Yang Chao, Shen Wenjin, He Yong, Tian Zhihong, Li Jianxiong
University of Chinese Academy of Sciences, Key Laboratory of South China Agricultural Plant Molecular Analysis and Genetic Improvement, and Guangdong Provincial Key Laboratory of Applied Botany, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, China.
College of Life Science, Yangtze University, Jingzhou, China.
PLoS Genet. 2016 Jun 22;12(6):e1006118. doi: 10.1371/journal.pgen.1006118. eCollection 2016 Jun.
OVATE gene was first identified as a key regulator of fruit shape in tomato. OVATE family proteins (OFPs) are characterized as plant-specific transcription factors and conserved in Arabidopsis, tomato, and rice. Roles of OFPs involved in plant development and growth are largely unknown. Brassinosteroids (BRs) are a class of steroid hormones involved in diverse biological functions. OsGKS2 plays a critical role in BR signaling by phosphorylating downstream components such as OsBZR1 and DLT. Here we report in rice that OsOFP8 plays a positive role in BR signaling pathway. BL treatment induced the expression of OsOFP8 and led to enhanced accumulation of OsOFP8 protein. The gain-of-function mutant Osofp8 and OsOFP8 overexpression lines showed enhanced lamina joint inclination, whereas OsOFP8 RNAi transgenic lines showed more upright leaf phenotype, which suggest that OsOFP8 is involved in BR responses. Further analyses indicated that OsGSK2 interacts with and phosphorylates OsOFP8. BRZ treatment resulted in the cytoplasmic distribution of OsOFP8, and bikinin treatment reduced the cytoplasmic accumulation of OsOFP8. Phosphorylation of OsOFP8 by OsGSK2 is needed for its nuclear export. The phospphorylated OsOFP8 shuttles to the cytoplasm and is targeted for proteasomal degradation. These results indicate that OsOFP8 is a substrate of OsGSK2 and the function of OsOFP8 in plant growth and development is at least partly through the BR signaling pathway.
OVATE基因最初被鉴定为番茄果实形状的关键调节因子。OVATE家族蛋白（OFPs）是植物特有的转录因子，在拟南芥、番茄和水稻中保守。OFPs在植物发育和生长中的作用很大程度上未知。油菜素类固醇（BRs）是一类参与多种生物学功能的类固醇激素。OsGKS2通过磷酸化下游组分如OsBZR1和DLT在BR信号传导中起关键作用。在此我们报道在水稻中OsOFP8在BR信号通路中起积极作用。BL处理诱导了OsOFP8的表达并导致OsOFP8蛋白积累增加。功能获得突变体Osofp8和OsOFP8过表达系显示叶片夹角增大，而OsOFP8 RNAi转基因系显示叶片表型更直立，这表明OsOFP8参与BR反应。进一步分析表明OsGSK2与OsOFP8相互作用并使其磷酸化。BRZ处理导致OsOFP8的细胞质分布，而碧卡宁处理减少了OsOFP8的细胞质积累。OsGSK2对OsOFP8的磷酸化是其核输出所必需的。磷酸化的OsOFP8穿梭到细胞质并靶向蛋白酶体降解。这些结果表明OsOFP8是OsGSK2的底物，且OsOFP8在植物生长发育中的功能至少部分通过BR信号通路实现。
