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

## TL;DR

A gene from a drought-tolerant plant helps transport nutrients and manage salt stress, offering a way to improve crop resilience.

## Contribution

Identifies PcNPF2.7 as a gene that enhances salt tolerance by managing nitrate and sodium transport in plants.

## Key findings

- PcNPF2.7 facilitates root-to-shoot nitrate transport in Pugionium cornutum.
- Overexpression of PcNPF2.7 in Arabidopsis reduces shoot sodium levels and improves salt tolerance.
- PcNPF2.7 expression is induced by salt and nitrate treatments in roots.

## Abstract

Pugionium cornutum is a typical xerophyte indigenous to arid and semi-arid regions of northwest China, exhibiting remarkable adaptability to drought and salt stresses. Unlike salt-sensitive plants, maintaining a stable NO3− concentration in the shoots is an important physiological strategy underlying the salt stress adaptation of P. cornutum. This study aimed to investigate the role of PcNPF2.7 from P. cornutum in the NO3− homeostasis and salt tolerance. Our results demonstrated that PcNPF2.7, which was mainly expressed in the stele tissue of the roots of P. cornutum, facilitates root-to-shoot NO3− transport and modulates Na+ accumulation in the shoot, thus contributing to the salt tolerance of the plant. The findings provide a potential candidate gene for improving salt tolerance in crops.

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 NPF2.7 homolog (PcNPF2.7) from the xerophyte Pugionium cornutum, which exhibits stable NO3− 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 NaNO3 treatments. PcNPF2.7 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, 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 NO3− from the roots to the shoots and indirectly reduces Na+ accumulation in the shoot, therefore contributing to the salt tolerance in plants.