Overexpression of Leymus chinensis vacuole transporter NRAMP2 in rice increases Mn and Cd accumulation

Phytoextraction using hyperaccumulating plants is an environmentally friendly phytoremediation technology for heavy metal-contaminated soils. Generating hyperaccumulating plants with high biomass is feasible using genetic engineering methods. Here, the Mn transporter natural resistance-associated macrophage protein 2 (LcNRAMP2) gene was identified from sheepgrass (Leymus chinensis), which is highly adaptable to many soil types. LcNRAMP2 expression was induced by high-Mn treatment in L. chinensis. LcNRAMP2 overexpression enhanced the tolerance of transgenic rice seedlings to high levels of Mn and Cd stress. Furthermore, transgenic rice seedlings overexpressing LcNRAMP2 accumulated more Mn and Cd compared to wild types after stress treatment. Subcellular localization revealed that LcNRAMP2 was predominantly localized in the prevacuole compartments (PVC) and vacuolar membranes. These results suggest that LcNRAMP2 may be the Mn and Cd transporter on PVC and vacuolar membranes, which sequesters excess Mn and Cd into the vacuole, thereby enhancing the Mn and Cd tolerance of transgenic rice seedlings. Our study revealed that LcNRAMP2 is a vital genetic resource for generating hyperaccumulating transgenic herbs with high biomass for phytoextraction in Mn- and Cd-contaminated soils.