The circadian clock is known to be evolved in most animals to adapt to the day and night cycle. It was recently found to be extremely important in the life cycle of plants. The circadian clock plays a crucial role in synchronizing sexual reproduction and improves seed production with compromise to both environment induction and internal developmental program of plants.
Arabidopsis thaliana, a model organism, is proven to have a circadian oscillator which rhythmically regulates the level of transcription. Circadian clocks are controlled in response to light and temperature signals for a prolonged period. The changes of signals will either inhibit or promote the expression of MADS-box gene, FLOWERING LOCUC C (FLC), which is characterized as a flowering repressor.
During winter, FLC alters its chromatin structure which in turns down-regulates the expression of FLC. Hence, flowering is promoted after winter. The exposure to a prolonged cold period which triggers flowering is termed vernalisation. Apart from FLC, another functional protein, FRIGIDA is also involved in promoting FLC expression and prevents plants from flowering during winter. Besides this, the autonomous pathway in Arabidopsis is also involved in controlling the circadian clock. Studies have found that this pathway is regulated independently from environmental signals. The aforementioned pathways are illustrated in Figure 1. Interaction of these pathways establishes vernalisation requirement and response.
Figure 1: Schematic of FLC’s role in the Arabidopsis circadian clock. Blunt arrow indicates inhibition while arrow indicates induction.References
- Amasino, Richard M. (2003) Flowering Time: A Pathway that Begins at the 3’ End. Current Biology 13, R670-R672.
- Slathia, Neeraj, Davis, Seth J, Lynn, James R, Michaels, Scott D, Amasino, Richard M and Millar, Andrew J (2006) FLOWERING LOCUS C -dependent and –independent regulation of the circadian clock by the autonomous and vernalization pathways. BMC Plant Biology 6:10.
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