The circadian clock regulates subcellular events including gene expression and cell signalling, manifested in behaviours such as leaf movement or foraging in higher organisms. The genetic structure of the network controlling circadian rhythms in the small, flowering plant Arabidopsis includes a central genetic oscillator. Evidence suggests that circadian oscillations in the concentration of cytosolic free calcium ([Ca2+]cyt) may regulate circadian clock gene expression. Scientists employed mathematical modelling, molecular biology and biochemistry to determine what role, if any, the dynamics of [Ca2+]cyt play in control of the circadian network. With EU support of the project 'The mechanism by which CML23/24 affects the circadian clock' (CIRCADIAN CLOCK), researchers studied the calcium-binding proteins — calmodulin-like 23 (CML23) and CML24. Understanding the circadian rhythms of plants could have important implications for selective plant breeding and enhanced crop performance both for food and biofuels. Researchers investigated key molecular targets of the proteins, interacting proteins and their effects on oscillator function. Researchers also looked for potential genetic interactions between CML23/CML24 and clock/light signalling genes. Scientists demonstrated that the Ca2+-binding proteins participate in circadian clock control in a Ca2+-dependent way, likely acting as [Ca2+]cyt sensors after Ca2+ binding. In addition, the team prepared mutants to investigate how the proteins regulate the circadian clock and elucidate factors affecting tissue and subcellular (cytosolic versus nuclear) localisation of CML23 and CML24. Finally, in pioneering experiments, researchers identified the only known circadian clock genes that respond to [Ca2+]cyt and provided evidence of where in the chain of the signalling pathway this might occur. CIRCADIAN CLOCK outcomes are providing important insight into the role of CML23/CML24 and [Ca2+]cyt in the workings of the Arabidopsis circadian clock and associated gene expression. Deeper understanding of circadian rhythms could be critical to enhanced agricultural performance for a variety of crops. Given the widespread function of [Ca2+]cyt in gene expression in general, the studies could have broader implications in many systems and numerous other pathways.
Circadian clock, plants, crop performance, cytosolic free calcium, gene expression, CML23, CML24