SMG2及其互作蛋白SMIP1调控水稻籽粒大小的分子机理研究

Rice is one of the most important cereal crop, and grain size is directly relating to rice yield. Although recent studies have isolated several factors for grain size in rice, the mechanisms that establish the final size of grains is largely unknown. Our group has isolated a set of grain size mutants in rice. The smg2 mutant forms smaller grains than wild type. By employing the Mutmap method, we have cloned the SMG2 gene, which encodes an unknown protein with protein kinase domain. Overexpression of SMG2 forms large grain, long panicle and tall plant, which has a big potential to increase yield. Yeast two-hybrid screening identified SMIP1 as an interacting protein of SMG2. SMIP1 encodes a ATP-binding domain-containing protein. Overexpression of SMIP1 also forms large grains. Thus these preliminary studies showed that SMG2 and SMIP1 are new regulators of rice grain size, and they may act in the same genetics pathway. In this proposal, we will study the genetic interactions between SMG2 and SMIP1, verify the physical interaction between SMG2 and SMIP1 in vitro and in vivo, investigate expression pattern and subcellular localization of SMG2 and SMIP1, test if SMG2 could phosphorylate SMIP1 directly, characterize the cellular basis of SMG2 and SMIP1 regulating grain size and measure the yield of mutants and overexpression lines of SMG2 and SMIP1. This study will elucidate the molecular mechanisms of SMG2 and SMIP1 in rice grain size control, and also evaluate the potential of employing SMG2 and SMIP1 to increase rice yield.

水稻是最重要的粮食作物之一，其籽粒大小同产量直接相关。目前为止，尽管已克隆了一些水稻籽粒大小相关的基因，但对水稻籽粒大小的调控机制有待进一步研究。我们的前期研究筛选了一系列粒型改变的水稻突变体，其中small grain 2（smg2）是一个小粒突变体。通过Mutmap方法克隆显示SMG2编码一个含有蛋白激酶结构域的未知蛋白。过表达SMG2的水稻植株籽粒变大、穗子变长、株高增加，表现出很好的增产潜力。酵母双杂交筛选到SMG2的互作蛋白SMIP1，且过表达SMIP1也形成大的籽粒。这些实验结果初步表明SMG2和SMIP1参与水稻籽粒大小的调控。本项目拟通过对SMG2和SMIP1的遗传关系分析、蛋白互作研究、体内和体外磷酸化研究、表达模式和蛋白亚细胞定位分析、调控籽粒大小的细胞学机制分析、以及对产量的影响研究等，来阐明这两个基因调控籽粒大小的分子机制，并评价它们在提高水稻产量方面的应用潜力。

水稻是最重要的粮食作物之一，其籽粒大小同产量直接相关。目前为止，尽管已克隆了一些水稻籽粒大小相关的基因，但对水稻籽粒大小的调控机制有待进一步研究。通过本项目的研究，我们发现OsMKKK10/SMG2-OSMKK4-OsMAPK6级联信号通路在水稻籽粒大小调控中发挥重要作用。在此基础上，我们进一步鉴定到了该级联信号通路的负调因子OsMKP1。OsMKP1可以通过失活OsMAPK6来抑制籽粒的生长，揭示了OsMAPK6可逆磷酸化在籽粒大小调控上的重要作用。相关研究成果已发表在Molecular Plant和The Plant Journal杂志上。