The causal gene of a novel small and round seed mutant 1 (srs1) was identified in rice by map-based cloning and named SMALL AND ROUND SEED 1 (SRS1). The SRS1 gene is identical to the previously identified DENSE AND ERECT PANICLE 2 (DEP2). The SRS1/DEP2 gene encodes a novel protein of 1365 amino acids residues without known functional domains. In the longitudinal direction of the lemma, both cell length and cell number are reduced in srs1-1 compared to the wild type, whereas in the lateral cross section of the lemma, cell length in srs1-1 is greater than that in the wild type, but the cell number in srs1-1 is the same as that in wild type. These results suggest that the small and round seed phenotype of srs1-1 is due to the reduction in both cell length and cell number in the longitudinal direction, and the elongation of the cells in the lateral direction of the lemma. The SRS1 mRNA and proteins are abundant in wild type rice specifically in young organs, namely young leaves, internodes and panicles. Interestingly, the tissues expressing SRS1 are closely related to the tissues that exhibit abnormalities in the srs1 mutants.
通過(guò)圖位克隆，水稻小圓粒種突變體srs1 的調(diào)控基因被成功克隆，并命名為SRS1。SRS1 基因域先前鑒定的DEP2 一致。SRS1/DEP2 基因編碼一個(gè)不含已知功能域、由1365氨基酸殘基組成的新蛋白。與野生型相比，srs1-1 突變體外稃的縱向細(xì)胞長(zhǎng)度和細(xì)胞數(shù)量都降低，而外稃橫向部位，srs1-1 突變體的細(xì)胞長(zhǎng)度比野生型要大，但細(xì)胞數(shù)量與野生型一致。這些結(jié)果暗示srs1-1 的小圓粒種子表型是因?yàn)橥怙v向細(xì)胞長(zhǎng)度和細(xì)胞數(shù)量降低，以及橫向細(xì)胞延長(zhǎng)所致。SRS1 mRNA和蛋白在野生型特別是幼嫩器官，如幼葉、節(jié)間和幼穗中富集。有意思的是，表達(dá)SRS1 的組織與srs1 突變體中異常組織緊密相關(guān)。