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 inflorescence, stems, flowers and siliques. Belongs to the NFYA/HAP2 subunit family.