Root-Specific Expression of VviNPF2.2 Modulates Shoot Anion Concentration in Transgenic .

Grapevines ( L., ) on their roots are generally sensitive to salt-forming ions, particularly chloride (Cl) when grown in saline environments. Grafting scions to Cl-excluding hybrid rootstocks reduces the impact of salinity. Molecular components underlying Cl-exclusion in species remain largely unknown, however, various anion channels and transporters represent good candidates for controlling this trait. Here, two nitrate/peptide transporter family (NPF) members and were isolated. Both highly homologous proteins localized to the plasma membrane of Arabidopsis () protoplasts. Both were expressed primarily in grapevine roots and leaves and were more abundant in a Cl-excluding rootstock compared to a Cl-includer. Quantitative PCR of grapevine roots revealed that . and expression was downregulated by high [NO ] resupply post-starvation, but not affected by 25 mM Cl. VviNPF2.2 was functionally characterized using an Arabidopsis enhancer trap line as a heterologous host which enabled cell-type-specific expression. Constitutive expression of exclusively in the root epidermis and cortex reduced shoot [Cl] after a 75 mM NaCl treatment. Higher expression levels of correlated with reduced Arabidopsis xylem sap [NO ] when not salt stressed. We propose that when expressed in the root epidermis and cortex, VviNPF2.2 could function in passive anion efflux from root cells, which reduces the symplasmic Cl available for root-to-shoot translocation. VviNPF2.2, through its role in the root epidermis and cortex, could, therefore, be beneficial to plants under salt stress by reducing net shoot Cl accumulation.