PARENT SESSION

Symposium S6B Photosynthetic acclimation: Mechanisms and gene expression
Thursday September 2nd, 2004 10:20 AM-12:40 PM Room 210A
Chair: Norio Murata
Co-Chair: Eva-Mari Aro

Global patterns of gene expression in Synechocystis sp. PCC 6803 in response to inorganic carbon limitation and the inactivation of ccmR (sll1594), a LysR family regulator. Hong-Liang Wang¹, Bradley Postier¹, Robert Burnap^*,1, ¹ Department of Microbiology & Molecular Genetics, Stillwater, Oklahoma, USA

ABSTRACT- The cyanobacterium Synechocystis sp. PCC 6803 possesses multiple inorganic carbon (Ci) uptake systems that are regulated according to Ci availability in the environment. The control mechanisms of these systems and their integration with other cell functions remain to be clarified. Full genome microarrays and RT-PCR techniques were used to analyze the changes in global gene expression in response to Ci downshift and the inactivation of ccmR (sll1594, formerly, ndhR), a LysR family regulator of Ci uptake. A relatively 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 in the cyanobacterial cells grown in Na2CO3-free BG-11 medium buffered at pH 7.0. The expression of slr1513 (designated sbtB, more recently) and sll1735, physically clustered with sbtA and ndhF3/ndhD3/cupA, respectively, were also coordinated with their upstream genes encoding the essential components for HCO3- and CO2 uptakes. Analyses of RT-PCR and DNA microarray hybridization revealed the expression of ndhD5/ndhD6, physically forming a probable transcriptional unit with downstream genes with homologies to antiporter proteins. This leads us to propose that these genes encode in sodium efflux system, driven by redox energy and used to drive the sodium dependent bicarbonate uptake transporter, SbtA, identified by Ogawa. An opposite regulation of the acquisition and thence assimilation of carbon and nitrogen occurred, demonstrating a striking expression coordination of relevant genes and operons. Based on the analyses of RT-PCR and DNA microarray hybridization, ndhR inactivation up-regulated the expressions of sbtA/sbtB, ndhF3/ndhD3/cupA/sll1735 and slr2006-13 including ndhD5 and ndhD6, indicating a vital role of the regulatory gene in both CO2 and HCO3-. We therefore suggest that ndhR is renamed ccmR to better represent its broader regulatory characteristics and that the regulated genes encode an integrated system of proteins operating to concentrate inorganic carbon using redox energy transduced by Type I dehydrogenases directly as with the CUP subsystem or indirectly via a sodium gradient generated by the NdhD5/NdhD6 subsystem.

KEY WORDS: Type I dehydrogenase, Microarray, carbon concentrating mechanism, Synechocystis