Circadian rhythm of photosynthesis and concurrent oscillations of transcript abundance of photosynthetic genes in the marine red alga
Many biological processes are under the control of an endogenous circadian clock, a prominent example within the plant kingdom being photosynthesis. Here we report a robust circadian rhythm of photosynthetic oxygen evolution in the marine red macroalga Grateloupia turuturu. The rhythm was obvious in continuous white light at irradiances ranging from 50 to 500 mol photons m−2s−1. To assess whether this physiological rhythm was correlated with changes at the level of gene transcription in G. turuturu, abundance of the transcripts encoding the phycoerythrin α and subunits and the ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) subunits was analysed under light-dark cycles (LD) and continuous illumination (LL). Abundance of both transcripts exhibited diurnal and circadian changes in G. turuturu. In LD conditions, abundance of the phycoerythrin transcript peaked between midday and late afternoon. This pattern was maintained under constant conditions (LL) for up to three cycles. For the Rubisco transcript, mRNA abundance started to increase in the morning and peaked around midday in LD cycles. In LL, Rubisco transcript abundance continued to oscillate, but the increase of mRNA started earlier, already during subjective night. Our results suggest control of both transcripts by the circadian clock in G. turuturu.