Delimiting a rice wide-compatibility gene S5n to a 50 kb region.

Wide-compatibility (WC) is one of the most important traits in rice, which can overcome the fertility barrier in the indica/japonica hybrids, and hence to make it possible to utilize the higher yield potential of inter-subspecific hybrids. The S5n gene located on chromosome 6 has been previously reported to be responsible for the wide-compatibility in rice. Here we report the precise location of the S5n gene. In the first-pass mapping, the S5n gene was restricted within a 200 kb region by using a population of 242 isogenic lines in combination with high-density markers developed in the S5 region. In the fine mapping, the S5 region was further saturated with newly developed markers and more isogenic lines (549 in total) were investigated. Eventually, the S5n gene was mapped within a 50 kb region delimited by the left marker J13 and the right marker J17. One BAC clone screened from the BAC library of the WC rice variety 02428 covered the whole S5 region. Sequence analysis of the 50 kb region revealed two candidate genes, coding an aspartyl protease and a hypothetical protein. This result would greatly accelerate both cloning and marker-assisted selection of this important S5n gene.