Copper (Cu) transporter that mediates Cu transport in root vacuoles. Involved in Cu detoxification by sequestrating Cu into root vacuoles and limiting translocation of Cu from the roots to the shoots, and accumulation in grains. ATP + Cu(+)(in) + H2O = ADP + Cu(+)(out) + H(+) + phosphate Highly expressed in roots. Expressed in vascular tissues of the stele, mainly in pericycle cells. Induced by copper in roots, but not in shoots. A single amino acid substitution of Val-914 to Ala increases HMA4 copper transport activity. This allele is found in a number of rice cultivars, such as cv. Lemont, and is associated with low accumulation of copper in rice grains. Identification of natural allelic variation in HMA4 may facilitate the development of rice varieties with grain copper concentrations adapted to dietary needs in function of the copper concentration in soil. Reduced plant height and biomass. Reduced fertility. Increased levels of copper in grain, leaf sheath and internodes. Belongs to the cation transport ATPase (P-type) (TC 3.A.3) family. Type IB subfamily.