ZxNPF7.3/NRT1.5 from the xerophyte Zygophyllum xanthoxylum modulates salt and drought tolerance by regulating NO3-, Na+ and K+ transport

The Nitrate Transporter1/Peptide Transporter family member NPF7.3/NRT1.5 is responsible for long-distance transport of NO3- and involved in affecting salt and drought tolerance in plants. However, current studies have only focused on AtNRT1.5 from the stress-sensitive glycophyte Arabidopsis. In this study, the function of the NRT1.5 homolog ZxNRT1.5 from the typical xerophyte Zygophyllum xanthoxylum in ion transport and plants' salt and drought tolerance was analyzed. The results indicated that ZxNRT1.5 was mainly expressed in the root stele, and its expression level was significantly induced by salt treatments and osmotic stress. Overexpression of ZxNRT1.5 in Arabidopsis showed that ZxNRT1.5 mediated root-to-shoot NO3- transport and contributed to enhancing NO3- uptake. Overexpression of ZxNRT1.5 increased Na+ accumulation by decreasing the expression of AtHKT1;1 in roots, and promoted root-to-shoot transport of K+ probably by changing polarization of cell membrane under salt stress. Meanwhile, ZxNRT1.5-overexpressing lines exhibited stronger tolerance to mannitol-induced osmotic stress, resulted from an increased accumulation of NO3- and the accumulation of a small quantity of Na+ that was beneficial for plant growth. These findings suggest that ZxNRT1.5 is not only essential for long-distance transport and accumulation of NO3-, but also involved in regulating Na+ and K+ transport, thereby modulating salt and drought tolerance.