Acts as a flavonoid/H(+)-antiporter that control the vacuolar sequestration of flavonoids in the seed coat endothelium (PubMed:11283341, PubMed:17601828). Could transport the anthocyanin cyanidin-3-O-glucoside (PubMed:17601828) and epicatechin 3'-O-glucoside (PubMed:19684242) in vitro. Secondary metabolite biosynthesis; flavonoid biosynthesis. Tonoplast. Expressed in reproductive tissues, from buds to siliques. Restricted to the endothelium layer of the ovule and the seed coat. Expressed with a peak at the early globular stage and until the late heart-torpedo stage of embryo development. Positively regulated by the TT2-TT8-TTG1 complex. Pale brown seeds due to a strong reduction of proanthocyanidin deposition in vacuoles of endothelial cells. Belongs to the multi antimicrobial extrusion (MATE) (TC 2.A.66.1) family.