Night-Break Experiments Shed Light on the Photoperiod1-Mediated Flowering.

Plants utilize variation in day length (photoperiod) to anticipate seasonal changes. They respond by modulating their growth and development to maximize seed production, which in cereal crops is directly related to yield. In wheat (), the acceleration of flowering under long days (LD) is dependent on the light induction of () by phytochromes. Under LD, activates (), a mobile signaling protein that travels from the leaves to the shoot apical meristem to promote flowering. Here, we show that the interruption of long nights by short pulses of light ("night-break" [NB]) accelerates wheat flowering, suggesting that the duration of the night is critical for wheat photoperiodic response. transcription was rapidly upregulated by NBs, and the magnitude of this induction increased with the length of darkness preceding the NB Cycloheximide abolished the NB up-regulation of , suggesting that this process is dependent on active protein synthesis during darkness. While one NB was sufficient to induce , more than 15 NBs were required to induce high levels of expression and a strong acceleration of flowering. Multiple NBs did not affect the expression of core circadian clock genes. The acceleration of flowering by NB disappeared in null mutants, demonstrating that this response is mediated by The acceleration of flowering was strongest when NBs were applied in the middle of the night, suggesting that in addition to , other circadian-controlled factors are required for the up-regulation of expression and the acceleration of flowering.