Modulation of defense-response gene expression in wheat during Hessian fly larval feeding

Abstract

Expression profiles of ten genes commonly up-regulated during plant defense against microbial pathogens were compared temporally during compatible and incompatible interactions with first-instar Hessian fly larvae, in two wheat lines carrying different resistance genes. Quantitative real-time PCR revealed that while a lipoxygenase gene (WCI-2) was strongly up-regulated during the incompatible interactions, genes encoding β-1,3 endoglucanase (GNS) and an integral membrane protein (WIR1) were moderately responsive. Genes for thionin-like protein (WCI-3), PR-17-like protein (WCI-5), MAP kinase (WCK-1), phenylalanine ammonia-lyase (PAL), pathogenesis-related protein-1 (PR-1), receptor-like kinase (LRK10) and heat shock protein 70 (HSP70) were minimally responsive. The application of signaling molecules, salicylic acid (SA), methyl jasmonate (MJ) and abscisic acid (ABA), to insect-free plants demonstrated association of these genes with specific defense-response pathways. SA-induced up-regulation of a gene related to lipoxygenases that are involved in jasmonic acid (JA)-biosynthesis is suggestive of positive cross-talk between SA- and JA-mediated signaling pathways. Data suggest that alternative mechanisms may be involved since few of these classical defense-response genes are significantly up-regulated during incompatible interactions between wheat and Hessian fly.     

Feeding by Hessian Fly (Mayetiola destructor [Say]) Larvae on Wheat Increases Levels of Fatty Acids and Indole-3-Acetic Acid but not Hormones Involved in Plant-Defense Signaling

Gall-inducing insects exert a unique level of control over the physiology of their host plants. This control can extend to host–plant defenses so that some, if not most, gall-inducing species appear to avoid or modify host plant defenses to effect production of their gall. Included among gall insects is Hessian fly (Mayetiola destructor [Say], Diptera: Cecidomyiidae), a damaging pest of wheat (Triticum aestivum L.) and an emerging model system for studying plant–insect interactions. We studied the dynamics of some defense-related phytohormones and associated fatty acids during feeding of first instar Hessian fly larvae on a susceptible variety of wheat. We found that Hessian fly larvae significantly elevated in their host plants’ levels of linolenic and linoleic acids, fatty acids that may be nutritionally beneficial. Hessian fly larvae also elevated levels of indole-3-acetic acid (IAA), a phytohormone hypothesized to be involved in gall formation, but not the defense-related hormones jasmonic (JA) and salicylic acids. Moreover, we detected in Hessian fly-infested plants a significant negative relationship between IAA and JA that was not present in control plants. Our results suggest that Hessian fly larvae may induce nutritionally beneficial changes while concomitantly altering phytohormone levels, possibly to facilitate plant-defense avoidance.     

Feeding by Hessian fly [Mayetiola destructor (Say)] larvae does not induce plant indirect defences

Abstract.  1. Recent research has addressed the function of herbivore-induced plant volatiles in attracting natural enemies of feeding herbivores. While many types of insect herbivory appear to elicit volatile responses, those triggered by gall insects have received little attention. Previous work indicates that at least one gall insect species induces changes in host-plant volatiles, but no other studies appear to have addressed whether gall insects trigger plant indirect defences.
2. The volatile responses of wheat to feeding by larvae of the Hessian fly Mayetiola destructor (Say) (Diptera: Cecidomyiidae) were studied to further explore indirect responses of plants to feeding by gall insects. This specialist gall midge species did not elicit a detectable volatile response from wheat plants, whereas a generalist caterpillar triggered volatile release. Moreover, Hessian fly feeding altered volatile responses to subsequent caterpillar herbivory.
3. These results suggest that Hessian fly larvae exert a degree of control over the defensive responses of their host plants and offer insight into plant-gall insect interactions. Also, the failure of Hessian fly larvae to elicit an indirect defensive response from their host plants may help explain why natural enemies, which often rely on induced volatile cues, fail to inflict significant mortality on M. destructor populations in the field.     

Gene-for-gene defense of wheat against the Hessian fly lacks a classical oxidative burst

Genetic similarities between plant interactions with microbial pathogens and wheat interactions with Hessian fly larvae prompted us to investigate defense and counterdefense mechanisms. Plant oxidative burst, a rapid increase in the levels of active oxygen species (AOS) within the initial 24 h of an interaction with pathogens, commonly is associated with defenses that are triggered by gene-for-gene recognition events similar to those involving wheat and Hessian fly larvae. RNAs encoded by Hessian fly superoxide dismutase (SOD) and catalase (CAT) genes, involved in detoxification of AOS, increased in first-instar larvae during both compatible and incompatible interactions. However, mRNA levels of a wheat NADPH oxidase (NOX) gene that generates superoxide (O2-) did not increase. In addition, inhibiting wheat NOX enzyme with diphenyleneiodonium did not result in increased survival of avirulent larvae. However, nitro blue tetrazolium staining indicated that basal levels of O2- are present in both uninfested and infested wheat tissue. mRNA encoded by wheat genes involved in detoxification of the cellular environment, SOD, CAT, and glutathione-S-transferase did not increase in abundance. Histochemical staining with 3,3-diaminobenzidine revealed no increases in wheat hydrogen peroxide (H2O2) during infestation that were correlated with the changes in larval SOD and CAT mRNA. However, treatment with 2',7'-dichlorofluorescin demonstrated the presence of basal levels of H2O2 in the elongation zone of both infested and uninfested plants. The accumulation of a wheat flavanone 3-hydroxylase mRNA did show some parallels with larval gene mRNA profiles. These results suggested that larvae encounter stresses imposed by mechanisms other than an oxidative burst in wheat seedlings.     

A novel wheat gene encoding a putative chitin-binding lectin is associated with resistance against Hessian fly

The gene-for-gene interaction triggering resistance of wheat against first-instar Hessian fly larvae utilizes specialized defence response genes not previously identified in other interactions with pests or pathogens. We characterized the expression of Hfr-3 , a novel gene encoding a lectin-like protein with 68–70% identity to the wheat germ agglutinins. Within each of the four predicted chitin-binding hevein domains, the HFR-3 translated protein sequence contained five conserved saccharide-binding amino acids. Quantification of Hfr-3 mRNA levels confirmed a rapid response and gradual increase, up to 3000-fold above the uninfested control in the incompatible interaction 3 days after egg hatch. Hfr-3 mRNA abundance was influenced by the number of larvae per plant, suggesting that resistance is localized rather than systemic. In addition, Hfr-3 was responsive to another sucking insect, the bird cherry-oat aphid, but not to fall armyworm attack, wounding or exogenous application of methyl jasmonate, salicylic acid or abscisic acid. Western blot analysis demonstrated that HFR-3 protein increased in parallel to mRNA levels in crown tissues during incompatible interactions. HFR-3 protein was detected in both virulent and avirulent larvae, indicating ingestion. Anti-nutritional proteins, such as lectins, may be responsible for the apparent starvation of avirulent first-instar Hessian fly larvae during the initial few days of incompatible interactions with resistant wheat plants.     

Fusarium oxysporum mediates systems metabolic reprogramming of chickpea roots as revealed by a combination of proteomics and metabolomics

Molecular changes elicited by plants in response to fungal attack and how this affects plant–pathogen interaction, including susceptibility or resistance, remain elusive. We studied the dynamics in root metabolism during compatible and incompatible interactions between chickpea and Fusarium oxysporum f. sp. ciceri (Foc), using quantitative label‐free proteomics and NMR‐based metabolomics. Results demonstrated differential expression of proteins and metabolites upon Foc inoculations in the resistant plants compared with the susceptible ones. Additionally, expression analysis of candidate genes supported the proteomic and metabolic variations in the chickpea roots upon Foc inoculation. In particular, we found that the resistant plants revealed significant increase in the carbon and nitrogen metabolism; generation of reactive oxygen species (ROS), lignification and phytoalexins. The levels of some of the pathogenesis‐related proteins were significantly higher upon Foc inoculation in the resistant plant. Interestingly, results also exhibited the crucial role of altered Yang cycle, which contributed in different methylation reactions and unfolded protein response in the chickpea roots against Foc. Overall, the observed modulations in the metabolic flux as outcome of several orchestrated molecular events are determinant of plant's role in chickpea–Foc interactions.     

Hypersensitive response of wheat to the Hessian fly

Hessian flyMayetiola destructor (Say) larvae are able to obtain food from their host plant without inflicting mechanical damage to the plant surface, apparently by secreting substances which elicit release of nutrients from plant cells surrounding the feeding site. Cells of fully susceptible plants retain their normal appearances, while in resistant plants extensive areas of cellular collapse occur. These responses indicate that hypersensitivity is the basis of wheat's resistance to the Hessian fly. The fly's feeding mechanism more closely resembles that of a pathogen than of a phytophagous insect; correspondingly, both the genetic relationship and resistance mechanism of the host plant to the parasite are of the sorts commonly associated with bacterial and fungal pathogens.     

Biotypes of Hessian fly (Dipt., Cecidomyiidae) in Morocco

Hessian fly, Mayetiola destructor (Say), is the most important insect pest of wheat in Morocco, where host plant resistance has been used successfully for control. Our objective was to determine the frequency of Hessian fly virulence on H5, H13 and H22 resistance genes. Five Hessian fly populations from the principal cereal‐growing regions in Morocco were studied. The variability in percentage of susceptible plants across Hessian fly populations was highly significant (P < 0.01), indicating differences in virulence frequencies. Plants with the H13 gene had the lowest percentage of susceptible plants, 1.77 and 1.51%, when infested with Hessian flies from Fes and Marchouch, respectively. A low level of virulence to H22 was detected in Fes, Abda and Marchouch populations, 1.87, 1.54 and 1.99% susceptible plants, respectively. The level of virulence to H5 was low in all the five populations. The Beni Mellal population gave the highest percentage of susceptible plants carrying H13 and H22 genes, 6.43 and 7.28%, respectively. The size of live larvae on susceptible plants of the three cultivars carrying H5, H13 and H22 was similar to that of the susceptible check, indicating that a true virulence (biotype) is developing in Hessian fly populations in Morocco. Thus, continuous monitoring of the development of Hessian fly biotypes is essential for optimal deployment of resistance genes.     

The NIa‐Pro protein of Turnip mosaic virus improves growth and reproduction of the aphid vector,Myzus persicae (green peach aphid)

Many plant viruses depend on aphids and other phloem‐feeding insects for transmission within and among host plants. Thus, viruses may promote their own transmission by manipulating plant physiology to attract aphids and increase aphid reproduction. Consistent with this hypothesis, Myzus persicae (green peach aphids) prefer to settle on Nicotiana benthamiana infected with Turnip mosaic virus (TuMV) and fecundity on virus‐infected N. benthamiana and Arabidopsis thaliana (Arabidopsis) is higher than on uninfected controls. TuMV infection suppresses callose deposition, an important plant defense, and increases the amount of free amino acids, the major source of nitrogen for aphids. To investigate the underlying molecular mechanisms of this phenomenon, 10 TuMV genes were over‐expressed in plants to determine their effects on aphid reproduction. Production of a single TuMV protein, nuclear inclusion a‐protease domain (NIa‐Pro), increased M. persicae reproduction on both N. benthamiana and Arabidopsis. Similar to the effects that are observed during TuMV infection, NIa‐Pro expression alone increased aphid arrestment, suppressed callose deposition and increased the abundance of free amino acids. Together, these results suggest a function for the TuMV NIa‐Pro protein in manipulating the physiology of host plants. By attracting aphid vectors and promoting their reproduction, TuMV may influence plant–aphid interactions to promote its own transmission.     

Accommodation of powdery mildew fungi in intact plant cells

Parasitic powdery mildew fungi have to overcome basic resistance and manipulate host cells to establish a haustorium as a functional feeding organ in a host epidermal cell. Currently, it is of central interest how plant factors negatively regulate basal defense or whether they even support fungal development in compatible interactions. Additionally, creation of a metabolic sink in infected cells may involve host activity. Here, we review the current progress in understanding potential fungal targets for host reprogramming and nutrient acquisition.     

Ultrastructural changes in the midguts of Hessian fly larvae feeding on resistant wheat

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 3 h of larval Hessian fly feeding on resistant wheat, midgut microvilli were disrupted, and after 6 h, 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.     

Archives of insect biochemistry and physiology guide for authors

Several carbohydrases and glycosidases from the alimentary cancal and/or salivary glands of feeding larvae of mayetiola destructor have been identified. Pectinase activity was identified in the midgut and may be present in the salivary glands. No endocellulase activity was found in larvae; however, hemicellulase activity was detected in extract of larvae. Amylase activity was present in midguts from feeding larvae and at a low level in extract of salivary glands. Amylases detected in the midgut showed mobilities during polyacrylamide gel electrophoresis similar to the two major amylases in tissues of the insect's host plant. The possibility exists that Hessian fly larvae utilize amylases obtained from their host plant in the digestion of starch. The major glycosidases detected in the midgut lumen of larve were: α-D-glucosidase and α-D-and β-D-galactosidase. The role of these enzymes in the feeding process of Hessian fly larvae is discussed as well as their potential role in feeding damage to wheat.