Stimulates the transcription of various genes by recognizing and binding to a CCAAT motif in promoters (By similarity). Involved in the blue light (BL) and abscisic acid (ABA) signaling pathways. 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 the whole plant, except roots. Present in etiolated seedlings. Altered response to blue light (BL) and abscisic acid (ABA). Belongs to the NFYA/HAP2 subunit family.