Wu Yue, Henderson Sam W, Walker Rob R, Gilliham Matthew
Australian Research Council (ARC) Centre of Excellence in Plant Energy Biology, School of Agriculture, Food and Wine and Waite Research Institute, University of Adelaide, Glen Osmond, SA, Australia.
School of Biomedicine, University of Adelaide, Adelaide, SA, Australia.
Front Plant Sci. 2022 May 25;13:863971. doi: 10.3389/fpls.2022.863971. eCollection 2022.
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.
葡萄（Vitis vinifera L.）在根部时通常对形成盐分的离子敏感，尤其是在盐渍环境中生长时对氯离子（Cl）敏感。将接穗嫁接到排斥氯离子的杂交砧木上可降低盐度的影响。然而，物种中氯离子排斥的分子成分在很大程度上仍然未知，不过，各种阴离子通道和转运蛋白是控制这一性状的良好候选者。在这里，分离出了两个硝酸盐/肽转运蛋白家族（NPF）成员VviNPF2.2和VviNPF6.5。这两种高度同源的蛋白质都定位于拟南芥原生质体的质膜上。它们主要在葡萄的根和叶中表达，与包含氯离子的砧木相比，在排斥氯离子的砧木中含量更高。对葡萄根进行定量PCR分析表明，VviNPF2.2和VviNPF6.5的表达在饥饿后重新供应高浓度[NO₃⁻]时被下调，但不受25 mM Cl的影响。使用拟南芥增强子捕获系作为异源宿主对VviNPF2.2进行功能表征，该宿主能够实现细胞类型特异性表达。仅在根表皮和皮层中组成型表达VviNPF2.2，在75 mM NaCl处理后可降低地上部[Cl]含量。在未受盐胁迫时，VviNPF2.2较高的表达水平与拟南芥木质部汁液中[NO₃⁻]含量降低相关。我们推测，当VviNPF2.2在根表皮和皮层中表达时，它可能在根细胞的被动阴离子外流中发挥作用，从而减少可供根向地上部转运的共质体Cl含量。因此，VviNPF2.2通过在根表皮和皮层中的作用，可能通过减少地上部Cl的净积累而对盐胁迫下的植物有益。
