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

J Biol Chem. 2019 Jan 25;294(4):1290-1299. doi: 10.1074/jbc.RA118.006315. Epub 2018 Dec 3.

Abstract

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.

Keywords: Arabidopsis thaliana; H+ pumping pyrophosphatase; PPi synthase; Saccharomyces cerevisiae; pH gradient; patch clamp; proton pump; pyrophosphate (PPi); tonoplast; vacuole.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / metabolism*
  • Cytosol / metabolism*
  • Diphosphates / metabolism*
  • Inorganic Pyrophosphatase / metabolism*
  • Proton Pumps / physiology*
  • Saccharomyces cerevisiae

Substances

  • Arabidopsis Proteins
  • Diphosphates
  • Proton Pumps
  • AVP1 protein, Arabidopsis
  • Inorganic Pyrophosphatase