Required for FRI-mediated up-regulation of FLC transcripts, but not redundant with FRI and only partially redundant with FRL2. Required for the stabilization of the FRI-C complex. Component of the transcription activator complex FRI-C composed of FRI, FRL1, SUF4, FLX and FES1. Interacts with FRI and SUF4. Expressed during seed development and in dry seed. Preferentially expressed in the chalazal endosperm during early stages of seed development. Reduced levels of FLC expression and early flowering, but not redundant with FRI. Frl1 and frl2 double mutants flower earlier than frl1 single mutant, due to a partial redundancy. In cv. Columbia and cv. Landsberg erecta, either FRL1 or FRL2, but not both, is functional and required for FRI-mediated up-regulation of FLC (PubMed:17056759). Belongs to the Frigida family. In cv. Landsberg erecta, FRL1 (AC P0DKC9) is not functional due to a naturally occurring premature stop codon at position 279.