Transcription factor involved in the negative regulation of flowering. May be involved in the repression of the flowering factor GI and HD1 by interacting with PIL13 and PIL15 and competing with PRR1. Possesses transactivation activity in yeast. Interacts with PIL13 and PIL15. The gain-of-function mutant A654 (T-DNA tagging) exhibit late flowering phenotype under short day (SD) and long day (LD) conditions. Belongs to the bHLH protein family. Contains a degenerate basic motif not likely to bind DNA. Truncated N-terminus.