Loss of by Somatic Exchange in Stem Rust Leads to Virulence for Resistance in Wheat

Race-specific resistance genes protect the global wheat crop from stem rust disease caused by f. sp. () but are often overcome owing to evolution of new virulent races of the pathogen. To understand virulence evolution in , we identified the protein ligand (AvrSr50) recognized by the Sr50 resistance protein. A spontaneous mutant of virulent to contained a 2.5 mega-base pair loss-of-heterozygosity event. A haustorial secreted protein from this region triggers -dependent defense responses in planta and interacts directly with the Sr50 protein. Virulence alleles of have arisen through DNA insertion and sequence divergence, and our data provide molecular evidence that in addition to sexual recombination, somatic exchange can play a role in the emergence of new virulence traits in .