The plasma membrane-localized transporter VrNramp5 of Vigna radiata L. governs cadmium tolerance and accumulation in Arabidopsis thaliana

Cadmium (Cd) is a highly toxic non-essential element, which requires the transporters of essential and beneficial elements to enter the plant, and poses threat to plant growth and development. However, the mechanism of Cd uptake and accumulation in mungbean is limited. Here, we reported a Cd transporter VrNramp5 in mungbean, and its functional roles in response to Cd toxicity were conducted. The expression of VrNramp5 was down-regulated by Cd toxicity. VrNramp5 localized at plasma membrane based on subcellular localization analysis in epidermal cells of Nicotiana benthamiana. Heterologous expression of VrNramp5 in Arabidopsis thaliana promoted Cd accumulation, displayed the Cd sensitive phenotype including decreased root elongation and fresh weight, and VrNramp5 could diminish the Cd tolerance phenotype of AtNramp1-deficient mutant (atnramp1). Non–invasive micro–test showed that VrNramp5-overexpressing lines possessed higher Cd absorption capacity in root tips. Moreover, the Cd fluorescence probe staining revealed that more Cd accumulated in the leaf protoplasts of VrNramp5-overexpressing Arabidopsis. Those were consistent with the plants grown in the absence or presence of Cd (10 mg kg−1 or 20 mg kg−1) in soil. Taken together, VrNramp5 is responsible for plant Cd tolerance via regulating the Cd absorption capacity of roots and altering the intracellular distribution of Cd. Our findings provide a theoretical basis for further exploring the mechanism of Cd tolerance and breeding variety of mungbean with low Cd accumulation.