The impact of the carbon-regulation protein SbtB on CO2-dependent gene expression in Synechocystis sp. PCC 6803 [dacA]

Gene expression changes were followed in cultures of the cyanobacterium Synechocystis sp. PCC 6803 three and 24 hours after shift from high carbon (HC) to low carbon (LC) concentrations. The acclimation to fluctuating inorganic carbon (Ci) concentrations is crucial for photoautotrophic organisms living in aquatic environments such as cyanobacteria. The PII-like regulator protein SbtB binds the second messengers cAMP or c-diAMP and is involved in the acclimation to LC. Here, we investigated the impact of SbtB and of second messengers on gene expression changes during this acclimation response. We analyzed cultures of the wild type (WT), the ΔsbtB mutant lacking the PII-like regulator protein SbtB, the ΔcyaI mutant, lacking the main soluble adenylate cyclase for cAMP production and ΔdacA, lacking the diadenylate cyclase for c-diAMP production. The majority of LC-induced genes behaved in these mutants like in wild type. However, a defined subset of LC-regulated genes in WT was found to be changed in mutant ΔsbtB already under high CO2. Collectively, the results indicate that SbtB regulates a particular subset of genes during the LC acclimation response. Total RNA was prepared from cells of Synechocystis sp. PCC 6803 wild type and the ΔdacA mutant, lacking the diadenylate cyclase for c-diAMP production. Samples were taken in biological replicates. For data analysis, the same raw data from wild type were taken as in the experiment with the ΔsbtB mutant but normalized here together with the data obtained for the ΔdacA mutant.