SnRK2在SnRK3调控下通过调节质膜H+-ATPase抵御渗透胁迫的机理研究

Determining the molecular basis of osmotic stress responses in plants is one of the most important progresses to understand stress tolerance of plants. Previous study revealed that SnRK2-type protein kinases are involved in the modulation of plant osmotic stress responses. However, the underlying mechanism remains enigmatic. Our recent data indicate that two SnRK2-type protein kinases function redundantly in plant osmoregulation. These two members have been divided into different subclasses in the plant SnRK2-type protein kinase family. Furthermore, the kinase activity of SnRK2-type protein kinases in response to osmotic stress may be modulated by SnRK3-type protein kinases. Based on above progresses, this project is attempted to demonstrate the underlying molecular basis of the impact of SnRK3-type protein kinases upon SnRK2-type protein kinases mediated plasma membrane H+-ATPase in plant osmoregulation. To accomplish it, we will adopt many techniques, i.e. determining the efflux of proton in roots, measuring the activity of plasma membrane H+-ATPase, protein-protein interaction assay, reconstitution of the proton transport mediated by plasma membrane H+-ATPase in a heterogeneous system, kinase assay, and osmotic potential measurement. When completed, it is hopeful to provide novel insight into understanding the activating mechanism of SnRK2-type protein kinases by osmotic stress. Moreover, it is also hopeful to understand the coordination between the established electrical potential across plasma membrane by H+-ATPase and plant water modulation in response to osmotic stress, which is attempted to increase water uptake in roots and decrease water loss in leaves under osmotic stress condition.

渗透胁迫应答反应分子作用机理的阐释是理解植物自身抗逆性建立的重要过程。尽管前期研究发现拟南芥SnRK2型蛋白激酶参与渗透胁迫应答反应调节，但相关的分子基础尚未知晓。本组近期研究表明同源进化树上不同分支的两个拟南芥SnRK2型蛋白激酶通过调节质膜H+-ATPase活性功能冗余地参与抵御渗透胁迫，并且这一过程很可能受到SnRK3型蛋白激酶的调控。本项目拟在此基础上，通过根际质子外流、质膜H+-ATPase活性、蛋白质-蛋白质相互作用、质膜H+-ATPase活性异源重建、蛋白激酶活性、植物渗透势等分析与测定，揭示SnRK2在SnRK3调控下通过调节质膜H+-ATPase活性参与植物抵御渗透胁迫的分子机理。这不仅有助于理解渗透胁迫激活SnRK2的作用机制，而且有助于理解质膜H+-ATPase形成的跨膜电势与渗透胁迫下植物水分调节（增加根部水分吸收和减少叶片水分散失）相互关联的作用机制。

渗透胁迫应答反应分子作用机理的阐释是理解植物自身抗逆性建立的重要过程。项目研究从两个SnRK2型蛋白激酶SnRK2.b/2.c参与渗透胁迫下细胞质膜H+-ATPase活性调控起步：发现功能缺失突变体snrk2.bsnrk2.c渗透胁迫下质子外流增加、质膜H+-ATPase活性升高、幼苗主根伸长对渗透胁迫敏感； SnRK2.b和SnRK2.c均能与AHAx C-末端胞内结构域发生蛋白质-蛋白质相互作用，并且此相互作用主要发生在质膜上；SnRK2.c能够磷酸化AHAx，并且主要在8XX位丝氨酸残基处赋予其磷酸化修饰；质膜H+-ATPase同工酶异源回补实验发现SnRK2.b和SnRK2.c均可抑制AHAx质子转运活性，并且可通过在8XX位丝氨酸残基处赋予其磷酸化修饰抑制其质子转运活性；渗透胁迫和ABA处理均可激活SnRK2，并且钙信号也参与调控SnRK2；SnRK2还与ABA处理下质膜H+-ATPase活性负向相关；SnRK2.b和SnRK2.c均能与SnRK3.a发生蛋白质-蛋白质相互作用，这一相互作用主要发生在细胞质膜和细胞核中并且在渗透胁迫下增强；SnRK3.a能够磷酸化SnRK2.c并抑制其激酶活性；异源回补与转基因回补实验等发现SnRK3.a通过磷酸化SnRK2.c抑制AHAx质子转运活性；综上，本项目研究结果表明SnRK3.a通过抑制SnRK2.b/2.c活性，进而影响AHAx的质子转运活性，抵御ABA和渗透胁迫。此外，还发现两个受体类蛋白激酶参与渗透胁迫下H+-ATPase活性，为阐释SnRK2激酶活性精细调节机制指明了研究方向。这些可以为深入理解质膜H+-ATPase活性发挥形成的跨膜电势影响胁迫下植物水分调节的分子作用机制奠定理论基础。