Conserved synteny-based anchoring of the barley genome physical map

Gene order is largely collinear in the small-grained cereals, a feature which has proved helpful in both marker development and positional cloning. The accuracy of a virtual gene order map (genome zipper) for barley (Hordeum vulgare), developed by combining a genetic map of this species with a large number of gene locations obtained from the maps constructed in other grass species, was evaluated here both at the genome-wide level and at the fine scale in a representative segment of the genome. Comparing the whole genome genome zipper maps with a genetic map developed by using transcript-derived markers, yielded an accuracy of > 94 %. The fine-scale comparison involved a 14 cM segment of chromosome arm 2HL. One hundred twenty-eight genes of the genome zipper interval were analysed. Over 95 % (45/47) of the polymorphic markers were genetically mapped and allocated to the expected region of 2HL, following the predicted order. A further 80 of the 128 genes were assigned to the correct chromosome arm 2HL by analysis of wheat-barley addition lines. All 128 gene-based markers developed were used to probe a barley bacterial artificial chromosome (BAC) library, delivering 26 BAC contigs from which all except two were anchored to the targeted zipper interval. The results demonstrate that the gene order predicted by the genome zipper is remarkably accurate and that the genome zipper represents a highly efficient informational resource for the systematic identification of gene-based markers and subsequent physical map anchoring of the barley genome.