Acetylates histones H3 and H4 in vitro (PubMed:28487409). Acetylates 'Lys-4' of histone H3 (H3K4ac), 'Lys-9' (H3K9ac), 'Lys-14' (H3K14ac), 'Lys-27' (H3K27ac), and 'Lys-5' of histone H4 (H4K5ac) (PubMed:28487409). Acetylation of histones gives a specific tag for epigenetic transcription activation (By similarity). Operates in concert with certain DNA-binding transcriptional activators (By similarity). ADA2 and GCN5 function to acetylate nucleosomes, opening up the promoter region (PubMed:28487409). The ADA2-GCN5 histone acetyltransferase (HAT) module is recruited by WOX11 to regulate crown root cell proliferation and stem cell maintenance of root meristem (PubMed:28487409). The ADA2-GCN5 HAT module together with WOX11 targets and regulates a set of root-specific genes involved in carbon metabolism, cell wall biosynthesis, and auxin transport and response (PubMed:28487409). acetyl-CoA + L-lysyl-[protein] = CoA + H(+) + N(6)-acetyl-L-lysyl-[protein] Interacts with ADA2. Expressed in roots, mature leaves, stems and panicles. Belongs to the acetyltransferase family. GCN5 subfamily.