The RNA-binding protein FCA and the adaptor protein ECAP coordinately repress FLC to facilitate flowering in Arabidopsis

Flowering is crucial for successful reproduction in angiosperms. The RNA-binding protein FLOWERING CONTROL LOCUS A (FCA) promotes flowering by repressing the transcription of FLOWERING LOCUS C (FLC), which encodes a key repressor of flowering. The EAR motif-containing protein (ECAP) is a recently identified adaptor protein that represses transcription. Here we show that ECAP facilitates FCA-mediated FLC repression and flowering in Arabidopsis thaliana. Genetically, similar to the fca mutant, the ecap mutant shows enhanced FLC transcription and thus a late-flowering phenotype, which is partially rescued when FLC is mutated or when FCA is overexpressed. Biochemically, ECAP physically interacts with FCA. ECAP binding at the FLC locus decreases in the fca mutant, and FCA binding at the FLC locus also decreases in the ecap mutant. ECAP also interacts with FVE/MULTICOPY SUPPRESSOR OF IRA1 4 (MSI4) and FLOWERING LOCUS D (FLD), which repress FLC transcription by regulating histone modifications. Consistent with this repression, the histone modifications at the FLC locus are de-regulated in the ecap mutant. Interestingly, ECAP represses FLC transcription in an EAR motif-independent manner. Our study reveals that ECAP and FCA facilitate flowering by coordinately regulating histone modifications at the FLC locus.