A novel salt responsive PvHAK16 negatively regulates salt tolerance in transgenic Arabidopsis thaliana

HAK/KUP/KT transporters play an important role in maintaining K+ and Na+ homeostasis in plants in response to salt stress. A salt induced PvHAK16 from halophyte seashore paspalum (Paspalum vaginatum O. Swartz) was identified in this study. PvHAK16 was localized in the plasma membrane and highly expressed in leaves but not in roots. Overexpression of PvHAK16 in Arabidopsis led to reduced seed germination rate, shoot weight, Fv/Fm and survival rate but increased ion leakage after salt stress as compared with the wild type. Increased Na+ and decreased K+ levels that led to higher Na+/K+ ratio was observed in transgenic lines after salt stress, which was a result of the net influx of Na+ and net efflux of K+ in transgenic plants. The results suggest that PvHAK16 confers Na+ uptake and K+ efflux under salt stress and thus negatively regulates salt tolerance. Moreover, PvHAK16 expression altered transcript levels of ion homeostasis genes K+-Uptake Permease 7 (KUP7), Potassium Transport 2/3 (AKT2), Salt Overly Sensitive 1 (SOS1) and Gated Outwardly-Rectifying K+ Channel (GORK), which were associated with the increased Na+/K+ ratio in transgenic plants. Transgenic plants had reduced transcript levels of stress responsive genes and showed promoted oxidative damage as a result of reduced SOD activity and proline accumulation.