The flip side of the Arabidopsis type I proton-pumping pyrophosphatase (AVP1): Using a transmembrane H+ gradient to synthesize pyrophosphate

• Published in: The Journal of biological chemistry 2019-01, Vol.294 (4), p.1290-1299
• Main Authors: Scholz-Starke, Joachim, Primo, Cecilia, Yang, Jian, Kandel, Raju, Gaxiola, Roberto A., Hirschi, Kendal D.
• Format: Article
• Language: English
• Subjects: Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Cytosol - metabolism; Diphosphates - metabolism; H+ pumping pyrophosphatase; Inorganic Pyrophosphatase - metabolism; patch clamp; pH gradient; Plant Biology; PPi synthase; proton pump; Proton Pumps - physiology; pyrophosphate (PPi); Saccharomyces cerevisiae; tonoplast; vacuole
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.RA118.006315

Energy partitioning and plant growth are mediated in part by a type I H+-pumping pyrophosphatase (H+-PPase). A canonical role for this transporter has been demonstrated at the tonoplast where it serves a job-sharing role with V-ATPase in vacuolar acidification. Here, we investigated whether the plant H+-PPase from Arabidopsis also functions in “reverse mode” to synthesize PPi using the transmembrane H+ gradient. Using patch-clamp recordings on Arabidopsis vacuoles, we observed inward currents upon Pi application on the cytosolic side. These currents were strongly reduced in vacuoles from two independent H+-PPase mutant lines (vhp1-1 and fugu5-1) lacking the classical PPi-induced outward currents related to H+ pumping, whereas they were significantly larger in vacuoles with engineered heightened expression of the H+-PPase. Current amplitudes related to reverse-mode H+ transport depended on the membrane potential, cytosolic Pi concentration, and magnitude of the pH gradient across the tonoplast. Of note, experiments on vacuolar membrane–enriched vesicles isolated from yeast expressing the Arabidopsis H+-PPase (AVP1) demonstrated Pi-dependent PPi synthase activity in the presence of a pH gradient. Our work establishes that a plant H+-PPase can operate as a PPi synthase beyond its canonical role in vacuolar acidification and cytosolic PPi scavenging. We propose that the PPi synthase activity of H+-PPase contributes to a cascade of events that energize plant growth.