A cyclic GMP-dependent signalling pathway regulates bacterial phytopathogenesis

An, Shi Qi, Chin, Ko Hsin, Febrer, Melanie, McCarthy, Yvonne, Yang, Jauo Guey, Liu, Chung Liang, Swarbreck, David, Rogers, Jane, Maxwell Dow, J., Chou, Shan Ho and Ryan, Robert P. (2013) A cyclic GMP-dependent signalling pathway regulates bacterial phytopathogenesis. EMBO Journal, 32 (18), 2430-2438. (doi:10.1038/emboj.2013.165).

Abstract

Cyclic guanosine 3',5'-monophosphate (cyclic GMP) is a second messenger whose role in bacterial signalling is poorly understood. A genetic screen in the plant pathogen Xanthomonas campestris (Xcc) identified that XC-0250, which encodes a protein with a class III nucleotidyl cyclase domain, is required for cyclic GMP synthesis. Purified XC-0250 was active in cyclic GMP synthesis in vitro. The linked gene XC-0249 encodes a protein with a cyclic mononucleotide-binding (cNMP) domain and a GGDEF diguanylate cyclase domain. The activity of XC-0249 in cyclic di-GMP synthesis was enhanced by addition of cyclic GMP. The isolated cNMP domain of XC-0249 bound cyclic GMP and a structure-function analysis, directed by determination of the crystal structure of the holo-complex, demonstrated the site of cyclic GMP binding that modulates cyclic di-GMP synthesis. Mutation of either XC-0250 or XC-0249 led to a reduced virulence to plants and reduced biofilm formation in vitro. These findings describe a regulatory pathway in which cyclic GMP regulates virulence and biofilm formation through interaction with a novel effector that directly links cyclic GMP and cyclic di-GMP signalling.

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