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

Abstract

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. 22Na+ 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.