The circadian oscillator in Synechococcus elongatus controls metabolite partitioning during diurnal growth (part I)
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ABSTRACT:
ORGANISM(S): Synechococcus Elongatus Pcc 7942
TISSUE(S): Bacterial Cells
PROVIDER: ST000394 | MetabolomicsWorkbench |
REPOSITORIES: MetabolomicsWorkbench
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Project description:Synechococcus elongatus PCC 7942 is a genetically tractable model cyanobacterium that has been engineered to produce industrially relevant biomolecules and is the best-studied model for a prokaryotic circadian clock. However, the organism is commonly grown in continuous light in the laboratory, and data on metabolic processes under diurnal conditions are lacking. Moreover, the influence of the circadian clock on diurnal metabolism has been investigated only briefly. Here, we demonstrate that the circadian oscillator influences rhythms of metabolism during diurnal growth, even though light-dark cycles can drive metabolic rhythms independently. Moreover, the phenotype associated with loss of the core oscillator protein, KaiC, is distinct from that caused by absence of the circadian output transcriptional regulator, RpaA (regulator of phycobilisome-associated A). Although RpaA activity is important for carbon degradation at night, KaiC is dispensable for those processes. Untargeted metabolomics analysis and glycogen kinetics suggest that functional KaiC is important for metabolite partitioning in the morning. Additionally, output from the oscillator functions to inhibit RpaA activity in the morning, and kaiC-null strains expressing a mutant KaiC phosphomimetic, KaiC-pST, in which the oscillator is locked in the most active output state, phenocopies a ΔrpaA strain. Inhibition of RpaA by the oscillator in the morning suppresses metabolic processes that normally are active at night, and kaiC-null strains show indications of oxidative pentose phosphate pathway activation as well as increased abundance of primary metabolites. Inhibitory clock output may serve to allow secondary metabolite biosynthesis in the morning, and some metabolites resulting from these processes may feed back to reinforce clock timing.
| S-EPMC4403147 | biostudies-literature
Project description: Not available
| ST000395 | MetabolomicsWorkbench
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
2009-08-01 | GSE14225 | GEO
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.
2009-07-31 | E-GEOD-14225 | biostudies-arrayexpress
Project description:Synechococcus elongatus strain PCC 7942 strictly depends upon the generation of photosynthetically derived energy for growth and is incapable of biomass increase in the absence of light energy. Obligate phototrophs' core metabolism is very similar to that of heterotrophic counterparts exhibiting diverse trophic behavior. Most characterized cyanobacterial species are obligate photoautotrophs under examined conditions. Here we determine that sugar transporter systems are the necessary genetic factors in order for a model cyanobacterium, Synechococcus elongatus PCC 7942, to grow continuously under diurnal (light/dark) conditions using saccharides such as glucose, xylose, and sucrose. While the universal causes of obligate photoautotrophy may be diverse, installing sugar transporters provides new insight into the mode of obligate photoautotrophy for cyanobacteria. Moreover, cyanobacterial chemical production has gained increased attention. However, this obligate phototroph is incapable of product formation in the absence of light. Thus, converting an obligate photoautotroph to a heterotroph is desirable for more efficient, economical, and controllable production systems.
| S-EPMC3591970 | biostudies-literature
Project description:In the unicellular cyanobacterium Synechococcus elongatus PCC 7942, essentially all promoter activities are under the control of the circadian clock under continuous light (LL) conditions. Here, we used 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 strains, >30% of transcripts oscillated significantly in a circadian fashion, peaking at subjective dawn and dusk. Such circadian control was severely attenuated in kaiABC-null strains. Although it has been proposed that KaiC globally represses gene expression, our analysis revealed that dawn-expressed genes were up-regulated by kaiC-overexpression so that the clock was arrested at subjective dawn. Transfer of cells to DD conditions from LL immediately suppressed expression of most of the genes, while the clock kept even time in the absence of transcriptional feedback. Thus, the Synechococcus genome seems to be primarily regulated by light/dark cycles and is dramatically modified by the protein-based circadian oscillator.
| S-EPMC2729038 | biostudies-literature
Project description:The recurrent pattern of light and darkness generated by Earth's axial rotation has profoundly influenced the evolution of organisms, selecting for both biological mechanisms that respond acutely to environmental changes and circadian clocks that program physiology in anticipation of daily variations. The necessity to integrate environmental responsiveness and circadian programming is exemplified in photosynthetic organisms such as cyanobacteria, which depend on light-driven photochemical processes. The cyanobacterium Synechococcus elongatus PCC 7942 is an excellent model system for dissecting these entwined mechanisms. Its core circadian oscillator, consisting of three proteins, KaiA, KaiB, and KaiC, transmits time-of-day signals to clock-output proteins, which reciprocally regulate global transcription. Research performed under constant light facilitates analysis of intrinsic cycles separately from direct environmental responses but does not provide insight into how these regulatory systems are integrated during light-dark cycles. Thus, we sought to identify genes that are specifically necessary in a day-night environment. We screened a dense bar-coded transposon library in both continuous light and daily cycling conditions and compared the fitness consequences of loss of each nonessential gene in the genome. Although the clock itself is not essential for viability in light-dark cycles, the most detrimental mutations revealed by the screen were those that disrupt KaiA. The screen broadened our understanding of light-dark survival in photosynthetic organisms, identified unforeseen clock-protein interaction dynamics, and reinforced the role of the clock as a negative regulator of a nighttime metabolic program that is essential for S. elongatus to survive in the dark.
| S-EPMC6064986 | biostudies-literature
Project description:The diurnal peak of phagocytosis by the retinal pigment epithelium (RPE) of photoreceptor outer segments (POS) is under circadian control and believed that this process involves interactions from the retina and RPE. Previous studies have demonstrated that a functional circadian clock exists within multiple retinal cell types and RPE. Thereby, the aim of this study was to determine whether the clock in the retina or RPE controls the diurnal phagocytic peak and whether disruption of the circadian clock in the RPE would affect cellular function and the viability during aging. To that, we generated and validated an RPE tissue-specific KO of the essential clock gene, Bmal1, and then determined the daily rhythm in phagocytic activity by the RPE in mice lacking a functional circadian clock in the retina or RPE. Then, using electroretinography, spectral domain-optical coherence tomography, and optomotor response of visual function we determined the effect of Bmal1 removal in young (6 months) and old (18 months) mice. RPE morphology and lipofuscin accumulation was determined in young and old mice. Our data shows that the clock in the RPE, rather than the retina clock, controls the diurnal phagocytic peak. Surprisingly, absence of a functional RPE clock and phagocytic peak does not result in any detectable age-related degenerative phenotype in the retina or RPE. Thus, our results demonstrate that the circadian clock in the RPE controls the daily peak of phagocytic activity. However, the absence of the clock in the RPE does not result in deterioration of photoreceptors or the RPE during aging.
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