Wheat NRAMP3 Transporters Govern Grain Cadmium Concentration

Wheat natural resistance-associated macrophage protein 3 (NRAMP3) are manganese (Mn) transporters that can also transport unwanted cadmium (Cd). However, their roles in regulating grain Cd concentration are unknown. Here, we functionally characterised TpNRAMP3-7A and TpNRAMP3-7B cloned from dwarf Polish wheat (Triticum polonicum L., AABB) in them of their expression patterns, transcript localisations, metal transport activities, and associated phenotypes. Both TpNRAMP3-7A and TpNRAMP3-7B were expressed in the epidermis, endodermis, and xylem parenchyma cells of roots, the xylem parenchyma cells and phloem region of nodes and leaf sheaths, and the phloem region of leaf blades. Knockout of TpNRAMP3-7A and/or TpNRAMP3-7B not only limited grain Cd concentration, but also reduced Cd uptake, root-to-shoot translocation, and shoot-to-grain distribution. They also limited grain Mn concentration by inhibiting shoot-to-grain Mn distribution when grown in the field (high-Mn concentration), and decreased Mn uptake and root-to-shoot translocation under low-Mn stress. Position 192F in TpNRAMP3 was the core amino acid determining Cd and Mn transport activity. These results provide a valuable guide and target gene for limiting Cd concentration in wheat grains.