Abstract
Cytosolic pH homeostasis is a precondition for the normal growth and stress responses in plants, and H+ flux across the plasma membrane is essential for cytoplasmic pH control. Hence, this review focuses on seven types of proteins that possess direct H+ transport activity, namely, H+-ATPase, NHX, CHX, AMT, NRT, PHT, and KT/HAK/KUP, to summarize their plasma-membrane-located family members, the effect of corresponding gene knockout and/or overexpression on cytosolic pH, the H+ transport pathway, and their functional regulation by the extracellular/cytosolic pH. In general, H+-ATPases mediate H+ extrusion, whereas most members of other six proteins mediate H+ influx, thus contributing to cytosolic pH homeostasis by directly modulating H+ flux across the plasma membrane. The fact that some AMTs/NRTs mediate H+-coupled substrate influx, whereas other intra-family members facilitate H+-uncoupled substrate transport, demonstrates that not all plasma membrane transporters possess H+-coupled substrate transport mechanisms, and using the transport mechanism of a protein to represent the case of the entire family is not suitable. The transport activity of these proteins is regulated by extracellular and/or cytosolic pH, with different structural bases for H+ transfer among these seven types of proteins. Notably, intra-family members possess distinct pH regulatory characterization and underlying residues for H+ transfer. This review is anticipated to facilitate the understanding of the molecular basis for cytosolic pH homeostasis. Despite this progress, the strategy of their cooperation for cytosolic pH homeostasis needs further investigation.
Highlights
As a fundamental activity in all living cells [1], cytosolic pH homeostasis is essential for the normal growth and stress responses of plants [2,3]
In comparison with numerous reviews that concentrate on the organelle-located proteins which are responsible for H+ flux across the endomembrane [1,6,7], summaries regarding proteins that are directly involved in H+ efflux/influx across the plasma membrane are scarce, except regarding plasma membrane H+ -ATPases [14,17]
The single knockout of AHA7 (Arabidopsis H+ -ATPase 7) significantly reduces the H+ efflux capacity in the root hair zone under low-phosphorus stress [39]. All these results indicate the contribution of plasma membrane H+ -ATPases to cytosolic pH control, but the direct measurement of cytosolic pH changes upon their mutation/overexpression is still lacking
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As a fundamental activity in all living cells [1], cytosolic pH homeostasis is essential for the normal growth and stress responses of plants [2,3]. This is because basic cytosolic processes such as biochemical reactions, protein stability, ion channel/transporter activity, compartmental integrity, and membrane trafficking have strict pH requirements [1,4]. In comparison with numerous reviews that concentrate on the organelle-located proteins which are responsible for H+ flux across the endomembrane [1,6,7], summaries regarding proteins that are directly involved in H+ efflux/influx across the plasma membrane are scarce, except regarding plasma membrane H+ -ATPases [14,17]. Roles of Plasma Membrane H+ -ATPases and Multiple Transporters in Cytosolic pH Homeostasis
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
