Liu Shuying, Hua Lei, Dong Sujun, Chen Hongqi, Zhu Xudong, Jiang Jun'e, Zhang Fang, Li Yunhai, Fang Xiaohua, Chen Fan
National Centre for Plant Gene Research, State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101, China.
State Key Laboratory of Rice Biology, China National Rice Research Institute, Hangzhou, 310006, China.
Plant J. 2015 Nov;84(4):672-81. doi: 10.1111/tpj.13025.
Grain size is an important agronomic trait in determining grain yield. However, the molecular mechanisms that determine the final grain size are not well understood. Here, we report the functional analysis of a rice (Oryza sativa L.) mutant, dwarf and small grain1 (dsg1), which displays pleiotropic phenotypes, including small grains, dwarfism and erect leaves. Cytological observations revealed that the small grain and dwarfism of dsg1 were mainly caused by the inhibition of cell proliferation. Map-based cloning revealed that DSG1 encoded a mitogen-activated protein kinase (MAPK), OsMAPK6. OsMAPK6 was mainly located in the nucleus and cytoplasm, and was ubiquitously distributed in various organs, predominately in spikelets and spikelet hulls, consistent with its role in grain size and biomass production. As a functional kinase, OsMAPK6 interacts strongly with OsMKK4, indicating that OsMKK4 is likely to be the upstream MAPK kinase of OsMAPK6 in rice. In addition, hormone sensitivity tests indicated that the dsg1 mutant was less sensitive to brassinosteroids (BRs). The endogenous BR levels were reduced in dsg1, and the expression of several BR signaling pathway genes and feedback-inhibited genes was altered in the dsg1 mutant, with or without exogenous BRs, indicating that OsMAPK6 may contribute to influence BR homeostasis and signaling. Thus, OsMAPK6, a MAPK, plays a pivotal role in grain size in rice, via cell proliferation, and BR signaling and homeostasis.
籽粒大小是决定粮食产量的一个重要农艺性状。然而，决定最终籽粒大小的分子机制尚未完全清楚。在此，我们报道了一个水稻（Oryza sativa L.）突变体——矮化小粒1（dsg1）的功能分析，该突变体表现出多效性表型，包括小粒、矮化和叶片直立。细胞学观察表明，dsg1的小粒和矮化主要是由细胞增殖受抑制引起的。图位克隆显示，DSG1编码一个丝裂原活化蛋白激酶（MAPK），即OsMAPK6。OsMAPK6主要定位于细胞核和细胞质中，在各个器官中普遍分布，在小穗和小穗颖壳中含量最高，这与其在籽粒大小和生物量生产中的作用一致。作为一种功能性激酶，OsMAPK6与OsMKK4强烈相互作用，表明OsMKK4可能是水稻中OsMAPK6的上游MAPK激酶。此外，激素敏感性测试表明，dsg1突变体对油菜素内酯（BRs）不太敏感。dsg1中内源BR水平降低，并且无论有无外源BRs，dsg1突变体中几个BR信号通路基因和反馈抑制基因的表达都发生了改变，这表明OsMAPK6可能有助于影响BR的稳态和信号传导。因此，MAPK OsMAPK6通过细胞增殖以及BR信号传导和稳态，在水稻籽粒大小中起关键作用。
