Race-specific resistance genes protect the global wheat crop from stem rust disease caused by Puccinia graminis f. sp. tritici (Pgt) but are often overcome owing to evolution of new virulent races of the pathogen. To understand virulence evolution in Pgt, we identified the protein ligand (AvrSr50) recognized by the Sr50 resistance protein. A spontaneous mutant of Pgt virulent to Sr50 contained a 2.5 mega-base pair loss-of-heterozygosity event. A haustorial secreted protein from this region triggers Sr50-dependent defense responses in planta and interacts directly with the Sr50 protein. Virulence alleles of AvrSr50 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 Pgt.
Bibliographical noteFunding Information:
Work described here was supported by the TwoBlades foundation, the Grains Research and Development Corporation (grants US00067 and CSP00161), University of Minnesota Lieberman-Okinow and Stakman Endowments, Experimental Station USDA– National Institute of Food and Agriculture Hatch Funds (project MIN-22-058), and the Biotechnology and Biological Sciences Research Council (project BB/P016855/1). J.C. was supported by the Judith and David Coffey Life Lab and the Plant Breeding Institute, University of Sydney. J.G.E. has a scientific advisory role with the TwoBlades foundation. Sequence data was deposited in the National Center for Biotechnology Information Sequencing Read Archive under bioprojects PRJNA396463 and PRJNA415866. DNA of the rust isolates used in this study is available from R.F.P. under a materials transfer agreement with the University of Sydney. We thank R. East and L. Ma for excellent technical assistance. Additional data are provided in the supplementary materials.