No abstract

Circadian regulation of transcriptional gene expression has been shown for a variety of taxa throughout the eukaryotic kingdom and for prokaryotic cyanobacteria but not previously for macroalgae. We reported earlier a strong circadian rhythm of photosynthetic capacity in the red macroalga Kappaphycus alvarezii (Doty) Doty. To determine whether this rhythm is correlated with circadian regulation of steady‐state transcript abundance, we analyzed transcripts of genes whose protein products are involved in photosynthesis. Transcript levels of two plastid‐encoded operons, one for phycoerythrin α and β subunits and another for RUBISCO large and small subunits, were analyzed under light:dark cycles (LD) and under constant illumination (LL) for several days. Both transcripts exhibited diurnal regulation under LD conditions with maximum transcript abundance during early daytime to midday. Under LL conditions, circadian oscillations of steady‐state mRNA abundance were detected for up to three cycles; thus, the analyzed transcripts exhibited diurnal and circadian regulation. Interestingly, peak abundance of the RUBISCO transcript shifted to subjective night under LL. To our knowledge, this is the first report demonstrating that circadian control of steady‐state transcript abundance occurs in a macroalga.

No abstract

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 mmol photons m 72 s 71 . 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 a and b 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.