GS6

Function:Our sequence analysis revealed that the GS6 gene encodes a GRAS protein, with a premature stop codon mutation causing the large grain size observed in the gs6 mutant. Further analysis of the CDS of GS6 showed that the GS6 gene was more strongly selected in japonica varieties than in indica ones by ancient humans, and that historically, the triplet (ggc) repeats in the GRAS domain of GS6 made an important contribution to the domestication of rice.Many findings suggested that the mutations in the CDS and promoter regions of the Type I haplotype could both change the function and decrease the abundance of GS6,either or both of which might contribute to increases in grain width and weight.Mutations that reside either in the coding region or the promoter region of GS6 might account for the increase of grain size and weight in gs6 mutants.Sequence analysis of the GS6 CDS regions of 76 rice varieties showed that the varieties could be clustered into three kinds of haplotypes,with the grain weights of the cultivars with the Type I haplotype(27.6 g) being significantly heavier than those of Type II (23.4 g)and Type III (18.7 g) haplotypes.Our cloning of the GS6 gene can enlarge the gene pool for MAS to increase the efficiency with which breeding programs can improve grain yield in rice.Taken together, the GS6 gene was closely associated with grain size and was strongly selected by ancient humans during the domestication of rice. The domestication process of the GS6 gene might provide new insights into the molecular mechanisms of development and evolution of rice plants, and could facilitate the genetic improvement of rice yield.