Possesses intrinsic histone acetyltransferase activity and acts as positive regulator of grain weight, hull size, yield, and plant biomass (PubMed:25535376, PubMed:34323980). Regulates postitively grain weight and yield by enlarging spikelet hulls via increasing cell number and accelerating grain filling (PubMed:25535376). In vitro, catalyzes the acetylation of histone H4 at Lys-6 (H4K5ac), Lys-13 (H4K12ac) and Lys-17 (H4K16ac) (PubMed:25535376). Involved in the regulation of plastochron (the time interval between leaf initiation event) (PubMed:33970916). Interacts (via C-terminus) with HDR3 (via N-terminus). Expressed in roots, leaf blades, leaf sheaths, shoot apical meristem and young panicles. Expressed at the basal part of the abaxial side of leaves in the vegetative phase (PubMed:25535376). In the reproductive phase, expressed in the bracts of initiating branches (PubMed:25535376). Ubiquitinated at Lys-63 by HDR3 (PubMed:34323980). Polyubiquitination of GW6A delays its degradation by the 26S proteasome and enhances GW6A histone acetyltransferase activity (PubMed:34323980). Over-expression of GWA6A enhances grain weight and yield by enlarging spikelet hulls via increasing cell number and accelerating grain filling, and increases global acetylation levels of histone H4. Belongs to the acetyltransferase family.