The barley serine/threonine kinase gene Rpg1 providing resistance to stem rust belongs to a gene family with five other members encoding kinase domains

The barley (Hordeum vulgare L.) stem rust (Puccinia graminis f. sp. tritici) resistance gene Rpg1 encodes a serine/threonine protein kinase with two tandem kinase domains. The Rpg1 gene family was identified from the cv. Morex and consists of five additional members with divergent homology to Rpg1. All family members encode serine/threonine kinase-like proteins with at least one predicted catalytically active kinase domain. The five family members were sequenced from cDNA and genomic DNA and genetically mapped. The family member most closely related to Rpg1, ABC1037, is located on chromosome 1(7H) bin 01, very near (similar to 50 kb) but not co-segregating with Rpg1. Two others, ABC1036 and ABC1040, are closely related to each other and tightly linked on chromosome 7(5H) bin 07. ABC1041 mapped to chromosome 7(5H) bin 13, tightly linked to the rust resistance genes rpg4 and Rpg5 providing resistance to barley stem rust pathotype QCC and rye stem rust pathotype 92-MN-90, respectively, but segregated away in a high-resolution population. ABC1063 was localized to chromosome 4(4H) bin 6. An interesting Rpg1 allele that appears to be the result of unequal recombination between Rpg1 and ABC1037 was characterized. No known resistance loci cosegregated with any family members, however characterization of the Rpg1 family has provided insight into the evolution of this novel gene family and may present tools for understanding the functional domains of Rpg1. The genetic mapping, gene structures, and analysis of amino-acid sequences of the Rpg1 gene family members are presented.