Abscisic acid and GIGANTEA signalling converge to regulate the recruitment of CONSTANS to the FT promoter and activate floral transition
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. In Arabidopsis, long-day photoperiods (LDs) stimulate the transcription of FLOWERING LOCUS T (FT), encoding the main florigenic signal. FT activation is mediated by the transcriptional regulator CONSTANS (CO), which binds to the CO responsive elements (COREs) located in the proximal FT promoter region. The phytohormone abscisic acid also (ABA) contributes to FT activation together with GIGANTEA (GI) to regulate drought escape (DE). Whether CO is a target of ABA and GI actions for the regulation of FT is, 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 the TRANSCRIPTION START SITE of FT. 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 and FT expression, thus dictating DE strategies in Arabidopsis. Overall design: ChIP-seq of transgenic SUC2::CO:CIT Arabidopsis thaliana plants in Col-0 background, with a wild type or mutant allele (aba1-6) at the ABA1 locus, resulting in two genotypes: SUC2::CO:CIT and SUC2::CO:CIT aba1-6. Two input replicates and two immuoprecipitated replicates were produced for each genotype.