The bHLH-PAS protein RITMO1 regulates diel biological rhythms
Station Biologique de Roscoff - Salle de conférence
The bHLH-PAS protein RITMO1 regulates diel biological rhythms in the marine diatom Phaeodactylum tricornutum
Periodic light-dark cycles govern the timing of basic biological processes in organisms inhabiting land as well as the sea, where life evolved.
Periodic light-dark cycles govern the timing of basic biological processes in organisms inhabiting land as well as the sea, where life evolved. Although prominent marine phytoplanktonic organisms such as diatoms show robust diel rhythms, the mechanisms regulating these processes are still obscure. By characterizing a Phaeodactylum tricornutum bHLH-PAS protein, hereby named RITMO1, we shade light on the regulation of the daily life of diatoms. RITMO1 is nuclear-localized and its ectopic over-expression results in lines with altered diurnal gene expression, compared to the wild-type cells. Reduced gene expression oscillations are also observed in these lines in darkness, showing that the regulation of rhythmicity by RITMO1 is not directly dependent on light inputs. We also describe strong diurnal rhythms of cellular fluorescence in wild-type cells, which persist in continuous light conditions, pinpointing the existence of an endogenous circadian clock in diatoms. The strong rhythm alteration observed in RITMO1 over-expression lines in absence of external light/dark cues supports the involvement of this protein in circadian rhythm regulation. RITMO1 homologs are widespread in diatom genomes, which may indicate a common function in many species. This study adds new elements to understand diatom biology and ecology and offers new perspectives to elucidate timekeeping mechanisms in marine organisms belonging to a major, but underinvestigated branch of the tree of life.