Identification and characterization of Sr13, a tetraploid wheat gene that confers resistance to the Ug99 stem rust race group
Tuesday, 2017/11/14 | 08:05:28
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Wenjun Zhang, Shisheng Chen, Zewdie Abate, Jayaveeramuthu Nirmala, Matthew N. Rouse, and Jorge Dubcovsky PNAS November 7 2017; vol.114 (45): E9483-E9492 SignificanceWheat provides a substantial proportion of the calories and proteins consumed by humans, but further production increases are necessary to feed a growing human population. Reducing yield losses caused by pathogens can contribute to these increases. In this study, we report the identification of Sr13, a gene from pasta wheat that confers resistance to the new virulent races of the stem rust pathogen that appeared in Africa at the beginning of this century. We identified three different resistance forms of Sr13 and developed a diagnostic marker to accelerate their deployment in wheat breeding programs. In addition, Sr13 can be a useful component of transgenic cassettes including multiple resistance genes. AbstractThe Puccinia graminis f. sp. tritici (Pgt) Ug99 race group is virulent to most stem rust resistance genes currently deployed in wheat and poses a threat to global wheat production. The durum wheat (Triticum turgidum ssp. durum) gene Sr13 confers resistance to Ug99 and other virulent races, and is more effective at high temperatures. Using map-based cloning, we delimited a candidate region including two linked genes encoding coiled-coil nucleotide-binding leucine-rich repeat proteins designated CNL3 and CNL13. Three independent truncation mutations identified in each of these genes demonstrated that only CNL13 was required for Ug99 resistance. Transformation of an 8-kb genomic sequence including CNL13 into the susceptible wheat variety Fielder was sufficient to confer resistance to Ug99, confirming that CNL13 is Sr13. CNL13 transcripts were slightly down-regulated 2–6 days after Pgt inoculation and were not affected by temperature. By contrast, six pathogenesis-related (PR) genes were up-regulated at high temperatures only when both Sr13 and Pgt were present, suggesting that they may contribute to the high temperature resistance mechanism. We identified three Sr13-resistant haplotypes, which were present in one-third of cultivated emmer and durum wheats but absent in most tested common wheats (Triticum aestivum). These results suggest that Sr13 can be used to improve Ug99 resistance in a large proportion of modern wheat cultivars. To accelerate its deployment, we developed a diagnostic marker for Sr13. The identification of Sr13 expands the number of Pgt-resistance genes that can be incorporated into multigene transgenic cassettes to control this devastating disease.
See http://www.pnas.org/content/114/45/E9483.abstract
Figure 1: Genetic and physical maps of Sr13. (A) B. distachyon chromosome 3 region colinear with the wheat Sr13-candidate region. Rectangles in red indicate NLR genes (likely nonfunctional since they carry frame-shift mutations and premature stop codons). (B) High-density genetic map of Sr13 on chromosome arm 6AL. (C) Physical map of the Sr13 region constructed with overlapping BACs from the Sr13-resistant durum wheat variety Langdon. (D) Diagrammatic representation of the annotated sequence of the Sr13 region (GenBank accession no. KY924305). Genes are indicated by arrows (uppercase names indicate complete genes and lowercase names 5′ or 3′ truncated genes). Red lines below this graph indicate regions where no CS orthologs were found.
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