A dephosphorylation-dependent molecular switch for FT repression mediates flowering in Arabidopsis.

The reproductive success of flowering plants greatly relies on the precise timing of floral transition, which is finely modulated by a complex network of floral regulators. As a main floral integrator, FLOWERING LOCUS T (FT) is also known as an essential constituent of the florigen that traffics from leaves to shoot apices to induce flowering. FT is specifically transcribed in leaf vascular tissues where its production is suppressed by many flowering repressors, including a MYB transcription factor, EARLY FLOWERING MYB PROTEIN (EFM). Here we show that a plant CTD phosphatase, C-TERMINAL DOMAIN PHOSPHATASE-LIKE 2 (CPL2), suppresses FT expression in leaf vascular tissues via modulating the binding activity of EFM. CPL2 interacts with and dephosphorylates EFM to facilitate the binding of dephosphorylated EFM to the FT chromatin, thereby inhibiting flowering. Our results suggest that CPL2-mediated dephosphorylation of the floral repressor EFM serves as a molecular switch, adding another layer of regulation to fine-tune FT transcription to ensure flowering occurring at the appropriate time in plants.