Identification and characterization of Sr22b, a new allele of the wheat stem rust resistance gene Sr22 effective against the Ug99 race group

Authors: LUO, JING - Peking University; Rouse, Matthew; HUA, LEI - Peking University; LI, HONGNA - Peking University; LI, TIANYA - Shenyang Agricultural University; ZHANG, WENJUN - University Of California, Davis; CAIXIA, GAO - Peking University; WANG, YANPENG - Peking University; DUBCOVSKY, JORGE - University Of California, Davis; CHEN, SHISHENG - Peking University

Submitted to: Plant Biotechnology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2021
Publication Date: 10/25/2021
Citation: Luo, J., Rouse, M.N., Hua, L., Li, H., Li, T., Zhang, W., Caixia, G., Wang, Y., Dubcovsky, J., Chen, S. 2021. Identification and characterization of Sr22b, a new allele of the wheat stem rust resistance gene Sr22 effective against the Ug99 race group. Plant Biotechnology Journal. 20:554-563. https://doi.org/10.1111/pbi.13737.
DOI: https://doi.org/10.1111/pbi.13737

Interpretive Summary: Wheat stem rust has been historically among the most devastating global fungal diseases of wheat. The recent occurrence and spread of new virulent races such as Ug99 have prompted global efforts to identify and isolate more effective stem rust resistance (Sr) genes. Here, we report the map-based cloning of the Ug99-effective Sr22b gene from diploid wheat Triticum monococcum. This gene is a new allele of Sr22. Biolistic transformation of Sr22b into the susceptible wheat variety Fielder was sufficient to confer resistance to Ug99. In a survey of 163 wheat genotypes, Sr22b was present only in cultivated T. monococcum subsp. monococcum accessions but absent in all tested tetraploid and hexaploid wheat lines. We developed a diagnostic molecular marker for Sr22b and successfully introgressed a T. monococcum chromosome segment containing this gene into hexaploid wheat to accelerate its deployment and pyramiding with other Sr resistance genes in wheat breeding programs. Sr22b can be a valuable component of gene pyramids or transgenic cassettes combining different resistance genes to control this devastating disease.

Technical Abstract: Wheat stem (or black) rust, caused by Puccinia graminis f. sp. tritici (Pgt), has been historically among the most devastating global fungal diseases of wheat. The recent occurrence and spread of new virulent races such as Ug99 have prompted global efforts to identify and isolate more effective stem rust resistance (Sr) genes. Here, we report the map-based cloning of the Ug99-effective SrTm5 gene from diploid wheat Triticum monococcum accession PI 306540 that encodes a typical coiled-coil nucleotide-binding leucine-rich repeat protein. This gene, designated as Sr22b, is a new allele of Sr22 with a rare insertion of a large (13.8-kb) retrotransposon into its second intron. Biolistic transformation of a ~112-kb circular BAC plasmid carrying Sr22b into the susceptible wheat variety Fielder was sufficient to confer resistance to stem rust. In a survey of 163 wheat genotypes, Sr22b was present only in cultivated T. monococcum subsp. monococcum accessions but absent in all tested tetraploid and hexaploid wheat lines. We developed a diagnostic molecular marker for Sr22b and successfully introgressed a T. monococcum chromosome segment containing this gene into hexaploid wheat to accelerate its deployment and pyramiding with other Sr resistance genes in wheat breeding programs. Sr22b can be a valuable component of gene pyramids or transgenic cassettes combining different resistance genes to control this devastating disease.