Ribonuclease H-like gene Small Grain2 regulates grain size in rice through brassinosteroids signal pathway

Yunshuai Huang,Hui Dong,Changling Mou,Ping Wang,Qixian Hao,Min Zhang,Hongmin Wu,Fulin Zhang,Tengfei Ma,Rong Miao,Kai Fu,Yaping Chen,Ziyan Zhu,Cheng Chen,Qikai Tong,Zhuoran Wang,Shirong Zhou,Xi Liu,Shijia Liu,Yunlu Tian,Ling Jiang,Jianmin Wan

First published: 29 July 2022 https://doi.org/10.1111/jipb.13333

Grain size is a key agronomic trait that determines the yield in plants. Regulation of grain size by brassinosteroids (BRs) in rice has been widely reported. However, the relationship between the BR signaling pathway and grain size still requires further study. Here, we isolated a rice mutant, named small grain2 (sg2), which displayed smaller grain and a semi‐dwarf phenotype. The decreased grain size was caused by repressed cell expansion in spikelet hulls of the sg2 mutant. Using map‐ased cloning combined with a MutMap approach, we cloned SG2, which encodes a plant‐specific protein with a Ribonuclease H‐like domain. SG2 is a positive regulator downstream of GSK2 in response to BR signaling, and its mutation causes insensitivity to exogenous BR treatment. Genetical and biochemical analysis showed that GSK2 interacts with and phosphorylates SG2. We further found that BRs enhance the accumulation of SG2 in the nucleus, and subcellular distribution of SG2 is regulated by GSK2 kinase activity. In addition, OsOFP19, a negative regulator of grain shape, interacts with SG2 and plays an antagonistic role with SG2 in controlling gene expression and grain size. Our results indicated that SG2 is a new component of GSK2‐ elated BR signaling response and regulates grain size by interacting with OsOFP19.

类核糖核酸酶H基因Small Grain2通过油菜素类固醇信号途径调节水稻籽粒大小

籽粒大小是决定植物产量的关键农艺性状，油菜素甾醇（BRs）对水稻籽粒大小的调节已被广泛报道。然而，BR信号通路与籽粒大小之间的关系仍需进一步研究。这里我们分离到一个水稻突变体，命名为small grain2（sg2），它表现出较小的籽粒和半矮秆表型。籽粒减小是由于sg2突变体颖壳中的细胞膨胀受到抑制所致。使用基于图位克隆结合MutMap方法，我们克隆了SG2，它编码一种具有核糖核酸酶H样结构域的植物特异性蛋白质。SG2是GSK2下游对BR信号的正向调节因子，其突变导致对外源BR处理不敏感。遗传和生化分析表明，GSK2与SG2相互作用并使其磷酸化。我们进一步发现，BRs促进SG2在细胞核中的积累，SG2的亚细胞分布受GSK2激酶活性的调节。此外，OsOFP19是粒形的负调控因子，与SG2相互作用，在控制基因表达和粒径方面与SG2起拮抗作用。我们的结果表明，SG2是GSK2相关BR信号反应的新成分，并通过与OsOFP19相互作用来调节籽粒大小。

值得注意的是，SG2与最近小麦中克隆的控制株高的RHT8/RNHL1均为RNase H-like protein。