Circadian protein regulation in the green lineage I. A phospho-dawn anticipates light onset before proteins peak in daytime

Zeenat B Noordally, Matthew Hindle, Sarah Martin, Daniel D Seaton, Thomas Simpson, Thierry Le Bihan, Andrew Millar

Research output: Working paper

Abstract

Daily light-dark cycles (LD) drive dynamic regulation of plant and algal transcriptomes via photoreceptor pathways and 24-hour, circadian rhythms. Diel regulation of protein levels and modifications has been less studied. Ostreococcus tauri, the smallest free-living eukaryote, provides a minimal model proteome for the green lineage. Here, we compare transcriptome data under LD to the algal proteome and phosphoproteome, assayed using shotgun mass-spectrometry. Under 10% of 855 quantified proteins were rhythmic but two-thirds of 860 phosphoproteins showed rhythmic modification(s). Most rhythmic proteins peaked in the daytime. Model simulations showed that light-stimulated protein synthesis largely accounts for this distribution of protein peaks. Prompted by dark-stable proteins, we sampled during prolonged dark adaptation, where stable RNAs and very limited change to the proteome suggested a quiescent, cellular "dark state". In LD, acid-directed protein phosphorylation sites were enriched in antiphase to proline-directed sites. Strikingly, 39% of rhythmic phospho-sites reached peak levels just before dawn. This anticipatory phosphorylation is distinct from light-responsive translation but consistent with plant phosphoprotein profiles, suggesting that a clock-regulated phospho-dawn prepares green cells for daytime functions.
Original languageEnglish
PublisherbioRxiv, at Cold Spring Harbor Laboratory
Number of pages35
DOIs
Publication statusPublished - 4 Apr 2018

Keywords

  • marine algae
  • systems biology
  • chronobiology
  • gene expression regulation
  • proteomics
  • phosphoproteomics
  • protein kinases
  • photoperiodism
  • plant sciences

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