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的非生物胁迫类型，被称为昼夜胁迫。昼夜节律逆境发生在光-暗节律的改变上，并首次在细胞分裂素缺乏的拟南芥植株中观察到，这种植物表现出特别强烈的逆境症状。这表明需要细胞分裂素来保护植物免受这种类型的胁迫。昼夜节律的胁迫症状包括许多胁迫反应基因的表达失控，光合作用活性降低，茉莉酸含量显著增加，最终导致叶片细胞程序性死亡。在茉莉酸合成减少的遗传背景下，应激症状得到强烈缓解，这表明这种激素的增加是导致昼夜应激症状的原因。许多生物钟突变体，特别是那些晨间基因CCA1和LHY活性缺失或活性降低的突变体，对昼夜压力高度敏感。这表明，一个功能良好的时钟对于应对昼夜压力很重要，并导致了一种假设，即昼夜压力条件会将通常平衡良好的时钟推向极限。研究生物钟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阻止或抑制生物钟产生的逆境信号的机制。该项目分为三个部分。在第一部分中，将回答一些基本问题，例如：除了树叶，还有哪些组织对昼夜节律压力做出反应？植物什么时候才能对昼夜节律胁迫做出反应？在昼夜应激处理后，代谢组发生了哪些变化？还有哪些激素参与调节对昼夜节律应激的反应？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)信号在昼夜应激导致细胞程序性死亡中的作用。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应激综合征的新成分，更深入地了解参与昼夜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反应谱及其动力学。最后但并非最不重要的一点是，我们提出了基因筛选的建议，目的是识别出现应激反应改变的突变体，并克隆相应的基因。总之，将对昼夜应激表型背后的分子和遗传机制进行深入的分析，以帮助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.