Circadian clocks in plants

Circadian rhythms are physiological processes with an approximately 24 hour periodicity that persist in the absence of environmental cues. These rhythms are ubiquitous in nature and are found in higher eukaryotes as well as many lower eukaryotic and some prokaryotic organisms. These rhythmic processes are driven by the circadian clock, an endogenous timekeeper responsible for generating and maintaining 24 hour rhythms. The clock is a key adaptation for life on earth since it allows an organism to coordinate its internal activities with daily and seasonal changes in the environment. Clock-regulated phenomena are not only widespread among all major groups of organisms but are pervasive within an organism occurring within most cell types and tissues.

Intense study of the circadian systems in several model organisms, including Arabidopsis, has revealed that the oscillator influences major aspects of physiology. In plants, the circadian clock contributes to photoperiodic control over growth and development, responses to cold stress and shading, as well as coordinating genome-wide changes in transcription. Recent work in Arabidopsis has concretely demonstrated that plants having a circadian oscillator matched to the environmental period exhibit higher overall biomass, elevated rates of photosynthesis, and improved chances of survival in a mixed population. Thus, the presence of a robust circadian clock elevates plant fitness

The circadian clock plays an important role in daily plant physiology as well as in seasonal responses. At the molecular level, the oscillatorŐs influence is mediated through both direct transcriptional and post-transcriptional regulation of large networks of genes and proteins. At present, little is know of the signaling network that contributes to these massive changes in message and protein levels. In addition, the vast majority of the work on the plant oscillator has been done with Arabidopsis. The use of this model species has been very productive, but the details of the signaling networks for the circadian systems in other species will be important to fully understand the relationship between the clock and plant physiology. The importance of understanding the circadian clock in crop plants is vital not only for basic biology, but also because the oscillator influences traits like flowering and stress responses that have direct agronomic importance.

At the molecular level, the oscillatorŐs influence is mediated through both direct transcriptional and post-transcriptional regulation of large networks of genes and proteins. At present, little is know of the signaling network that contributes to these massive changes in message and protein levels. In addition, the vast majority of the work on the plant oscillator has been done with Arabidopsis. The use of this model species has been very productive, but the details of the signaling networks for the circadian systems in other species will be important to fully understand the relationship between the clock and plant physiology. The importance of understanding the circadian clock in crop plants is vital not only for basic biology, but also because the oscillator influences traits like flowering and stress responses that have direct agronomic importance.