Time to grow: circadian regulation of growth and metabolism in photosynthetic organisms

•Sunflower apices compute day length in order to regulate rhythmic growth rates.•Photosynthetic organisms adjust metabolic rates to manage carbon reserves at night.•Shifts in the circadian pace may have enabled tomato adaptation to higher latitudes.

Circadian clocks are molecular devices that help adjust organisms to periodic environmental changes. Although formally described as self-sustaining oscillators that are synchronized by external cues and produce defined outputs, it is increasingly clear that physiological processes not only are regulated by, but also regulate the function of the clock. We discuss three recent examples of the intimate relationships between the function of the clock, growth and metabolism in photosynthetic organisms: the daily tracking of sun by sunflowers, the fine computations plants and cyanobacteria perform to manage carbon reserves and prevent starvation, and the changes in clock parameters that went along with domestication of tomato.