Participates in ABA-regulated gene expression during seed development and subsequent vegetative stage by acting as the major mediator of ABA repression of growth. Binds to the embryo specification element and the ABA-responsive element (ABRE) of the Dc3 gene promoter and to the ABRE of the Em1 and Em6 genes promoters. Can also trans-activate its own promoter, suggesting that it is autoregulated. Plays a role in sugar-mediated senescence. DNA-binding homodimer. DNA-binding heterodimer with AREB3/DPBF3 or EEL/DPBF4. Interacts with ABI3, KEG, the mediator subunit MED25, and the AFP proteins AFP1, AFP2, AFP3 and AFP4. Interacts with TAP46. Interacts with the 36 kDa catalytic subunit (subunit C) of PP2A (PubMed:11489176, PubMed:12569131, PubMed:16247556, PubMed:17194765, PubMed:18484180, PubMed:22822206, PubMed:24357600). Interacts with FYPP1 and FYPP3 (PubMed:22715043). Interacts with FREE1 (via C-terminus) (PubMed:30962512). Predominantly expressed in seeds. Expressed in embryo during the latest stages of seed maturation. Up-regulated by drought, salt, abscisic acid (ABA) and glucose or 2-deoxy-glucose (2DG). Autoregulated. Positively regulated by the light-signaling component HY5. Phosphorylated by SRK2D and SRK2I in vitro. Ubiquitinated. AFP1, KEG and RPN10 mediate its proteasome-dependent degradation. Its stability or degradation plays a central role in abscisic acid response. Sumoylated at Lys-391 by SIZ1. Sumoylation protects ABI5 from proteasome degradation, attenuating ABA signaling and sensitivity to ABA. Exhibits abscisic acid (ABA) insensitivity. Belongs to the bZIP family. ABI5 subfamily.