Role of cyclic di-GMP in Caulobacter crescentus development and cell cycle control

This chapter summarizes the current knowledge of cyclic di-GMP (c-di-GMP)-mediated control in Caulobacter crescentus. Several members of this family dynamically position to distinct polar sites during the C. crescentus cell cycle, where they contribute to the temporal and spatial regulation of pole morphogenesis and cell cycle progression. The finding that C. crescentus pole development is regulated by c-di-GMP raised several important questions. Recent in vitro and in vivo studies provided convincing evidence that DivK acts as an allosteric regulator of PleC kinase activity. The primary function of the complex regulatory mechanism responsible for cell cycle-dependent PleD phosphorylation is to limit PleD diguanylate cyclase (DGC) activity to the sessile stalked (ST) cell and exclude it from the motile swarmer (SW) cell. The wide range of different cellular processes and molecular targets that are regulated by c-di-GMP reflects its remarkable versatility as a signaling device. Recently, cell cycle control and regulated proteolysis have been added to this growing list of cellular functions controlled by c-di-GMP. The C. crescentus cell cycle is controlled by a cascade of four master regulators that are activated sequentially and in a hierarchical manner. The molecular and cellular mechanisms that underlie the characteristic behavior of Caulobacter cells and its regulation by c-di-GMP might thus be of general relevance for the understanding of processes involved in the motile-sessile transition in many other bacteria.