Component of the NF-Y/HAP transcription factor complex. The NF-Y complex stimulates the transcription of various genes by recognizing and binding to a CCAAT motif in promoters. 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). Expressed in flowers and mature rosettes. Belongs to the NFYB/HAP3 subunit family.