CONICET | Buscador de Institutos y Recursos Humanos

The transition to flowering in plants is controlled by a regulatory network that responds to both developmental and environmental signals. The MADS-box genes FLOWERING LOCUS C (FLC) and SHORT VEGETATIVE PHASE (SVP) are major flowering repressors that enhance responses to environmental cues such as winter temperatures, high ambient temperatures and photoperiod. FLC and SVP physically interact in vivo and mutation of each gene causes early flowering while the double mutant is more extreme. The molecular mechanisms underlying these genetic interactions are mostly unknown. We addressed the regulatory input of these two key transcription factors (TFs) both individually and as a complex at the genome-wide level through ChIP-seq and microarray expression analysis in single and double mutants. Analysis of each TF demonstrated that the complex acts predominantly via functional redundancy in the repression of flowering. SVP and FLC bind to the same regions of the flowering genes SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FLOWERING LOCUS T (FT) but do not require the presence of the other to bind. However, genome-wide identification of SVP and FLC occupancy events revealed that their binding scenarios are quantitatively and qualitatively affected by the presence of the cognate partner. A subgroup of genes whose regulation by these TFs depends exclusively on combinatorial binding of both proteins was identified, demonstrating a qualitatively essential role of the SVP-FLC complex. Cis-regulatory elements enriched only at such complex-bound sites were identified. Thus the regulatory output mediated by SVP and FLC reveals substantial flexibility, leading to dependent and independent DNA binding that enables additive, cooperative and repressive modes of co-regulation. Furthermore, we address FLC transcriptional repression in the perennial species Arabis alpina, a relative of Arabidopsis.