Light and circadian regulation of clock components aids flexible responses to environmental signals.
The circadian clock measures time across a 24 h period, increasing fitness by phasing biological processes to the most appropriate time of day. The interlocking feedback loop mechanism of the clock is conserved across species; however, the number of loops varies. Mathematical and computational analyses have suggested that loop complexity affects the overall flexibility of the oscillator, including its responses to entrainment signals. We used a discriminating experimental assay, at the transition between different photoperiods, in order to test this proposal in a minimal circadian network (in Ostreococcus tauri) and a more complex network (in Arabidopsis thaliana). Transcriptional and translational reporters in O. tauri primarily tracked dawn or dusk, whereas in A. thaliana, a wider range of responses were observed, consistent with its more flexible clock. Model analysis supported the requirement for this diversity of responses among the components of the more complex network. However, these and earlier data showed that the O. tauri network retains surprising flexibility, despite its simple circuit. We found that models constructed from experimental data can show flexibility either from multiple loops and/or from multiple light inputs. Our results suggest that O. tauri has adopted the latter strategy, possibly as a consequence of genomic reduction.
SynthSys, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JD, UK.|Department of Crop Genetics, John Innes Centre, Norwich Research Park, Norwich, NR4 7UH, UK.
Laura E
LE
Dixon
SynthSys, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JD, UK.
Sarah K
SK
Hodge
SynthSys, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JD, UK.
Gerben
G
van Ooijen
Department of Astronomy and Theoretical Physics, Lund University, 223 62, Lund, Sweden.
Carl
C
Troein
SynthSys, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JD, UK.|Centre for Systems, Dynamics and Control, College of Engineering, Mathematics & Physical Sciences, University of Exeter, Exeter, EX4 4QF, UK.
Ozgur E
OE
Akman
SynthSys, University of Edinburgh, Kings Buildings, Mayfield Road, Edinburgh, EH9 3JD, UK.
Andrew J
AJ
Millar
D017360:Arabidopsis / Q000235:genetics / Q000502:physiology*; D000460:Chlorophyta / Q000235:genetics / Q000502:physiology*; D057906:Circadian Clocks; D025461:Feedback, Physiological; D018506:Gene Expression Regulation, Plant; D008027:Light; D008954:Models, Biological; D017440:Photoperiod; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism
D010940:Plant Proteins
biological clocks; flexibility; marine algae; mathematical analysis; nonlinear dynamics; photoperiod; systems biology