Transcription factor involved in the developmental regulation of the endothelium and in the accumulation of proanthocyanidins (PAs) or condensed tannins which give the seed its brown pigmentation after oxidation (PubMed:12368498, PubMed:16080001). Necessary for the normal activation of the BANYULS promoter in the endothelium body (PubMed:12368498). Is required, together with AGL11/STK for the maternal control of endothelium formation, which is essential for female gametophyte development and fertilization, and seed formation (PubMed:22176531). Interacts genetically with AGL1/SHP1 and AGL5/SHP2 in a partially antagonistic manner and represses AGL1/SHP1, AGL5/SHP2, and AGL8/FUL during flower development. Is essential for the coordination of cell divisions in ovule, seed coat development and endosperm formation (PubMed:27776173). Mediates the crosstalk between endothelium and nucellus to ensure proper seed formation. Functions redundantly with AGL63/GOA to repress nucellus growth and promote its degeneration. Represses the negative regulator of autophagy and programmed cell death HVA22D in the proximal nucellus (PubMed:27233529). Binds specifically to the CArG box DNA sequence 5'-CC (A/T)6 GG-3' (PubMed:16080001). Interacts with AP1/AGL7, SEP1/AGL2, SEP2/AGL4, SEP3/AGL9 and AGL3/SEP4. Expressed in buds, flowers and immature seeds, but not in roots, stems, leaves, seedlings or siliques valves. Expression in seed coat is confined to the endothelium layer. Expressed during seed development. The two isoforms were always coexpressed in the tissues investigated. The pigmentation of the chalaza-micropyle region is not under the control of ABS, as opposed to the pigmentation of the seed body.