The MLA6 coiled-coil, NBS-LRR protein confers AvrMla6-dependent resistance specificity to Blumeria graminis f. sp. hordei in barley and wheat

Authors

  • Dennis Halterman,

    1. Corn Insects and Crop Genetics Research, USDA-ARS, Iowa State University, Ames, IA 50011–1020 USA,
    2. Department of Plant Pathology, Iowa State University, Ames, IA 50011–1020 USA,
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  • Fasong Zhou,

    1. Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK
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  • Fusheng Wei,

    1. Department of Plant Pathology, Iowa State University, Ames, IA 50011–1020 USA,
    2. Interdepartmental Genetics Program, Iowa State University, Ames, IA 50011–1020 USA, and
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  • Roger P. Wise,

    Corresponding author
    1. Corn Insects and Crop Genetics Research, USDA-ARS, Iowa State University, Ames, IA 50011–1020 USA,
    2. Department of Plant Pathology, Iowa State University, Ames, IA 50011–1020 USA,
    3. Interdepartmental Genetics Program, Iowa State University, Ames, IA 50011–1020 USA, and
      For correspondence (fax +515 294 9240; e-mail rpwise@iastate.edu).
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  • Paul Schulze-Lefert

    1. Sainsbury Laboratory, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK
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    • Present address: Max-Planck-Institut für Züchtungsforschung, Abteilung Biochemie, Carl-von-Linne-Weg 10, D-50829 Köln, Germany.


For correspondence (fax +515 294 9240; e-mail rpwise@iastate.edu).

Summary

The barley Mla locus confers multiple resistance specificities to the obligate fungal biotroph, Blumeria (= Erysiphe) graminis f. sp. hordei. Interspersed within the 240 kb Mla complex are three families of resistance gene homologs (RGHs). Probes from the Mla-RGH1 family were used to identify three classes of cDNAs. The first class is predicted to encode a full-length CC-NBS-LRR protein and the other two classes contain alternatively spliced, truncated variants. Utilizing a cosmid that contains a gene corresponding to the full-length candidate cDNA, two single-cell expression assays were used to demonstrate complementation of AvrMla6-dependent, resistance specificity to B. graminis in barley and wheat. The first of these assays was also used to substantiate previous genetic data that the Mla6 allele requires the signaling pathway component, Rar1, for function. Computational analysis of MLA6 and the Rar1-independent, MLA1 protein reveals 91.2% identity and shows that the LRR domain is subject to diversifying selection. Our findings demonstrate that highly related CC-NBS-LRR proteins encoded by alleles of the Mla locus can dictate similar powdery mildew resistance phenotypes yet still require distinct downstream signaling components.

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