Dear Editor,Plants use light as an environmental signal to coordinate diverse physiological and developmental processes,thereby increasing their fitness.Light quality,quantity,and photoperiod change periodically under natural conditions of daily and seasonal cycles.Plants have developed a circadian clock to respond to these predictable,periodic environmental changes,providing plants with the ability to anticipate daily and seasonal environmental changes.Conceptually,the circadian clock systems are composed of the environmental input pathways,circadian clock,and physiological outputs.An important input to the circadian clock in plants is the daily changes of light.Accordingly,the daily cycle of light and dark as an input entrains the rhythmic behavior of plant circadian clock.On the other hand,the circadian clock modulates the light responsiveness of physiological outputs at different times of the day through a gating mechanism.The intimate connection between the light and clock responses in plants renders the timely and prepared regulation of various physiological output processes to cope with the periodic environmental changes.