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The role of the Synechocystis sp. PCC 6803 homolog of the circadian clock output regulator RpaA in day-night transitions

ABSTRACT: 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.

ORGANISM(S): Synechocystis sp. PCC 6803

PROVIDER: GSE116795 | GEO | 2018/10/01

REPOSITORIES: GEO

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Project description:In the unicellular cyanobacterium, Synechococcus elongatus PCC 7942, essentially all promoter activities are under the control of the circadian clock in continuous light (LL) conditions. Here, we employed high-density oligonucleotide arrays to explore comprehensive profiles of genome-wide Synechococcus gene expression in wild type, kaiABC-null and kaiC-overexpressor strains under LL and continuous dark (DD) conditions. In the wild type strain more than 30% of transcripts significantly oscillated in a circadian fashion, peaking at subjective dawn and dusk. Such circadian control was nullified in kaiABC-null strains. Although KaiC has been proposed to globally repress gene expression, our analysis revealed that dawn expressing genes were upregulated by kaiC-overexpression, such that the clock was arrested at subjective dawn. Transfer of cells to continuous dark (DD) conditions from LL immediately suppressed expression of most of genes, while the clock keeps time even in the absence of transcriptional feedback. Thus, the Synechococcus genome seems primarily regulated by the light/dark cycles and dramatically modified by the protein-based circadian oscillator. Keywords: timecourse data (~48 hours under continuous light or darkness) from Synechococcus elongatus PCC 7942 (wild type, kaiABC-null, and inducible kaiC-overexpressor) strains Wild type (WT), kaiABC-null (Dkai), and inducible kaiC-overexpressor (oxC) S. elongatus PCC 7942 strains were analyzed under continuous light (LL), continuous dark (DD) using Affymetrix high-density oligonucleotide microarrays (GeneChip CustomExpress Arrays) representing predicted 2,515 protein-coding genes on the genome of Synechococcus elongatus PCC 6301, which can be used also to the almost homologous strain, S. elongatus PCC 7942: Two independent experiments in WT under LL (hours 0 to 52) and DD (hours 0 to 48); Two independent experiments in Dkai under LL (hours 0 to 48); Two independent experiments in oxC under LL in the presence or absence of an inducer, IPTG, from hour 25 to 33 in LL; a single experiment in WT under DD in the presence of an transcriptional inhibitor, rifampicin.

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The role of the Synechocystis sp. PCC 6803 homolog of the circadian clock output regulator RpaA in day-night transitions

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