OsELF3介导的泛素化途径调控水稻抽穗期的研究

Flowering is one of the most critical shoot apex meristem decisions from vegetative to reproductive phase in high plants. Heading date is one of the important agronomic traits in rice breeding, which determines the variety growth adaptation in various growth seasons and regions. Our previous studies have identified that OsELF3 acts as a floral activator via its crosstalk with the circadian clock and suppression of OsGI and Ghd7 in the flowering time control under long-day conditions in rice. In this study, we will elucidate the function of an E3 ubiquitin ligase, CDF1 (Constitutive Delayed Flowering 1), mediated by OsELF3 in heading date control of rice. We will focus on the study of the activity of E3 ubiquitin ligase of CDF1, and the ubiquitination of OsELF3 or other target proteins mediated by OsELF3. Employing the mutant lines, we will study the relationship of CDF1 with other flowering time genes, especially OsPhyB，OsELF3，OsGI and Hd1, in rice heading date regulation through analysis of their mutant phenotype, genes expression and protein interactions. The results of this project might uncover the molecular basis of rice heading date which induced by light transduction, circadian clock regulation.

开花期决定了植物茎顶端分生组织从营养生长到生殖生长的重要形态发生过程。抽穗期是水稻重要农业性状之一，它决定了品种的地区与季节适应性。前期研究结果表明OsELF3在长日照条件下通过抑制OsGI和Ghd7的表达和影响主要的生物钟基因来控制水稻的抽穗期。本研究基于一个与OsELF3互作的E3泛素连接酶基因CDF1探讨其在水稻抽穗期调控中的功能。拟重点研究CDF1蛋白的E3连接酶活性并分析CDF1泛素化降解OsELF3还是OsELF3介导的其他靶蛋白，从而确定CDF1在水稻抽穗期调控中发挥作用的靶蛋白；利用相关基因的突变体，通过突变体表型、基因表达及蛋白互作研究，系统分析CDF1与抽穗期相关基因尤其是OsPhyB、OsELF3、OsGI、Hd1之间的调控关系，初步探讨水稻中光输入路径、昼夜节律钟之间相互作用调控水稻抽穗期的分子机理。

植物在生长发育过程中通过蛋白泛素化降解系统来调节蛋白的时空表达水平从而适应外部环境和内源的发育信号。光周期影响水稻抽穗时间，是决定产量的重要因素之一。水稻中虽然鉴定了一些参与光周期的转录因子，但它们的互作关系及翻译后水平的调控机制尚不清楚。本研究分离克隆了影响水稻抽穗期的HAF1 (Heading date Associated Factor 1)基因，HAF1编码一个具有RING finger 结构域的泛素连接酶（E3）。HAF1通过与Hd1和OsELF3互作，分别调控水稻在短日照和长日照条件下的抽穗期。突变体haf1表现为长短日条件下均晚抽穗，haf1/hd1双突变体的抽穗期与hd1单突变体一致，说明在短日照条件下HAF1通过与Hd1调控抽穗期；但haf1/oself3双突变体的抽穗期与oself3单突变体一致，表明HAF1可能在长日照条件下还参与了某个开花抑制因子的降解。泛素化蛋白降解实验证明HAF1通过26S蛋白酶复合体特异性降解Hd1和OsELF3。我们的研究结果表明HAF1调节了Hd1和OsELF3的昼夜节律性累积来调控水稻在不同光周期条件下的抽穗期。另外，我们还鉴定了一个恢复抽穗的突变体sid1 (Suppressor of RID1)，SID1与RID1相互协同来启动水稻的成花转换。相关的研究结果发表在《Plant Cell》和《PLoS Genetics》杂志上。