Inorganic Carbon Limitation Induces Transcripts Encoding Components of the CO2-Concentrating Mechanism in Synechococcus sp. PCC7942 through a Redox-Independent Pathway

Abstract

The cyanobacterial CO 2-concentrating mechanism (CCM) allows photosynthesis to proceed in CO 2-limited aquatic environments , and its activity is modulated in response to inorganic carbon (Ci) availability. Real-time reverse transcriptase-PCR analysis was used to examine the transcriptional regulation of more than 30 CCM-related genes in Synechococcus sp. strain PCC7942 with an emphasis on genes encoding high-affinity Ci transporters and carboxysome-associated proteins. This approach was also used to test hypotheses about sensing of Ci limitation in cyanobacteria. The transcriptional response of Synechococcus sp. to severe Ci limitation occurs rapidly, being maximal within 30 to 60 min, and three distinct temporal responses were detected: (a) a rapid, transient induction for genes encoding carboxysome-associated proteins (ccmKLMNO, rbcLS, and icfA) and the transcriptional regulator, cmpR; (b) a slow sustained induction of psbAII; and (c) a rapid sustained induction of genes encoding the inducible Ci transporters cmpABCD, sbtA, and ndhF3-D3-chpY. The Ci-responsive transcripts investigated had half-lives of 15 min or less and were equally stable at high and low Ci. Through the use of a range of physiological conditions (light and Ci levels) and inhibitors such as 3-(3,4-dichlorophenyl)-1,1dimethylurea, glycolaldehyde, dithiothreitol, and ethoxyzolamide, we found that no strict correlation exists between expression of genes known to be induced under redox stress, such as psbAII, and the expression of the Ci-responsive CCM genes. We argue that redox stress, such as that which occurs under highlight stress, is unlikely to be a primary signal for sensing of Ci limitation in cyanobacteria. We discuss the data in relation to current theories of CO 2 sensing in cyanobacteria.

Metabolic and Transcriptomic Phenotyping of Inorganic Carbon Acclimation in the Cyanobacterium Synechococcus elongatus PCC 7942

“…Genes coding for proteins involved in the active uptake of C i (bicarbonate and/or CO 2 ) as part of the CCM showed the highest increase in transcript levels 6 h after the LC shift, as was found previously by reverse transcription-PCR and northern-blot hybridization in Synechococcus species (Woodger et al, 2003(Woodger et al, , 2007 and in Synechocystis 6803 (Wang et al, 2004;Eisenhut et al, 2007). The strongest responses are found for the bicarbonate-specific ATP-binding cassette transporter BCT1 and the symporter SbtA (Table II).…”

“…Furthermore, the transcript levels of the pyruvate kinase-encoding gene orf0098 and the gene orf2384, which encodes a component of the pyruvate dehydrogenase, are also approximately 3.5-fold increased after the long-term LC shift. However, the gene for PEP carboxylase (ppc; orf2252) did not change expression under LC conditions (Table I), as reported previously (Woodger et al, 2003). It may further be hypothesized that the glyceraldehyde-3-phosphate dehydrogenase isoform encoded by orf1939 is implicated in the glycolytic pathway rather than in the Calvin-Benson cycle.…”

“…NdhF4 and NdhD4), whereas an additional CO 2 -converting NDH1 complex is activated under LC (e.g. NdhD3; Table II), as was reported previously (Woodger et al, 2003). However, these LC-induced transcript levels are clearly not controlled by the PII-based C-N sensor system, since the changes are similar in the wild type and the MP2 mutant (Table II).…”

“…The acclimation to LC increased the affinity toward bicarbonate approximately 4-fold in both cultures (wildtype K 1/2 = 35.5 6 6.4 mM, mutant MP2 K 1/2 = 46.2 6 19.6 mM). Previous studies revealed similar C i affinities for HC cells (approximately 150 mM) that increased up to 10-fold during the first few hours after the shift from HC to LC conditions in Synechococcus 7942 (Woodger et al, 2003(Woodger et al, , 2005.…”

Transport functions dominate the SAR11 metaproteome at low-nutrient extremes in the Sargasso Sea

“…In addition to general photosystem proteins, proteomic evidence of the pigment differences between Prochlorococcus and Synechococcus were observed with chlorophyll and carotenoid synthesis proteins detected for Prochlorococcus and phycobilisome proteins detected for Synechococcus. Carboxysome proteins, which are induced by inorganic carbon limitation and are thought to be signaled by high light (McKay et al, 1993;Woodger et al, 2003) were also observed, with peptides for the Synechococcus orthologs appearing more frequently. The carboxysome allows cyanobacteria to overcome inorganic carbon limitation by concentrating CO 2 for its conversion to organic carbon by the enzyme ribulose 1, 5 bisphosphate carboxylase/oxygenase (RuBis-CO), which was also detected.…”