Abscisic acid and GIGANTEA signalling converge to regulate the recruitment of CONSTANS to theFTpromoter and activate floral transition

Abstract

Plants align flowering with optimal seasonal conditions to increase reproductive success. This process depends on modulating signalling pathways that respond to diverse environmental and hormonal inputs, thereby regulating the transition to flowering at the shoot apical meristem. InArabidopsis, long-day photoperiods (LDs) stimulate the transcription ofFLOWERING LOCUS T(FT), encoding the main florigenic signal.FTactivation is mediated by the transcriptional regulator CONSTANS (CO), which binds to the CO responsive elements (COREs) located in the proximalFTpromoter region. The phytohormone abscisic acid also (ABA) contributes toFTactivation together with GIGANTEA (GI) to regulate drought escape (DE). Whether CO is a target of ABA and GI actions for the regulation ofFTis, however, unknown. Here we report that ABA and its signalling components promote CO recruitment to the COREs, without causing clear effects on the diel pattern of CO protein accumulation. We also found that GI promotes CO recruitment to the COREs region, and that CO recruitment is required for the accumulation of RNAPol II at theTRANSCRIPTION START SITEofFT. Finally, we show that GI and ABA signalling pathways are largely epistatic in the control of flowering time, suggesting their involvement in the same molecular process. Taken together, these observations suggest that varying water deficit conditions modulate CO recruitment andFTexpression, thus dictating DE strategies inArabidopsis.HighlightABA and GIGANTEA signalling promoteFLOWERING LOCUS T(FT) transcriptional activation by regulating the binding of the transcription factor CONSTANS to the proximalFTpromoter.