Metallochaperone OsHIPP9 is involved in the retention of cadmium and copper in rice.

Metallochaperones are a unique class of proteins that play crucial roles in metal homeostasis and detoxification. However, few metallochaperones have been functionally characterized in rice. Heterologous expression of Heavy metal-associated Isoprenylated Plant Protein 9 (OsHIPP9), a metallochaperone, altered yeast tolerance to cadmium (Cd) and copper (Cu). We investigated the physiological role of OsHIPP9 according to its expression pattern, tissue and subcellular localization, metal binding ability, and metal ion tolerance, and the mineral element contents of knockout (KO) and overexpression (OX) lines in rice. OsHIPP9 was primarily expressed in the root exodermis and xylem region of enlarged vascular bundles (EVB) at nodes. KO of OsHIPP9 increased the Cd concentrations of the upper nodes and panicle, but decreased Cd in expanded leaves. KO of OsHIPP9 decreased Cu uptake and accumulation in rice. Constitutive OX of OsHIPP9 increased Cd and Cu accumulation in aboveground tissues and brown rice. OsHIPP9 showed binding capacity for Cd and Cu. We propose that OsHIPP9 has dual metallochaperone roles, chelating Cd in the xylem region of EVB for Cd retention in the nodes and chelating Cu in rice roots to aid Cu uptake. This article is protected by copyright. All rights reserved.