In the last 20 years, severe wheat stem rust outbreaks have been recorded in Africa, Europe, and Central Asia. This previously well controlled disease, caused by the fungus Puccinia graminis f. sp. tritici, has reemerged as a major threat to wheat cultivation. The stem rust (Sr) resistance gene Sr22 encodes a nucleotide-binding and leucine-rich repeat receptor which confers resistance to the highly virulent African stem rust isolate Ug99. Here, we show that the Sr22 gene is conserved among grasses in the Triticeae and Poeae lineages. Triticeae species contain syntenic loci with single-copy orthologs of Sr22 on chromosome 7, except Hordeum vulgare, which has experienced major expansions and rearrangements at the locus. We also describe 14 Sr22 sequence variants obtained from both Triticum boeoticum and the domesticated form of this species, T. monococcum, which have been postulated to encode both functional and nonfunctional Sr22 alleles. The nucleotide sequence analysis of these alleles identified historical sequence exchange resulting from recombination or gene conversion, including breakpoints within codons, which expanded the coding potential at these positions by introduction of nonsynonymous substitutions. Three Sr22 alleles were transformed into wheat cultivar Fielder and two postulated resistant alleles from Schomburgk (hexaploid wheat introgressed with T. boeoticum segment carrying Sr22) and T. monococcum accession PI190945, respectively, conferred resistance to P. graminis f. sp. tritici race TTKSK, thereby unequivocally confirming Sr22 effectiveness against Ug99. The third allele from accession PI573523, previously believed to confer susceptibility, was confirmed as nonfunctional against Australian P. graminis f. sp. tritici race 98-1,2,3,5,6.

Copyright © 2020 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

在过去的20年中，非洲，欧洲和中亚已经出现了严重的小麦茎锈病暴发。这种以前控制良好的疾病，是由真菌Puccinia graminis f引起的。sp。小麦再次出现，对小麦种植构成重大威胁。茎锈病（Sr）抗性基因Sr22编码一种核苷酸结合且富含亮氨酸的重复受体，可赋予对高毒性非洲茎锈病分离株Ug99的抗性。在这里，我们表明Sr22基因在Triticeae和Poeae世系的草丛中是保守的。小麦属物种包含同系位点，在7号染色体上具有Sr22的单拷贝直系同源物，但大麦除外，在位置上经历了重大的扩展和重新排列。我们还描述了从小麦（Triticum boeoticum）和该物种的驯化形式（T. monococcum）获得的14个Sr22序列变体，已假定其编码功能性和非功能性Sr22等位基因。这些等位基因的核苷酸序列分析确定了重组或基因转化产生的历史序列交换，包括密码子内的断点，通过引入非同义取代扩大了这些位置的编码潜能。三个Sr22等位基因分别转化为小麦品种Fielder和两个假定的抗性等位基因（Schomburgk（六倍体小麦渗入带有Sr22的T. boeoticum段）和单球菌属PI190945），赋予了对P. graminis f。sp。小麦比赛TTKSK，从而明确证实SR22对Ug99真菌效力。先前被认为具有药敏性的保藏号PI573523的第三个等位基因被证实对澳大利亚的澳大利亚假单胞菌无功能。sp。小麦比赛98-1,2,3,5,6。

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