Toward the Molecular Cloning of the Septoria nodorum Blotch Susceptibility Gene Snn2 in Wheat

Septoria nodorum blotch is a disease of wheat caused by the necrotrophic fungus Parastagonospora nodorum. In the wheat-P. nodorum pathosystem, recognition of pathogen-produced necrotrophic effectors (NEs) by dominant host genes leads to host cell death, which allows the pathogen to gain nutrients and proliferate. Among the nine host gene-NE interactions reported, the Snn2-SnTox2 interaction has been shown to be important in both seedling and adult plant susceptibility. The overall goal of this study is to clone and characterize the Snn2 gene. A saturated genetic linkage map was developed using a segregating population of 164 F_7:8 recombinant inbred lines derived from a cross between the SnTox2-insensitive wheat line BR34 and the SnTox2-sensitive line Grandin. Markers were identified by SNP genotyping using the 90K iSelect wheat SNP chip and previously mapped simple sequence repeat markers. New markers were developed based on whole-genome sequence scaffolds and wheat survey sequences identified using SNP contextual sequences. Currently, Snn2 is delineated to a genetic interval of 1.5 cM corresponding to a physical segment of 1.7 Mb on the short arm of the wheat chromosome 2D. Sixteen candidate genes for Snn2 were identified in this region. Further marker development and high-resolution mapping is currently underway to further narrow the Snn2 region. In addition, we have developed multiple EMS-induced Snn2-disrupted mutants for functional analyses and for conducting RenSeq in parallel with a map-based cloning approach. Results of this study will increase our knowledge of wheat-P. nodorum interactions, which will help to develop better host resistance through genetic manipulation.