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The Gene Sr33, an Ortholog of Barley Mla Genes, Encodes Resistance to Wheat Stem Rust Race Ug99

Science  16 Aug 2013:
Vol. 341, Issue 6147, pp. 786-788
DOI: 10.1126/science.1239028

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Resistance May Not Be Futile

Recently, Ug99, a particularly devastating strain of wheat stem rust fungus, has emerged, which could potentially threaten food security. Now, two genes have been cloned that offer resistance to Ug99. Saintenac et al. (p. 783, published online 27 June) cloned Sr35 from Triticum monococcum, a diploid wheat species not often cultivated. Periyannan et al. (p. 786, published online 27 June) cloned Sr33 from Aegilops tauschii, a diploid wild grass that contributed to the hexaploid genome of cultivated wheat. The genes both encode proteins that show features typical of other disease resistance proteins and offer opportunities to slow the pace of Ug99 progression.

Abstract

Wheat stem rust, caused by the fungus Puccinia graminis f. sp. tritici, afflicts bread wheat (Triticum aestivum). New virulent races collectively referred to as “Ug99” have emerged, which threaten global wheat production. The wheat gene Sr33, introgressed from the wild relative Aegilops tauschii into bread wheat, confers resistance to diverse stem rust races, including the Ug99 race group. We cloned Sr33, which encodes a coiled-coil, nucleotide-binding, leucine-rich repeat protein. Sr33 is orthologous to the barley (Hordeum vulgare) Mla mildew resistance genes that confer resistance to Blumeria graminis f. sp. hordei. The wheat Sr33 gene functions independently of RAR1, SGT1, and HSP90 chaperones. Haplotype analysis from diverse collections of Ae. tauschii placed the origin of Sr33 resistance near the southern coast of the Caspian Sea.

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