Transcription factor required for the transition to flowering promoted by FT. Self-interacts (PubMed:16099979). Interacts with FT and FDP/BZIP27 (PubMed:16099979, PubMed:16099980, PubMed:25661797). Interacts with GRF3 and GRF4, and in a calcium-independent manner, with CPK6 and CPK33 (PubMed:25661797). Highly expressed in shoot apex. Phosphorylated at Thr-282 in a calcium-dependent manner by CPK6 and CPK33. Belongs to the bZIP family.