γ-氨基丁酸代谢支路增强茶树抗热性的机制研究

Since high temperature caused by greenhouse effect severely affects tea plant (Camellia sinensis) growth and tea production, the mechanism of high temperature resistance warrants significant attention. GABA shunt plays an important role in resisting to stressful environment in plants. Our previous study found that GABA accumulation in tea via polyamine degradation is one of responses to temperature stress. Furthermore, exogenous GABA would prevent water loss through guard cell stomata closure under microscopy observation. However, the reasons led to heat tolerance by GABA-induced-stomata closure are still unclear. The mechanism of enhanced TCA cycle functions through GABA shunt and polyamine degradation also still unknown. In order to understand the mechanism of improving heat resistance via polyamine metabolism, stomata movement, as well as GABA shunt in tea plant, experiments on polyamine biosynthesis pathway, stomata signal, and TCA cycle will be carried out to focus on studying GABA shunt pathway in this project. Metabolome will be employed to identify differentially expressed metabolites between control and heat treated tea plants. Finally, the key genes expression combined with key enzymes activity analysis will be also performed to explore and identify the genes responding to the GABA shunt. This project will be of critical importance to understand the heat stress related compounds in tea plants as well as expression and regulation mechanism underlying GABA metabolism, and provide possible basis for the further study of genes in regulating heat resistance in tea plants.

温室效应引起的持续高温会严重影响茶树生长及茶叶生产，茶树抗热耐热机制的研究具有重要意义。γ-氨基丁酸（GABA）支路在植物抵抗逆境胁迫中发挥着重要作用。前期研究发现，多胺降解形成GABA是茶树响应温度胁迫的一种重要反应，且外源GABA能诱导保卫细胞的气孔关闭以减少蒸腾作用来抵抗高温逆境，而GABA通过气孔运动调节茶树热害的作用机制尚未清楚。本项目将以茶树GABA支路为研究核心，从多胺合成的角度探讨GABA对茶树诱导抗热性的调节机制，通过代谢组结合定量分析研究气孔运动信号物质含量，进一步明确气孔在GABA诱导茶树抗热性中的作用，从GABA支路的角度探讨GABA对茶树诱导抗热性的调节机制，及研究GABA在茶树体内对三羧酸循环的回补作用。本项目将通过系统研究外源GABA对高温胁迫下茶树多胺的合成、气孔运动及对三羧酸循环的回补功能，揭示外源GABA诱导提高茶树抗热性的作用机制。

茶树抗热耐热机制的研究具有重要意义。本项目围绕外源γ-氨基丁酸（GABA）诱导提高茶树抗热性的作用机制入手，从多胺合成的角度探讨GABA对茶树诱导抗热性的调节机制，从高温胁迫的角度考察GABA对茶叶中多酚类物质积累及抗氧化活性的影响，从逆境胁迫下考察腐胺合成GABA关键酶及其基因的功能分析等方面为调控提高茶树抗热性、开发茶树耐热新技术提供理论基础。本研究用外源GABA结合多胺合成抑制剂（MGBG）处理茶苗，从生化水平及分子水平等方面监测叶片中抗热性诱导的状态。从细胞膜热稳定性（丙二醛含量、超氧自由基等），光合作用、呼吸作用，氮素代谢（脯氨酸等），多胺（腐胺、亚精胺、精胺等）的产生及多胺合成相关酶（ADC、ODC、SPDS、SPMS、SAMDC等）活性及基因表达，研究GABA对多胺合成的调控效果。结果也显示5mM-GABA对茶多酚特别是对儿茶素的积累有很大的促进作用，并在一定程度上上调了黄酮类化合物代谢中的相关基因，增强了热胁迫下茶树的抗氧化活性。项目从蛋白质网络互作视角来研究GABA对茶树抗性的影机理的方向，同时也揭示了GABA对茶树一些代谢途径的影响，如类黄酮代谢、氨基酸代谢、AsA /谷胱甘肽循环、三羧酸循环、乙醛酸循环、光合生物固碳作用、氧化磷酸戊糖途径和嘌呤代谢。高温胁迫下外源GABA直接或间接地影响了氨基酸和咖啡因的生物合成，并调节了植物的能量代谢。外源GABA可能通过调节氧化戊糖磷酸途径和嘌呤代谢来影响茶树的抗热性和茶叶风味。通过RT-qPCR验证筛选的与氧化戊糖磷酸途径和嘌呤代谢关键基因的相对表达情况。结果表明，这些基因的表达模式与其相对应的差异蛋白表达模式一致。