Abstract
Florigen triggers photoperiodic flowering in plants. Here, we show that morning expression of the florigen gene Heading date 3a (Hd3a) is acutely triggered by only a 30-min reduction in daylength in rice, a short-day plant. This Hd3a expression is induced by Early heading date 1 (Ehd1) expression when blue-lights coincide with the morning phase set by OsGIGANTEA (OsGI)-dependent circadian clocks, regardless of the photoperiod. Morning expression of Ehd1 is repressed by both night-breaks under short-day and morning-light signals under long-day; where a floral repressor, Grain number, plant height and heading date 7 (Ghd7), was acutely induced when phytochrome-signals coincide with a photo-sensitive phase set differently by distinct photoperiods. Taken together with these results, we will discuss how two distinct gating mechanisms on both floral promoter and floral repressor enable the use of slight differences in daylength to control Hd3a transcription with a critical daylength threshold in rice.
