Abstract
Nitrate Excretion Transporter 1 (NAXT1/NPF2.7) is known to regulate NO(3)(-) transport in Arabidopsis, a salt-sensitive glycophyte that exhibits a significant reduction in the NO(3)(-) content under salt stress. However, its role in the NO(3)(-) homeostasis and salt tolerance of xerophytes, which exhibit strong stress tolerance, remains unclear. In the present study, we cloned the NPF2.7 homolog (PcNPF2.7) from the xerophyte Pugionium cornutum, which exhibits stable NO(3)(-) content in the shoot under salt stress, and investigated its function in ion homeostasis and salt tolerance. PcNPF2.7 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 NaNO(3) treatments. PcNPF2.7 overexpression driven by a stelar-specific promoter significantly increased NO(3)(-) accumulation and reduced Na(+) levels in the shoots of Arabidopsis under 75 mM NaCl or NaNO(3) treatments, resulting in an enhanced salt tolerance. Furthermore, PcNPF2.7 overexpression significantly induced AtHKT1;1, which mediates the unloading of Na(+) from xylem in the roots. Taken together, our findings showed that PcNPF2.7 facilitates the transport of NO(3)(-) from the roots to the shoots and indirectly reduces Na(+) accumulation in the shoot, therefore contributing to the salt tolerance in plants.