Alterations in global patterns of gene expression in Synechocystis sp. PCC 6803 in response to inorganic carbon limitation and the inactivation of ndhR, a LysR family regulator.

The cyanobacterium Synechocystis sp. PCC 6803 possesses multiple inorganic carbon (Ci) uptake systems that are regulated by Ci availability. The control mechanisms of these systems and their integration with other cell functions remain to be clarified. An analysis of the changes in global gene expression in response to Ci downshift and the inactivation of ndhR (sll1594), a LysR family regulator of Ci uptake is presented in this report. Mild Ci limitation (3% CO2 (v/v) in air to air alone) induced a dramatic up-regulation of genes encoding both inducible CO2 and HCO3- uptake systems. An induction of ndhD5/ndhD6 and other genes in a probable transcriptional unit was observed, suggesting a function in inducible Ci uptake. The expression of slr1513 and sll1735, physically clustered with sbtA and ndhF3/ndhD3/cupA, respectively, were also coordinated with upstream genes encoding the essential components for HCO3- and CO2 uptake. Ci limitation induced the regulatory genes slr1214, sll1292, slr1594, sigD, sigG, and sigH, among which slr1214, a two-component response regulator, showed the earliest induction, implying a role for the early response to Ci limitation. Opposite regulation of genes encoding the assimilation of carbon and nitrogen demonstrated a striking coordination of expression to balance C- and N-fluxes. The analyses revealed that ndhR inactivation up-regulated the expression of sbtA/sbtB, ndhF3/ndhD3/cupA/sll1735, and slr2006-13 including ndhD5 and ndhD6, indicating a vital role of this regulatory gene in both CO2 and HCO3- acquisition of the cyanobacterium. We therefore suggest that ndhR be renamed ccmR to better represent its broader regulatory characteristics.