Cysteine biosynthesis acts as a regulatory hub for ABA-mediated stomatal closure

气孔关闭是植物对土壤干燥、高光和空气湿度降低等干旱胁迫反应最快、最关键的反应。植物激素苦艾酸(ABA)是气孔关闭的重要触发因子。综合研究发现，保卫细胞中存在ABA受体复合体和ABA信号转导通路。相比之下，关于应激诱导的ABA合成的定位和主要触发因素的知识才刚刚开始出现。我们发表的工作建立了木质部运输硫酸盐作为一种新的远程信号，允许气孔感知土壤水分状态。我们证明，在叶片中，硫酸盐通过触发从头产生ABA来促进半胱氨酸的合成，原则上这一过程足以促进气孔关闭。此外，我们还发现，强光胁迫诱导的气孔关闭还依赖于半胱氨酸和ABA从头合成的能力。在这里，我们将通过筛选与水分亏缺相关的一系列胁迫来研究这一机制的一般意义，以确定它们对硫酸盐/半胱氨酸触发的气孔关闭的依赖性。关于植物对干旱胁迫的生理反应，我们将调查ABA途径的两个限制性步骤是否、如何以及在哪些细胞类型中被硫酸盐触发。氧化脂质OPDA所传递的信号被认为可以调节一系列不同的胁迫反应，其中包括对土壤干燥的反应中的气孔关闭。然而，任何OPDA特异性受体和信号转导级联尚不清楚。OPDA与叶绿体基质中的伴侣蛋白CYP20-3结合，促进半胱氨酸合成酶复合体的结合和活性。我们认为，CYP20-3/PCSC继电器作为OPDA的受体复合体，通过控制半胱氨酸的生物合成来刺激ABA的生物合成，并将利用拟南芥突变体和胁迫条件的组合来研究这一功能。如果这些假设成立，植物将能够通过将这些不同的刺激包含到一个内源信号中来协调不同的干旱相关胁迫：半胱氨酸诱导的ABA产生。

Stomatal closure is the fastest and most critical response of plants towards the drought-associated stresses soil drying, high light, and decreased air humidity. The phyto¬hormone absicic acid (ABA) is the crucial trigger for stomatal closure. Comprehensive studies identified the ABA receptor complex and the ABA signal transduction cascade in guard cells. In contrast, the knowledge about the localization and the dominant triggers of stress-induced ABA synthesis is only beginning to emerge. Our published work established xylem-transported sulfate as a new long-distance signal that allows the stomata to perceive the soil water status. We showed that in the leaf sulfate promotes the synthesis of cysteine by triggering de novo ABA production and that in principle this process is sufficient to promote stomatal closure. In addition, we found that high light stress-induced stomatal closure also depends on the ability to synthesize cysteine and ABA de novo. Here we will investigate the general significance of this mechanism by screening a spectrum of water deficit related stresses for their dependence on sulfate/cysteine triggered stomatal closure. With respect to the physiological response of the plant to drought-related stresses we will investigate if, how and in which cell types the two limiting steps of the ABA pathway are triggered by sulfate. Signaling by the oxylipin OPDA is known to mediate a distinct set of stress responses, among them stomatal closure in reaction to soil drying. However, any OPDA-specific receptor and signal transduction cascade is unknown. OPDA binds to the chaperone CYP20-3 in the chloroplast stroma where is promotes association and activity of the cysteine synthase complex. We propose that the CYP20-3/pCSC relay functions as a receptor complex for OPDA that stimulates ABA biosynthesis by controlling cysteine biosynthesis and will investigate this function using combinations of Arabidopsis mutants and stress conditions.If these hypotheses hold, plants would be able to coordinate different drought-associated stresses by the inclusion of these diverse stimuli into one endogenous signal: cysteine-induced ABA production.