Required for the function of some acidic activation domains, which activate transcription from a distant site. The exact mechanism of action is not yet known (By similarity). ADA2 stimulates the acetyltransferase activity of GCN5 on free histones or nucleosomes, probably by opening up the promoter region. Mediates auxin and cytokinin signals in the control of cell proliferation and might be involved in repression of a freezing tolerance pathway at warm temperature (PubMed:12615937, PubMed:12747832). Involved in the positive regulation of salt-induced gene expression by maintaining locus-specific acetylation of histones H4 and H3 (PubMed:21193996). Interacts in vitro with the HAT domain of GCN5 and with the DNA-binding domain of the transcriptional activator DREB1B/CBF1 (PubMed:11266554, PubMed:16603259). Interacts with BZIP11 (PubMed:24861440). Expressed in roots, leaves, stems, flowers and siliques, with the strongest activity in the meristematic zones. The middle domain of ADA2b is sufficient for interaction with the HAT catalytic domain of GCN5. Acetylated in vitro by GCN5, but acetylation is not essential for biological activity. Plants have pleiotropic effects on plant growth and development, including dwarf size, aberrant root development, and short petals and stamens in flowers. ADA2a cannot rescue any of the mutant phenotypes.