Grain size and shape are two crucial traits that influence grain yield and grain appearance in rice. Although several factors that affect grain size have been described in rice, the molecular mechanisms underlying the determination of grain size and shape are still elusive. In this study we report that WIDE AND THICK GRAIN 1 (WTG1) functions as an important factor determining grain size and shape in rice. The wtg1‐1 mutant exhibits wide, thick, short and heavy grains and also shows an increased number of grains per panicle. WTG1 determines grain size and shape mainly by influencing cell expansion. WTG1 encodes an otubain‐like protease, which shares similarity with human OTUB1. Biochemical analyses indicate that WTG1 is a functional deubiquitinating enzyme, and the mutant protein (wtg1‐1) loses this deubiquitinating activity. WTG1 is expressed in developing grains and panicles, and the GFP–WTG1 fusion protein is present in the nucleus and cytoplasm. Overexpression of WTG1 results in narrow, thin, long grains due to narrow and long cells, further supporting the role of WTG1 in determining grain size and shape. Thus, our findings identify the otubain‐like protease WTG1 to be an important factor that determines grain size and shape, suggesting that WTG1 has the potential to improve grain size and shape in rice.
籽粒大小和形狀是影響稻谷產(chǎn)量和外觀的兩個(gè)關(guān)鍵性狀。盡管已發(fā)現(xiàn)幾個(gè)影響籽粒大小的因素，但調(diào)控籽粒大小和形狀的分子機(jī)制仍未可知。在本研究中，我們報(bào)道了寬厚粒WTG1是影響水稻籽粒大小和形狀的重要因素。wtg1-1突變體表現(xiàn)出粒型變寬、變厚、變短和粒重增加、穗粒數(shù)增加的表型。WTG1主要通過影響細(xì)胞膨大以影響籽粒大小和形狀，該基因編碼與人OTUB1類似的otubain樣蛋白酶。生化分析表明，WTG1是一個(gè)有功能的去泛素化酶，突變蛋白（wtg1-1）失去了去泛素化酶的活性。WTG1在發(fā)育中的籽粒和穗中表達(dá)，GFP-WTG1融合蛋白定位在細(xì)胞核和細(xì)胞質(zhì)中。過表達(dá)WTG1，由于產(chǎn)生細(xì)長的細(xì)胞，而導(dǎo)致產(chǎn)生細(xì)長粒，這進(jìn)一步支持WTG1在決定籽粒大小和形狀中的發(fā)揮重要作用的論斷。因此，我們的研究結(jié)果表明otubain樣蛋白酶WTG1是決定籽粒大小和形狀的重要因素，具有改善水稻籽粒大小和形狀的潛力。