Fine mapping of a resistance gene to bacterial leaf pustule in soybean

Soybean bacterial leaf pustule (BLP) is a prevalent disease caused by Xanthomonas axonopodis pv. glycines. Fine mapping of the BLP resistant gene, rxp, is needed to select BLP resistant soybean cultivars by marker-assisted selection (MAS). We used a total of 227 recombinant inbred lines (RILs) derived from a cross between 'Taekwangkong' (BLP susceptible) and 'Danbaekkong' (BLP resistant) for rxp fine mapping and two different sets of near isogenic lines (NILs) from Hwangkeumkong x SS2-2 and Taekwangkong x SS2-2 were used for confirmation. Using sequences between Satt372 and Satt486 flanking rxp from soybean genome sequences, eight simple sequence repeats (SSR) and two single nucleotide polymorphism (SNP) markers were newly developed in a 6.2-cM interval. Linkage mapping with the RILs and NILs allowed us to map the rxp region with high resolution. The genetic order of all markers was completely consistent with their physical order. QTL analysis by comparison of the BLP phenotyping data with all markers showed rxp was located between SNUSSR17_9 and SNUSNP17_12. Gene annotation analysis of the 33 kb region between SNUSSR17_9 and SNUSNP17_12 suggested three predicted genes, two of which could be candidate genes of BLP resistance: membrane protein and zinc finger protein. Candidate genes showed high similarity with their paralogous genes, which were located on the duplicated regions obtaining BLP resistance QTLs. High-resolution map in rxp region with eight SSR and two SNP markers will be useful for not only MAS of BLP resistance but also characterization of rxp.