Regulation of photosynthesis by thylakoid K+/H+ antiport

反式类囊体离子通量的研究是植物生物能量学的一个新兴领域。近年来，在鉴定一些长期寻找的类囊体离子转运体的分子性质，并通过分析缺乏这些蛋白质的植物来表征它们的生理功能方面取得了进展，揭示了这些转运系统在调节光合作用以响应光能水平方面发挥着重要作用。我们之前在该领域的贡献包括发现，在高光到弱光转换时，类囊体K+/H+反端口通过K+外流反转运体KEA3加速了光保护光能猝灭的下调。因此，KEA3活性提高了弱光条件下光合作用的光效。然而，人们对KEA3在这一过程中的确切作用知之甚少。在这个项目中，我们试图全面表征kea3介导的离子通量的作用和调节。最近对不同KEA3变异的分析表明，类囊体K+/H+反端口活性受到涉及KEA3 c端的机制的高度调节。此外，我们有证据表明KEA3在非常低的管径ph条件下具有质子安全阀功能。通过目前的研究项目，我们试图解决以下两个具体问题：(i)在高到低光转换期间光合过程中的瓶颈是什么，KEA3是如何抵消这种限制的；（ii） KEA3活性调节的分子机制是什么？我们将通过综合策略结合互补方法来解决这些问题，包括光谱学，离子，代谢物和蛋白质分析，遗传学和计算建模。

The study of trans-thylakoid ion fluxes represents an emerging field in plant bioenergetics. Recent advances in identifying the molecular nature of some long sought-for thylakoid ion transporters, and characterizing their physiological function by analyzing plants devoid of these proteins, have revealed that these transport systems play important roles in regulating photosynthesis in response to light energy levels. Our previous contribution to the field includes the finding that, upon high to low light transition, thylakoid K+/H+ antiport via the K+ efflux antiporter KEA3 accelerates the downregulation of photoprotective light energy quenching. Thus, KEA3 activity increases the light efficiency of photosynthesis in low light. However, the exact role of KEA3 in this process is poorly understood. With the proposed project we seek to achieve a comprehensive characterization of the role and regulation of KEA3-mediated ion fluxes. The recent analysis of different KEA3 variants has indicated that thylakoid K+/H+ antiport activity is highly regulated by a mechanism involving the KEA3 C-terminus. Additionally, we have evidence for a proton safety valve function of KEA3 under conditions of very low lumenal pH. With the present research project we seek to approach the following two specific questions: (i) Which is the bottleneck in the photosynthetic process during high to low light transitions and how exactly does KEA3 counteract this limitation and (ii) which are the molecular mechanisms underlying KEA3 activity regulation? We will approach these questions by a comprehensive strategy combining complementary approaches, including spectroscopy, ion, metabolite and protein analyses, genetics and computational modeling.