Timing in plants – A rhythmic arrangement

The circadian clock regulates many aspects of plant physiology, growth and development. It produces daily rhythms of growth and metabolism, and interacts with signalling pathways controlling environmental responses over the course of a day or a year. Over the last decade, a combination of empirical research in molecular genetics and mathematical modelling, mostly utilising Arabidopsis thaliana, has led to the identification of many plant clock components and an understanding of their interlocking roles within the biochemical mechanism. The plant clock shares many characteristics of circadian clocks in other taxa, being temperature-compensated, capable of generating endogenous rhythms, of entraining to environmental cycles and regulated by means of transcription–translation feedback loops; however, few, if any, components of the plant clock appear to be shared with other organisms, indicating an independent evolutionary origin. In this review, we describe our current understanding of the central clockwork and how it receives input and regulates outputs. We also discuss the interaction between the clock and the environment, identifying areas, such as the integration of non-photic stimuli, where future work will lead to a fuller understanding of how the circadian system is embedded in plant physiology.