Fine mapping of GS2, a dominant gene for big grain rice

Grain shape as a major determinant of rice yield and quality is widely believed to be controlled by quantitative trait loci (QTL). We have identified a novel gene “GS2” to largely regulate grain length and width in rice. The GS2 allele in the big-grain rice line ‘CDL’ functioned in a dominant manner. In the present study, we employed a chromosome walking strategy in the residual heterozygous lines from recombinant inbred population between cultivar “R1126” and CDL, and located the GS2 gene in an interval of ~ 33.2 kb flanked by marker GL2-35-1 and GL2-12 in the long arm of rice chromosome 2. According to genome annotations, three putative gene loci, LOC_Os02g47280, LOC_Os02g47290 and LOC_Os02g47300, exist in this candidate region. In addition, allelic analysis with previously reported genes demonstrated that GS2 was novel for regulating rice grain shape. These results will help promote the cloning and functional characterization of the GS2 gene and further develop linked markers to be used in marker-assisted breeding.