A win-win scenario for photosynthesis and the plasma membrane H⁺ pump

In plants, cytosolic and extracellular pH homeostasis are crucial for various physiological processes, including the uptake of macronutrients and micronutrients, cell elongation, cell expansion, and enzyme activity. Proton (H⁺) gradients and the membrane potential are generated by a H⁺ pump consisting of an active primary transporter. Plasma membrane (PM) H⁺-ATPase, a PM-localized H⁺ pump, plays a pivotal role in maintaining pH homeostasis in plant cells and extracellular regions. PM H⁺-ATPase activity is regulated by protein abundance and by post-translational modifications. Several stimuli have been found to activate the PM H⁺-ATPase through phosphorylation of the penultimate threonine (Thr) of the carboxy terminus. Light- and photosynthesis-induced phosphorylation of PM H⁺-ATPase are conserved phenomena among various plant species. In this work, we review recent findings related to PM H⁺-ATPase regulation in the photosynthetic tissues of plants, focusing on its mechanisms and physiological roles. The physiological roles of photosynthesis-dependent PM H⁺-ATPase activation are discussed in the context of nitrate uptake and cytoplasmic streaming in leaves.