SUN1介导植物糖信号的分子机理研究

In plants, sugar signaling is the core signaling system which reflects the internal physiology situation and the external environment condition, regulating the expression of thousands of genes including the plastocyanin gene. Sugar signaling interacts with the hormone signaling, light signaling, stress signaling, defense signaling and mineral nutrition signaling and plays an critical role in plant growth and development. Based on the cloning of the Arabidopsis sun1 mutant which showed the the sucrose uncoupled regulating of the expression of plastocyanin gene, early flowering and small/dwarf phenotypes, this proposal will systematiclly research the functions on acetylated modification of cell wall polysaccharides, and on influencing plant sugar signal transduction, plant growth and development and biotic/abiotic responses of SUN1/TBL37 gene using the methods of molecular genetics, plant physiology, systems biology etc, and reveal the relationships between the cell wall structure variation and the sugar signal, plant growth and development and stress resistance. By searching the transcription factor which is regulated by SnRK1 and regulates the expression of TBL37 and confirming in vitro and in vivo, we will illustrate a SnRK1-transcription factor-SUN1/TBL37 regulation pathaway, and the mechanism of its coordinating the balance of plant growth and the stress response.

糖信号是反映植物体内生理状况和外界环境条件的核心信号系统，调控了包括质体蓝素基因在内的数千个基因的表达，与激素、光、胁迫、防卫和矿质营养信号密切互作，对植物生长发育具有重要的作用。在前期研究中，我们克隆了一个质体蓝素基因表达蔗糖非偶联、且长势矮小、早花的拟南芥sun1突变体，通过转基因互补确认SUN1编码Trichome Birefringence-Like蛋白家族成员TBL37。在此基础上，本申请拟运用分子遗传学、植物生理学、系统生物学等的方法，系统研究SUN1/TBL37基因参与细胞壁多糖乙酰化修饰和该基因调控糖信号转导、生长发育以及对胁迫响应的功能；揭示细胞壁结构变异与糖信号转导、生长发育和胁迫响应之间的关系；寻找并验证既能调控TBL37转录、同时又受SnRK1磷酸化调控的转录因子，阐明一个“SnRK1-转录因子-TBL37”调控途径，以及该途径平衡植物生长和胁迫响应的机制。

在植物中，细胞壁不仅是植物物理强度的支撑结构，也是植物抵御病虫害入侵的第一道屏障。植物的细胞壁主要由纤维素，半纤维素，果胶，木质素和少量结构蛋白构成，其中半纤维素和果胶多糖分子的主链和侧链上都存在大量的乙酰化修饰，该修饰对植物的生长发育以及生物和非生物胁迫响应具有至关重要的作用，目前细胞壁乙酰化酶的表达调控和特异功能仍有待充分理解。本研究使用混合池组测序（BSA）的方法克隆了一个矮小的拟南芥突变体SUCROSE UNCOUPLED-1 (sun1)，发现其突变基因为TRICHOME BIREFRINGEN-LIKE家族的一个成员TBL37，并通过转基因互补实验和基因编辑手段进行了遗传验证。TBL33在快速生长的植物组织中高度表达，编码一种高尔基体定位蛋白，sun1/tbl37该基因突变体的茎秆中出现了明显的木质部塌陷，且叶片和茎秆中半纤维素的乙酰化水平均明显下降，此外还发现sun1/tbl37的昆虫防御能力显著降低。利用分子生物学和遗传学手段我们发现MYC2转录因子可直接结合于TBL37基因启动子上游的G-box元件上激活其转录，MYC2还促进许多其他TBL基因的表达。此外，MYC活性增强细胞壁乙酰化。myc2-2背景中TBL37的过度表达减少了食草动物的摄食。我们的研究揭示了受茉莉酸信号调控的细胞壁O-乙酰化在控制植物细胞壁特性、植物发育和食草动物防御中的作用。