Transcription activator that binds DNA to the C-box-like motif (5'-TGCTGACGTCA-3'), ABRE elements, G-box-like motif (5'-CCACGTGGCC-3'), DOF (5'-AAAG-3'), I-box (5'-GATAA-3'), BS1 (5'-AGCGGG-3'), MY3 (5'-CGACG-3'), 5'-CAGTGCGC-3' and 5'-ACTCAT-3' sequence in target gene promoters (PubMed:15047879, PubMed:16810321, PubMed:19531597, PubMed:21278122, PubMed:25108460). DNA-binding and subsequent transcription activation is triggered by heterodimerization with other bZIP proteins (e.g. BZIP1, BZIP10 and BZIP25) (PubMed:16810321, PubMed:19531597, PubMed:21278122). Promotes POX1/PRODH1 expression in response to hypoosmolarity stress (PubMed:15047879, PubMed:16810321). Transcriptional activator of seed maturation (MAT) genes (e.g. AT2S2), including seed storage protein (SSP) and late embryogenesis abundant (LEA) genes (PubMed:19531597). Activated by low energy stress both by transcriptional and post-transcriptional mechanisms. Promotes dark-induced senescence and participates in the transcriptional reprogramming of amino acid metabolism during the dark-induced starvation response, especially when heterodimerized with BZIP1, by triggering accumulation of specific proteins including ASN1 and POX1/PRODH1 (PubMed:21278122). Forms heterodimers with other bZIP proteins such as BZIP1, BZIP9, BZIP10, BZIP25 and BZIP63 (PubMed:16810321, PubMed:16709202, PubMed:19531597, PubMed:21278122). BZIP heterodimers form complexes with ABI3 that enhance G-box element-binding to increase the expression of seed maturation (MAT) genes (PubMed:19531597). Expressed in developing seeds. In developing seeds, accumulates in embryo cotyledons during late maturation, from the torpedo to the green cotyledon stages. Also present in endosperm. By hypoosmolarity (PubMed:15047879, PubMed:16810321). Accumulates during dark-induced starvation (PubMed:21278122). Reduced seed maturation (MAT) genes expression (PubMed:19531597). Slight reduction in the dark-induced activation of POX1/PRODH1 transcript accumulation (PubMed:21278122). Belongs to the bZIP family.