A c-di-GMP binding effector controls cell size in a cyanobacterium

Abstract

Cyclic-di-GMP (c-di-GMP) is a ubiquitous bacterial signaling molecule. It is also a critical player in the regulation of cell size and cell behaviors such as cell aggregation and phototaxis in cyanobacteria, which constitute an important group of prokaryotes for their roles in the ecology and evolution of the Earth. However, c-di-GMP receptors have never been revealed in cyanobacteria. Here, we report the identification of a c-di-GMP receptor, CdgR, from the filamentous cyanobacterium Anabaena PCC 7120. Crystal structural analysis and genetic studies demonstrate that CdgR binds c-di-GMP at the dimer interface and this binding is required for the control of cell size in a c-di-GMP-dependent manner. Different functions of CdgR, in ligand binding and signal transmission, could be separated genetically, allowing us to dissect its molecular signaling functions. The presence of the apo-form of CdgR triggers cell size reduction, consistent with the similar effects observed with a decrease of c-di-GMP levels in cells. Furthermore, we found that CdgR exerts its function by interacting with a global transcription factor DevH, and this interaction was inhibited by c-di-GMP. The lethal effect triggered by conditional depletion of DevH or by the production of several point-mutant proteins of CdgR in cells indicates that this signaling pathway plays critical functions in Anabaena . Our studies revealed a mechanism of c-di-GMP signaling in the control of cell size, an important and complex trait for bacteria. CdgR is highly conserved in cyanobacteria, which will greatly expand our understanding of the roles of c-di-GMP signaling in these organisms.

Control of light-dependent behaviour in cyanobacteria by the second messenger cyclic di-GMP

“…Very recently, a new cyanobacteria-specific c-di-GMP receptor, CdgR, has been described that controls cell size in the filamentous strain Anabaena sp. PCC 7120 (Zeng et al 2023 ). CdgR harbours a c-di-GMP binding site that has no similarity in sequence or structure to known motifs.…”

“…There are two c-di-GMP binding pockets in CdgR, which are located at the dimer interface. Structural and mutational analyses revealed that dimerization of CdgR is essential for c-di-GMP binding, but dimerization does not depend on the binding of the second messenger as in other c-di-GMP receptor proteins (Zeng et al 2023 ). In Anabaena sp.…”

“…PCC 7120, but its targets need to be identified. Synechocystis encodes a homologue of this receptor (Slr1970), and Zeng et al ( 2023 ) also showed c-di-GMP binding for this protein. CdgR is highly conserved in cyanobacteria, and T. vulcanus encodes a homologue of this protein (NIES2134_110 700/Tlr0849) as well.…”

“…In both systems, the signal for the activation of c-di-GMP-related enzymes is unknown. Zeng et al ( 2023 ) further proposed that the newly discovered c-di-GMP receptor, CdgR, functions together with the transcription factor DevH downstream of the CdgK–CdgS two-component system to control cell size and, most probably, essential functions in Anabaena . These studies revealed that c-di-GMP signalling might be involved in many more cyanobacterial responses than reflected in the current literature.…”

The second messenger c-di-AMP controls natural competence via ComFB signaling protein

“…1G). Remarkably, a recent study showed that the ComFB homolog in the multicellular cyanobacterium Nostoc , named CdgR, controls cell size by binding c-di-GMP (Zeng et al 2023). In fact, the filamentous cyanobacterium Nostoc sp.…”