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: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:Regulation of gene expression is a sophisticated process leading to the activation or suppression of genes due to adaptation to environmental stimuli. The membrane-embedded FtsH proteases conserved in bacteria, chloroplasts and mitochondria, are involved in such regulation. The genome of the cyanobacterium Synechocystis sp. PCC 6803 encodes four FtsH homologues FtsH1-4, functioning in the form of oligomeric complexes. Homologue FtsH3 is bound in two hetero-oligomeric complexes, FtsH1/FstH3 and/or FtsH2/FtsH3, respectively. Previous data showed that the FtsH1/FtsH3 complex is involved in the acclimation of cells to iron deficiency by controlling the availability of the transcriptional regulator Fur (Sll0567). To gain more comprehensive insight into the physiological role of FtsH hetero-complexes, we carried out genome-wide expression profiling of a mutant conditionally depleted in FtsH3, grown under nutrient sufficiency and iron depletion. Our results show, that besides Fur, also the SufR and Pho regulons belong to the set of genes controlled by FtsH. Moreover, by combining the transcriptome data with in silico prediction we identified novel targets of Fur in Synechocystis PCC 6803. Fur tends to evoke mostly repression, but also appears to activate some target genes. We monitored the global gene expression in a conditional Synechocystis PCC6083 ftsH knockdown strain (FtsHdown) (Boehm et al., 2012) and a control strain (WT) at standard conditions and at iron depletion. The presence of ammonia to induced the conditional knockdown. Each sample was done in biological replicates.
Project description:Regulation of gene expression is a sophisticated process leading to the activation or suppression of genes due to adaptation to environmental stimuli. The membrane-embedded FtsH proteases conserved in bacteria, chloroplasts and mitochondria, are involved in such regulation. The genome of the cyanobacterium Synechocystis sp. PCC 6803 encodes four FtsH homologues FtsH1-4, functioning in the form of oligomeric complexes. Homologue FtsH3 is bound in two hetero-oligomeric complexes, FtsH1/FstH3 and/or FtsH2/FtsH3, respectively. Previous data showed that the FtsH1/FtsH3 complex is involved in the acclimation of cells to iron deficiency by controlling the availability of the transcriptional regulator Fur (Sll0567). To gain more comprehensive insight into the physiological role of FtsH hetero-complexes, we carried out genome-wide expression profiling of a mutant conditionally depleted in FtsH3, grown under nutrient sufficiency and iron depletion. Our results show, that besides Fur, also the SufR and Pho regulons belong to the set of genes controlled by FtsH. Moreover, by combining the transcriptome data with in silico prediction we identified novel targets of Fur in Synechocystis PCC 6803. Fur tends to evoke mostly repression, but also appears to activate some target genes.
Project description:The rpoZ gene encodes the small ω subunit of RNA polymerase (RNAP). A ∆rpoZ strain of the cyanobacterium Synechocystis sp. PCC 6803 grew well in standard conditions (constant illumination at 40 µmol photons m-2s-1; 32 °C; ambient CO2) but was heat sensitive and died at 40 °C. In the control strain , 71 genes were at least two-fold up-regulated and 91 genes down-regulated after a 24-h treatment at 40 °C, while in ∆rpoZ 394 genes responded to heat. Only 62 of these heat-responsive genes were similarly regulated in both strains, and 80 % of heat-responsive genes were unique for ΔrpoZ. The RNAP core and the primary σ factor SigA were down-regulated in control strain at 40 °C, but not in ΔrpoZ. In accordance with reduced RNAP content, the total RNA content of mild-heat-stress-treated cells was lower in control strain than in ΔrpoZ. Light-saturated photosynthetic activity decreased more in ΔrpoZ than in control strain upon mild heat stress. The amounts of Photosystem II and Rubisco decreased at 40 °C in both strains while PSI and the phycobilisome antenna protein allophycocyanin remained at the same level as in standard conditions. The phycobilisome rod proteins, phycocyanins, diminished during the heat treatment in ΔrpoZ but not in control strain, and the nblA1 and nblA2 genes (encode NblA proteins required for phycobilisome degradation) were up-regulated only in ΔrpoZ. Our results show that the ω subunit of RNAP is essential in heat stress because it is required for heat acclimation of diverse cellular processes.
Project description:In contrast to Synechococcus elongatus PCC 7942, which has been the model cyanobacterium for the study of the prokaryotic circadian clock for more than 20 years, only few data exist on the circadian behaviour of the widely used cyanobacterium Synechocystis sp. PCC 6803. The standard kaiABC operon present in this organism was shown to encode a functional KaiC protein which interacts with KaiA, similar to the Synechococcus elongatus PCC 7942 clock. Inactivation of this operon in Synechocystis sp. PCC 6803 resulted in a mutant with a strong growth defect in light-dark cycles, which was even more pronounced when glucose was added to the growth medium. In addition, mutants showed a bleaching phenotype. No effects were detected in mutant cells grown in constant light. Microarray experiments performed with cells grown for one day in a light-dark cycle revealed many differentially regulated genes with known functions in the M-NM-^TkaiABC mutant in comparison to the wild type. Most interestingly, we identified genes like the gene encoding the cyanobacterial phytochrome Cph1 and the light repressed protein LrtA as well as several hypothetical open reading frames with a complete inverse behaviour in the light cycle. These transcripts showed a stronger accumulation in the light but a weaker accumulation in the dark in M-NM-^TkaiABC cells in comparison to the wild type. In addition, we found a considerable overlap with microarray data obtained for hik31 and sigE mutants. These genes are known to be important regulators of cell metabolism in the dark. Three timepoints with two samples (WT and Mutant). Two replicates for each timepoint/sample. RNA hybridization.