Expression of Inducible Inorganic Carbon Acquisition Complexes Is Under the Control of the FtsH Protease in Synechocystis sp. PCC 6803

Cyanobacteria possess a complex CO2-concentrating mechanism (CCM), which makes them survive and acclimate in a variety of CO2 environments. The efficiency of CCM is enhanced under low inorganic carbon environments by expression of a set of protein complexes. The inducible CCM genes are regulated by LysR family proteins NdhR and CmpR. To investigate the involvement of proteases in induction of the CCM complexes, we studied the FtsH2 protease mutant of Synechocystis sp. PCC 6803. The cells were grown under high CO2 and then shifted to low CO2, followed by a proteome analysis of the membrane protein complexes and RT-PCR. Interestingly, the inducible CCM complexes were not detected in the FtsH2 mutant upon shift to low CO2. The transcripts of the inducible CCM genes and their regulator ndhR failed to accumulate, indicating that the regulation by the FtsH2 protease is upstream of NdhR. Moreover, functional photosynthesis was shown a prerequisite for induction of CCM in WT at low CO2, possibly via generation of oxidative stress, which was shown here to transiently enhance the expression of inducible CCM genes even at high CO2 conditions.