Phenotypic and molecular characterization of Hessian fly resistance in diploid wheat, Aegilops tauschii

Authors: Nemacheck, Jill; Schemerhorn, Brandi; Scofield, Steven - Steve; Subramanyam, Subhashree

Submitted to: BMC Plant Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2019
Publication Date: 10/22/2019
Publication URL: https://handle.nal.usda.gov/10113/6744194
Citation: Nemacheck, J.A., Schemerhorn, B.J., Scofield, S.R., Subramanyam, S.N. 2019. Phenotypic and molecular characterization of Hessian fly resistance in diploid wheat, Aegilops tauschii. Biomed Central (BMC) Plant Biology. 19:439. https://doi.org/10.1186/s12870-019-2058-6.
DOI: https://doi.org/10.1186/s12870-019-2058-6

Interpretive Summary: Hessian fly, is a devastating pest of modern-day bread wheat. Despite identification of several genes involved in wheat defense against Hessian fly, pinpointing their function/role is difficult. This is because bread wheat is a complex hexaploid that has three different genomes (A, B and D). This problem can be overcome by using less complex wheat genome such as the diploid wheat which (i) has only one genome (D); (ii) shares close relationship with modern-day bread wheat; and (iii) harbors useful defense response genes. In the current study, we screened five and identified two diploid wheat lines that are resistant to two Hessian fly biotypes and resemble the common bread wheat at the physical and molecular level. We demonstrate the usefulness of these diploid wheat lines as an alternate tool to study genes identified from modern-day bread wheat, and further our understanding of wheat defense against Hessian fly. This information will be useful for geneticists and plant breeders working to improve Hessian fly resistance in wheat.

Technical Abstract: 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. In this study we screened five Ae. tauschii accessions and identified two that exhibited a homozygous resistance response to feeding by both vH13 and biotype L Hessian fly larvae. The resistant diploid wheat accessions resembled hexaploid wheat in their phenotypic responses, including larval developmental stages, leaf and plant growth, and cell wall permeability, to Hessian fly. Furthermore, molecular responses in select resistant diploid wheat lines shared similarities with resistant hexaploid wheat. Physical 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 diploid accessions mount an early defense strategy involving defense proteins including lectins, secondary metabolites and 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.