FHY3 and FAR1 mediate red light input to the Arabidopsis circadian clock

The circadian clock is tightly tied to the light environment. Transcriptional feedback loops are able to generate a self-sustaining rhythm of approximately 24 h which impinges on almost every aspect of physiology in higher organisms. However, light signals are essential to maintain an exact 24 h rhythm.

In the model plant, Arabidopsis thaliana, an endogenous circadian rhythm is generated by a set of interlocked transcriptional feedback loops. Light directly affects the level of a number of the clock components in plants. The photoreceptors involved have been well characterised but the way in which they affect clock components is only beginning to be understood.

The transcription factors, FHY3 and FAR1, play a key role in red light input to the clock. We have shown that FHY3 and FAR1 positively regulate transcription of key clock components in red light. As a result, fhy3 and far1 mutant seedlings specifically display aberrant circadian rhythmicity under these conditions. Moreover, this specific action of FHY3 and FAR1 has revealed novel interactions between the various clock loops and has given us new insights into the mechanism by which light can fine-tune the clock throughout the cycle of day and night.