The Multidrug Resistance Protein OsMDR4 Is Involved in Cadmium Absorption in Rice (Oryza sativa L.)

Cadmium (Cd) is a toxic metal that poses a significant threat to crop production and global food security. Transporters play a critical role in mediating the uptake of metal ions, including Cd. However, a substantial number of Cd transporters in rice remain uncharacterized. In this study, we identify OsMDR4, a member of the multidrug resistance protein family, as a mediator of Cd uptake in rice. Heterologous overexpression of OsMDR4 in yeast increased both Cd sensitivity and intracellular Cd accumulation. Consistent with this, the Cd concentrations in both roots and shoots of the mdr4 mutants were significantly lower than those in wild type. Kinetic analysis further revealed that the maximum Cd uptake rate in mdr4 mutants was markedly reduced compared with wild type. Expression analysis showed that OsMDR4 is primarily expressed in the epidermis and root hairs of rice seedlings and in floral organs during the flowering stage. Notably, OsMDR4 expression in seedling roots was upregulated in response to Cd exposure. Subcellular localization analysis revealed that OsMDR4–EGFP was predominantly localized to the plasma membrane in a heterologous Arabidopsis protoplast system. In summary, we have identified and characterized OsMDR4 as a previously uncharacterized protein that contributes to cadmium accumulation in rice.