Over‐expression of an Na + ‐ and K + ‐permeable HKT transporter in barley improves salt tolerance

Abstract

Summary: Soil salinity is an increasing menace that affects agriculture across the globe. Plant adaptation to high salt concentrations involves integrated functions, including control of Na + uptake, translocation and compartmentalization. Na + transporters belonging to the HKT family have been shown to be involved in tolerance to mild salt stress in glycophytes such as Arabidopsis, wheat and rice by contributing to Na + exclusion from aerial tissues. Here, we have analysed the role of the HKT transporter HKT2;1, which is permeable to K + and Na + , in barley, a relatively salt‐tolerant crop that displays a salt‐including behaviour. In Xenopus oocytes, HvHKT2;1 co‐transports Na + and K + over a large range of concentrations, displaying low affinity for Na + , variable affinity for K + depending on external Na + concentration, and inhibition by K + ( K i approximately 5 m m ). HvHKT2;1 is predominantly expressed in the root cortex. Transcript levels are up‐regulated in both roots and shoots by low K + growth conditions, and in shoots by high Na + growth conditions. Over‐expression of HvHKT2;1 led to enhanced Na + uptake, higher Na + concentrations in the xylem sap, and enhanced translocation of Na + to leaves when plants were grown in the presence of 50 or 100 m m NaCl. Interestingly, these responses were correlated with increased barley salt tolerance. This suggests that one of the factors that limits barley salt tolerance is the capacity to translocate Na + to the shoot rather than accumulation or compartmentalization of this cation in leaf tissues. Thus, over‐expression of HvHKT2;1 leads to increased salt tolerance by reinforcing the salt‐including behaviour of barley.