MAPK级联信号通路调控植物气孔免疫的分子机理研究

Stomatal immunity is the first line of plant defense against pathogen invasion. Once pathogens enter the apoplastic space of plants, plants have to reallocate more resources/energy to mount an effective defense, which causes reduction in biomass and crop yield. Therefore, it is important for us to understand the mechanism of stomatal immunity, which will reveal suitable targets for us to improve plant immunity and crop yield. In the past 20 years, our research has been focused on the functions of two Arabidopsis mitogen-activated protein kinases (MAPKs), MPK3 and MPK6, in plant immunity and growth/development. Recently, we found that MPK3/MPK6 and their upstream kinases, MKK4/MKK5, are essential to stomatal immunity. Genetic analysis also revealed that MPK3/MPK6 activation-induced stomatal closure is ABA independent. Furthermore, our data suggests that MPK3/MPK6 regulate stomatal immunity by controlling the metabolism of organic acids such as malate, a well-known osmolyte in stomatal opening and closure. The specific goals of this proposal are, 1) to identify the MAPKKKs upstream of MKK4/MKK5-MPK3/MPK6 in plant stomatal immunity; 2) to identify the downstream target genes of MPK3/MPK6 that regulate organic acid metabolism; and 3) to elucidate the molecular mechanism underlying the regulation of stomatal immunity from pathogen sensing, to a complete MAPK cascade, to the downstream genes, and to the change of organic acid metabolism, which alters the turgor pressure of guard cells and regulates stomatal opening/closure. We believe that this research not only has important theoretical value, but also provide a foundation for improving stomatal immunity, and therefore, the yield of crops.

气孔免疫是植物抵御病原菌入侵的第一道屏障。病原菌一旦突破气孔免疫进入植物体内，通常会造成植物生物量的下降，甚者可导致植株死亡。因此，研究气孔免疫的机理具有重要的意义。植物MAPK级联途径由MPKs、MKKs及MAPKKKs三级激酶组成，我们发现拟南芥两个病原菌响应MAPKs，MPK3/MPK6，及其上游的MKK4/MKK5对于气孔免疫是必需的；遗传分析表明MPK3/MPK6激活诱导的气孔关闭并不依赖ABA信号途径。初步研究表明MKK4/MKK5-MPK3/MPK6信号模块通过调控保卫细胞内有机酸代谢来介导气孔免疫。本项目拟寻找MKK4/MKK5上游的MAPKKK(s)及鉴定介导MPK3/MPK6调控有机酸代谢的下游靶基因，力图阐释一条完整的MAPK级联信号途径在气孔免疫过程中的作用及分子机制。本研究的开展不仅具有重要的理论价值，也将为提高农作物的气孔免疫能力提供依据，具有潜在的应用价值。

气孔免疫是植物免疫的第一道屏障，但其调控机理还远不清楚。本项目旨在全面揭示植物免疫反应中重要信号通路MAPK级联信号对气孔免疫的调控机制，为农作物抗病分子育种提供理论依据。在本项目支持下，我们对MPK3/MPK6级联信号途径在气孔免疫中的功能及分子调控机制进行了系统研究。野生型植株受到病原菌侵染会主动关闭气孔以限制病原菌侵入，我们发现MPK3/MPK6信号缺失后，植物面对病原菌侵染时不能关闭气孔，导致其抗病能力显著下降。相反，MPK3/MPK6激活可以促使气孔关闭。MKK4/MKK5在MPK3/MPK6上游发挥作用。外源施加苹果酸或柠檬酸能够显著抑制MPK3/MPK6激活以及致病病原菌假丁香单胞杆菌Pst DC3000诱导的气孔关闭。MPK3/MPK6激活或病原菌处理均显著提高了有机酸代谢相关酶类的活性。遗传学及生化证据表明MPK3/MPK6是通过提高保卫细胞内有机酸代谢来介导气孔免疫。此外，ABA与MPK3/MPK6两条信号途径能够互相独立的介导气孔关闭。但面对病原菌入侵时，二者任何一条途径的缺失都会导致气孔不能有效的关闭。基于这些发现，我们提出了MPK3/MPK6与ABA信号途径相互依赖介导气孔免疫的新模型。此外，我们还揭示了植物通过MPK3/MPK6主动调控叶绿体活性氧的生成抑制光合作用来促进植物免疫反应的调控机制。我们的研究结果对理解植物抗病性的分子机制有重要理论参考意义。鉴于MAPK级联信号在高等植物中的保守性，我们的研究可以为作物抗病改良提供了重要理论参考。在本项目支持下，共发表SCI论文4篇。