Map-Based Cloning of the Stagonospora nodorum Susceptibility Gene Snn1 in Wheat By Exploiting the Chinese Spring 1BS Arm-Specific BAC Library

Wheat-Stagonospora nodorum interactions involve pathogen-produced necrotrophic effectors (NEs) that are recognized by corresponding dominant host sensitivity genes to cause disease. The Snn1 gene, which confers sensitivity to the NE SnTox1, was previously mapped on the distal end of wheat chromosome 1BS. Here, we report the positional cloning and initial characterization of Snn1. High-resolution mapping and marker development in a population of 17,000 gametes derived from a cross between Chinese Spring (CS) and a CS-Hope 1B disomic substitution line delineated Snn1 to a 2.06 cM segment. Screening of the CS 1BS minimum tiling path pools with flanking markers led to the identification of a 2.5 Mb BAC contig spanning the Snn1 locus. BAC end sequences and genomic survey sequences were used to develop additional markers, which delineated Snn1 to a 0.16 cM segment encompassed by four BAC clones. Sequencing and analysis of the four BACs revealed six putative genes, five of which were excluded as candidates by recombination leaving one putative gene to cosegregate with Snn1. Sequence analysis of 15 EMS-induced resistant mutants provided final validation that Snn1 is a cell wall-associated kinase (WAK) gene with a cytoplasmic serine/threonine protein kinase domain and extracellular epidermal growth factor-calcium binding and galacturonan binding domains, all of which are essential for function. Further results regarding expression and characterization will be presented. This work allows us to gain better understanding of host-necrotrophic pathogen interactions, and together with related research demonstrates that S. nodorum can hijack different wheat genes and pathways to cause disease.