Cyclic di-GMP Signalling and the Regulation of Virulence in Bacterial Plant Pathogens
J. Maxwell Dow, Yvonne Fouhy, Belén Fernandez Garcia and Robert P. Ryan
from: Plant Pathogenic Bacteria: Genomics and Molecular Biology (Edited by: Robert W. Jackson). Caister Academic Press, U.K. (2009)
Cyclic di-GMP is a novel second messenger that regulates a range of functions including developmental transitions, adhesion, biofilm formation and virulence in diverse bacteria including plant pathogens. Cellular levels of cyclic di-GMP are influenced by both synthesis and degradation. The GGDEF protein domain synthesises cyclic di-GMP, whereas EAL and HD-GYP domains are involved in cyclic di-GMP hydrolysis. The majority of proteins with GGDEF, EAL and HD-GYP domains contain additional signal input domains, suggesting that their activities (and consequently cyclic di-GMP levels) are responsive to environmental cues. Cyclic di-GMP exerts its effects on certain cellular functions by binding to proteins containing a PilZ domain. This domain may occur either as a stand-alone domain, which may act as an "adaptor" to bind other proteins, or as part of a larger protein as is found in the BcsA subunit of cellulose synthase. Some details of the organisation and function of cyclic di-GMP signalling systems have emerged, where both networks of systems regulating the same functions and systems apparently dedicated to specific other tasks occur together in bacterial cells. This has lead to the controversial concept of discrete pools of cyclic di-GMP that are generated and act in a highly localised fashion read more ...