[show abstract][hide abstract] ABSTRACT: Artemisia annua, which produces the anti-malaria compound artemisinin, occurs as high-artemisinin production (HAP) and low-artemisinin production (LAP) chemotypes. Understanding the basis of the difference between these chemotypes would assist breeding and optimising artemisinin biosynthesis. Here we present a systematic comparison of artemisinin biosynthesis genes that may be involved in determining the chemotype (CYP71AV1, DBR2 and ALDH1). These genes were isolated from the two chemotypes and characterized using transient expression in planta. The enzyme activity of DBR2 and ALDH1 from the two chemotypes did not differ, but structural differences in CYP71AV1 from LAP and HAP chemotypes (AMOLAP and AMOHAP, respectively) resulted in altered enzyme activity. AMOLAP displays a seven amino acids N-terminal extension compared with AMOHAP. The GFP fusion of both proteins show equal localization to the ER but AMOHAP may have reduced stability. Upon transient expression in Nicotiana benthamiana, AMOLAP displayed a higher enzyme activity than AMOHAP. However, expression in combination with the other pathway genes also resulted in a qualitatively different product profile ('chemotype'); that is, in a shift in the ratio between the unsaturated and saturated (dihydro) branch of the pathway.
[show abstract][hide abstract] ABSTRACT: Strigolactones (SLs) are newly identified hormones that regulate multiple aspects of plant development, infection by parasitic weeds, and mutualistic symbiosis in the roots. In this study, the role of SLs was studied for the first time in the model plant Lotus japonicus using transgenic lines silenced for CAROTENOID CLEAVAGE DIOXYGENASE 7 (LjCCD7), the orthologue of Arabidopsis More Axillary Growth 3. Transgenic LjCCD7-silenced plants displayed reduced height due to shorter internodes, and more branched shoots and roots than the controls, and an increase in total plant biomass, while their root:shoot ratio remained unchanged. Moreover, these lines had longer primary roots, delayed senescence, and reduced flower/pod numbers from the third round of flower and pod setting onwards. Only a mild reduction in determinate nodule numbers and hardly any impact on the colonization by arbuscular mycorrhizal fungi were observed. The results show that the impairment of CCD7 activity in L. japonicus leads to a phenotype linked to SL functions, but with specific features possibly due to the peculiar developmental pattern of this plant species. It is believed that the data also link determinate nodulation, plant reproduction, and senescence to CCD7 function for the first time.
Journal of Experimental Botany 04/2013; · 5.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: During evolution, plants have adapted an ecological balance with their associates, competitors, predators, and pests. Keeping this balance intact is an active process during which the plant needs to respond to many dif-ferent stimuli in order to survive. For example, plants have developed an array of physiological and bio-chemical responses to phosphate deprivation. One of these responses is the production of isoprenoid-derived molecules called strigolactones. Strigolactones are used to stimulate the formation of symbiotic associations
[show abstract][hide abstract] ABSTRACT: Strigolactones belong to a newly identified class of plant hormones that are involved in the inhibition of shoot branching. Prior to this finding, strigolactones were proven to be root rhizosphere-signaling molecules that mediate plant–parasitic plant, and the symbiotic plant–AM fungi interactions. More recently, strigolactones were shown to have other biological functions as endogenous plant hormones in shoot development, root architecture, and seed germination (also in nonparasitic plants) and to regulate plant developmental processes in interaction with other signaling pathways (i.e., light and senescence signaling) or hormones. Gene discovery in the strigolactone biosynthesis and signal perception pathways is a key step in elucidating the mechanism and mode of action of the existing roles and discovering potential additional roles of strigolactones. Furthermore, insights into strigolactone and strigolactone-associated pathways will provide more knowledge for the control of parasitic weeds and improvement of crop yield. In this chapter, we outline different aspects of the roles that strigolactones play both in the rhizosphere and during plant development. Gene characterization in strigolactone pathways and strigolactone-related hormone cross-talk is also addressed.
[show abstract][hide abstract] ABSTRACT: Plant hormones are small molecules derived from various metabolic pathways and are important regulators of plant development. The most recently discovered phytohormone class comprises the carotenoid-derived strigolactones (SLs). For a long time these compounds were only known to be secreted into the rhizosphere where they act as signaling compounds, but now we know they are also active as endogenous plant hormones and they have been in the spotlight ever since. The initial discovery that SLs are involved in the inhibition of axillary bud outgrowth, initiated a multitude of other studies showing that SLs also play a role in defining root architecture, secondary growth, hypocotyl elongation, and seed germination, mostly in interaction with other hormones. Their coordinated action enables the plant to respond in an appropriate manner to environmental factors such as temperature, shading, day length, and nutrient availability. Here, we will review the current knowledge on the crosstalk between SLs and other plant hormones-such as auxin, cytokinin, abscisic acid (ABA), ethylene (ET), and gibberellins (GA)-during different physiological processes. We will furthermore take a bird's eye view of how this hormonal crosstalk enables plants to respond to their ever changing environments.
[show abstract][hide abstract] ABSTRACT: The strigolactones are rhizosphere signaling molecules as well as a new class of plant hormones with a still increasing number of biological functions being uncovered. Here, we review a recent major breakthrough in our understanding of strigolactone biosynthesis, which has revealed the unexpected simplicity of the originally postulated complex pathway. Moreover, the discovery and localization of a strigolactone exporter sheds new light on putative strigolactone fluxes to the rhizosphere as well as within the plant. The combination of these data with information on the expression and regulation of strigolactone biosynthetic and downstream signaling genes provides new insights into how strigolactones control the many different aspects of plant development and how their rhizosphere signaling role may have evolved.
Trends in Plant Science 11/2012; · 11.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: Strigolactones are plant hormones that regulate both above- and belowground plant architecture. Strigolactones were initially identified as rhizosphere signaling molecules. In the present work, the tomato (Solanum lycopersicum) CAROTENOID CLEAVAGE DIOXYGENASE 8 (SlCCD8) was cloned and its role in rhizosphere signaling and plant physiology assessed by generating knock-down lines. Transgenic SlCCD8 plants were generated by RNAi-mediated silencing. Lines with different levels of strigolactone reduction - confirmed by UPLC-MS/MS - were selected and their phenotypes investigated. Lines exhibiting reduced SlCCD8 levels displayed increased shoot branching, reduced plant height, increased number of nodes and excessive adventitious root development. In addition, these lines exhibited reproductive phenotypes such as smaller flowers, fruits, as well as fewer and smaller seeds per fruit. Furthermore, we show that strigolactone loading to the xylem sap is possibly restricted to orobanchol. Infestation by Phelipanche ramosa was reduced by 90% in lines with a relatively mild reduction in strigolactone biosynthesis and secretion while arbuscular mycorrhizal symbiosis, apical dominance and fruit yield were only mildly affected. This demonstrates that reduction of strigolactone biosynthesis could be a suitable tool in parasitic weed management. Furthermore, our results suggest that strigolactones are involved in even more physiological processes than so far assumed.
New Phytologist 08/2012; 196(2):535-47. · 6.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Strigolactones are known as germination stimulants for seeds of root parasitic plants of the Orobanchaceae and as the presymbiotic branching factor for arbuscular mycorrhizal fungi. They were also recently identified as a new class of plant hormones and have been the subject of many studies, leading to much advancement in our knowledge of how these molecules are involved in controlling plant development. In the first place, this concerns their role in the inhibition of shoot branching, but a number of studies have also revealed a role for strigolactones in shaping root system architecture or have suggested involvement of strigolactones in seed germination, hypocotyl elongation, and reproductive development. In all these studies, the interaction of strigolactones with other plant hormones such as auxin, abscisic acid, and ethylene is becoming clear. In this review we discuss the progress over the past 5 years in our understanding of the physiological role of strigolactones in the regulation of plant development.
[show abstract][hide abstract] ABSTRACT: Strigolactones are signaling molecules that play a role in host recognition by parasitic plants of the Striga, Orobanche and Phelipanche genera which are among the most detrimental weeds in agriculture. The same class of molecules is also involved in the establishment of the symbiosis of plants with arbuscular mycorrhizal (AM) fungi. In addition, the strigolactones are being shown to be involved in an increasing number of physiological processes in plants, such as the regulation of plant architecture and the response to abiotic factors such as nutrient availability and light. These new findings suggest that biosynthesis and perception of strigolactones are conserved throughout the plant kingdom. The structural variation in the strigolactones discovered so far and its possible role in host recognition by the parasites and AM fungi as well as the evolution of strigolactone-dependent-germination in parasitic plants will be discussed. Finally, due to the recent advance in strigolactone research, new insights are emerging on the relation between parasitic and host plants which may result in new strategies to control parasitic plant infestation that will be discussed in this review.
[show abstract][hide abstract] ABSTRACT: The biosynthesis of the recently identified novel class of plant hormones, strigolactones, is up-regulated upon phosphate deficiency in many plant species. It is generally accepted that the evolutionary origin of strigolactone up-regulation is their function as a rhizosphere signal that stimulates hyphal branching of arbuscular mycorrhizal fungi. In this work, we demonstrate that this induction is conserved in Arabidopsis (Arabidopsis thaliana), although Arabidopsis is not a host for arbuscular mycorrhizal fungi. We demonstrate that the increase in strigolactone production contributes to the changes in shoot architecture observed in response to phosphate deficiency. Using high-performance liquid chromatography, column chromatography, and multiple reaction monitoring-liquid chromatography-tandem mass spectrometry analysis, we identified two strigolactones (orobanchol and orobanchyl acetate) in Arabidopsis and have evidence of the presence of a third (5-deoxystrigol). We show that at least one of them (orobanchol) is strongly reduced in the putative strigolactone biosynthetic mutants more axillary growth1 (max1) and max4 but not in the signal transduction mutant max2. Orobanchol was also detected in xylem sap and up-regulated under phosphate deficiency, which is consistent with the idea that root-derived strigolactones are transported to the shoot, where they regulate branching. Moreover, two additional putative strigolactone-like compounds were detected in xylem sap, one of which was not detected in root exudates. Together, these results show that xylem-transported strigolactones contribute to the regulation of shoot architectural response to phosphate-limiting conditions.
[show abstract][hide abstract] ABSTRACT: In this study, the role of the recently identified class of phytohormones, strigolactones, in shaping root architecture was addressed. Primary root lengths of strigolactone-deficient and -insensitive Arabidopsis (Arabidopsis thaliana) plants were shorter than those of wild-type plants. This was accompanied by a reduction in meristem cell number, which could be rescued by application of the synthetic strigolactone analog GR24 in all genotypes except in the strigolactone-insensitive mutant. Upon GR24 treatment, cells in the transition zone showed a gradual increase in cell length, resulting in a vague transition point and an increase in transition zone size. PIN1/3/7-green fluorescent protein intensities in provascular tissue of the primary root tip were decreased, whereas PIN3-green fluorescent protein intensity in the columella was not affected. During phosphate-sufficient conditions, GR24 application to the roots suppressed lateral root primordial development and lateral root forming potential, leading to a reduction in lateral root density. Moreover, auxin levels in leaf tissue were reduced. When auxin levels were increased by exogenous application of naphthylacetic acid, GR24 application had a stimulatory effect on lateral root development instead. Similarly, under phosphate-limiting conditions, endogenous strigolactones present in wild-type plants stimulated a more rapid outgrowth of lateral root primordia when compared with strigolactone-deficient mutants. These results suggest that strigolactones are able to modulate local auxin levels and that the net result of strigolactone action is dependent on the auxin status of the plant. We postulate that the tightly balanced auxin-strigolactone interaction is the basis for the mechanism of the regulation of the plants' root-to-shoot ratio.
[show abstract][hide abstract] ABSTRACT: A key point in the biosynthesis of the antimalarial drug artemisinin is the formation of dihydroartemisinic aldehyde which represents the key difference between chemotype specific pathways. This key intermediate is the substrate for several competing enzymes, some of which increase the metabolic flux towards artemisinin, and some of which--as we show in the present study--may have a negative impact on artemisinin production. In an effort to understand the biosynthetic network of artemisinin biosynthesis, extracts of A. annua flowers were investigated and found to contain an enzyme activity competing in a negative sense with artemisinin biosynthesis. The enzyme Red1 is a broad substrate oxidoreductase belonging to the short chain dehydrogenase/reductase family with high affinity for dihydroartemisinic aldehyde and valuable monoterpenoids. Spatial and temporal analysis of cDNA revealed Red1 to be trichome specific. The relevance of Red1 to artemisinin biosynthesis is discussed.
[show abstract][hide abstract] ABSTRACT: SUMMARY: *Strigolactones are considered a novel class of plant hormones that, in addition to their endogenous signalling function, are exuded into the rhizosphere acting as a signal to stimulate hyphal branching of arbuscular mycorrhizal (AM) fungi and germination of root parasitic plant seeds. Considering the importance of the strigolactones and their biosynthetic origin (from carotenoids), we investigated the relationship with the plant hormone abscisic acid (ABA). *Strigolactone production and ABA content in the presence of specific inhibitors of oxidative carotenoid cleavage enzymes and in several tomato ABA-deficient mutants were analysed by LC-MS/MS. In addition, the expression of two genes involved in strigolactone biosynthesis was studied. *The carotenoid cleavage dioxygenase (CCD) inhibitor D2 reduced strigolactone but not ABA content of roots. However, in abamineSG-treated plants, an inhibitor of 9-cis-epoxycarotenoid dioxygenase (NCED), and the ABA mutants notabilis, sitiens and flacca, ABA and strigolactones were greatly reduced. The reduction in strigolactone production correlated with the downregulation of LeCCD7 and LeCCD8 genes in all three mutants. *The results show a correlation between ABA levels and strigolactone production, and suggest a role for ABA in the regulation of strigolactone biosynthesis.
New Phytologist 07/2010; 187(2):343-54. · 6.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: From Artemisia annua L., a new oxidoreductase (Red 1) was cloned, sequenced and functionally characterized. Through bioinformatics, heterologous protein expression and enzyme substrate conversion assays, the elucidation of the enzymatic capacities of Red1 was achieved. Red1 acts on monoterpenoids, and in particular functions as a menthone:neomenthol oxidoreductase. The kinetic parameter k(cat)/K(m) was determined to be 939-fold more efficient for the reduction of (-)-menthone to (+)-neomenthol than results previously reported for the menthone:neomenthol reductase from Mentha x piperita. Based on its kinetic properties, the possible use of Red1 in biological crop protection is discussed.
Plant and Cell Physiology 07/2010; 51(7):1219-28. · 4.13 Impact Factor
[show abstract][hide abstract] ABSTRACT: Parasitic weeds cause severe damage to important agricultural crops. Although some promising control methods against these parasitic plants have been developed, new strategies continue to be relevant in integrated approaches. The life cycle for root parasitic weeds is intimately associated with their host and is a suitable target for such new control strategies, particularly when directed at the early stages of the host-parasite interaction. Here, the authors focus on knowledge of the germination stimulants-strigolactones-for the root parasitic plants Striga and Orobanche spp. and discuss their biosynthetic origin, ecological significance and physiological and biochemical regulation. In addition, the existing and possible new control strategies that are based on this knowledge, and that could lead to more efficient control methods against these root parasitic weeds, are reviewed.
Pest Management Science 01/2009; 65(5):471-7. · 2.59 Impact Factor