Characterization of the response to circadian stress in Arabidopsis thaliana

这项拨款提案的目的是研究最近在植物中发现的一种新型非生物应激，这种应激被命名为昼夜节律应激。昼夜应激发生于光暗节律的变化，并首次在细胞分裂素缺乏的拟南芥植物中观察到，其表现出特别强烈的应激症状。这表明需要细胞分裂素来保护植物免受这种类型的胁迫。昼夜应激症状包括许多应激反应基因的表达失调，光合活性降低，茉莉酸含量强烈增加，最终导致叶片程序性细胞死亡。在茉莉酸合成减少的遗传背景下，应激症状得到强烈缓解，表明这种激素的增加是诱发昼夜应激症状的原因。各种生物钟突变体，特别是那些早晨基因CCA1和LHY活性被废除或降低的突变体，对昼夜节律应激高度敏感。这表明，一个功能良好的生物钟对应对昼夜节律压力很重要，并导致了昼夜节律压力条件将正常平衡的生物钟推向极限的假设。研究昼夜节律应激综合征将有助于了解植物生物钟的功能，细胞分裂素在稳定生物钟功能中的作用，以及通常防止或抑制生物钟产生的应激信号的机制。本项目分为三个部分。在第一部分中，将回答一些基本问题，例如：除了叶子之外，还有哪些组织对昼夜节律压力有反应？植物什么时候开始有能力对昼夜节律压力做出反应？生理应激治疗后代谢组发生哪些变化？还有哪些激素参与调节对昼夜节律压力的反应？最后，细胞分裂素和生物钟之间有什么联系？在第二部分中，我们将详细研究茉莉酸和活性氧（ROS）信号在昼夜应激下引起程序性细胞死亡中的作用。在第三部分中，我们的目标是通过识别参与产生或预防昼夜节律应激综合征的新成分，深入了解参与昼夜节律应激反应的分子机制。确定候选基因的一种方法是研究转录组反应谱及其动力学。最后但并非最不重要的是，提出了基因筛选，旨在识别显示改变应激反应的突变体并克隆相应的基因。总之，深入分析昼夜应激表型的分子和遗传机制将有助于更好地理解昼夜应激综合征。

The objective of this grant proposal is to study a recently discovered novel type of abiotic stress in plants, which has been named circadian stress. Circadian stress occurs upon changes of the light-dark rhythm and has been first observed in cytokinin-deficient Arabidopsis thaliana plants which showed particularly strong stress symptoms. This indicated that cytokinin is required to protect plants from this type of stress. The circadian stress symptoms include deregulated expression of numerous stress response genes, a reduced photosynthetic activity, a strong increase of the jasmonic acid content and eventually programmed cell death in leaves. Stress symptoms were strongly alleviated in a genetic background with reduced jasmonic acid synthesis showing that the increase in this hormone is causal for inducing circadian stress symptoms. Various circadian clock mutants, in particular those with an abolished or reduced activity of the morning genes CCA1 and LHY, are highly sensitive to circadian stress. This shows that a well-functioning clock is important to respond to circadian stress and led to the hypothesis that circadian stress conditions push the normally well-balanced clock to its limit. Studying the circadian stress syndrome will be informative about the functioning of the circadian clock in plants, about the role of cytokinin in stabilizing clock function and about mechanisms normally preventing or dampening clock-generated stress signals. The project is divided into three parts. In the first part a number of basic questions will be answered such as: Which other tissues than leaves are responding to circadian stress? When do plants become competent to respond to circadian stress? Which changes occur in the metabolome after a circadian stress treatment? Which other hormones are involved in regulating the response to circadian stress? And finally, what are the links between cytokinin and the circadian clock? In a second part we will study in detail the roles of jasmonic acid and reactive oxygen species (ROS) signaling in causing programmed cell death upon circadian stress. In the third part we aim to get deeper insight into the molecular mechanisms involved in the response to circadian stress by identifying new components involved in generating or preventing the circadian stress syndrome. One approach to identify candidate genes is to study the transcriptomic response profile and its dynamics. Last but not least genetic screens are proposed aiming to identify mutants showing altered stress responses and to clone the corresponding genes. Together, a profound analysis of the molecular and the genetic mechanisms underlying the circadian stress phenotype will be performed to contribute to a better understanding of the circadian stress syndrome.