PcNPF2.7 from the Xerophyte Pugionium cornutum Facilitates Root-to-Shoot NO3− Transport and Affects Na+ Transport Under Salt Stress

Nitrate Excretion Transporter 1 (NAXT1/NPF2.7) is known to regulate NO₃^- transport in Arabidopsis, a salt-sensitive glycophyte that exhibits a significant reduction in the NO₃^- content under salt stress. However, its role in the NO₃^- homeostasis and salt tolerance of xerophytes, which exhibit strong stress tolerance, remains unclear. In the present study, we cloned the <i>NPF2.7</i> homolog (<i>PcNPF2.7</i>) from the xerophyte <i>Pugionium cornutum</i>, which exhibits stable NO₃^- content in the shoot under salt stress, and investigated its function in ion homeostasis and salt tolerance. <i>PcNPF2.7</i> was specifically expressed in the stele tissue of roots and localized to the plasma membrane; its expression level in the roots was significantly induced by NaCl and NaNO₃ treatments. <i>PcNPF2.7</i> overexpression driven by a stelar-specific promoter significantly increased NO₃^- accumulation and reduced Na⁺ levels in the shoots of Arabidopsis under 75 mM NaCl or NaNO₃ treatments, resulting in an enhanced salt tolerance. Furthermore, <i>PcNPF2.7</i> overexpression significantly induced <i>AtHKT1;1</i>, which mediates the unloading of Na⁺ from xylem in the roots. Taken together, our findings showed that PcNPF2.7 facilitates the transport of NO₃^- from the roots to the shoots and indirectly reduces Na⁺ accumulation in the shoot, therefore contributing to the salt tolerance in plants.