Participates in abscisic acid-regulated gene expression during seed development. Regulates the transcription of SGR1 and SGR2 that are involved in leaf and embryo degreening. Interacts (via C-terminus) with SPK1, SCAR3, ABI5, APRR1, AIP2, AIP3 and AIP4. Binds to BZIP10 and BZIP25 and forms complexes made of ABI3, BZIP53 and BZIP25 or BZIP10. Predominantly found in the nucleus. A number of isoforms are produced. Splicing is regulated by SUA. Isoform 2 accumulates only at the end of seed maturation. Expressed in the embryos, endosperm, and outer teguments of the seed throughout seed development. Repressed by silencing mediated by polycomb group (PcG) protein complex containing EMF1 and EMF2. Ubiquitinated by AIP2. Ubiquitination probably leads to its subsequent degradation, thus negatively regulating ABA signaling. The truncated abi3-6 mutant lacking the DNA-binding domain is unable to localize to the nucleus and is an embryo stay-green mutant. Due to a cryptic intron removal.