A Magnesium Transporter OsMGT1 Plays a Critical Role in Salt Tolerance in Rice.

Salt stress is one of the major factors limiting rice () production globally. Although several transporters involved in salt tolerance have been identified in rice, the mechanisms regulating their transport activity are still poorly understood. Here, we show evidence that a rice Mg transporter OsMGT1 is required for salt tolerance probably by regulating transport activity of OsHKT1;5, a key transporter for the removal of Na from the xylem sap at the root mature zone. Knockout of did not affect total Na uptake, but increased Na concentration in the shoots and xylem sap, resulting in a significant increase in salt sensitivity at low external Mg concentration (20-200 μm). However, such differences were abolished at a higher Mg concentration (2 mm), although the total Na uptake was not altered. was expressed in both the roots and shoots, but only that in the roots was moderately up-regulated by salt stress. Spatial expression analysis revealed that was expressed in all root cells of the root tips but was highly expressed in the pericycle of root mature zone. was also expressed in the phloem region of basal node, leaf blade, and sheath. When expressed in oocytes, the transport activity of OsHKT1;5 was enhanced by elevating external Mg concentration. Furthermore, knockout of in mutant background did not further increase its salt sensitivity. Taken together, our results suggest that Mg transported by OsMGT1 in the root mature zone is required for enhancing OsHKT1;5 activity, thereby restricting Na accumulation to the shoots.