Circadian Rhythms in Plants

Abstract

The circadian oscillator is a complex network of interconnected feedback loops that regulates a wide range of physiological processes. Indeed, variation in clock genes has been implicated in an array of plant environmental adaptations, including growth regulation, photoperiodic control of flowering, and responses to abiotic and biotic stress. Although the clock is buffered against the environment, maintaining roughly 24-h rhythms across a wide range of conditions, it can also be reset by environmental cues such as acute changes in light or temperature. These competing demands may help explain the complexity of the links between the circadian clock network and environmental response pathways. Here, we discuss our current understanding of the clock and its interactions with light and temperature-signaling pathways. We also describe different clock gene alleles that have been implicated in the domestication of important staple crops.

Figure 1.

A highly simplified representation of the plant circadian regulatory network. Similar genes operating at similar times during the day in a similar manner are grouped together in white circles. Black lines with blunt ends indicate genes function as repressors in the negative feedback loops. Gray lines and arrows indicate genes acting as activators in the regulatory network.

Figure 2.

Schematic representation of how light and temperature-signaling pathways integrate with the circadian clock regulatory network. The underlying clock network is the same as Figure 1 with either the light-signaling pathway (A) or the temperature-signaling pathway (B) linking to points in the circadian regulatory network. (A) Red and blue pathways indicate how these different wavelengths of light are integrated into the clock at different points via independent pathways. (B) Different temperatures influence the same pathway (blue to orange shaded box), with cooler temperatures stabilizing complex formation and warmer temperatures releasing growth factors such as PIFs.