Explore the vast range of titles available.

The Hessian fly is an obligate parasite of wheat causing significant economic damage, and triggers either a resistant or susceptible reaction. However, the molecular mechanisms of susceptibility leading to the establishment of the larvae are unknown. Larval survival on the plant requires the establishment of a steady source of readily available nutrition. Unlike other insect pests, the Hessian fly larvae have minute mandibles and cannot derive their nutrition by chewing tissue or sucking phloem sap. Here, we show that the virulent larvae produce the glycoside hydrolase MdesGH32 extra-orally, that localizes within the leaf tissue being fed upon. MdesGH32 has strong inulinase and invertase activity aiding in the breakdown of the plant cell wall inulin polymer into monomers and converting sucrose, the primary transport sugar in plants, to glucose and fructose, resulting in the formation of a nutrient-rich tissue. Our finding elucidates the molecular mechanism of nutrient sink formation and establishment of susceptibility.

Background Wheat production is increasingly challenged by the devastating damage caused by insect pests. The advent of global warming is further exacerbating this threat. Hessian fly ( Mayetiola destructor ), a dipteran gall midge, is a destructive pest of host wheat ( Triticum aestivum ) having severe economic consequences. Planting wheat cultivars harboring resistance genes is the most effective and economical Hessian fly management strategy. However, heat stress poses a challenge to this strategy, as elevated temperature often breaks down Hessian fly resistance in wheat. Our prior study identified temperature-independent resistant T. turgidum (durum wheat) accessions that maintained resistance to Hessian fly when challenged with an increased temperature of 30 °C. In this study, we carried out follow-up characterization of these durum lines to highlight molecular components involved during Hessian fly resistance or susceptibility in wheat following heat stress. Results Temperature-independent resistant durum lines were greater than 70% resistant to multiple Hessian fly biotypes at the elevated temperature of 30 °C. At the molecular level, these lines showed increased transcripts of Hfr-1 , a gene encoding an antinutrient lectin, unlike the heat-triggered susceptible durum wheat. The Hessian fly susceptibility-associated biomarker genes were significantly upregulated in the durum wheat with heat-triggered susceptibility at 30 °C, resembling the gene expression profile observed in susceptible wheat. None of these susceptibility-associated genes were differentially expressed in the temperature-independent resistant wheat. Genes involved in oxidative stress and jasmonic acid pathways did not reveal any specific expression pattern attributed to either heat stress or larval feeding. Neutral red staining revealed limited cell wall permeability in the temperature-independent resistant wheat, unlike the heat-triggered susceptible durum plants that were highly permeable similar to a wheat line susceptible to Hessian fly at 20 °C. Conclusions Temperature-independent resistant durum wheat lines provided robust resistance to multiple Hessian fly biotypes at higher temperatures. These lines offer a valuable resource for wheat producers for providing resistance following heat stress.

The greenbug aphid (Schizaphis graminum (Rondani)) is a major pest of wheat and an important vector of wheat viruses. An RNA-seq study was conducted to investigate the microbial effects of two greenbug genotypes, the presence or absence of cereal yellow dwarf virus, and the condition of the wheat host over a 20-day time course of unrestricted greenbug feeding. Messenger RNA reads were mapped to ca. 47,000 bacterial, 1218 archaeal, 14,165 viral, 571 fungal, and 94 protozoan reference or representative genomes, plus greenbug itself and its wheat host. Taxon counts were analyzed with QIIME2 and DESeq2. Distinct early (days 1 through 10) and late (days 15 and 20) communities differed in the abundance of typical enteric genera (Shigella, Escherichia, Citrobacter), which declined in the late community, while the ratio of microbial to greenbug read counts declined 50% and diversity measures increased. The nearly universal aphid endosymbiont, Buchnera aphidicola, accounted for less than 25% of the read counts in both communities. There were 302 differentially expressed (populated) genera with respect to early and late dates, while 25 genera differed between the greenbug genotypes and nine differed between carrier and virus-free greenbugs. The late community was likely responding to starvation as the wheat host succumbed to aphid feeding. Our results add to basic knowledge about aphid microbiomes and offer an attractive alternative method to assess insect microbiomes.

Insect UDP-glycosyltransferases (UGTs) play an important role in detoxification of substrates such as plant allelochemicals, and cuticle formation by the process of glucosidation. Hessian fly ( Mayetiola destructor ), belonging to the order Diptera (Family: Cecidomyiidae), is a destructive pest of host wheat causing significant economic losses. In the current study, using the assembled genome, we identified thirteen genes in M. destructor that belong to the family of UGTs ( MdesUGT ). Expression profiling revealed differential expression of MdesUGT genes in Hessian fly feeding instars. Further, we report the molecular cloning of MdesUGT1 , designated as UGT301F1, from M. destructor . Characterization of the MdesUGT1 amino acid sequence revealed a conserved signature motif and sugar donor-binding domains characteristic of UGT proteins. Further expression analysis revealed dramatic increase in transcript accumulation of MdesUGT1 in the first and second feeding instars during compatible interactions (susceptible wheat, virulent larvae) but lacked significant upregulation during incompatible wheat Hessian fly interactions. Similar increase in MdesUGT1 transcripts was also observed during interactions of Hessian fly with nonhost, Brachypodium distachyon . These findings suggest the possible early involvement of MdesUGT1 in detoxification of plant toxins, and subsequent role in cuticular formation, thus contributing to the growth and development of this dipteran insect pest. Identification and characterization of insect UGTs could provide valuable insights into the detoxification and growth inhibitory mechanisms and facilitate future plant pest management strategies.

The Hessian fly is a destructive pest of wheat causing severe economic damage. Numerous genes and associated biological pathways have been implicated in defense against Hessian fly. However, due to limited genetic resources, compounded with genome complexity, functional analysis of the candidate genes are challenging in wheat. Physically, Brachypodium distachyon (Bd) exhibits nonhost resistance to Hessian fly, and with a small genome size, short life cycle, vast genetic resources and amenability to transformation, it offers an alternate functional genomic model for deciphering plant-Hessian fly interactions. RNA-sequencing was used to reveal thousands of Hessian fly-responsive genes in Bd one, three, and five days after egg hatch. Genes encoding defense proteins, stress-regulating transcription factors, signaling kinases, and secondary metabolites were strongly up-regulated within the first 24 hours of larval feeding indicating an early defense, similar to resistant wheat. Defense was mediated by a hypersensitive response that included necrotic lesions, up-regulated ROS-generating and -scavenging enzymes, and H 2 O 2 production. Suppression of cell wall-associated proteins and increased cell permeability in Bd resembled susceptible wheat. Thus, Bd molecular responses shared similarities to both resistant and susceptible wheat, validating its suitability as a model genome for undertaking functional studies of candidate Hessian fly-responsive genes.

Highly specialized obligate plant-parasites exist within several groups of arthropods (insects and mites). Many of these are important pests, but the molecular basis of their parasitism and its evolution are poorly understood. One hypothesis is that plant parasitic arthropods use effector proteins to defeat basal plant immunity and modulate plant growth. Because avirulence (Avr) gene discovery is a reliable method of effector identification, we tested this hypothesis using high-resolution molecular genetic mapping of an Avr gene (vH13) in the Hessian fly (HF, Mayetiola destructor), an important gall midge pest of wheat (Triticum spp.). Chromosome walking resolved the position of vH13, and revealed alleles that determine whether HF larvae are virulent (survive) or avirulent (die) on wheat seedlings carrying the wheat H13 resistance gene. Association mapping found three independent insertions in vH13 that appear to be responsible for H13-virulence in field populations. We observed vH13 transcription in H13-avirulent larvae and the salivary glands of H13-avirulent larvae, but not in H13-virulent larvae. RNA-interference-knockdown of vH13 transcripts allowed some H13-avirulent larvae to escape H13-directed resistance. vH13 is the first Avr gene identified in an arthropod. It encodes a small modular protein with no sequence similarities to other proteins in GenBank. These data clearly support the hypothesis that an effector-based strategy has evolved in multiple lineages of plant parasites, including arthropods.

The Hessian fly (Hf) and greenbugs (Gb) are major pests of wheat, causing severe economic losses globally. Deploying resistant wheat is the most effective strategy for managing these destructive insects. However, the resistance is not effective against all Hf or Gb biotypes and can impose selection pressure on insects, resulting in the development of virulent biotypes. These challenges must be met through the discovery of new and novel sources of resistance to these pests. Synthetic Hexaploid Wheat (SHW)-developed cultivars are a rich source of resistance against a diverse array of pathogens and pests. In this study, 80 SHW lines were evaluated for their resistance to Hf and Gb under controlled environmental conditions. Of these, a total of 36 SHW lines showed resistance independently to Hf biotype L and Gb biotype E, while 27 lines showed combined resistance to both Hf and Gb. Further, a subset of 10 SHW lines showed resistance to additional Hf biotypes, Great Plains and vH13. The identification of SHW lines resistant to multiple insects and biotypes offers an invaluable resource to breeders who are looking to stack resistance traits to develop elite cultivars as a strategy to alleviate economic impacts upon global wheat production.

The Hessian fly causes severe economic losses in host wheat. The genome complexity of hexaploid wheat makes functional characterization of candidate defense genes extremely challenging. Kitaake rice, a model and simpler genome, exhibits responses resembling nonhost resistance to Hessian fly. Larvae feeding on Kitaake rice plants do not develop beyond first-instars similar to resistant host wheat, although, they show prolonged survival. Kitaake nonhost differs from nonhost Brachypodium, where some larvae develop into second-instars. Kitaake rice plants exhibit a molecular response similar to not only resistant but also susceptible host wheat for six Hessian fly-responsive biomarker genes assayed. Further, in Kitaake, lectins and secondary metabolites may play an important role in early defense preventing the larvae from developing. The phenotypic and molecular characterization of Kitaake rice reveals its suitability as a surrogate model genome for undertaking downstream functional genomics studies of candidate wheat genes that respond to Hessian fly larval attack.

Background The Hessian fly ( Mayetiola destructor ), belonging to the gall midge family (Cecidomyiidae), is a devastating pest of wheat ( Triticum aestivum ) causing significant yield losses. Despite identification and characterization of numerous Hessian fly-responsive genes and associated biological pathways involved in wheat defense against this dipteran pest, their functional validation has been challenging. This is largely attributed to the large genome, polyploidy, repetitive DNA, and limited genetic resources in hexaploid wheat. The diploid progenitor Aegilops tauschii , D-genome donor of modern-day hexaploid wheat, offers an ideal surrogate eliminating the need to target all three homeologous chromosomes (A, B and D) individually, and thereby making the functional validation of candidate Hessian fly-responsive genes plausible. Furthermore, the well-annotated sequence of Ae. tauschii genome and availability of genetic resources amenable to manipulations makes the functional assays less tedious and time-consuming. However, prior to utilization of this diploid genome for downstream studies, it is imperative to characterize its physical and molecular responses to Hessian fly. Results In this study we screened five Ae. tauschii accessions for their response to the Hessian fly biotypes L and vH13 . Two lines were identified that exhibited a homozygous resistance response to feeding by both Hessian fly biotypes. Studies using physical measurements and neutral red staining showed that the resistant Ae. tauschii accessions resembled hexaploid wheat in their phenotypic responses to Hessian fly, that included similarities in larval developmental stages, leaf and plant growth, and cell wall permeability. Furthermore, molecular responses, characterized by gene expression profiling using quantitative real-time PCR, in select resistant Ae. tauschii lines also revealed similarities with resistant hexaploid wheat. Conclusions Phenotypic and molecular characterization of Ae. tauschii to Hessian fly infestation revealed resistant accessions that shared similarities to hexaploid wheat. Resembling the resistant hexaploid wheat, the Ae. tauschii accessions mount an early defense strategy involving defense proteins including lectins, secondary metabolites and reactive oxygen species (ROS) radicals. Our results reveal the suitability of the diploid progenitor for use as an ideal tool for functional genomics research in deciphering the wheat-Hessian fly molecular interactions.

Dirigent proteins regulate coupling of monolignol plant phenols to generate the cell wall polymers lignins and lignans that are involved in structural fortification and defense against pathogens and pests. In this study, we report the temporal expression of a putative Hessian fly-responsive disease resistance dirigent-like protein-encoding gene, HfrDrd , in wheat. HfrDrd transcript abundance was quantified under biotic stresses imposed by Hessian fly, bird cherry-oat aphid, barley and cereal yellow dwarf virus, fall army worm and silverleaf white fly, after mechanical wounding, as well as during treatment with signaling elicitors. Quantitative transcriptional analysis indicated increased abundance of HfrDrd mRNA in both susceptible and resistant wheat after Hessian fly attack. However, within 24 h, resistant wheat accumulated 2.5- to >20-fold higher HfrDrd mRNA levels than the susceptible wheat. The increase in transcripts as early as 2 h after egg hatch suggested a role for HfrDrd in early defense against Hessian fly larvae. HfrDrd transcript abundance was not responsive to exogenous application of plant defense-signaling pathway molecules, salicylic acid, methyl jasmonate or abscisic acid. Lack of HfrDrd response during other wheat–insect interactions or mechanical wounding indicated that HfrDrd is not a general stress-responsive gene, but is specific to the defense mechanisms responding to probing by Hessian fly larvae.