赤霉素信号转导途径中新调控因子的功能和作用机制

Gibberellin (GA) regulates a number of plant agronomic traits including plant height. Although the GA signal transduction pathway “G1D1-GA-DELLA-GAMYB- response genes” is widely recognized, the intermediate steps or regulatory factors between DELLD and GAMYB remain unclear. We have previously obtained a slender and tall rice mutant named “similar to slender” (ssl). Preliminary data showed that the phenotype of the mutant was negatively related to the expression level of SSL, but not affected by the GA synthesis inhibitor (unicoazole-P). We also showed that the SSL protein could bind the GAMYB protein, while the expression level of Della in the ssl mutant stayed unchanged as compared to that in the wild type rice plants. Together, the obtained data suggest SSL is a newly identified negative regulator between DELLA and GAMYB in the GA signal transduction pathway. In this proposal, we plan to further study the epistasis between SSL and other components of the GA pathway, clarify the function of SSL and elucidate the molecular mechanism of SSL. We hope to determine the relationship between SSL and DELLA/GAMYB and fill-in the gap in the GA transduction pathway.

赤霉素（GA）调节株高等植物重要农艺性状。虽然GA信号转导途径“GID1－GA－DELLA－GAMYB－效应基因”已被广泛接受，但在负调控因子DELLA与转录因子GAMYB之间的中间步骤和调控因子尚不清楚。我们先期获得一个植株细高的水稻突变体（similar to slender, ssl）。实验表明该突变体表型与SSL表达水平负相关，且不受GA合成抑制剂影响。SSL蛋白可与GAMYB结合，但突变体中DELLA表达量正常，说明SSL可能是一个介于DELLA和GAMYB之间的负调控因子。本项目拟从SSL与GA信号途径中其他成员的上位关系、SSL的功能及SSL的作用机制等方面进一步研究，以确定SSL与DELLA和GAMYB的互作关系，为完善GA信号转导途径的模型作出贡献。

赤霉素(GA)是重要的植物激素之一，与植物生长发育的多种过程相关。本项目对GA信号途径中三个新的重要因子SSL (similar to slender mutant, SSL)、OsPILA(PIF- like gene)和OsGLPa (germin-like protein)分别参与调控水稻株高、分蘖及种子休眠的功能进行了深入研究。(1) SSL对水稻株高和淀粉酶活性的调控: GA处理抑制SSL的表达，对SSL的功能进行研究，发现在转基因水稻中SSL的高表达明显抑制水稻的株高，而其突变体种子中的α-淀粉酶活性显著提高。进一步分析证明，SSL能够与GAMYB互作，而且其转录受DELLA的正向调控，因此SSL对水稻株高和α-淀粉酶活性的调控作用可能与GA信号途径中SLR1及GAMYB对SSL的调控相关。 (2) OsPILA调控水稻分蘖的分子机理:本研究发现水稻中的PIF-like 基因 OsPILA能够响应GA信号，并负向调控水稻分蘖。BiFC和酵母双杂交分析表明，OsPILA与光敏色素B互作。反向遗传学分析表明，与野生型水稻的分蘖数目相比，OsPILA过表达植株的分蘖数目明显减少，而其显性抑制转基因植株的分蘖数明显增多。进一步分析表明，分蘖负调控因子TB1在OsPILA过表达水稻中的表达量显著高于野生型，推测OsPILA通过正向调控TB1的表达从而抑制水稻的分蘖。(3) OsGLPa基因作为ABA和GA双重信号途径的靶标调控水稻种子的休眠:反向遗传学分析表明，RNAi抑制OsGLPa表达的转基因水稻的前熟种子的萌发率显著提高；而过量表达OsGLPa的转基因水稻则相反，其前熟种子萌发率下降。实验分析表明，ABA信号途径中的ABI5为OsGLPa表达的正调控子而GA信号途径中的GAMYB为OsGLPa表达的负调控子，它们分别作用于OsGLPa启动子中ABRE (G-box) 和 GARE 顺式元件，共同调控OsGLPa的表达，进而调控种子的休眠和萌发状态的转换。.总之，本项目对赤霉素信号转导途径中SSL，OsPILA 和OsGLPa分别对水稻株高、分蘖和种子休眠的调控功能和作用机制的研究结果，有助于完善GA在植物中调控多种生长发育性状的分子机理，并在水稻育种方面具有潜在的应用价值。