Rice Na(+)-Permeable Transporter OsHAK12 Mediates Shoots Na(+) Exclusion in Response to Salt Stress

Soil salinity has become a major stress factor that reduces crop productivity worldwide. Sodium (Na(+)) toxicity in a number of crop plants is tightly linked with shoot Na(+) overaccumulation, thus Na(+) exclusion from shoot is crucial for salt tolerance in crops. In this study, we identified a member of the high-affinity K(+) transport family (HAK), OsHAK12, which mediates shoots Na(+) exclusion in response to salt stress in rice. The Oshak12 mutants showed sensitivity to salt toxicity and accumulated more Na(+) in the xylem sap, leading to excessive Na(+) in the shoots and less Na(+) in the roots. Unlike typical HAK family transporters that transport K(+), OsHAK12 is a Na(+)-permeable plasma membrane transporter. In addition, OsHAK12 was strongly expressed in the root vascular tissues and induced by salt stress. These findings indicate that OsHAK12 mediates Na(+) exclusion from shoot, possibly by retrieving Na(+) from xylem vessel thereby reducing Na(+) content in the shoots. These findings provide a unique function of a rice HAK family member and provide a potential target gene for improving salt tolerance of rice.