Metal transporter that transports the trivalent cation aluminum (Al(3+)), but does not seem to transport divalent cations such as iron (Fe(2+)), manganese (Mg(2+)) or Cadmium (Cd(2+)). Involved in Al tolerance by taking up Al in root cells, where it is detoxified by chelation with organic acid anions and sequestration into the vacuoles. Expressed at low levels in roots. By Al in roots. Positively regulated by ART1. No visible phenotype under normal growth condition, but after exposure to Al, decreased levels of Al in root-cell sap, increased Al content in the cell wall and increased inhibition of root growth. Belongs to the NRAMP (TC 2.A.55) family.