Kartenorientierte Isolierung des Rar1 Locus

The Mla12 allele of the barley-Mla locus confers resistance to powdery mildew isolates expressing the matching avirulence gene avrMla12. The Rar1 (Required for Mla12-specified resistance) locus has been found to be part of the Mla12-governed signal transduction pathway. Previous analysis has demonstrated that rar1-mutant alleles abolish not only Mla12 but also other R gene specificities. To elucidate the molecular mechanisms of R-gene mediated plant defence Rar1 was isolated by map-based cloning. The Rar1-cosegregating marker MWG87 was employed for the identification of five barley YAC clones. Genetic mapping of the YACends showed that the corresponding clones cover the Rar1-containing genome segment. Two of the YAC clones were subcloned into BACs and a Rar1-cosegregating interval of 66kb was defined. Comparative sequencing of the two Rar1-mutants revealed mutations in a candidate gene within the 66kb genome segment. These data provide strong evidence that the candidate gene is in fact the Rar1-encoding locus. The Rar1 protein covers 233 amino acids and has two domains (CHORD) with significant intramolecular homology. These domains show also significant homology to zinc-finger motifs and are conserved most eukaryotic organisms