Department of Cell Biology and Molecular Genetics and Department of Plant Science and Landscape Architecture, University of Maryland, College Park, Maryland 20742
College of Life Sciences, Zhejiang University, Hangzhou 310058, China.
Plant Physiol. 2018 Jul;177(3):875-895. doi: 10.1104/pp.18.00142. Epub 2018 Apr 24.
Plants remodel their cells through the dynamic endomembrane system. Intracellular pH is important for membrane trafficking, but the determinants of pH homeostasis are poorly defined in plants. Electrogenic proton (H) pumps depend on counter-ion fluxes to establish transmembrane pH gradients at the plasma membrane and endomembranes. Vacuolar-type H-ATPase-mediated acidification of the trans-Golgi network is crucial for secretion and membrane recycling. Pump and counter-ion fluxes are unlikely to fine-tune pH; rather, alkali cation/H antiporters, which can alter pH and/or cation homeostasis locally and transiently, are prime candidates. Plants have a large family of predicted cation/H exchangers (CHX) of obscure function, in addition to the well-studied K(Na)/H exchangers (NHX). Here, we review the regulation of cytosolic and vacuolar pH, highlighting the similarities and distinctions of NHX and CHX members. In planta, alkalinization of the trans-Golgi network or vacuole by NHXs promotes membrane trafficking, endocytosis, cell expansion, and growth. CHXs localize to endomembranes and/or the plasma membrane and contribute to male fertility, pollen tube guidance, pollen wall construction, stomatal opening, and, in soybean (), tolerance to salt stress. Three-dimensional structural models and mutagenesis of Arabidopsis () genes have allowed us to infer that AtCHX17 and AtNHX1 share a global architecture and a translocation core like bacterial Na/H antiporters. Yet, the presence of distinct residues suggests that some CHXs differ from NHXs in pH sensing and electrogenicity. How H pumps, counter-ion fluxes, and cation/H antiporters are linked with signaling and membrane trafficking to remodel membranes and cell walls awaits further investigation.
植物通过动态的内膜系统重塑细胞。细胞内 pH 对膜运输很重要，但植物中质膜和内膜的 pH 稳态决定因素还未被很好地定义。质子 (H) 泵依赖于反离子流在质膜和内膜上建立跨膜 pH 梯度。液泡型 H+-ATP 酶介导的高尔基网络酸化对于分泌和膜循环至关重要。泵和反离子流不太可能微调 pH；相反，能够局部和短暂地改变 pH 和/或阳离子稳态的碱金属阳离子/H 反向转运蛋白是主要候选者。除了研究充分的 K(Na)/H 反向转运蛋白 (NHX) 外，植物还拥有一大类预测的阳离子/H 交换器 (CHX)，其功能尚不明确。在这里，我们回顾了细胞质和液泡 pH 的调节，强调了 NHX 和 CHX 成员的相似性和区别。在植物中，NHX 使高尔基网络或液泡碱化，促进膜运输、内吞作用、细胞扩张和生长。CHX 定位于内膜系统和/或质膜，并有助于雄性育性、花粉管导向、花粉壁构建、气孔开放，以及在大豆（）中对盐胁迫的耐受性。拟南芥（）基因的三维结构模型和突变分析使我们能够推断出 AtCHX17 和 AtNHX1 具有全局结构和类似于细菌 Na/H 反向转运蛋白的转运核心。然而，存在独特的残基表明，一些 CHX 在 pH 感应和电生成方面与 NHX 不同。H 泵、反离子流和阳离子/H 反向转运蛋白如何与信号转导和膜运输相关联，以重塑膜和细胞壁，有待进一步研究。
