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

The barley Mla locus confers multiple resistance specificities to the oblig ate fungal biotroph, Blumeria (= Erysiphe) graminis f. sp. hordei. Interspe rsed within the 240 kb Mla complex are three families of resistance gene ho mologs (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-N BS-LRR protein and the other two classes contain alternatively spliced, tru ncated variants. Utilizing a cosmid that contains a gene corresponding to t he 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 use d to substantiate previous genetic data that the Mla6 allele requires the s ignaling pathway component, Rar1, for function. Computational analysis of M LA6 and the Rar1-independent, MLA1 protein reveals 91.2% identity and shows that the LRR domain is subject to diversifying selection. Our findings dem onstrate that highly related CC-NBS-LRR proteins encoded by alleles of the Mla locus can dictate similar powdery mildew resistance phenotypes yet stil l require distinct downstream signaling components.