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, 341 (6147), 783-786

Identification of Wheat Gene Sr35 That Confers Resistance to Ug99 Stem Rust Race Group

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Identification of Wheat Gene Sr35 That Confers Resistance to Ug99 Stem Rust Race Group

Cyrille Saintenac et al. Science.

Abstract

Wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), is a devastating disease that can cause severe yield losses. A previously uncharacterized Pgt race, designated Ug99, has overcome most of the widely used resistance genes and is threatening major wheat production areas. Here, we demonstrate that the Sr35 gene from Triticum monococcum is a coiled-coil, nucleotide-binding, leucine-rich repeat gene that confers near immunity to Ug99 and related races. This gene is absent in the A-genome diploid donor and in polyploid wheat but is effective when transferred from T. monococcum to polyploid wheat. The cloning of Sr35 opens the door to the use of biotechnological approaches to control this devastating disease and to analyses of the molecular interactions that define the wheat-rust pathosystem.

Figures

Fig. 1
Fig. 1
Genetic and physical maps of Sr35. (A) 174-kb collinear region of Brachypodium (). Only genes for which a wheat orthologous gene was found in databases are represented. (B) Genetic map of Sr35 locus. (C) Screening the DV92 BAC library with proximal markers SFGH and AK331487 (only BACs from the minimum tilling path are shown). (D) High density map. (E) Graphical representation of the T. monococcum annotated sequences (KC573058). CNL= coiled coil-nucleotide binding-leucine rich repeat genes, ‘p’ before gene name = pseudogene (pCNL3 has an inserted retroelement). The Sr35 candidate gene region is highlighted in yellow. (F) Comparison of T. monococcum DV92 and T. urartu G1812 (KC816724) orthologous regions (92% identity threshold).
Fig. 2
Fig. 2
(A) CNL9 gene structure. Green=UTR, black= coding exons, yellow= coiled-coil domain, orange= nucleotide-binding domain, red= leucine-rich repeat domain, arrows= amino acid changes in susceptible induced mutants cnl91296 (W856*) and cnl91120 or natural mutants (Table S2, RLWFT to HLRFS) (B) Infection types produced on T. monococcum G2919 and CNL9 mutants cnl91120 and cnl91296 inoculated with Pgt race TRTTF. TRTTF is Sr35-avirulent and Sr21-virulent, which is required because of the presence of Sr21 in these lines. (C) Infection types on seedlings of T1 lines from event #1123 segregating for the CNL9 transgene. Plants carrying the CNL9 transgene (+) were resistant to Ug99 (R) and plants without the transgene (−) were susceptible (S) (Table S8). When inoculated with Sr35-virulent race QTHJC all plants were susceptible suggesting similar race specificity between the transgenic and the natural Sr35. Red circles indicate available progeny tests in Figure S5. (D) Relative transcript levels of candidate genes APPG1, CNL4, CNL6, and CNL9 (main isoform) in G2919 six days after inoculation with race RKQQC (E) Transcript levels of CNL9 main isoform (red) and isoform two (green, retained intron) in mock- or race RKQQC inoculated G2919 plants. Leaves were collected at 0, 24, 48, 96 and 144 h after inoculation. Transcript levels are expressed relative to the Phytochelatin synthase internal control using the 2−ΔCt method. Bars are standard errors of the means based on six biological and two technical replicates.

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