Involved in the acylation of the 6'' position of the 3-O-glucose residue of anthocyanin. Also able to use flavonol 3-glucosides as the acyl acceptor. kcat is 7.6 sec(-1) for p-coumaroyl-CoA. kcat is 8.5 sec(-1) for feruloyl-CoA. kcat is 9.3 sec(-1) for caffeoyl-CoA. kcat is 7.6 sec(-1) for cyanidin 3-glucoside. kcat is 8.0 sec(-1) for pelargonidin 3-glucoside. kcat is 7.8 sec(-1) for malvidin 3-glucoside. kcat is 1.2 sec(-1) for quercetin 3-glucoside. kcat is 1.1 sec(-1) for kaempferol 3-glucoside. kcat is 2.6 sec(-1) for kaempferol 7-glucoside. kcat is <0.001 sec(-1) for cyanidin 3,5-diglucoside. kcat is <0.001 sec(-1) for pelargonidin 3,5-diglucoside. Highly expressed in flowers, leaves and roots. Lower levels of expression in stems and siliques. Up-regulated by high sucrose and by low phosphate stresses. No visible phenotype, probably due to the redundancy with 3AT2. Belongs to the plant acyltransferase family.