Abstract
The circadian clock, known as an endogenous timekeeping system, can integrate various cues to regulate plant physiological functions for adapting to the changing environment and thus ensure optimal plant growth. The synchronization of internal clock with external environmental information needs a process termed entrainment, and light is one of the predominant entraining signals for the plant circadian clock. Photoreceptors can detect and transmit light information to the clock core oscillator through transcriptional or post-transcriptional interactions with core-clock components to sustain circadian rhythms and regulate a myriad of downstream responses, including photomorphogenesis and photoperiodic flowering which are key links in the process of growth and development. Here we summarize the current understanding of the molecular network of the circadian clock and how light information is integrated into the circadian system, especially focus on how the circadian clock and light signals coordinately regulate the common downstream outputs. We discuss the functions of the clock and light signals in regulating photoperiodic flowering among various crop species.