Open AccessFrequency doubling in the cyanobacterial circadian clock
Author(s) -
Martins Bruno MC,
Das Arijit K,
Antunes Liliana,
Locke James CW
Publication year - 2016
Publication title -
molecular systems biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 8.523
H-Index - 148
ISSN - 1744-4292
DOI - 10.15252/msb.20167087
Subject(s) - circadian rhythm , circadian clock , biology , oscillation (cell signaling) , oscillating gene , rhythm , gene expression , clock , microbiology and biotechnology , genetics , gene , neuroscience , physics , acoustics
Abstract 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.