Stb6 is a Wall-Associated Kinase Gene that provides Gene-for-Gene Resistance against Zymoseptoria tritici in Wheat

W975W975Septoria tritici blotch (STB) is a devastating foliar disease of wheat encountered in most wheat growing areas of the world resulting from infection by the ascomycete fungus Zymoseptoria tritici. Emergence and dispersal of fungicide resistance in Z. tritici field populations seriously threatens wheat production, therefore STB resistance breeding is considered a high priority. To date, 21 major genes conferring isolate-specific resistance as well as 89 resistance QTLs have been characterized genetically. However, none of these have as yet been cloned and mechanisms of resistance remain poorly understood. Here, we report isolation of the Stb6 gene controlling resistance to Z. tritici isolates carrying the matching AvrStb6 gene. This wheat gene confers a semi-dominant resistance to Z. tritici, which does not involve induction of HR. Fine-mapping using a large F2 mapping population derived from a cross between the resistant wheat Chinese Spring (Stb6) and the susceptible wheat Courtot and subsequent BAC and genomic DNA contigs sequence analysis revealed a cluster of wall-associated receptor kinase (WAK) like genes. Using VIGS, TILLING and genetic complementation, we demonstrated that one of these candidates corresponds to Stb6. Disease susceptibility in Courtot results most likely from a point-mutation in the Stb6 kinase domain leading to a loss of defense signaling. Stb6 allele mining revealed an ancient origin of this gene and the predominance of a major resistance haplotype. Furthermore, genotyping a large wheat collection using diagnostic markers showed that Stb6 is present in nearly half of European cultivated wheat. Stb6 is the first gene to be cloned that confers resistance to the STB disease. Isolation of this gene is the first step toward in depth characterization of the wheat - Z. tritici molecular interactions