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

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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.