Frequency doubling in the cyanobacterial circadian clock

Molecular Systems Biology
Bruno M C MartinsJames C W Locke


Organisms use circadian clocks to generate 24-h rhythms in gene expression. However, the clock can interact with other pathways to generate shorter period oscillations. It remains unclear how these different frequencies are generated. Here, we examine this problem by studying the coupling of the clock to the alternative sigma factor sigC in the cyanobacterium Synechococcus elongatus Using single-cell microscopy, we find that psbAI, a key photosynthesis gene regulated by both sigC and the clock, is activated with two peaks of gene expression every circadian cycle under constant low light. This two-peak oscillation is dependent on sigC, without which psbAI rhythms revert to one oscillatory peak per day. We also observe two circadian peaks of elongation rate, which are dependent on sigC, suggesting a role for the frequency doubling in modulating growth. We propose that the two-peak rhythm in psbAI expression is generated by an incoherent feedforward loop between the clock, sigC and psbAI Modelling and experiments suggest that this could be a general network motif to allow frequency doubling of outputs.


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Nov 10, 2018·Proceedings of the National Academy of Sciences of the United States of America·Bruno M C MartinsJames C W Locke
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Related Concepts

Single-Cell Analysis
Molecular Imaging
Gene Expression Regulation, Bacterial
Biochemical Pathway
Bacterial Proteins
Circadian Clocks
Time-Lapse Imaging
Cyanobacterium (antigen)
Gene Expression

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