RT Journal Article
SR Electronic
T1 Circadian protein regulation in the green lineage I. A phospho-dawn anticipates light onset before proteins peak in daytime
JF bioRxiv
FD Cold Spring Harbor Laboratory
SP 287862
DO 10.1101/287862
A1 Zeenat B. Noordally
A1 Matthew M. Hindle
A1 Sarah F. Martin
A1 Daniel D. Seaton
A1 T. Ian Simpson
A1 Thierry Le Bihan
A1 Andrew J. Millar
YR 2018
UL http://biorxiv.org/content/early/2018/04/04/287862.abstract
AB 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 apparently 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 and proline-directed protein phosphorylation sites were regulated in antiphase. 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.