Plant H+-PPases: Reversible Enzymes with Contrasting Functions Dependent on Membrane Environment

Abstract

ACKNOWLEDGMENTSWe thank E.G. Baxter (Arizona State University School of Life Sciences Visualization Laboratory) for help with the model figure. We apologize to authors of several excellent papers that were not directly cited due to reference number restrictions.

H+‐pyrophosphatase IbVP1 promotes efficient iron use in sweet potato [Ipomoea batatas(L.) Lam.]

“…Under stressful conditions, up‐regulation of enzyme expression enables plant cells to use PPi as an energy source and maintain membrane integrity and intracellular transport via hydrolysis‐mediated ion transport (Gaxiola et al ., 2016; Greenway and Gibbs, 2003; Stitt, 1998). Increased abiotic stress tolerance and enhanced growth performance in Pi or nitrogen deficiency were observed during H + ‐PPase overexpression in Arabidopsis (Gaxiola et al ., 2001), tomato(Dong et al ., 2011; Park et al ., 2005; Yang et al ., 2007), tobacco (Khoudi et al ., 2012), rice (Zhang et al ., 2011; Zhao et al ., 2006), maize (Li et al ., 2008), lettuce (Paez‐Valencia et al ., 2013) and cotton (Lv et al ., 2009; Pasapula et al ., 2011).…”

“…The H + ‐PPase overexpression enhances apoplastic acidification by increasing the abundance and activity of H + ‐ATPase at the plasma membrane (Gaxiola et al ., 2016; Li et al ., 2005; Undurraga et al ., 2012). It increases root and shoot biomass, photosynthetic capacity and nutrient uptake under normal or nutrient‐limited conditions, such as low NO 3− and Pi (Khadilkar et al ., 2016; Li et al ., 2005; Lv et al ., 2015; Paez‐Valencia et al ., 2013; Pizzio et al ., 2015; Yang et al ., 2007, 2014).…”

Structural basis for the reversibility of proton pyrophosphatase

“…[1][2][3][4] This is congruent with the distinct localization of H C -PPases in the vacuoles of actively dividing cells of plants. [5][6][7][8][9][10] However, H C -PPase also saliently localizes at the vascular tissues of plants, wherein this protein is predominantly localized at the plasma membrane (PM) of the sieve element companion cell (SE-CC) complexes. 8,[11][12][13] Thermodynamic, 14 genetic, immunohistochemical, and physiological evidence 8,15,16 is consistent with a reverse PPi synthase activity of H C -PPase at the PM in the phloem, where it plays an important role in PPi homeostasis and photosynthate partitioning.…”

“…8,[11][12][13] Thermodynamic, 14 genetic, immunohistochemical, and physiological evidence 8,15,16 is consistent with a reverse PPi synthase activity of H C -PPase at the PM in the phloem, where it plays an important role in PPi homeostasis and photosynthate partitioning. 10,[15][16][17] We contend that the magnitude of proton gradients associated with the tonoplast or PM location of this enzyme drives the protein's structurally congruent potential to work in a reversible manner -either in the synthesis or hydrolysis of its substrate, PPi. 10,17 That the proton gradient drives the hydrolytic or synthetic activity of H C -PPase is corroborated by experimental evidence in maize coleoptiles and oranges.…”

“…10,[15][16][17] We contend that the magnitude of proton gradients associated with the tonoplast or PM location of this enzyme drives the protein's structurally congruent potential to work in a reversible manner -either in the synthesis or hydrolysis of its substrate, PPi. 10,17 That the proton gradient drives the hydrolytic or synthetic activity of H C -PPase is corroborated by experimental evidence in maize coleoptiles and oranges. 18,19 The dual membrane-specificity and the concomitant reversibility is in fact not a novel plant-specific attribute of this elegant pump.…”