FtsH protease is required for induction of inorganic carbon acquisition complexes in Synechocystis sp. PCC 6803.

Cyanobacteria possess a complex CO(2)-concentrating mechanism (CCM), which is induced by low inorganic carbon conditions. To investigate the involvement of proteases in the processes of induction and degradation of the CCM complexes, we studied the FtsH2 (DeltaSlr0228) and Deg-G (DeltaSlr1204/DeltaSll1679/DeltaSll1427) protease mutants of Synechocystis sp. PCC 6803. WT and protease mutant cells were grown under high CO(2) and then shifted to low CO(2), followed by a proteome analysis of the membrane protein complexes. Interestingly, in the FtsH2 protease mutant, inducible CCM complexes were not detected upon shift to low CO(2), whereas the Deg-G mutant behaved like WT. Also the transcripts of the inducible CCM genes and their regulator ndhR failed to accumulate upon shift of FtsH2 mutant cells from high to low CO(2), 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 CO(2), possibly via generation of oxidative stress, which was shown here to enhance the expression of inducible CCM genes even at high CO(2) conditions. Once synthesized, the CCM complexes were not subject to proteolytic degradation, even when dispensable upon a shift of cells to high CO(2).