Circadian proteomics reveal rampant tuning of post-transcriptional apparatus by Chlamydomonas clock

Timing of biological processes enable organisms to sustain the diurnal fluctuations resulting from earth’s rotation. Circadian clocks execute this temporal regulation by modulating temporal expression of genes. Clock regulation of mRNAs was envisioned as the primary driver of daily rhythms. However, mRNA oscillations often don’t concur with the downstream protein oscillations. To assess the contribution from post-transcriptional processes, we quantitatively probed the Chlamydomonas proteome for two circadian cycles. Our study suggests rampant role of posttranscriptional processes in clock regulation of Chlamydomonas metabolism. We quantified >1000 proteins, half of which demonstrate circadian rhythms. Among these rhythmic proteins, >40% originate from non-rhythmic mRNAs and > 90% peak around midday or midnight. Accumulation rhythms of proteins rather than their encoding mRNAs shows extreme coordination. We uncovered new rhythms and accounted for physiological rhythms whose mechanistic details remained undocumented from earlier transcriptomic studies. We envisage our study will refine and enrich the evaluation of temporal metabolic processes in Chlamydomonas. Owing to Chlamydomonas’s unique phylogeny this study can lead to new insights into evolution of clock regulation across kingdoms.