Rice OsHKT2;1 transporter mediates large Na + influx component into K + ‐starved roots for growth

Excessive accumulation of sodium in plants causes toxicity. No mutation that greatly diminishes sodium (Na + ) influx into plant roots has been isolated. The OsHKT2;1 (previously named OsHKT1) transporter from rice functions as a relatively Na + ‐selective transporter in heterologous expression systems, but the in vivo function of OsHKT2;1 remains unknown. Here, we analyzed transposon‐insertion rice lines disrupted in OsHKT2;1 . Interestingly, three independent oshkt2;1 ‐null alleles exhibited significantly reduced growth compared with wild‐type plants under low Na + and K + starvation conditions. The mutant alleles accumulated less Na + , but not less K + , in roots and shoots. OsHKT2;1 was mainly expressed in the cortex and endodermis of roots. 22 Na + tracer influx experiments revealed that Na + influx into oshkt2;1 ‐null roots was dramatically reduced compared with wild‐type plants. A rapid repression of OsHKT2;1‐mediated Na + influx and mRNA reduction were found when wild‐type plants were exposed to 30 mM NaCl. These analyses demonstrate that Na + can enhance growth of rice under K + starvation conditions, and that OsHKT2;1 is the central transporter for nutritional Na + uptake into K + ‐starved rice roots.