Discovery of avirulence gene candidates in the Hessian fly (Mayetiola destructor) genome

The Hessian fly is believed to have a gene-for-gene relationship with its host plant, wheat (Triticum spp.). This relationship suggests that a single Hessian fly avirulence (Avr) gene product interacts with a specific wheat resistance (R) gene product. This interaction then triggers a resistance reaction in the plant that kills the insect. Loss-of-function mutations in the Avr genes are believed to cause these interactions to fail, rendering the insects that carry these mutations “virulent” to the R genes. To test this hypothesis, we have genetically and physically mapped the Avr genes that elicit avirulence and virulence to wheat R genes H6, H9, and H13. Here, we describe the effort that genetically and physically positioned the Avr gene (vH13) that elicits H13-based resistance. This effort mapped vH13 within a single Hessian fly bacterial artificial chromosome (BAC). Candidate genes within this BAC have been sequenced and both virulent and avirulent candidate alleles have been identified and compared. As a result of this effort, a BAC contig was constructed that extends nearly the full length of the short arm of Hessian fly chromosome X2, 3-5 Mb in length. Results of this investigation strongly support the hypothesis that gene-for-gene relationships exist between certain insects and their host plants. They also indicate that a single vH13 gene product will be identified in the near future using a combination of genetic and functional assays.