Seasonal changes in daily temperature fluctuation control flowering through a time-dependent regulation of FLOWERING LOCUS T in Arabidopsis.

Temperature changes along seasonal transitions control flowering. Under natural long-day conditions, flowering is controlled by a bimodal expression pattern of the florigen gene, FLOWERING LOCUS T (FT), in Arabidopsis. Although cool ambient temperatures delay flowering through FT repression, it is unknown how daily temperature fluctuations regulate bimodal FT profiles. Seasonal increases in nighttime temperatures are less variable than those during the daytime in spring, potentially providing more reliable timing information. By simulating daily temperature fluctuations of spring, we showed that cool night-to-morning temperatures activate multiple mechanisms to control morning and evening FT peaks separately. Lowering night temperatures regulates the CONSTANS (CO) protein function by reducing its stability from midday to dusk and increasing its interaction with a colder-night induced repressor, B-BOX DOMAIN PROTEIN 29 (BBX29), in the morning. Our results demonstrated the dynamics of time-specific regulatory mechanisms in temperature signaling during spring when cooler temperatures determine the timing of flowering.