Night-Break Experiments Shed Light on PHOTOPERIOD1-Mediated Flowering in Wheat.

Plants utilize variation in day length (photoperiod) to anticipate seasonal changes. They respond by modulating their growth and development to maximize seed production, which directly relates to yield in cereal crops. A better understanding of the mechanisms regulating this response will help breeders select higher-yielding varieties adapted to diverse environments. In wheat, long days accelerate flowering in a process dependent on the light induction of the PHOTOPERIOD1 (PPD1) gene. PPD1 activates FLOWERING LOCUS T1 (FT1), a mobile signaling protein that travels from the leaves to the shoot apical meristem to promote flowering. Our research shows that the interruption of long nights by short pulses of light (“night-break”) is sufficient to upregulate PPD1 and to accelerate wheat flowering. This suggests that the duration of the night, rather than day length, is critical for the wheat photoperiodic response. Night-breaks had the strongest effect on flowering when given in the middle of the night, suggesting that in addition to PPD1, other circadian-controlled factors are required for the acceleration of flowering. Furthermore, while one night-break was sufficient to induce PPD1, more than 15 night-breaks were required for a strong induction of FT1 and the acceleration of flowering. These findings provide insight into the photoperiod-mediated regulation of flowering time in wheat and a basis for future experiments to dissect the molecular pathways regulating this response.