Three cyanobacteriochromes work together to form a light color-sensitive input system for c-di-GMP signaling of cell aggregation

Cyanobacteria have sophisticated photosensory systems to adapt to ambient-light conditions to improve oxygenic photosynthesis efficiency. Their genomes contain many genes encoding cyanobacteriochromes (CBCRs), which are the photoreceptors of light-signaling pathways. Although the photochemical properties of many CBCRs have been characterized, whether and how multiple photoreceptors work together are unknown. Herein we describe how three CBCRs work together in a light color-sensitive manner to regulate cyanobacterial cell aggregation. The three CBCRs have distinguishable, but congruent, light color-dependent c-di-GMP synthetic and/or degrading activities. Ours is the first report, to our knowledge, concerning synchronization of distinctive CBCR activities, which emphasizes the underlying need for CBCR photoreceptors with diverse activities.