CHROMOSOME LANDING AT THE BARLEY RAR1 LOCUS

The barley Rar1 gene is an essential component of the race-specific, M la-12-specified powdery mildew resistance reaction. As part of a map-b ased cloning strategy designed to isolate Rar1, five barley yeast arti ficial chromosomes (YACs) have been identified, ranging in size from 3 00 to 1100 kb. PCR-based YAC end-specific markers have been establishe d and were employed to construct a local YAC contig. Four out of five YAC clones were found to be non-colinear with the source DNA. High-res olution genetic mapping of the YAC ends demonstrated that the set of f ive overlapping YAC clones encompasses the barley Rar1 gene.