[Show abstract][Hide abstract] ABSTRACT: Background
Hessian fly (Mayetiola destructor), a member of the gall midge family, is one of the most destructive pests of wheat (Triticum aestivum) worldwide. Probing of wheat plants by the larvae results in either an incompatible (avirulent larvae, resistant plant) or a compatible (virulent larvae, susceptible plant) interaction. Virulent larvae induce the formation of a nutritive tissue, resembling the inside surface of a gall, in susceptible wheat. These nutritive cells are a rich source of proteins and sugars that sustain the developing virulent Hessian fly larvae. In addition, on susceptible wheat, larvae trigger a significant increase in levels of amino acids including proline and glutamic acid, which are precursors for the biosynthesis of ornithine and arginine that in turn enter the pathway for polyamine biosynthesis.ResultsFollowing Hessian fly larval attack, transcript abundance in susceptible wheat increased for several genes involved in polyamine biosynthesis, leading to higher levels of the free polyamines, putrescine, spermidine and spermine. A concurrent increase in polyamine levels occurred in the virulent larvae despite a decrease in abundance of Mdes-odc (ornithine decarboxylase) transcript encoding a key enzyme in insect putrescine biosynthesis. In contrast, resistant wheat and avirulent Hessian fly larvae did not exhibit significant changes in transcript abundance of genes involved in polyamine biosynthesis or in free polyamine levels.Conclusions
The major findings from this study are: (i) although polyamines contribute to defense in some plant-pathogen interactions, their production is induced in susceptible wheat during interactions with Hessian fly larvae without contributing to defense, and (ii) due to low abundance of transcripts encoding the rate-limiting ornithine decarboxylase enzyme in the larval polyamine pathway the source of polyamines found in virulent larvae is plausibly wheat-derived. The activation of the host polyamine biosynthesis pathway during compatible wheat-Hessian fly interactions is consistent with a model wherein the virulent larvae usurp the polyamine biosynthesis machinery of the susceptible plant to acquire nutrients required for their own growth and development.
[Show abstract][Hide abstract] ABSTRACT: Evidence is emerging that some proteins secreted by gall-forming parasites of plants act as effectors responsible for systemic changes in the host plant, such as galling and nutrient tissue formation. A large number of secreted salivary gland proteins (SSGPs) that are the putative effectors responsible for the physiological changes elicited in susceptible seedling wheat by Hessian fly, Mayetiola destructor (Say), larvae have been documented. However, how the genes encoding these candidate effectors might respond under field conditions is unknown. The goal of this study was to use microarray analysis to investigate variation in SSGP transcript abundance amongst field collections from different geographical regions (southeastern USA, central USA, and the Middle East). Results revealed significant variation in SSGP transcript abundance amongst the field collections studied. The field collections separated into three distinct groups that corresponded to the wheat classes grown in the different geographical regions as well as to recently described Hessian fly populations. These data support previous reports correlating Hessian fly population structure with micropopulation differences owing to agro-ecosystem parameters such as cultivation of regionally adapted wheat varieties, deployment of resistance genes and variation in climatic conditions.
[Show abstract][Hide abstract] ABSTRACT: Deployment of resistance (R) genes is the most effective control for Hessian fly, Mayetiola destructor (Say); however, deployment of R genes results in an increased frequency of pest genotypes that display virulence to them. RNA interference (RNAi) is a useful reverse genetics tool for studying such insect virulence pathways, but requires a systemic phenotype, which is not found in all species. In an effort to correlate our observed weak RNAi phenotype in M. destructor with a genetic basis, we have aggregated and compared RNAi related genes across M. destructor, three other insect species, and the nematode Caenorhabditis elegans. We report here the annotation of the core genes in the small interfering RNA (siRNA) and microRNA (miRNA) pathways in M. destructor. While most of the miRNA pathway genes were highly conserved across the species studied, the siRNA pathway genes showed increased relative variability in comparison to the miRNA pathway. In particular, the Piwi/Argonaute/Zwille (PAZ) domain of Dicer-2 (DCR-2) had the least amount of sequence similarity of any domain among species surveyed, with a trend of increased conservation in those species with amenable systemic RNAi. A homolog of the systemic interference defective-1 (Sid-1) gene of C. elegans was also not annotated in the M. destructor genome. Indeed, it is of interest that a Sid-1 homolog has not been detected in any dipteran species to date. We hypothesize the sequence architecture of the PAZ domain in the M. destructor DCR-2 protein is related to reduced efficacy of this enzyme and this taken together with the lack of a Sid-1 homolog may account for the weak RNAi response observed to date in this species as well as other dipteran species.
[Show abstract][Hide abstract] ABSTRACT: Gall midges constitute an important group of plant-parasitic insects. The Hessian fly (HF; Mayetiola destructor), the most investigated gall midge, was the first insect hypothesized to have a gene-for-gene interaction with its host plant, wheat (Triticum spp.). Recent investigations support that hypothesis. The minute larval mandibles appear to act in a manner that is analogous to nematode stylets and the haustoria of filamentous plant pathogens. Putative effector proteins are encoded by hundreds of genes and expressed in the HF larval salivary gland. Cultivar-specific resistance (R) genes mediate a highly localized plant reaction that prevents the survival of avirulent HF larvae. Fine-scale mapping of HF avirulence (Avr) genes provides further evidence of effector-triggered immunity (ETI) against HF in wheat. Taken together, these discoveries suggest that the HF, and other gall midges, may be considered biotrophic, or hemibiotrophic, plant pathogens, and they demonstrate the potential that the wheat-HF interaction has in the study of insect-induced plant gall formation.
[Show abstract][Hide abstract] ABSTRACT: Samples of a dipteran pest of wheat were tested to confirm identity, describe local populations and suggest the use of deploying resistance (R) genes in wheat cultivars for control of Mayetiola destructor, Hessian fly (HF). Morphological evaluation of adults and a free-choice oviposition preference test documenting that females overwhelmingly preferred to oviposit on wheat instead of barley supported they were HF. Using the cytochrome c oxidase subunit I (coxI), the Barcoding Region, nine haplotypes were revealed. Two were found only in the Israeli collections and averaged 3% sequence divergence compared to the other seven haplotypes found in the United States, Israel and Syria. In evaluations of virulence, the Israeli HF in culture was virulent to 11 of the 19 (R) genes tested, and complementation analysis documented that, for four of the R genes tested, the Israeli HF shared loci for virulence with HF from the United States. Levels of HF infestation at seven Israeli fields were at least at the 5-8% level, which historically has indicated a significant yield loss. Microsatellite genotyping of the five HF collections from Israel revealed mixed populations in Israel that are distinctly separate from the single population in Syria.
Bulletin of entomological research 05/2012; 102(06):1-12. DOI:10.1017/S0007485312000235 · 1.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: One strategy to enhance the durability of Hessian fly resistance (R) genes in wheat is to combine them with transgenes for resistance. To identify potential transgenes for resistance a protocol for rapidly screening the proteins they encode for efficacy toward resistance is required. However, the Hessian fly is an obligate parasite of wheat and related grasses. Consequently, no protocol for in vitro delivery of antinutrient or toxic proteins to feeding larvae is available. We report here the development of a Hessian fly in plantatranslocation (HIT) feeding assay and the evaluation of eight lectins and the Bowman-Birk serine proteinase inhibitor for potential in transgenic resistance. Of the antinutrient proteins evaluated, Galanthus nivalis L. agglutinin (GNA), commonly termed snowdrop lectin, was the most efficacious. Ingestion of GNA caused a significant reduction in growth of Hessian fly larvae, disruption of midgut microvilli, and changes in transcript level of genes involved in carbohydrate metabolism, digestion, detoxification, and stress response. These effects of GNA are discussed from the perspective of larval Hessian fly physiology.
[Show abstract][Hide abstract] ABSTRACT: Mayetiola destructor (Say) (Diptera: Cecidomyiidae), the Hessian fly, is distributed across most of the wheat (Triticum aestivum L.)-growing areas of the world and can cause significant yield losses in wheat production. Native to the Old World, Hessian fly reportedly came to the United States in a single introduction during the Revolutionary War and has since spread across North America. Using a nuclear marker, the population structure of North American Hessian fly was examined with regard to collections from the Old World. White intron 1 (wint1) showed insignificant recombination within collections and a large number of informative characters, allowing its use as a phylogenetic marker. Thirty-three alleles of wint1 were identified. Population structure analyses divided the collections into four populations: Middle East, Old World I, Old World II, and New World. More variation was found within populations than between populations, indicating that gene flow exists between local areas. However, shared ancestral characteristics resulted in mixing of Hessian fly collections into more than one population as revealed by the population structure reconstruction. North American and Spanish collections were a mixture of the Old and New World populations. With the sharing of ancestral characters as well as wint1 alleles, this study indicates that the North American lineage may actually be associated to an unsampled location, perhaps northern Europe. If the single introduction hypothesis were correct, then both lineages would have to have been present at the time of introduction.
Annals of the Entomological Society of America 07/2011; 104(Jul 2011):666-674. DOI:10.1603/AN10154 · 1.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Salivary secretions of neonate Hessian fly larvae initiate a two-way exchange of molecules with their wheat host. Changes in properties of the leaf surface allow larval effectors to enter the plant where they trigger plant processes leading to resistance and delivery of defence molecules, or susceptibility and delivery of nutrients. To increase understanding of the host plant's response, the timing and characteristics of the induced epidermal permeability were investigated. Resistant plant permeability was transient and limited in area, persisting just long enough to deliver defence molecules before gene expression and permeability reverted to pre-infestation levels. The abundance of transcripts for GDSL-motif lipase/hydrolase, thought to contribute to cuticle reorganization and increased permeability, followed the same temporal profile as permeability in resistant plants. In contrast, susceptible plants continued to increase in permeability over time until the entire crown of the plant became a nutrient sink. Permeability increased with higher infestation levels in susceptible but not in resistant plants. The ramifications of induced plant permeability on Hessian fly populations are discussed.
[Show abstract][Hide abstract] ABSTRACT: Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is currently the most important insect pest of soybean (Glycine max (L.) Merr.) in the United States and causes significant economic damage worldwide, but little is known about the aphid at the molecular level. Mariner-like transposable elements (MLEs) are ubiquitous within the genomes of arthropods and various other invertebrates. In this study, we report the cloning of MLEs from the soybean aphid genome using degenerate PCR primers designed to amplify conserved regions of mariner transposases. Two of the ten sequenced clones (designated as Agmar1 and Agmar2) contained partial but continuous open reading frames, which shared high levels of homology at the protein level with other mariner transposases from insects and other taxa. Phylogenetic analysis revealed Agmar1 to group within the irritans subfamily of MLEs and Agmar2 within the mellifera subfamily. Southern blot analysis and quantitative PCR analysis indicated a low copy number for Agmar1-like elements within the soybean aphid genome. These results suggest the presence of at least two different putative mariner-like transposases encoded by the soybean aphid genome. Both Agmar1 and Agmar2 could play influential roles in the architecture of the soybean aphid genome. Transposable elements are also thought to potentially mediate resistance in insects through changes in gene amplification and mutations in coding sequences. Finally, Agmar1 and Agmar2 may represent useful genetic tools and provide insights on A. glycines adaptation.
Bulletin of entomological research 05/2011; 101(6):697-704. DOI:10.1017/S0007485311000253 · 1.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genetic resistance in wheat, Triticum aestivum L., is the most efficacious method for control of Hessian fly, Mayetiola destructor (Say) (Diptera: Cecidomyiidae). However, because of the appearance of new genotypes (biotypes) in response to deployment of resistance, field collections of Hessian fly need to be evaluated on a regular basis to provide breeders and producers information on the efficacy of resistance (R) genes with respect to the genotype composition of Hessian fly in regional areas. We report here on the efficacy of 21 R genes in wheat to field collections of Hessian fly from the southeastern United States. Results documented that of the 21 R genes evaluated only five would provide effective protection of wheat from Hessian fly in the southeastern United States. These genes were H12, H18, H24, H25, and H26. Although not all of the 33 identified R genes were evaluated in the current study, these results indicate that identified genetic resistance to protect wheat from Hessian attack in the southeastern United States is a limited resource. Historically, R genes for Hessian fly resistance in wheat have been deployed as single gene releases. Although this strategy has been successful in the past, we recommend that in the future deployment of combinations of highly effective previously undeployed genes, such as H24 and H26, be considered. Our study also highlights the need to identify new and effective sources of resistance in wheat to Hessian fly if genetic resistance is to continue as a viable option for protection of wheat in the southeastern United States.
[Show abstract][Hide abstract] ABSTRACT: Nous avons récupéré deux séquences complètes d'ADN complémentaire qui codent pour les sérines protéases digestives (désignées SmPROT-1 et SmPROT-2) dans le tube digestif moyen de la cécidomyie orangée du blé, Sitodiplosis mosellana (Géhin) (Dipera : Cecidomyiidae), dans le cadre d'une étude en cours sur les marqueurs de séquences exprimées. Les séquences d'acides aminés déduites partagent des homologies avec les sérines protéases digestives d'espèces d'insectes et de non insectes, incluant les régions conservées, telles que la triade catalytique, la poche d'interaction et les motifs structuraux conservés. Des peptides de signal de sécrétion dans les deux protéases aux terminaux N indiquent que ces protéines pourraient servir de sérines protéases digestives dans le tube digestif moyen. Une analyse phylogénétique regroupe SmPROT-1 et SmPROT-2 respectivement avec les sérines protéases de type trypsine et chymotrysine. Une analyse d'amplification en chaîne par polymérase (PCR) quantitative en temps réel montre que SmPROT-1 et SmPROT-2 sont exprimées plus dans le tube digestif moyen par comparaison aux autres tissus (corps gras et glandes salivaires). Des analyses d'expression génique montrent des concentrations élevées d'ARNm chez les stades qui s'alimentent (larves de 1er et 2e stades) par rapport aux autres stades (néonates, larves de 3e stade, nymphes et adultes). Nos résultats ouvrent de nouvelles perspectives sur la biologie de S. mosellana; nous en discutons dans le contexte de la mise au point de stratégies de contrôle de rechange. [Traduit par la Rédaction]
The Canadian Entomologist 11/2010; 142(Dec 2010):532-545. DOI:10.4039/n10-042 · 0.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In most protein-coding genes, greater sequence variation is observed in noncoding regions (introns and untranslated regions) than in coding regions due to selective constraints. During characterization of genes and transcripts encoding small secreted salivary gland proteins (SSSGPs) from the Hessian fly, we found exactly the opposite pattern of conservation in several families of genes: the non-coding regions were highly conserved, but the coding regions were highly variable.
Seven genes from the SSSGP-1 family are clustered as one inverted and six tandem repeats within a 15 kb region of the genome. Except for SSSGP-1A2, a gene that encodes a protein identical to that encoded by SSSGP-1A1, the other six genes consist of a highly diversified, mature protein-coding region as well as highly conserved regions including the promoter, 5'- and 3'-UTRs, a signal peptide coding region, and an intron. This unusual pattern of highly diversified coding regions coupled with highly conserved regions in the rest of the gene was also observed in several other groups of SSSGP-encoding genes or cDNAs. The unusual conservation pattern was also found in some of the SSSGP cDNAs from the Asian rice gall midge, but not from the orange wheat blossom midge. Strong positive selection was one of the forces driving for diversification whereas concerted homogenization was likely a mechanism for sequence conservation.
Rapid diversification in mature SSSGPs suggests that the genes are under selection pressure for functional adaptation. The conservation in the noncoding regions of these genes including introns also suggested potential mechanisms for sequence homogenization that are not yet fully understood. This report should be useful for future studies on genetic mechanisms involved in evolution and functional adaptation of parasite genes.
[Show abstract][Hide abstract] ABSTRACT: The Hessian fly (Mayetiola destructor) is an agriculturally important pest of wheat. A mariner element (Desmar1) has been previously identified in the Hessian fly genome. Using Desmar1 as a probe, we isolated individual copies of Desmar-like elements from the Hessian fly genome cloned in bacterial artificial chromosomes (BACs) and studied their structural variability and flanking DNA sequences. The partial Desmar-like copies are relatively more abundant (∼64%) than full length copies (∼36%) in the Hessian fly genome. Most of the full length copies are consistently flanked by an EcoRI restriction site that occurs 32 bp from one end and 66 bp from the other end of the mariner. Using an amplified fragment length polymorphism-PCR (AFLP-PCR) based method, we identified segregating polymorphisms associated with Desmar elements in a F₂ mapping population. We were able to use the segregation data to localize the chromosomal position of three Desmar elements by linkage analysis. As paternal chromosomes are eliminated in the Hessian fly during early embryogenesis, two-thirds of the AFLPs were expected to be polymorphic in the mapping population and this was observed for AFLPs anchored to full length Desmar copies but not to the partial copies. Thus, our data indicate that dead and partial Desmar-like copies are probably associated with less polymorphic regions and may represent mariner graveyards in the Hessian fly genome.
[Show abstract][Hide abstract] ABSTRACT: The focus of the present study was to compare ultrastructure in the midguts of larvae of the Hessian fly, Mayetiola destructor (Say), under different feeding regimens. Larvae were either fed on Hessian fly-resistant or -susceptible wheat, and each group was compared to starved larvae. Within 3h of larval Hessian fly feeding on resistant wheat, midgut microvilli were disrupted, and after 6h, microvilli were absent. The disruption in microvilli in larvae feeding on resistant wheat were similar to those reported for midgut microvilli of European corn borer, Ostrinia nubilasis (Hubner), larvae fed a diet containing wheat germ agglutinin. Results from the present ultrastructural study, coupled with previous studies documenting expression of genes encoding lectin and lectin-like proteins is rapidly up-regulated in resistant wheat to larval Hessian fly, are indications that the midgut is a target of plant resistance compounds. In addition, the midgut of the larval Hessian fly is apparently unique among other dipterans in that no peritrophic membrane was observed. Ultrastructural changes in the midgut are discussed from the prospective of their potential affects on the gut physiology of Hessian fly larvae and the mechanism of antibiosis in the resistance of wheat to Hessian fly attack.
[Show abstract][Hide abstract] ABSTRACT: The Hessian fly, Mayetiola destructor, is a serious pest of wheat and an experimental organism for the study of gall midge-plant interactions. In addition to food digestion and detoxification, the gut of Hessian fly larvae is also an important interface for insect-host interactions. Analysis of the genes expressed in the Hessian fly larval gut will enhance our understanding of the overall gut physiology and may also lead to the identification of critical molecules for Hessian fly-host plant interactions. Over 10,000 Expressed Sequence Tags (ESTs) were generated and assembled into 2007 clusters. The most striking feature of the Hessian fly larval transcriptome is the existence of a large number of transcripts coding for so-called small secretory proteins (SSP) with amino acids less than 250. Eleven of the 30 largest clusters were SSP transcripts with the largest cluster containing 11.3% of total ESTs. Transcripts coding for diverse digestive enzymes and detoxification proteins were also identified. Putative digestive enzymes included trypsins, chymotrypsins, cysteine proteases, aspartic protease, endo-oligopeptidase, aminopeptidases, carboxypeptidases, and alpha-amylases. Putative detoxification proteins included cytochrome P450s, glutathione S-transferases, peroxidases, ferritins, a catalase, peroxiredoxins, and others. This study represents the first global analysis of gut transcripts from a gall midge. The identification of a large number of transcripts coding for SSPs, digestive enzymes, detoxification proteins in the Hessian fly larval gut provides a foundation for future studies on the functions of these genes.
[Show abstract][Hide abstract] ABSTRACT: The Hessian fly is a serious pest of wheat and an experimental organism for the study of gall midge-plant interactions. In addition to food digestion and detoxification, the gut of Hessian fly larvae is also an important interface for insect-host interactions. Analysis of the genes expressed in the Hessian fly larval gut will enhance our understanding of the overall gut physiology and may also lead to the identification of critical molecules for Hessian fly host plant interactions. Over 10,000 Expressed Sequence Tags (ESTs) were generated and assembled into 2,007 clusters (contigs and singletons). The most striking feature of the Hessian fly larval transcriptome is the existence of a large number of transcripts coding for so-called small secretory proteins (SSP) with amino acids less than 250. Eleven of the 30 largest clusters were SSP transcripts with the largest cluster containing 11.3% of total ESTs. Micorarray and qPCR analyses of representative SSP transcripts revealed that most of them were predominantly present in the gut tissue and the transcript levels of many SSP were affected by plant types on which larvae feed. This study represents the first global analysis of gut transcripts from a gall midge.
Entomological Society of America Annual Meeting 2009; 12/2009