Abstract: This paper reviews the current progresses in studying molecular mechanism of the circadian clock in plants, especially in Arabidopsis. The circadian clock contributes to plant physiology by regulating the phase of entrained rhythms. A gene circuit of negative feedback comprises 3 main genes: CCA1, LHY, and TOC1. The “external coincidence” model has been proposed for photoperiodic regulation of flowering time. The key gene in this model, CO, is necessary and sufficient for flowering.

Key words: Arabidopsis, Circadian clock, Negative feedback ciecuit, Photoperiod