Submitted to: Plant and Animal Genome Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 12/17/2001
Publication Date: N/A
Technical Abstract: The barley Mla locus on chromosome 5 (1H) confers multiple resistance specificities to the powdery mildew fungus, Blumeria (=Erysiphe) graminis f. sp. hordei. In order to clone Mla alleles by map-based methods, we constructed a BAC contig from the cultivar Morex [Wei et al. (1999) Genetics 153:1929-1948] and determined the complete DNA sequence of two overlapping BACs that encompassed the Mla locus. Computational analysis o the 261-kb Mla-spanning sequence has revealed approximately 30 putative genes. Among these 30 candidate ORFs are eight NBS-LRR resistance gene homologs (RGHs) and six chymotrypsin inhibitor genes. Coding regions are positioned in two gene islands bridged by nested retrotransposons. Probes from the Mla-RGH1 family were used to identify three classes of cDNAs from C.I. 16151, a cultivar containing the Mla6 allele. The first of these cDNAs is predicted to encode a full-length CC-NBS-LRR protein and the other rtwo are truncated variants. A cosmid containing a gene corresponding to the full-length candidate cDNA was used in a single-cell expression assay to complement AvrMla6-dependent, resistance specificity to B. graminis in barley and wheat. This assay was also used to substantiate previous genetic data that the Mla6 allele requires the signaling pathway component, Rar1, for function. Comparison of Mla6 and the Rar1-independent Mla1 protein reveals 91.2% sequence identity, demonstrating that highly related CC-NBS-LRR proteins encoded by alleles at the Mla locus can dictate similar powdery mildew resistance phenotypes, yet require distinct signaling components. Research supported by USDA-NRI/CGP grant 98-35300-6169.