Project description:To investigate acclimation mechanisms employed under extreme high light conditions, gene expression analysis was performed using the model microalgae Synechocystis sp. PCC 6803 (PCC 6803) cultured under various light intensities. From the low to the mid light conditions, the expression of genes related to light harvesting systems was repressed, whereas that of CO2 fixation and of D1 protein turnover-related genes was induced. Gene expression data also revealed that the down-regulation of genes related to flagellum synthesis (pilA2), pyridine nucleotide transhydrogenase (pntA and pntB), and sigma factor (sigA and sigF) represents acclimation mechanisms of PCC 6803 under excessive high light conditions.
Project description:Acclimation to low CO2 conditions in cyanobacteria involves the coordinated regulation of genes mainly encoding components of the carbon concentration mechanism (CCM). Making use of several independent microarray datasets a core set of CO2-regulated genes was defined for the model strain Synechocystis sp. PCC 6803. On the transcriptional level, the CCM is mainly regulated by the well-characterized transcriptional regulators NdhR and CmpR, whereas the role of an additional regulatory protein, namely cyAbrB2 belonging to the widely distributed AbrB regulator family that was originally characterized in the genus Bacillus, is less defined. Here we present results of transcript profiling of the wild type and a ΔcyabrB2 mutant of Synechocystis sp. PCC 6803 after shifts from high CO2 (5% in air, HC) to low CO2 (0.04%, LC). Evaluation of the transcriptomic data revealed that cyAbrB2 is involved in the regulation of several CCM-related genes such as sbtA/B, ndhF3/ndhD3/cupA and cmpABCD under LC conditions, but apparently acts supplementary to the main regulators. Under HC conditions, cyAbrB2 deletion changes the expression of photosystem II subunits, light-harvesting components, and Calvin-Benson-Bassham cycle enzymes.
Project description:Like many other organisms, cyanobacteria exhibit rhythmic gene expression with a period length of 24 hours to adapt to daily environmental changes. In the model organism Synechococcus elongatus PCC 7942 the central oscillator consists of three proteins: KaiA, KaiB and KaiC and utilizes the histidine kinase SasA and its response regulator RpaA as output-signaling pathway. Synechocystis sp. PCC 6803 contains two additional homologs of the kaiB and kaiC genes. Here we demonstrate that RpaA interacts with the core oscillator KaiAB1C1 of Synechocystis sp. PCC 6803 via SasA, similar to Synechococcus elongatus PCC 7942. However, interaction with the additional Kai homologs was not detected, suggesting different signal transduction components for the clock homologs. Inactivation of rpaA in Synechocystis sp. PCC 6803, lead to reduced viability of the mutant in light-dark cycles that aggravated under mixotrophic growth conditions. Chemoheterotrophic growth in the dark was abolished completely. In accordance, transcriptomic data revealed that RpaA is involved in the regulation of genes related to CO2‑acclimation and carbon metabolism under diurnal light conditions. Further, our results indicate that RpaA functions in the posttranslational regulation of glycogen metabolism as well, and a potential link between the circadian clock and motility was identified.
Project description:Gene expression changes were followed in cultures of the cyanobacterium Synechocystis sp. PCC 6803 substrain GT-T cultivated at ambient air or supplemented with 3% CO2. The acclimation to different CO2 concentrations is crucial for photoautotrophic organisms living in aquatic environments such as cyanobacteria. Samples were taken before and 1 h and 24 h after transfer to the3 % CO2 environment. The analyzed strains were wild type, a deletion mutant of gene ssl2982/rpoZ (ΔrpoZ) and two suppressor strains (R1, ΔrpoZ-S1 and R2, ΔrpoZ-S2). In cyanobacteria, elevated CO2 is known to down-regulate carbon concentrating mechanisms and accelerate photosynthesis and growth, but mechanism(s) of carbon signalling remains only poorly understood. Here we reveal a novel signalling cascade connecting the amount of CO2 and growth in the model cyanobacterium Synechocystis sp. PCC 6803. Deletion of the small ω subunit of the RNA polymerase (RNAP) in the ΔrpoZ strain prevents normal high-CO2-induced up-regulation of numerous photosynthetic genes, and low expression of peptidoglycan synthesis genes induced lysis of dividing ΔrpoZ cells in high CO2. Spontaneously raised secondary mutations in the ssr1600 gene rescued the high-CO2-sensitive phenotype of the ΔrpoZ strain. Biochemical analyses showed that the ssr1600 gene encodes an anti-σ factor antagonist of group 2 σ factor SigC, and 3D structural modelling suggest that Slr1861 functions as an anti-SigC factor. In ΔrpoZ, excess formation of RNAP-SigC lead to high CO2 sensitive phenotype, whereas the drastically reduced Ssr1600 content in the suppressor mutants reduce the formation of the RNAP-SigC holoenzyme to the similar level as in the control strain, allowing almost normal transcriptome and growth of suppressor lines in high CO2. We propose that the SigC σ factor, the anti-SigC factor Slr1861 and the anti-SigC antagonist Ssr1600 forms a growth regulating signalling cascade in cyanobacteria.
Project description:Cyanobacteria are the only prokaryotes that perform plant-like oxygenic photosynthesis. They evolved an inorganic carbon-concentrating mechanism to adapt to low CO2 conditions. Quantitative phospho-proteomics was applied to analyze regulatory features during the acclimation to low CO2 conditions in the model cyanobacterium Synechocystis sp. PCC 6803. Overall, more than 2500 proteins were quantified, equivalent to approximately 70% of the Synechocystis theoretical proteome. Proteins with changing abundances correlated largely with mRNA expression levels. Functional annotation of the non-correlating proteins revealed an enrichment of key metabolic processes fundamental for maintaining cellular homeostasis. Furthermore, 105 phospho-proteins harboring over 200 site-specific phosphorylation events were identified. Subunits of the bicarbonate transporter BCT1 and the redox switch protein CP12 were among phospho-proteins with significantly reduced phosphorylation levels at lower CO2, whereas the serine/threonine protein kinase SpkC revealed increased phosphorylation levels. The corresponding spkC mutant was characterized and showed decreased ability to acclimate to low CO2 conditions. Possible phosphorylation targets of SpkC including a BCT1 subunit were identified by phospho-proteomics. Collectively, our study highlights the importance of post-transcriptional regulation of protein abundances as well as post-translational regulation by protein phosphorylation for the successful acclimation towards low CO2 conditions in Synechocystis and possibly among cyanobacteria.
Project description: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.
Project description: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.