Environmental and Genetic Factors Regulating Localization of the Plant Plasma Membrane H⁺-ATPase

Abstract

A P-type H + -ATPase is the primary transporter that converts ATP to electrochemical energy at the plasma membrane of higher plants. Its product, the proton-motive force, is composed of an electrical potential and a pH gradient. Many studies have demonstrated that this proton-motive force not only drives the secondary transporters required for nutrient uptake, but also plays a direct role in regulating cell expansion. Here, we have generated a transgenic Arabidopsis (Arabidopsis thaliana) plant expressing H + -ATPase isoform 2 (AHA2) that is translationally fused with a fluorescent protein and examined its cellular localization by live-cell microscopy. Using a 3D imaging approach with seedlings grown for various times under a variety of light intensities, we demonstrate that AHA2 localization at the plasma membrane of root cells requires light. In dim light conditions, AHA2 is found in intracellular compartments, in addition to the plasma membrane. This localization profile was age-dependent and specific to cell types found in the transition zone located between the meristem and elongation zones. The accumulation of AHA2 in intracellular compartments is consistent with reduced H + secretion near the transition zone and the suppression of root growth. By examining AHA2 localization in a knockout mutant of a receptor protein kinase, FERONIA, we found that the intracellular accumulation of AHA2 in the transition zone is dependent on a functional FERONIA-dependent inhibitory response in root elongation. Overall, this study provides a molecular underpinning for understanding the genetic, environmental, and developmental factors influencing root growth via localization of the plasma membrane H + -ATPase.A unique feature of the plasma membrane in plants and fungi compared to animals is the proton electrochemical gradient produced by a P-type H + -ATPase (proton pump), rather than by a sodium pump. Because the proton pump is moving only one proton per ATP molecule, the proton reversal potential of the enzyme is much larger than that of the sodium/potassium pump, which moves three sodium ions out of a cell for every two potassium ions moving in. In concert with this intrinsic biochemical difference between the two enzymes, the membrane potential of plants is routinely found to be much more negative than in animals. It has allowed plants to evolve rapid hydraulicbased methods for organ movement, such as is readily apparent in touch-sensitive plants, e.g. Mimosa pudica (sensitive plant) and Dionaea muscipula (Venus flytrap). However, all plants, even the slower growth movements that underlie plant specific phenomena such as photo and gravitropism, also rely on the deep membrane potential to ensure that the major osmolyte, the potassium ions (K + ), is concentrated in the cytoplasm and its movement across the membrane mediated by potassium channels ultimately induces the changes in cellular turgor pressure. The proton pump is also involved in tight regulation of the cell-wall pH. This apoplastic pH in turn controls the exte...

Early mannitol-triggered changes in the Arabidopsis leaf (phospho)proteome reveal growth regulators

“…Finally, the importance of the plasma membrane H + -ATPase for plant growth and its tight regulation via phosphorylation was established in the past decades ( Haruta et al , 2010 , 2018 ; Falhof et al , 2016 ). AHA2, a H + -ATPase, was transcriptionally not regulated or differentially abundant in the short-term proteome data set but purely post-translationally regulated.…”

Osmotic Stress Activates Two Reactive Oxygen Species Pathways with Distinct Effects on Protein Nanodomains and Diffusion

“…contrast, endocytosis of the AHA2 H + -ATPase was insensitive to the same treatment. Because AHA2 cycling is, along with AHA1, responsible for the maintenance of a proton gradient across the cell PM (Haruta and Sussman, 2012;Haruta et al, 2018), we speculate that this function has to be critically maintained for energizing turgor regulation under hyperosmotic conditions. Also unknown is the mechanism that allows selection of specific cargos for either internalization or retention.…”

Uncovering pH at both sides of the root plasma membrane interface using noninvasive imaging

“…S13H). The two major P-type ATPases in Arabidopsis roots, AHA1 and AHA2, are known to participate in media acidification and are necessary for plant growth in alkaline conditions (40)(41)(42)(43). Interestingly, AHA2 activity is regulated by PKS5 kinase, which is in turn regulated by apoplastic pH (44).…”