解析植物叶绿体活性氧感受器的作用方式和植物光损伤调控的基本机制

Growing body of evidence suggests that chloroplasts act as environmental sensors that translate environmental fluctuations into various forms of chemical signals. These distinct forms of chemical languages appear to activate chloroplasts-to-nucleus retrograde signaling to readjust intracellular homeostasis under changing environment. Among those distinct signaling molecules, our research mainly focuses on chloroplast-generated reactive oxygen species (ROS), particularly singlet oxygen (1O2). 1O2 has long been implicated in photodamage of photosynthetic apparatus, which is one of the major constraints of crop production. However, multiple lines of evidence strongly suggest that 1O2 involves in retrograde signaling pathway, which primes a wide range of physiological responses including acclimation, growth inhibition and cell death. An unbiased genetic screen using Arabidopsis conditional flu mutant that generates 1O2 upon a dark-to-light shift reveals that a nuclear-encoded plastid protein EXECUTER1 (EX1) mediates 1O2 signaling. We previously showed that in response to 1O2, a rapid proteolysis of EX1 via plastid FtsH2 metalloprotease is an integral part of 1O2 signaling (Wang et al., 2016, PNAS; Dogra et al., 2017, Front Plant Sci). We now found that oxidative post-translational modification (Oxi-PTM) of EX1 by 1O2 is essential in instigating 1O2 signaling. The biological relevance of this Oxi-PTM will be further investigated in order to gain insight into the mode of action of this putative 1O2 sensor EX1.

目前，许多研究表明植物叶绿体具有“环境感受器”的功能。既叶绿体可以感知环境变化并转变为各种化学信号，而这些化学信号激活叶绿体向细胞核的逆行信号通路调节细胞内稳态，使植物适应多变的环境。而叶绿体合成的单线氧是我们主要研究化学信号。光合器官发生的光损伤是限制农作物产量的主要原因之一，而单线氧被认为参与了光损伤过程。有证据表明单线氧也可以激活逆行信号通路，并引起包括环境适应、生长抑制和细胞死亡等多种生理反应。拟南芥flu突变体在经历暗光转变后可产生单线氧，通过对flu的遗传筛选，我们发现核编码叶绿体蛋白EXECUTER1（EX1）调控单线氧信号。我们的最新研究显示FtsH2金属蛋白酶水解EX1是单线氧信号的一个重要的部分。我们发现EX1通过转录后修饰被单线氧氧化，进而激活了单线氧信号通路。我们将通过研究氧化翻译后修饰和单线氧信号的生物学联系，探究EX1蛋白作为潜在单线氧感受器的作用方式。

光合作用产生的单线态氧（1O2）与叶绿体到细胞核的逆行信号传递密切相关。我们的研究旨在揭示潜在的1O2传感器蛋白EXECUTER1（EX1）和EX2如何感知临界水平的1O2并将活性氧（ROS）信号传递到细胞核的机制。我们发现，1O2介导的EX1的氧化翻译后修饰以及FtsH蛋白酶对EX1的降解是启动1O2衍生信号传递的关键。具体来说，EX1的DUF3506结构域的第643位色氨酸（Trp643）残基容易被1O2氧化。用对1O2不敏感的氨基酸取代Trp643以及敲除DUF3506结构域都能维持EX1的稳定性并阻碍EX1介导的1O2信号传递。我们还发现，EX1的类似物EX2的第530位色氨酸（Trp530）也会发生依赖于1O2的氧化，这一过程通过减缓EX1-Trp643的氧化以及后续的EX1降解而减弱1O2信号传导。有趣的是，系统发育分析表明EX2的出现可能是为了减弱EX1对1O2的敏感性。总之，我们的研究表明，EX2通过其自身的1O2依赖性氧化来充当EX1信号体的负向调节器，为EX1介导的1O2信号的调节提供了一个新的机制性见解。