Domain-switch analysis of PeNHX3 from Populus euphratica reveals the critical role of the transmembrane domain 11 in Na+ and Li+ transport

Abstract Populus euphratica, the well-known tree halophyte, tolerates the stress of high levels of salt. We previously showed that the transmembrane domain 11 (TM11) of PeNHX3, a Na + ,K + /H + antiporter from P. euphratica , was crucial for Na + and Li + transport in a yeast growth assay. Here, we examined the role of TM11 in catalyzing Na + and Li + transport in transgenic Arabidopsis . We found that PeNHX3 localized to the tonoplasts in Arabidopsis . Overexpression of PeNHX3 in Arabidopsis improved seedling growth and enhanced salt tolerance and Li + detoxification. However, overexpression of PeNHX3 did not improve Arabidopsis growth at KCl concentrations higher than 0.1 mM, suggesting a low K + transport activity for PeNHX3 in plants. We performed in planta domain-switch analysis by replacing the C-terminal domain of AtNHX1 with a C-terminal segment of PeNHX3 containing the TM11 domain. We demonstrated that TM11 was critical for the Na + and Li + transport activities by PeNHX3. Taken together, PeNHX3 plays an important role in salt tolerance and Li + detoxification in plants. TM11 controls the Na + and Li + transport activities of PeNHX3 in Arabidopsis .