Somatic recombination in wheat stem rust leads to virulence for Ug99-effective SR50 resistance

Authors: CHEN, JIAPENG - University Of Sydney; UPADHYAYA, NARAYANA - Commonwealth Scientific And Industrial Research Organisation (CSIRO); ORTIZ, DIANA - Commonwealth Scientific And Industrial Research Organisation (CSIRO); SPERSCHNEIDER, JANA - Commonwealth Scientific And Industrial Research Organisation (CSIRO); LI, FENG - University Of Minnesota; BOUTON, CLEMENT - Rothamsted Research; BREEN, SUSAN - Commonwealth Scientific And Industrial Research Organisation (CSIRO); DONG, CHONGMEI - University Of Sydney; XU, BO - Commonwealth Scientific And Industrial Research Organisation (CSIRO); ZHANG, XIAOXIAO - Commonwealth Scientific And Industrial Research Organisation (CSIRO); MAGO, ROHIT - Commonwealth Scientific And Industrial Research Organisation (CSIRO); NEWELL, KIM - Commonwealth Scientific And Industrial Research Organisation (CSIRO); XIA, XIAODI - Commonwealth Scientific And Industrial Research Organisation (CSIRO); BERNOUX, MAUD - Commonwealth Scientific And Industrial Research Organisation (CSIRO); TAYLOR, JENNIFER - Commonwealth Scientific And Industrial Research Organisation (CSIRO); STEFFENSON, BRIAN - University Of Minnesota; Jin, Yue; ZHANG, PENG - University Of Sydney; KANYUKA, KOSTYA - Rothamsted Research; FIGUEROA, MELANIA - University Of Minnesota; ELLIS, JEFFREY - Commonwealth Scientific And Industrial Research Organisation (CSIRO); PARK, ROBERT - University Of Sydney; DODDS, PETER - Commonwealth Scientific And Industrial Research Organisation (CSIRO)

Submitted to: Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2017
Publication Date: 12/22/2017
Citation: Chen, J., Upadhyaya, N.M., Ortiz, D., Sperschneider, J., Li, F., Bouton, C., Breen, S., Dong, C., Xu, B., Zhang, X., Mago, R., Newell, K., Xia, X., Bernoux, M., Taylor, J.M., Steffenson, B.J., Jin, Y., Zhang, P., Kanyuka, K., Figueroa, M., Ellis, J.G., Park, R.F., Dodds, P.N. 2017. Somatic recombination in wheat stem rust leads to virulence for Ug99-effective SR50 resistance. Science. 358:1607-1610.

Interpretive Summary: Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is an important disease that can cause devastating crop losses. Resistance, especially the type utilizing race-specific resistance genes, protects much of the global wheat crop from stem rust disease , but often break down due to evolution of new virulent pathogen races. To understand the molecular mechanisms of virulence evolution in Pgt we identified the protein ligand (AvrSr50) recognized by the Sr50 resistance protein. Sequencing a spontaneous mutant of Pgt virulent to Sr50 detected a 2.5Mbp loss-of-heterozygosity event. A single candidate 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 by 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. Identification of AvrSr50 allows for direct surveys of this gene in field populations of this important pathogen. The information is crucial for developing resistance gene deployment strategies in wheat improvement for stem rust resistance.

Technical Abstract: Race-specific resistance genes protect much of the global wheat crop from stem rust disease caused by Puccinia graminis f. sp. tritici (Pgt), but often break down due to evolution of new virulent pathogen races. To understand the molecular mechanisms of virulence evolution in Pgt we identified the protein ligand (AvrSr50) recognized by the Sr50 resistance protein. Sequencing a spontaneous mutant of Pgt virulent to Sr50 detected a 2.5Mbp loss-of-heterozygosity event. A single candidate 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 by 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. Identification of AvrSr50 allows for direct surveys of this gene in field populations of this important pathogen.