Stimulates the transcription of various genes by recognizing and binding to a CCAAT motif in promoters (By similarity). Promotes the expression of heat stress-inducible genes by contributing to the formation of a heat stress-specific transcriptional complex with NF-Y subunits (e.g. DPB3-1, NF-YA2 and NF-YB3) and DREB2A at the promoter of target genes, thus promoting heat tolerance (PubMed:25490919). Heterotrimeric transcription factor composed of three components, NF-YA, NF-YB and NF-YC (By similarity). NF-YB and NF-YC must interact and dimerize for NF-YA association and DNA binding (By similarity). Component of a heat stress-inducible transcriptional complex with NF-YA and NF-YB subunits made, at least, of NFYA2, NFYB3 and DPB3-1 in cooperation with DREB2A (PubMed:25490919). Ubiquitous (PubMed:11250072, PubMed:9662544). Expressed in seedlings, roots, petioles, hypocotyls, reproductive organ tissues and leaves (PubMed:25490919). In seedlings, first expressed in petioles and leaf blades of the cotyledons as well as tops and bottoms of the hypocotyls. Belongs to the NFYA/HAP2 subunit family.