Séminaire IBIP
Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)

Jeudi 3 mai 2012
Amphi 206 (Coeur d’Ecole) à 14h

Unraveling clock-work in the simple eukaryotic unicellular system: Ostreococcus

Florence Corellou
Laboratoire d’océanographie microbienne (LOMIC), Banyuls/Mer

Simple eukaryotic models can contribute to unveiling the molecular clockwork at a cellular level. We have developed the marine picoeucaryote Ostreococcus tauri as a model system to study the integration of environmental signals by the clock and to unravel molecular cross-talk between metabolism and the circadian clock. We have implemented genetic transformation and luciferase strategies to create reporter lines for functional analysis through gene repression (antisense) and overexpression. Most importantly we recently achieved homologous gene recombination and created the first O. tauri knock-out circadian mutant. Coordinated regulation of the expression of genes associated with specific physiological processes occurs under diurnal entrainment, suggesting widespread transcriptional control of Ostreococcus metabolism. How the circadian clock regulates this transcriptional control is an important question which can be more easily answered in a simple eukaryotic system such as Ostreococcus with a restricted number (~ 170). of transcription factors In Ostreococcus the Transcriptional Translational Oscillator (TTO) is composed of a feedback loop between the only two conserved plant genes TOC1 and CCA1 that can be accurately reproduced by a minimal model. Recently persisting rhythms of peroxiredoxin sulfonation in the absence of transcription evidenced a non-Transcriptional Translational Oscillator (Pos-Translational Oscillator, PTO). Modelling works predicted on one hand a minimal light-coupling of the entrained TOC1/CCA1 oscillator restricted to dawn and dusk and on the other hand, considerable complexity of clock circuit regulation in response to changing light condition. Experimental works identified two blue light photoreceptors, a cryptochrome (CRY) and a LOV-histidine kinase and a unique putative green/red photoreceptor, the Rhod-histidine kinase. All of these were shown to be required for circadian function. LOV-HK and Rhod-HK are the only two Histidine-kinases in Ostreococcus. TOC1 is likely to be a true response regulator and the LOV-HK and Rhod-HK are good candidates for integration of environmental and metabolic signals into the clock. The coupling of TTO and PTO in eukaryotic cells remains to be elucidated.

Contact : Stéphane Mari

Contacts IBIP :
Sabine Zimmermann
Philippe Nacry
Christine Granier
Chantal Baracco