水稻GL3基因调控表皮毛发育的遗传和分子机制解析

Trichomes are specialized structures located on the cuticle of plant aerial organs and protect plant from environmental stresses to some extent. However, the absence of trichomes in rice which leads to glabrous leaf and hulls is a favorite agronomic trait in rice production, and the glabrous rice is also regarded as important germplasm resource in rice breeding. Because trichomes originate from pluripotent epidermal cells (promeristem) and are easily accessible, their development has become an excellent model system to study all aspects of cell differentiation and growth in Arabidopsis. However, their molecular mechanism in rice and other monocots remains unclear. In our previous studies, a novel rice gene, namely GL3 (Glabrous Leaf and Hull 3), which encodes a member of the AP2/EREBP transcription factor superfamily, were found to be tightly involved in the regulation of trichome development. The loss-of-function of GL3 results in the absence of trichomes which leads to glabrous leaf and hulls in rice plants, similar to the phenotype caused by the loss of GL1/NUDA. In contrast, the overexpression of GL3 promotes trichome elongation intensively in rice. Based on these results, a comprehensive investigation will be proposed to elucidate the biological functions and regulatory network of GL3, as well as the potential genetic interaction between GL3 and GL1/NUDA, in the control of trichome development. Hence, a series of approaches including RT-PCR analysis, genetic transformation, chromatin immunoprecipitation (ChIP), transcriptome sequencing, yeast one-hybrid and double mutant analysis will be employed in the present project. In sum, our genetic and molecular elucidation of GL3 will have theoretical implications for dissecting the molecular mechanism of trichome development in rice, as well as improving the trichome related traits in rice breeding and seed production.

表皮毛是植物表皮组织的一种特化结构，对植物体起保护作用。但在水稻生产中表皮毛缺失引起的光叶、光壳是受人喜爱的性状；光叶（壳）稻还是水稻育种的重要种质资源。表皮毛起源于原分生组织，在拟南芥中是细胞分化等研究的模式系统，但在水稻等单子叶植物中其调控机制还远未阐明。在前期研究中，我们克隆到一个与水稻表皮毛发育密切相关的AP2/EREBP转录因子GL3，其功能缺失导致表皮毛减少，植株表现光叶光壳，类似GL1/NUDA功能缺失突变表型；其超表达导致表皮毛极度增长，植株表现多毛。本项目拟在前期研究的基础上，综合利用基因表达、遗传转化、染色质免疫共沉淀、转录组测序、酵母单杂交和双突变体分析等方法，系统解析GL3的生物学功能和调控机制，以及GL3与GL1/NUDA的遗传互作，进而阐明GL3调控表皮毛发育的遗传和分子机理。预期研究结果对水稻表皮毛发育机制的阐明以及表皮毛性状的改良和利用都具有重要理论价值。

表皮毛是植物表皮组织的一种特化结构，通常对植物体起保护作用；但在水稻生产中表皮毛缺失引起的叶片和颍壳无毛表型是有利农艺性状并被应用于水稻育种和生产实践。表皮毛起源于原分生组织，拟南芥表皮毛是细胞分化等研究的模式系统，但在水稻等单子叶植物中其发育调控机制还远未阐明。本研究通过GL3/OsPLT2的生物学功能、转录调控和蛋白质互作分析等研究内容，从而揭示了GL3/OsPLT2调控水稻表皮毛长度发育的分子基础。GL3/OsPLT2与先前已被报道的HL6基因（Mol Plant, 2017, 10, 1417-1433）等位。本项目研究表明GL3/OsPLT2在水稻愈伤和分生组织等未分化细胞中高水平表达，其编码蛋白为AP2/ERF转录因子定位于细胞核，其基因功能缺失突变体表型同野生型，但过表达GL3/OsPLT2导致表皮毛长度显著增加，因而植株表现为多毛。我们进一步发现GL/OsPLT2同源基因OsPLTx基因超表达会产生相同表型——由于表皮毛长度剧烈增加导致植株多毛。GL3/OsPLT2基因超表达导致表皮毛长度增加亦伴随生长素和细胞分裂素途径被显著激活。GL/OsPLT2和OsPLTx均与水稻表皮毛起始调控关键因子OsWOX3b/GL-1存在蛋白互作，osplt2-oswox3b双突变体和oswox3b单突变体一样——表皮毛缺失，但双突变体的花器官发育存在多种异常且植株败育。我们还发现，在oswox3b温和突变体（仅叶边缘有表皮毛）中超表达GL3/OsPLT2虽不能使oswox3b突变体表皮毛缺失表型恢复，但能够促使叶边缘表皮毛长度剧烈增加。综上，结果表明GL3/OsPLT2和其同源基因调控表皮毛长度并不依赖于GL1/OsWOX3b的功能。本项目研究结果不仅对于深入认识单子叶植物表皮毛发育调控机制具有理论意义，也能为水稻遗传育种中表皮毛性状的合理利用提供理论基础。