Towards map-based cloning of the barley stem rust resistance genes Rpg1 and rpg4 using rice as an intergenomic cloning vehicle.

摘要

Genes Rpg1 and rpg4, conferring resistance to stem rust (Puccinia graminis f.sp. tritici) in barley, were mapped on chromosomes 1P and 7M, respectively, and the syntenous rice chromosomes identified as 6P and 3P by mapping of common probes. Rice yeast artificial chromosome (YAC), bacterial artificial chromosome (BAC) and cosmid clones were used to isolate probes mapping to the Rpg1 region. The rice BAC isolated with the pM13 probe was an excellent source of probes. A high-resolution map of the Rpg1region was established using 1400 gametes and yielding a map density of 3.6 markers/0.1 cM. A detailed physical map was established for the rice BAC fragment containing the Rpg1-flanking markers pM13 and B24. This fragment covers a barley genetic distance of 0.6 cM and a rice DNA physical distance of ?0 kb. The distribution of barley crossovers in relation to physical distances of rice DNA was extremely uneven. Genetic distance between the pM13 marker and Rpg1 in barley was 0.1 cM/?5 kb whilst on theproximal side it was 0.5 cM/?5 kb. Three probes from the distal end of the pM13 BAC mapped 2.5 cM proximal to Rpg1 and out of synteny with rice, suggesting a 10-15 kb region of rice DNA has moved to a non-syntenic location in barley, or vice versa. Large insert rice clones can therefore be used as probe sources to saturate small barley (and other large genome cereals) genome regions with markers, although there may be small DNA fragments that have transposed and are no longer in syntenous positions.