AUTHOR=Wu Yue , Henderson Sam W. , Walker Rob R. , Gilliham Matthew 

TITLE=Root-Specific Expression of Vitis vinifera VviNPF2.2 Modulates Shoot Anion Concentration in Transgenic Arabidopsis

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 13 - 2022

YEAR=2022

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2022.863971

DOI=10.3389/fpls.2022.863971

ISSN=1664-462X

ABSTRACT=<p>Grapevines (<italic>Vitis vinifera</italic> L., <italic>Vvi</italic>) on their roots are generally sensitive to salt-forming ions, particularly chloride (Cl<sup>–</sup>) when grown in saline environments. Grafting <italic>V. vinifera</italic> scions to Cl<sup>–</sup>-excluding hybrid rootstocks reduces the impact of salinity. Molecular components underlying Cl<sup>–</sup>-exclusion in <italic>Vitis</italic> 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 <italic>VviNPF2.1</italic> and <italic>VviNPF2.2</italic> were isolated. Both highly homologous proteins localized to the plasma membrane of Arabidopsis (<italic>Arabidopsis thaliana</italic>) protoplasts. Both were expressed primarily in grapevine roots and leaves and were more abundant in a Cl<sup>–</sup>-excluding rootstock compared to a Cl<sup>–</sup>-includer. Quantitative PCR of grapevine roots revealed that <italic>VviNPF2</italic>.<italic>1</italic> and <italic>2.2</italic> expression was downregulated by high [NO<sub>3</sub><sup>–</sup>] resupply post-starvation, but not affected by 25 mM Cl<sup>–</sup>. VviNPF2.2 was functionally characterized using an Arabidopsis enhancer trap line as a heterologous host which enabled cell-type-specific expression. Constitutive expression of <italic>VviNPF2.2</italic> exclusively in the root epidermis and cortex reduced shoot [Cl<sup>–</sup>] after a 75 mM NaCl treatment. Higher expression levels of <italic>VviNPF2.2</italic> correlated with reduced Arabidopsis xylem sap [NO<sub>3</sub><sup>–</sup>] 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<sup>–</sup> 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<sup>–</sup> accumulation.</p>