting the importance of plant volatiles in determining insect community structures. Moreover, the results imply that the manipulation of volatile emissions in crops has great potential for the control of pest populations.
While the role of herbivore-induced volatiles in plant-herbivore-natural enemy interactions is well documented aboveground, new evidence suggests that belowground volatile emissions can protect plants by attracting entomopathogenic nematodes (EPNs). However, due to methodological limitations, no study has previously detected belowground herbivore-induced volatiles in the field or quantified their impact on attraction of diverse EPN species. Here we show how a belowground herbivore-induced volatile can enhance mortality of agriculturally significant root pests. First, in real time, we identified pregeijerene (1,5-dimethylcyclodeca-1,5,7-triene) from citrus roots 9-12 hours after initiation of larval Diaprepes abbreviatus feeding. This compound was also detected in the root zone of mature citrus trees in the field. Application of collected volatiles from weevil-damaged citrus roots attracted native EPNs and increased mortality of beetle larvae (D. abbreviatus) compared to controls in a citrus orchard. In addition, field applications of isolated pregeijerene caused similar results. Quantitative real-time PCR revealed that pregeijerene increased pest mortality by attracting four species of naturally occurring EPNs in the field. Finally, we tested the generality of this root-zone signal by application of pregeijerene in blueberry fields; mortality of larvae (Galleria mellonella and Anomala orientalis) again increased by attracting naturally occurring populations of an EPN. Thus, this specific belowground signal attracts natural enemies of widespread root pests in distinct agricultural systems and may have broad potential in biological control of root pests.
Many plant species respond to herbivory with increased emission of volatile organic compounds (VOCs): these attract carnivorous arthropods and thereby function as an indirect defence mechanism. Whether neighbouring plants can ‘eavesdrop’ on such airborne cues and tailor their defences accordingly, remains controversial.
We used Lima bean plants ( Phaseolus lunatus ) to investigate whether herbivore‐induced VOCs induce another indirect defence strategy, i.e. the secretion of extrafloral nectar (EFN) in conspecific plant neighbours, and whether this enhances the defence status of the receiving plant under natural conditions.
EFN secretion was induced by VOCs released from herbivore‐damaged bean tendrils as well as by a synthetic VOC mixture resembling the natural one. One constituent of the herbivore‐induced blend – the green leaf volatile (3 Z )‐hex‐3‐enyl acetate – was sufficient to elicit the defence reaction.
A long‐term experiment comparing the defensive effect of EFN alone with the VOC‐mediated effect (EFN induction plus attraction of plant defenders) suggested that Lima bean benefits from both indirect defences. Repeated treatment of tendrils with either an artificial blend of VOCs or with EFN led to the attraction of a higher cumulative number of predatory and parasitoid insects (i.e. ants and wasps) as well as to less herbivore damage and an increased production of inflorescences and leaves.
Our results demonstrate that one indirect defence mechanism can induce another one in conspecific plants, and that Lima bean plants can benefit from this VOC‐induced EFN secretion under natural conditions. Both extrafloral nectaries and the capability to release VOCs upon herbivory are present in many plant taxa and airborne signalling may thus represent a common mechanism for regulating the secretion of EFN in plant parts which face an increased risk of herbivory.
The flowers of the sexually deceptive orchid Ophrys sphegodes are pollinated by pseudocopulating males of the solitary bee Andrena nigroaenea. We investigated the changes in odor emission and reduced attractiveness that occur after pollination in these plants. We analyzed floral odor of unpollinated and pollinated flowers by gas chromatography and compared relative and absolute amounts of electrophysiologically active compounds. Headspace odor samples of O. sphegodes flowers showed a significant increase in absolute and relative amounts of all-trans-farnesyl hexanoate after pollination. Flower extracts also indicated an increase of farnesyl hexanoate after pollination. The total amount of the other physiologically active odor compounds decreased slightly. Farnesyl hexanoate is a major constituent of the Dufour's gland secretion in females of the pollinator bees, A. nigroaenea, where it functions in the lining of the brood cells. Furthermore, this compound lowers the number of copulation attempts in males. In dual-choice tests, we showed that flowers artificially scented with an amount of farnesyl hexanoate equal to the increased amount after pollination were significantly less attractive than flowers treated with solvent only. We propose that the increased production of farnesyl hexanoate in pollinated flowers is a signal to guide pollinators to unpollinated flowers of the inflorescence, which represents a new mechanism in this pollination system.
Successful biological invaders often exhibit enhanced performance following introduction to a new region. The traditional explanation for this phenomenon is that natural enemies (e.g., competitors, pathogens, and predators) present in the native range are absent from the introduced range. The purpose of this study was to test the escape‐from‐enemy hypothesis using the perennial plant Silene latifolia as a model system. This European native was introduced to North America in the 1800s and subsequently spread to a large part of the continent. It is now considered a problematic weed of disturbed habitats and agricultural fields in the United States and Canada. Surveys of 86 populations in the United States and Europe revealed greater levels of attack by generalist enemies (aphids, snails, floral herbivores) in Europe compared with North America. Two specialists (seed predator, anther smut fungus) that had dramatic effects on plant fitness in Europe were either absent or in very low frequency in North America. Overall, plants were 17 times more likely to be damaged in Europe than in North America. Thus, S. latifolia's successful North American invasion can, at least in part, be explained by escape from specialist enemies and lower levels of damage following introduction.
This chapter gives an introduction to the field of carotenoid-derived aroma compounds and illustrates the importance of short-chain carotenoid metabolites as flavor and fragrance substances. Although carotenoid-derived aroma compounds (so-called norterpenoids or norisoprenoids) are ubiquitous constituents in plant derived aromas, very little is known about their biogeneration. Hence, possibilities for an efficient biotechnological production are still limited. After a brief summary of the historical development of norisoprenoid chemistry, this introductory chapter reviews the present knowledge about the occurrence and formation of carotenoid-derived aroma compounds in natural tissues and discusses possibilities for a biotechnological production.
Flowers attract pollinator animals through a concert of visual and olfactory stimuli, and the role of floral scent volatiles in attracting as well as eliciting landing, feeding, and in some cases mating and ovipositing behaviors on the flower varies with each flower-animal association.1-3 Flower-animal interactions include a broad diversity of both invertebrates (insects) and vertebrates that function as pollinators,4,5 and the relative importance of floral scent in pollination depends on both the purpose of the animal’s visit to the flower and features of the animal’s biology. Flowers reward pollinators with food used in direct consumption or to provision nests (e.g., nectar, pollen, oils), or with materials used in nest building or sexual reproduction (e.g., resins, fragrance chemicals). Some flowers are deceitful in attracting animals, whereby they mimic oviposition sites, mates, or food sources of pollinator animals; other flowers have a nursery pollination system where they provide a breeding site for their pollinators. In each plant species, flower visitation is restricted to only a subset of the local flower-visiting animals by the phenology of bloom (e.g., seasonal, day versus night); the type, quality, and quantity of food rewards; the floral morphology, which limits access to the rewards; and the floral advertisement stimuli, such as colors, shapes, and scents, which variously stimulate animals to seek, locate, and land on the flowers. Most flowers are visited by a diversity of animal species, but only a few may actually effect pollination, as revealed in careful field studies (see, e.g., Kandori6). Furthermore, the assemblage of animal species that pollinate may differ in their relative importance in the plant’s pollination and in the selective pressures they exert on floral traits, including floral scent chemistry.7-9 Therefore identifying pollinators among visitors and identifying the most important and floral trait selecting of the pollinators is essential in any attempt to determine if floral scent chemistry is associated with and being selected by the type of pollinator.
Emission of methyl benzoate, one of the most abundant scent compounds of bee-pollinated snapdragon flowers, occurs in a rhythmic manner, with maximum emission during the day, and coincides with the foraging activity of bumblebees. Rhythmic emission of methyl benzoate displays a “free-running” cycle in the absence of environmental cues (in continuous dark or continuous light), indicating the circadian nature of diurnal rhythmicity. Methyl benzoate is produced in upper and lower snapdragon petal lobes by enzymatic methylation of benzoic acid in the reaction catalyzed by S-adenosyl-l-methionine:benzoic acid carboxyl methyltransferase (BAMT). When a detailed time-course analysis of BAMT activity in upper and lower petal lobes during a 48-hr period was performed, high BAMT activity was found at night as well as in continuous darkness, indicating that the BAMT activity is not an oscillation-determining factor. Analysis of the level of benzoic acid during a 24-hr period revealed oscillations in the amount of benzoic acid during the daily light/dark cycle that were retained in continuous darkness. These data clearly show that the total amount of substrate (benzoic acid) in the cell is involved in the regulation of the rhythmic emission of methyl benzoate. Our results also suggest that similar molecular mechanisms are involved in the regulation of methyl benzoate production in diurnally (snapdragon) and nocturnally (tobacco and petunia) emitting plants.
We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146, 191–199.
2
H- And 13C-labelled mevalonates (MVA) are
incorporated at a higher rate into the phytyl side-chain of chlorophyll a
and β-carotene than into diterpenes in suspension cultures of
liverworts, Heteroscyphus planus and Lophocolea
heterophylla. The distribution of labels in the biosynthetically
labelled chlorophyll a, phytol and β-carotene incorporating MVA
determined by 2H and 13C NMR analyses indicates
preferential labelling of the farnesyl diphosphate (FPP)-derived portion of
these compounds. These findings suggest that all compounds formed from
geranylgeranyl diphosphate within the chloroplasts are biosynthesized
partly via the condensation of FPP derived from exogenous MVA and
endogenous isopentenyl diphosphate, and that the pigments and normal
diterpenes are biosynthesized separately at different sites within the
chloroplasts. In contrast, [2-13C]glycine administered to the
cultured cells of H. planus equivalently labels both the phytyl
side-chain and β-carotene, indicating that endogenously formed MVA
via glycine is equivalently incorporated both into the phytyl
moiety and β-carotene. Intense doublets due to
13C–13C coupling, observed in the
13C-labelled phytyl side-chain and β-carotene, suggest that
acetyl-CoA is mainly formed from serine derived from
5,10-methylenetetrahydrofolic acid and glycine.
Pollinator selectivity is thought to influence the evolution of separate sexes in plants because of its potential to limit plant reproductive success. Selective visitation could also constrain or promote the phenotypic divergence of the sexes. In this study, I explored the causes and consequences of selectivity by generalist pollinators of a gynodioecious wild strawberry (Fragaria virginiana) and thus provide insight into potential pollinator-mediated selection for dioecy and sexual dimorphism. I found that flowers of F. virginiana show pronounced sexual dimorphism in petal length, stamen length, nectar and pollen production, and that this results in dramatic and consistent levels of sex-differential visitation by ants, bees, and flies. I performed manipulations of hermaphrodite flowers to understand the basis of selectivity and found that much of bee and fly preference for hermaphrodite flowers derived from their strong preference for longer petals, but also from a more subtle preference for pollen-filled anthers. These studies also revealed that other traits contribute to the observed discrimination against females. A stronger relationship existed between bee visitation and pollen receipt in females than between bee visitation and pollen removal from hermaphrodites. An analysis of natural variation in petal and stamen length confirmed the central role of petal length and also showed a lack of an effect of vestigial stamen length in pollination success of females. It also revealed a significant effect of stamen length, but not of petal length, on pollen removal. The data suggest that pollinator selectivity may affect the evolution of floral sexual dimorphism, both by exerting selection that could lead to the maintenance of stamens in females and by exerting selection to increase petal length in females.
By increasing floral apparency to promote fertilization, plants risk attracting herbivores with the same signals that they use to lure pollinators. We hypothesized that fragrance is emitted in patterns that correspond to pollinators, with high emissions during periods of pollinator activity and low emissions otherwise, especially during periods of peak floral herbivore activity. Using a combination of analytical chemistry and field observations, we examined both the diel and ontogenetic patterns of fragrance in two Cirsium species, in relation to visitation patterns of pollinators and florivores. Emission rates were highest at reproductive maturity, when insect visitation by both pollinators and florivores was also highest. In Cirsium arvense, the diel pattern of fragrance emission matched patterns of pollinator activity and was lowest when florivores were active. In contrast, scent in Cirsium repandum peaked at midday rather than with insect activity; neither species had a diel pattern that followed ambient temperature. Fragrance emission from C. repandum was 25 times lower than from staminate C. arvense and may not be essential for pollinator attraction, at least from a distance. The scent dynamics we observed in C. arvense are consistent with the hypothesis that fragrance emissions correspond with pollinator activity and are low when florivores are active.
Floral scent constitutes an ancient and important channel of communication between flowering plants, their pollinators, and enemies. Fragrance is a highly complex component of floral phenotype, with dynamic patterns of emission and chemical composition. The information content of specific volatile compounds is highly context dependent, and scent can function in direct and indirect ways from landscape to intrafloral scales. Floral scent promotes specialization in plant–pollinator relationships through private channels of unusual compounds, unique ratios of more widespread compounds, or through multicomponent floral filters. Floral scent also promotes outcrossing and reproductive isolation through floral constancy, via appetitive conditioning and discrimination on the basis of diverse mechanisms, including pheromone mimicry, odor intensity, complexity, composition, and synergy with visual stimuli. Finally, floral scent is a sexual signal and should be subject to the same selective pressures and modes of sig...
Flowers recruit floral visitors for pollination services by emitting fragrances. These scent signals can be intercepted by antagonists such as florivores to locate host plants. Hence, as a consequence of interactions with both mutualists and antagonists, floral bouquets likely consist of both attractive and defensive components. While the attractive functions of floral bouquets have been studied, their defensive function has not, and field-based evidence for the deterrence of floral-scent constituents is lacking. In field and glasshouse experiments with five lines of transgenic Petunia x hybrida plants specifically silenced in their ability to release particular components of their floral volatile bouquet, we demonstrate that the emission of single floral-scent compounds can dramatically decrease damage from generalist florivores. While some compounds are used in host location, others prevent florivory. We conclude that the complex blends that comprise floral scents are likely sculpted by the selective pressures of both pollinators and herbivores.
This study was designed to investigate antennal response of honey bees, Apis mellifera L., to alfalfa /loral volatiles and to assess among- and within-hive variation in average antennal response to these Cornpounds. Ten of the principal (Medicago sativa L.) alfalfa /loral volatiles were analyzed for hO'{leybee antennal response using a Cornbined gas chromatography-electroantennal detector system. All 10 alfalfa /loral volatiles elicited antennal responses, and significant differences were observed in average honey bee antennal response to these 10 Cornpounds. Linaloiil and methyl salicylate elicited "sticky" antennal signals (slow recovery toward baseline physio-electrical output). This "sticky" response may suggest a biologically active role for these two Cornpounds. Support for a biologically active role for linaloiil and cis-3-hexenyl acetate Cornes from the chemical and structural similarity between these two Cornpounds and two honey bee pheromones, geraniol (nasonov) and n-hexyl acetate (alarm), respectively. Selection for increased emanation oflinaloiil and methyl salicylate, and decreased emanation of cis-3-hexenyl acetate, is suggested as a possible method for increasing the attractiveness of alfalfa to honey bees. Finally, significant differences were demonstrated in both among- and within-hive average antennal response to most of the volatile Cornpounds. Based on the results of this study and those of other investigators, we hypothesize that host-pollinator interrelationships can be strengthened by directed selection in both honey bees and alfalfa.
In this article we focus on the vital ecological services provided by insects. We restrict our focus to services provided
by “wild” insects; we do not include services from domesticated or mass-reared insect species. The four insect services for
which we provide value estimates—dung burial, pest control, pollination, and wildlife nutrition—were chosen not because of
their importance but because of the availability of data and an algorithm for their estimation. We base our estimations of
the value of each service on projections of losses that would accrue if insects were not functioning at their current level.
We estimate the annual value of these ecological services provided in the United States to be at least $57 billion, an amount
that justifies greater investment in the conservation of these services.
Tomato plants respond to herbivory by emitting volatile organic compounds (VOCs), which are released into the surrounding atmosphere. We analyzed the tomato herbivore-induced VOCs and tested the ability of tomato receiver plants to detect tomato donor volatiles by analyzing early responses, including plasma membrane potential (V(m)) variations and cytosolic calcium ([Ca(2+)](cyt)) fluxes. Receiver tomato plants responded within seconds to herbivore-induced VOCs with a strong V(m) depolarization, which was only partly recovered by fluxing receiver plants with clean air. Among emitted volatiles, we identified by GC-MS some green leaf volatiles (GLVs) such as (E)-2-hexenal, (Z)-3-hexenal, (Z)-3-hexenyl acetate, the monoterpene α-pinene, and the sesquiterpene β-caryophyllene. GLVs were found to exert the stronger V(m) depolarization, when compared to α-pinene and β-caryophyllene. Furthermore, V(m) depolarization was found to increase with increasing GLVs concentration. GLVs were also found to induce a strong [Ca(2+)](cyt) increase, particularly when (Z)-3-hexenyl acetate was tested both in solution and with a gas. On the other hand, α-pinene and β-caryophyllene, which also induced a significant V(m) depolarization with respect to controls, did not exert any significant effect on [Ca(2+)](cyt) homeostasis. Our results show for the first time that plant perception of volatile cues (especially GLVs) from the surrounding environment is mediated by early events, occurring within seconds and involving the alteration of the plasma membrane potential and the [Ca(2+)](cyt) flux.
Background:
Most insect-resistant transgenic crops employ toxins to control pests. A novel approach is to enhance the effectiveness of natural enemies by genetic engineering of the biosynthesis of volatile organic compounds (VOCs). Before the commercialisation of such transgenic plants can be pursued, detailed fundamental studies of their effects on herbivores and their natural enemies are necessary. The linalool/nerolidol synthase gene FaNES1 was constitutively expressed from strawberry in three Arabidopsis thaliana accessions, and the behaviour of the aphid Brevicoryne brassicae L., the parasitoid Diaeretiella rapae McIntosh and the predator Episyrphus balteatus de Geer was studied.
Results:
Transgenic FaNES1-expressing plants emitted (E)-nerolidol and larger amounts of (E)-DMNT and linalool. Brevicoryne brassicae was repelled by the transgenic lines of two of the accessions, whereas its performance was not affected. Diaeretiella rapae preferred aphid-infested transgenic plants over aphid-infested wild-type plants for two of the accessions. In contrast, female E. balteatus predators did not differentiate between aphid-infested transgenic or wild-type plants.
Conclusion:
The results indicate that the genetic engineering of plants to modify their emission of VOCs holds considerable promise for facilitating biological control of herbivores. Validation for crop plants is a necessary next step to assess the usefulness of modified volatile emission in integrated pest management.
In a laboratory study, we investigated the monoterpene emissions from Quercus ilex, an evergreen sclerophyllous Mediterranean oak species whose emissions are light dependent. We examined the light and temperature responses of individual monoterpenes emitted from leaves under various conditions, the effect of heat stress on emissions, and the emission-onset during leaf development. Emission rate increased 10-fold during leaf growth, with slight changes in the composition. At 30 °C and saturating light, the monoterpene emission rate from mature leaves averaged 4.1 nmol m-2 s-1, of which α-pinene, sabinene and β-pinene accounted for 85%. The light dependence of emission was similar for all monoterpenes: it resembled the light saturation curve of CO2 assimilation, although monoterpene emission continued in the dark. Temperature dependence differed among emitted compounds: most of them exhibited an exponential increase up to 35 °C, a maximum at 42 °C, and a slight decline at higher temperatures. However, the two acyclic isomers cisβ-ocimene and trans-β-ocimene were hardly detected below 35 °C, but their emission rates increased above this temperature as the emission rates of other compounds fell, so that total emission of monoterpenes exponentially increased from 5 to 45 °C. The ratio between ocimene isomers and other compounds increased with both absolute temperature and time of heat exposure. The light dependence of emission was insensitive to the temperature at which it was measured, and vice versa the temperature dependence was insensitive to the light regime. The results demonstrated that none of the models currently applied to simulate isoprene or monoterpene emissions correctly predicts the short-term effects of light and temperature on Q. ilex emissions. The percentage of fixed carbon lost immediately as monoterpenes ranged between 0.1 and 6.0% depending on temperature, but rose up to 20% when leaves were continuously exposed to temperatures between 40 and 45 °C.
Summary • Patterns of floral scent are generally assumed to have been shaped by pollinator-mediated natural selection. However, while many studies document behavioural responses of pollinators to floral scent, few document the relationship between floral scent and fitness. • In this study, we explore the effect of variation in floral scent emission in colour polymorphic Hesperis matronalis on both pollinator visitation and seed fitness. • Using target inflorescences augmented with colour-specific floral scent extracts, we find that diurnal floral visitors significantly prefer night-scent extracts to non-augmented controls; inflorescences augmented with day-scent extracts receive an intermediate level of visits. Colour did not have a significant effect on visitation. • We characterized the relationship between natural variation in floral scent emission rate and seed production for plants under two settings: in small experimental arrays exposed to either day- or night-flying pollinators, and in wild populations exposed to all pollinators. In arrays, we found greater emission rate led to higher seed production, but only in plants exposed to day-flying pollinators. In contrast, we found a significant positive relationship between night-time floral emission rate and seed fitness in wild populations. In neither setting did floral anthocycanin concentration (colour) affect fitness. • This study reinforces the idea that scent-mediated pollinator visitation is an important component of plant fitness. Moreover, our results suggest that plants emitting more scent have higher fitness, although there is variation as to when this positive relationship occurs (i.e., at day or night). Research connecting floral scent and fitness is a necessary first step in understanding the evolution of floral scent.
Summary • In the nursery pollination system of figs (Ficus, Moraceae), flower-bearing receptacles called syconia breed pollinating wasps and are units of both pollination and seed dispersal. Pollinators and mammalian seed dispersers are attracted to syconia by volatile organic compounds (VOCs). In monoecious figs, syconia produce both wasps and seeds, while in (gyno)dioecious figs, male (gall) fig trees produce wasps and female (seed) fig trees produce seeds. • VOCs were collected using dynamic headspace adsorption methods on freshly collected figs from different trees using Super Q® collection traps. VOC profiles were determined using gas chromatography–mass spectrometry (GC–MS). • The VOC profile of receptive and dispersal phase figs were clearly different only in the dioecious mammal-dispersed Ficus hispida but not in dioecious bird-dispersed F. exasperata and monoecious bird-dispersed F. tsjahela. • The VOC profile of dispersal phase female figs was clearly different from that of male figs only in F. hispida but not in F. exasperata, as predicted from the phenology of syconium production which only in F. hispida overlaps between male and female trees. Greater difference in VOC profile in F. hispida might ensure preferential removal of seed figs by dispersal agents when gall figs are simultaneously available. • The VOC profile of only mammal-dispersed female figs of F. hispida had high levels of fatty acid derivatives such as amyl-acetates and 2-heptanone, while monoterpenes, sesquiterpenes and shikimic acid derivatives were predominant in the other syconial types. A bird- and mammal-repellent compound methyl anthranilate occurred only in gall figs of both dioecious species, as expected, since gall figs containing wasp pollinators should not be consumed by dispersal agents.
As part of a genomics strategy to characterize inducible defences against insect herbivory in poplar, we developed a comprehensive suite of functional genomics resources including cDNA libraries, expressed sequence tags (ESTs) and a cDNA microarray platform. These resources are designed to complement the existing poplar genome sequence and poplar (Populus spp.) ESTs by focusing on herbivore- and elicitor-treated tissues and incorporating normalization methods to capture rare transcripts. From a set of 15 standard, normalized or full-length cDNA libraries, we generated 139 007 3′- or 5′-end sequenced ESTs, representing more than one-third of the c. 385 000 publicly available Populus ESTs. Clustering and assembly of 107 519 3′-end ESTs resulted in 14 451 contigs and 20 560 singletons, altogether representing 35 011 putative unique transcripts, or potentially more than three-quarters of the predicted c. 45 000 genes in the poplar genome. Using this EST resource, we developed a cDNA microarray containing 15 496 unique genes, which was utilized to monitor gene expression in poplar leaves in response to herbivory by forest tent caterpillars (Malacosoma disstria). After 24 h of feeding, 1191 genes were classified as up-regulated, compared to only 537 down-regulated. Functional classification of this induced gene set revealed genes with roles in plant defence (e.g. endochitinases, Kunitz protease inhibitors), octadecanoid and ethylene signalling (e.g. lipoxygenase, allene oxide synthase, 1-aminocyclopropane-1-carboxylate oxidase), transport (e.g. ABC proteins, calreticulin), secondary metabolism [e.g. polyphenol oxidase, isoflavone reductase, (–)-germacrene D synthase] and transcriptional regulation [e.g. leucine-rich repeat transmembrane kinase, several transcription factor classes (zinc finger C3H type, AP2/EREBP, WRKY, bHLH)]. This study provides the first genome-scale approach to characterize insect-induced defences in a woody perennial providing a solid platform for functional investigation of plant–insect interactions in poplar.
Summary 199
Acknowledgements 206
References 209
The low molecular weight hydrocarbons produced by plants form a uniquely exciting group of compounds. Produced by a common biosynthetic route, they play multiple and complex roles in organismal, ecological, and atmospheric processes. While some of these compounds have clearly identified functions within plants, others are made for reasons not yet fully understood. Here, both light-dependent and light-independent emissions are reviewed, together with regulation of production and possible functions of light-dependent volatile organic carbon (VOC). In addition to issues regarding the phylogenetic origins of VOC emissions, the origins of the pivotal enzymes that give rise to the observed emission phenotypes are discussed. Studies on the evolution and regulation of their production and emission provide an amazing opportunity for scientists working from the molecular to the tropospheric scales to interact.