Identification of an 85-kb DNA fragment containing pms1, a locus for photoperiod-sensitive genic male sterility in rice

Photoperiod-sensitive genic male-sterile rice has a number of desirable characteristics for hybrid rice production. Previous studies identified pms1, located on chromosome 7, as a major locus for photoperiod-sensitive genic male sterility. The objective of this study was to localize the pms1 locus to a specific DNA fragment by genetic and physical mapping. Using 240 highly sterile individuals and a random sample of 599 individuals from an F2 population of over 5000 individuals from a cross between Minghui 63 and 32001S, we localized the pms1 locus by molecular marker analysis to a genetic interval of about 4 cM, 0.25 cM from RG477 on one side and 3.8 cM from R1807 on the other side. A contig map composed of seven BAC clones spanning approximate 500 kb in length was constructed for the pms1 region by screening a BAC library of Minghui 63 DNA using RFLP markers and chromosomal walking. Analysis of recombination events in the pms1 region among the highly sterile individuals reduced the length of the contig map to three BAC clones. Sequencing of one BAC clone, 2109, identified two SSR markers located 85 kb apart in the clone that flanked the pms1 locus on both sides, as indicated by the distribution of recombination events. We thus concluded that the pms1 locus was located on the fragment bounded by the two SSR markers.