Description:
<p>Salt stress is one of the major factors limiting rice (<italic>Oryza sativa</italic>) 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 <italic>OsMGT1</italic> 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 Mg²⁺ concentration (20–200 𝜇M). However, such differences were abolished at a higher Mg²⁺ concentration (2 mM), although the total Na uptake was not altered. <italic>OsMGT1</italic> 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 <italic>OsMGT1</italic> was expressed in all root cells of the root tips but was highly expressed in the pericycle of root mature zone. <italic>OsMGT1</italic> was also expressed in the phloem region of basal node, leaf blade, and sheath. When expressed in <italic>Xenopus laevis</italic> oocytes, the transport activity of OsHKT1;5 was enhanced by elevating external Mg²⁺ concentration. Furthermore, knockout of <italic>OsHKT1;5</italic> in <italic>osmgt1</italic> mutant background did not further increase its salt sensitivity. Taken together, our results suggest that Mg²⁺ transported by OsMGT1 in the root mature zone is required for enhancing OsHKT1;5 activity, thereby restricting Na accumulation to the shoots.</p>