Probable transcription factor involved in the regulation of flowering time under long day (LD) conditions. Functions as repressor of flowering, independently of HD1 and GHD7. Controls flowering time by negatively regulating the expression of EHD1 and HD3A (PubMed:26542958). Component of the NF-Y/HAP transcription factor complex (By similarity). Heterotrimeric transcription factor composed of three components, NF-YA, NF-YB and NF-YC. NF-YB and NF-YC must interact and dimerize for NF-YA association and DNA binding (By similarity). Interacts with NFYB8, NFYB10 and HD5/NFYB11 (PubMed:26542958). Circadian-regulation under long day (LD) conditions. Expression increases at the end of the dark period, peaks in the beginning of the light period and gradually decreases during daytime. Belongs to the NFYC/HAP5 subunit family.