Puccinia graminis f. sp. tritici (Pgt) causes wheat stem rust, a devastating fungal disease. The Sr35 resistance gene confers immunity against this pathogen's most virulent races, including Ug99. We used comparative whole-genome sequencing of chemically mutagenized and natural Pgt isolates to identify a fungal gene named AvrSr35 that is required for Sr35 avirulence. The AvrSr35 gene encodes a secreted protein capable of interacting with Sr35 and triggering the immune response. We show that the origin of Pgt isolates virulent on Sr35 is associated with the nonfunctionalization of the AvrSr35 gene by the insertion of a mobile element. The discovery of AvrSr35 provides a new tool for Pgt surveillance, identification of host susceptibility targets, and characterization of the molecular determinants of immunity in wheat.
Bibliographical noteFunding Information:
Data are available from the National Center for Biotechnology Information database: MF474174, MF596174, PRJNA415853, PRJNA313186, SRX1619622-SRX1619626, and GEO GSE106397. The project is funded by U.S. Department of Agriculture (USDA) National Institute of Food and Agriculture grant 2012-67013-19401 and Bill and Melinda Gates Foundation grant BMGF:01511000146 to E.A., and USDA Agricultural Research Service funding 3020-21000-010-00-D to B.B. J.D. acknowledges support from the Howard Hughes Medical Institute. We thank Y. Jin for providing stem rust cultures, H. Liang and Y. Lun for technical assistance, R. Todd for valuable suggestions, and D. Cantu for initial contribution to the sequencing of Pgt races. The supplementary materials contain additional data. This work is licensed under a Creative Commons Attribution 4.0 International (CC BY 4.0) license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. This license does not apply to figures/photos/artwork or other content included in the article that is credited to a third party; obtain authorization from the rights holder before using such material.