P _II -like signaling protein SbtB links cAMP sensing with cyanobacterial inorganic carbon response

Abstract

Significance Life on Earth depends on photosynthetic CO 2 fixation to form organic carbon. This process evolved in cyanobacteria and was later conveyed to eukaryotes, giving rise to plastids in algae and plants. To cope with low atmospheric CO 2 concentrations that developed over the course of evolution, cyanobacteria evolved a CO 2 -concentrating mechanism (CCM), which elevates CO 2 levels in the vicinity of RubisCO, the key enzyme of CO 2 fixation. Here we describe a conserved cyclic AMP receptor protein, SbtB, which participates in the sensing of fluctuating C i levels to regulate the cyanobacterial CCM system. SbtB represents a new principle of C i sensing, which is important for acclimation to varying C i regimes in the ecological niches of cyanobacteria.