A high activity zinc transporter OsZIP9 mediates zinc uptake in rice.

: Zinc (Zn) is an essential micronutrient for most organisms including humans, and Zn deficiency is widespread in human populations especially in underdeveloped regions. Cereals such as rice (Oryza sativa) are the major dietary source of Zn for most people. However, the molecular mechanism underlying Zn uptake in rice is still not fully understood. Here, we report that a member of ZIP (ZRT, IRT-like protein) family, OsZIP9, functions in Zn uptake in rice. It was expressed in the epidermal and exodermal cells of lateral roots, localized in the plasma membrane, and induced under Zn deficiency. Yeast-expressed OsZIP9 showed much higher Zn influx transport activity than other rice ZIP proteins in a wide range of Zn concentrations. OsZIP9 knockout rice plants showed a significant reduction in growth at low Zn concentration, but could be rescued by high Zn supply. Compared to the wildtype, accumulation of Zn in root, shoot and grain was much lower in knockout lines, especially with low Zn supply under both hydroponic and paddy soil conditions. OsZIP9 also showed Co uptake activity. Natural variation of OsZIP9 expression level is highly associated with Zn content in milled grain among rice varieties in the germplasm collection. Taken together, these results show that OsZIP9 is an important influx transporter responsible for uptake of Zn and Co from external media into root cells.