Molecular basis of flowering under natural long-day conditions in Arabidopsis

Plants sense light and temperature changes to regulate flowering time. Here we show that expression of the Arabidopsis florigen gene, FLOWERING LOCUS T (FT), peaks in the morning during spring, a different pattern than we observe in the lab. Providing our lab growth conditions with a red/far-red light ratio similar to open field conditions and daily temperature oscillation is sufficient to mimic the FT expression and flowering time in natural long days. Under the adjusted growth conditions, key light signaling components, such as phytochrome A (phyA) and EARLY FLOWERING 3 (ELF3), play important roles in morning FT expression. These conditions stabilize CONSTANS (CO) protein, a major FT activator, in the morning, which is likely a critical mechanism for photoperiodic flowering in nature. Refining the parameters of our standard growth conditions to more precisely mimic plant responses in nature can provide a powerful method for improving our understanding of seasonal response.