Abstract
AbstractThe circadian clock coordinates plant physiology and development. Mathematical clock models have provided a rigorous framework to understand how the observed rhythms emerge from disparate, molecular processes. However, models of the plant clock have largely been built and tested against RNA time-series data in arbitrary, relative units. This limits model transferability, refinement from biochemical data and applications in synthetic biology. Here, we incorporate absolute mass units into a detailed model of the clock gene network in Arabidopsis thaliana. We re-interpret the established P2011 model, highlighting a transcriptional activator that overlaps the function of REVEILLE 8/LHY-CCA1-LIKE 5. The new U2020 model incorporates the repressive regulation of PRR genes, a key feature of the most detailed clock model KF2014, without greatly increasing model complexity. We tested the experimental error distributions of qRT–PCR data calibrated for units of RNA transcripts per cell and of circadian period estimates, in order to link the models to data more appropriately. U2019 and U2020 models were constrained using these data types, recreating previously described circadian behaviours with RNA metabolic processes in absolute units. To test their inferred rates, we estimated a distribution of observed, transcriptome-wide transcription rates (Plant Empirical Transcription Rates, PETR) in units of transcripts per cell per hour. The PETR distribution and the equivalent degradation rates indicated that the models’ predicted rates are biologically plausible, with individual exceptions. In addition to updated clock models, FAIR (Findable, Accessible, Interoperable, Re-usable) data resources and a software environment in Docker, this validation process represents an advance in biochemical realism for models of plant gene regulation.
Highlights
The circadian clock in plants temporally coordinates an extensive repertoire of developmental and physiological processes
The fact that mutations of the clock genes have such pleiotropic effects can be explained at the molecular level, by observations that more than 30% of the Arabidopsis thaliana transcriptome exhibits circadian rhythmicity (Covington et al 2008; Edwards et al 2006; Harmer et al 2000)
Studies of seasonal timing in crops are uncovering the effects of clock genes that are homologous to those first identified in Arabidopsis, and the impact of Genotype x Environment interactions (Bendix et al 2015; Millar 2016)
Summary
The circadian clock in plants temporally coordinates an extensive repertoire of developmental and physiological processes. These include seedling establishment, photosynthesis, cell division, and flowering time, amongst others. The fact that mutations of the clock genes have such pleiotropic effects can be explained at the molecular level, by observations that more than 30% of the Arabidopsis thaliana transcriptome exhibits circadian rhythmicity (Covington et al 2008; Edwards et al 2006; Harmer et al 2000). Studies of seasonal timing (phenology) in crops are uncovering the effects of clock genes that are homologous to those first identified in Arabidopsis, and the impact of Genotype x Environment interactions (Bendix et al 2015; Millar 2016). Understanding the clock gene circuit and its outputs to physiology and phenology holds promise to guide further breeding and/or engineering of crop varieties (Preuss et al 2012 p. 32) and the clock regulation of RNA levels is of particular interest
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