A significant role for the circadian clock in the long-term water use efficiency of Arabidopsis

In plants, water use efficiency is a complex trait derived from numerous physiological and developmental characteristics. Here, we investigated the involvement of circadian regulation in long-term water use efficiency. Circadian rhythms are generated by the circadian oscillator, which provides a cellular measure of the time of day. In plants, the circadian oscillator contributes to the regulation of many aspects of physiology, including stomatal opening, the rate of photosynthesis, carbohydrate metabolism and developmental processes. We investigated in Arabidopsis the impact upon whole plant, long-term water use efficiency of the misregulation of genes encoding a large number of components of the circadian oscillator, identifying a major role for the circadian oscillator in plant water use. This appears to be due to contributions of the circadian clock to the control of transpiration and biomass accumulation. We also identified that the circadian oscillator specifically within guard cells contributes to both long-term water use efficiency and dehydration tolerance. Our experiments indicate that knowledge of circadian regulation will be important for developing future crops that use less water.