Retrograde Signalling as an Informant of Circadian Timing

The circadian system comprises of interlocking transcriptional–translational feedback loops that regulate gene expression and consequently modulate plant development and physiology. In order to maximize utility, the circadian system is entrained by changes in temperature and light, allowing endogenous rhythms to be synchronized with both daily and seasonal environmental change. While a great deal of environmental information is decoded by a suite of photoreceptors, it is also becoming apparent that changes in cellular metabolism also contribute to circadian timing, either through the stimulation of metabolic pathways or through the accumulation of metabolic intermediates as a consequence of environmental stress. As the source of many of these metabolic byproducts, mitochondria and chloroplasts have begun to be viewed as environmental sensors, and rapid advancement of this field is revealing the complex web of signalling pathways initiated by organelle perturbation. This review will highlight recent advances in our understanding of how this metabolic regulation influences circadian timing.