How does cyclic-di-GMP regulate biosynthesis of a key P. syringae phytotoxin?

丁香假单胞菌是一种广泛存在的植物病原菌，在世界范围内造成农作物产量损失。冠状毒素(COR)是由几个紫丁香菌致病变种产生的，在引发植物侵染过程中起着重要作用。COR抑制植物免疫，抑制气孔关闭，并诱导受感染组织的黄化。我们最近发现，广泛存在的细菌信号分子CDG与COR生物合成途径的三种酶结合。这一发现表明CDG参与了COR的调节和对紫丁香根结线虫侵染的控制。在这个项目中，我们将结合遗传学、生物化学和结构生物学来确定CDG结合是如何控制紫丁香中COR的生物合成的。该项目将首先对CDG与核心生物合成酶的结合进行深入的生化分析。通过X射线结晶学的结构表征，将进一步完善CDG与各酶调控的关系。同时，我们将利用遗传学、分子生物学和植物侵染实验来确定CDG结合与COR生物合成的生理相关性，以及它对植物中丁香疫霉毒力的影响。

Pseudomonas syringae is a widespread plant pathogen responsible for yield losses in crops worldwide. The phytotoxin coronatine (COR) is produced by several P. syringae pathovars and plays an important role in initiating plant infections. COR suppresses plant immunity, inhibits the closure of stomata, and induces chlorosis (yellowing) of infected tissues. We recently showed that the widespread bacterial signalling molecule cyclic-di-GMP (cdG) binds to three enzymes of the COR biosynthesis pathway. This finding implicates cdG in COR regulation and in the control of P. syringae plant infection. In this project, we will use a combination of genetics, biochemistry and structural biology to define how cdG-binding controls COR biosynthesis in P. syringae. The project will first conduct an indepth biochemical analysis of cdG-binding to the COR-biosynthetic enzymes. The relationship between cdG and regulation of each enzyme will be further refined through structural characterization by X-ray crystallography. In parallel, we will use genetics, molecular biology and plant infection experiments to determine the physiological relevance of cdG-binding to COR biosynthesis, and its impact on P. syringae virulence in planta.