Abstract
Concerted changes in the transcriptional pattern and physiological traits that result from long-term (here defined as up to 24 h) limitation of inorganic carbon (C(i)) have been investigated for the cyanobacterium Synechocystis sp. strain PCC 6803. Results from reverse transcription-polymerase chain reaction and genome-wide DNA microarray analyses indicated stable up-regulation of genes for inducible CO(2) and HCO(3)(-) uptake systems and of the rfb cluster that encodes enzymes involved in outer cell wall polysaccharide synthesis. Coordinated up-regulation of photosystem I genes was further found and supported by a higher photosystem I content and activity under low C(i) (LC) conditions. Bacterial-type glycerate pathway genes were induced by LC conditions, in contrast to the genes for the plant-like photorespiratory C2 cycle. Down-regulation was observed for nitrate assimilation genes and surprisingly also for almost all carboxysomal proteins. However, for the latter the observed elongation of the half-life time of the large subunit of Rubisco protein may render compensation. Mutants defective in glycolate turnover (DeltaglcD and DeltagcvT) showed some transcriptional changes under high C(i) conditions that are characteristic for LC conditions in wild-type cells, like a modest down-regulation of carboxysomal genes. Properties under LC conditions were comparable to LC wild type, including the strong response of genes encoding inducible high-affinity C(i) uptake systems. Electron microscopy revealed a conspicuous increase in number of carboxysomes per cell in mutant DeltaglcD already under high C(i) conditions. These data indicate that an increased level of photorespiratory intermediates may affect carboxysomal components but does not intervene with the expression of majority of LC inducible genes.
Highlights
Concerted changes in the transcriptional pattern and physiological traits that result from long-term limitation of inorganic carbon (Ci) have been investigated for the cyanobacterium Synechocystis sp. strain PCC 6803
Though it is widely believed that the sophisticated concentrating mechanism (CCM) should inhibit oxygenase activity of Rubisco in cyanobacteria making a photorespiratory C2 cycle unnecessary, we have recently shown that an active 2PG metabolism operates in cyanobacteria
A Synechocystis mutant impaired in the central step of this metabolism, the glycolate dehydrogenase (GlcD) converting glycolate into glyoxylate, accumulated the photorespiratory intermediate glycolate already at high concentrations of CO2 (HC), indicating a lower efficiency of CCM than generally assumed
Summary
Concerted changes in the transcriptional pattern and physiological traits that result from long-term (here defined as up to 24 h) limitation of inorganic carbon (Ci) have been investigated for the cyanobacterium Synechocystis sp. strain PCC 6803. Mutants defective in glycolate turnover (DglcD and DgcvT) showed some transcriptional changes under high Ci conditions that are characteristic for LC conditions in wild-type cells, like a modest down-regulation of carboxysomal genes. Properties under LC conditions were comparable to LC wild type, including the strong response of genes encoding inducible high-affinity Ci uptake systems. Electron microscopy revealed a conspicuous increase in number of carboxysomes per cell in mutant DglcD already under high Ci conditions These data indicate that an increased level of photorespiratory intermediates may affect carboxysomal components but does not intervene with the expression of majority of LC inducible genes. A genomewide DNA microarray has been employed to study short-term changes accompanying acclimation toward low concentrations of Ci (LC) in Synechocystis, where about 200 genes including those encoding BCT1, SbtA, and NDH-13 were found to be strongly up-regulated (Wang et al, 2004). It was suggested that the glycolate formed could be metabolized either by a plant-like C2 cycle or a bacterial-like glycerate pathway with domination of the plant-like C2 cycle (Eisenhut et al, 2006)
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