Grain size is a major determinant of grain yield in cereal crops. qSW5/GW5, which exerts the greatest effect on rice grain width and weight, was fine-mapped to a 2,263-bp/21-kb genomic region containing a 1,212-bp deletion, respectively. Here, we show that a gene encoding a calmodulin binding protein, located ～5?kb downstream of the 1,212-bp deletion, corresponds to qSW5/GW5. GW5 is expressed in various rice organs, with highest expression level detected in young panicles. We provide evidence that the 1,212-bp deletion affects grain width most likely through influencing the expression levels of GW5. GW5 protein is localized to the plasma membrane and can physically interact with and repress the kinase activity of rice GSK2 (glycogen synthase kinase 2), a homologue of Arabidopsis BIN2 (BRASSINOSTEROID INSENSITIVE2) kinase, resulting in accumulation of unphosphorylated OsBZR1 (Oryza sativa BRASSINAZOLE RESISTANT1) and DLT (DWARF AND LOW-TILLERING) proteins in the nucleus to mediate brassinosteroid (BR)-responsive gene expression and growth responses (including grain width and weight). Our results suggest that GW5 is a novel positive regulator of BR signalling and a viable target for genetic manipulation to improve grain yield in rice and perhaps in other cereal crops as well.
粒型是影響谷類作物糧食產(chǎn)量的主要決定因素。qSW5精細定位在2,263bp范圍內(nèi)，GW5精細定位于含有1,212-bp缺失的21-kb基因組區(qū)域，它顯著影響水稻粒寬和粒重。在這里，我們發(fā)現(xiàn)在1,212-bp缺失下游約5kb的區(qū)域，有一個編碼鈣調(diào)素結(jié)合蛋白的基因，即為qSW5/GW5。GW5在各個水稻器官中均表達，其中在幼穗中表達水平最高。我們證實1,212-bp缺失通過影響GW5的表達水平，影響粒寬。GW5蛋白定位于質(zhì)膜，可與糖原合酶激酶GSK2物理互作，并抑制GSK2激酶活性，從而影響細胞核中未磷酸化的OsBZR1和DLT蛋白的積累，從而調(diào)節(jié)油菜素內(nèi)酯（BR）響應(yīng)基因的表達水平和生長響應(yīng)（包括粒寬和粒重）。水稻GSK2是擬南芥BIN2激酶的同源蛋白。我們的研究結(jié)果表明，GW5是BR信號傳導(dǎo)的新型正調(diào)因子，也是通過遺傳操作提高水稻和其他谷類作物糧食產(chǎn)量的可行靶標(biāo)。