Fine mapping and candidate identification of SST, a gene controlling seedling salt tolerance in rice (Oryza sativa L.)

Using a recessive mutant with enhanced salt tolerance at seedling stage obtained from an indica rice cultivar R401 by gamma-ray irradiation, a novel gene controlling salt tolerance in rice was previously mapped to a 406-kb region on chromosome 6. We named the gene Seedling Salt Tolerance (SST). In this study, with a large F-2 population derived from a cross between mutant sst and a japonica cultivar Nipponbare (salt sensitive), SST was further fine mapped to a 17-kb interval between InDel markers ID27101 and ID27118, in which only one gene (OsSPL10) was predicted. Sequencing analysis indicated that the 232nd base of the coding sequence of OsSPL10 was deleted in the sst allele, resulting in a frameshift mutation. The result strongly suggested that OsSPL10 should be the candidate of SST. OsSPL10 is a member of the SBP-box gene family. This is the first time that the SBP-box gene family is found to be probably involved in the regulation of seedling salt tolerance in plant.