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Accueil > EN > Research Areas > Complex Systems Dynamics > BIological Systems > Circadian Clocks

Robustness and Flexibility of the {O. Tauri} Circadian Clock

par Benjamin PFEUTY, Marc LEFRANC, Webmestre - publié le , mis à jour le

The team of F.Y. Bouget at the Observatoire océanologique de Banyuls (CNRS / UPMC) has characterized the biological clock of the unicellular green alga Ostreococcus tauri [1] whose central oscillator consists of a feedback loop two genes.

Measurements of the rhythmic activity of both TOC1 and CCA1 genes could be reproduced by a simple mathematical model in which TOC1 activates the expression of CCA1 which represses the expression of TOC1 [1,2]. Surprisingly, we have shown that this oscillator locks to day night cycle using a coupling to light that disappears when the clock is on time, with accurate timing ! With this trick, the clock, when the time is blind to light and therefore the brightness fluctuations due to weather hazards eg [1,3]. In contrast, if the phase of the clock has to be shifted, the coupling to the light occurs in a different phase of oscillation, and can then act on the oscillator to reset the hour.

If the circadian clock is insensitive to light fluctuations, it must however be able to follow seasonal changes in day length (photoperiod). Mathematical modeling of the clock Ostreoccocus Tauri has resolved this paradox by showing that light affects both at short time scales to induce a robust synchronization day night cycle and long time scales to orchestrate time peaks TOC1 and CCA1 in accordance with the requirements of the season. [4,5]

We are currently seeking to clarify the light input pathways to the circadian clock and their roles. The team of F.-Y. Bouget has identified two histidine kinases responsive to different wavelengths (in the green and in the blue).
These kinases are at the top of histidine phosphorylation transfer cascade down to a central player in the Ostreococcus clock (TOC1) while the expressions of the two kinase are under circadian control. An extension of the model of the clock is to understand the cooperative role of these photoreceptors [7].

Publications

- [1] Robustness of circadian clocks to daylight fluctuations : hints from the picoeucaryote Ostreococcus tauri. PLoS Comput. Biol., 6:e1000990 (2010)
- [2] A robust two-gene oscillator at the core of Ostreococcus tauri circadian clock. Chaos, 20:045108 (2010)
- [3] Robust entrainment of circadian oscillators requires specific phase response curves. Biophys J, 100:2557-67 (2011)
- [4] Robust and flexible response of Ostreococcus tauri circadian clock to light/dark cycles of varying photoperiod. FEBS J. (2012)
- [5] Circadian clocks in changing weather and seasons : lessons from the microscopic algae Ostreococcus tauri. BioEssays, 34:781-90 (2012)
- [6] Transcriptional versus non-transcriptional clocks : A case study in Ostreococcus. Marine Genomics 14:17-22 (2014)
- [7] Probing entrainment of Ostreococcus tauri circadian clock by green and blue light through a mathematical modeling approach. Frontiers in genetics 6:65 (2015)

Press release

- PloS
- CNRS
- CNRS Scientific repport 2010

Collaboration

- François-Yves Bouget (Observatoire océanologique de Banyuls/mer)