Grain size is one of the key factors determining grain yield. However, it remains largely unknown how grain size is regulated by developmental signals. Here, we report the identification and characterization of a dominant mutant big grain1 (Bg1-D) that shows an extra-large grain phenotype from our rice T-DNA insertion population. Overexpression of BG1 leads to significantly increased grain size, and the severe lines exhibit obviously perturbed gravitropism. In addition, the mutant has increased sensitivities to both auxin and N-1-naphthylphthalamic acid, an auxin transport inhibitor, whereas knockdown of BG1 results in decreased sensitivities and smaller grains. Moreover, BG1 is specifically induced by auxin treatment, preferentially expresses in the vascular tissue of culms and young panicles, and encodes a novel membrane-localized protein, strongly suggesting its role in regulating auxin transport. Consistent with this finding, the mutant has increased auxin basipetal transport and altered auxin distribution, whereas the knockdown plants have decreased auxin transport. Manipulation of BG1 in both rice and Arabidopsis can enhance plant biomass, seed weight, and yield. Taking these data together, we identify a novel positive regulator of auxin response and transport in a crop plant and demonstrate its role in regulating grain size, thus illuminating a new strategy to improve plant productivity.
籽粒大小是決定糧食產(chǎn)量的一個(gè)重要因素。然而，發(fā)育信號(hào)如何調(diào)節(jié)粒型仍然不清楚。本文，我們從水稻T-DNA插入突變體庫中鑒定并描述了一個(gè)顯性大粒突變體Bg1-D，表現(xiàn)出超大粒的表型。過表達(dá)Bg1導(dǎo)致籽粒明顯增大，表型嚴(yán)重的株系向地性受到顯著影響。另外，突變體對生長素和生長素轉(zhuǎn)運(yùn)抑制劑萘乙酸更為敏感，而Bg1敲減株系敏感性降低、籽粒變小。此外，Bg1受生長素處理特異誘導(dǎo)，主要在莖部維管組織和幼穗表達(dá)，編碼一個(gè)新的膜定位蛋白，這表明它很有可能在調(diào)節(jié)生長素運(yùn)輸過程中發(fā)揮作用。與該結(jié)果一致的是，突變體增加了生長素向基部運(yùn)輸，改變了生長素的分布，而敲減植株生長素的轉(zhuǎn)運(yùn)減少。在水稻和擬南芥中操作Bg1，能增加植物生物量、粒重和產(chǎn)量?？偨Y(jié)以上結(jié)果，我們在作物中發(fā)現(xiàn)了一個(gè)新的生長素響應(yīng)和轉(zhuǎn)運(yùn)的正調(diào)因子，證明了它在調(diào)節(jié)粒型的作用，因此為提高植物生產(chǎn)力提供新的方法。