SummaryCellular life emerged ~3.7 billion years ago. With scant exception, terrestrial organisms have evolved under predictable daily cycles due to the Earth’s rotation. The advantage conferred upon organisms that anticipate such environmental cycles has driven the evolution of endogenous circadian rhythms that tune internal physiology to external conditions. The molecular phylogeny of mechanisms driving these rhythms has been difficult to dissect because identified clock genes and proteins are not conserved across the domains of life: Bacteria, Archaea and Eukaryota. Here we show that oxidation-reduction cycles of peroxiredoxin proteins constitute a universal marker for circadian rhythms in all domains of life, by characterising their oscillations in a variety of model organisms. Furthermore, we explore the interconnectivity between these metabolic cycles and transcription-translation feedback loops of the clockwork in each system. Our results suggest an intimate co-evolution of cellular time-keeping with redox homeostatic mechanisms following the Great Oxidation Event ~2.5 billion years ago.

Circadian clocks are fundamental to the biology of most eukaryotes, coordinating behavior and physiology to resonate with the environmental cycle of day and night through complex networks of clock-controlled genes1-3. A fundamental knowledge gap exists however, between circadian gene expression cycles and the biochemical mechanisms that ultimately facilitate circadian regulation of cell biology4,5. Here we report circadian rhythms in the intracellular concentration of magnesium ions, [Mg 2+ ] i , which act as a cell-autonomous timekeeping component to determine key clock properties in both a human cell line and a unicellular alga that diverged from metazoans more than 1 billion years ago6. Given the essential role of Mg 2+ as a cofactor for ATP, a functional consequence of [Mg 2+ ] i oscillations is dynamic regulation of cellular energy expenditure over the daily cycle. Mechanistically, we find that these rhythms provide bilateral feedback linking rhythmic metabolism to clock-controlled gene expression. The global regulation of nucleotide triphosphate turnover by intracellular Mg 2+ availability has potential to impact upon many of the cell's >600 MgATP-dependent enzymes7 and every cellular system where MgNTP hydrolysis becomes rate limiting. Indeed, we find that circadian control of translation by mTOR8 is regulated through [Mg 2+ ] i oscillations. It will now be important to identify which additional biological # To whom correspondence should be sent: Gerben.vanOoijen@ed.ac.uk, oneillj@mrc-lmb.cam.ac.uk. Author contributions GvO and JSO conceived the approach and designed the study. LFL and COY generated the Neurospora result. JD and LE performed ICP analyses. GvO and LLH performed Ostreococcus experiments. Human U2OS cell experiments were performed by KAF. MP performed mouse fibroblast experiments. NPH provided analytical and intellectual contributions. GvO and JSO wrote the manuscript.

Background: Hexaploid wheat is one of the most important cereal crops for human nutrition. Molecular understanding of the biology of the developing grain will assist the improvement of yield and quality traits for different environments. High quality transcriptomics is a powerful method to increase this understanding.

Phototropins (phot1 and phot2) are plasma membrane-associated receptor kinases that respond specifically to blue and UV wavelengths. In addition to a C-terminal Ser/Thr kinase domain, phototropins contain two N-terminal chromophore binding LOV domains that function as photoswitches to regulate a wide range of enzymatic activities in prokaryotes and eukaryotes. Through domain swapping, we show that the photochemical properties of Arabidopsis thaliana phot1 rely on interactions between LOV1 and LOV2, which are facilitated by their intervening linker sequence. Functional analysis of domain-swap proteins supports a mechanism whereby LOV2 acts as a dark-state repressor of phot1 activity both in vitro and in vivo. Moreover, we find a photoactive role for LOV1 in arresting chloroplast accumulation at high light intensities. Unlike LOV2, LOV1 cannot operate as a dark-state repressor, resulting in constitutive receptor autophosphorylation and accelerated internalization from the plasma membrane. Coexpression of active and inactive forms of phot1 demonstrates that autophosphorylation can occur intermolecularly, independent of LOV1, via light-dependent receptor dimerization in vivo. Indeed, transphosphorylation is sufficient to promote phot1 internalization through a clathrin-dependent endocytic pathway triggered primarily by phosphorylation of Ser-851 within the kinase activation loop. The mechanistic implications of these findings in regard to light-driven receptor activation and trafficking are discussed.