High V‐PPase activity is beneficial under high salt loads, but detrimental without salinity

Abstract

Summary The membrane‐bound proton‐pumping pyrophosphatase (V‐PPase), together with the V‐type H+‐ATPase, generates the proton motive force that drives vacuolar membrane solute transport. Transgenic plants constitutively overexpressing V‐PPases were shown to have improved salinity tolerance, but the relative impact of increasing PPi hydrolysis and proton‐pumping functions has yet to be dissected.For a better understanding of the molecular processes underlying V‐PPase‐dependent salt tolerance, we transiently overexpressed the pyrophosphate‐driven proton pump (NbVHP) in Nicotiana benthamiana leaves and studied its functional properties in relation to salt treatment by primarily using patch‐clamp, impalement electrodes and pH imaging.NbVHP overexpression led to higher vacuolar proton currents and vacuolar acidification. After 3 d in salt‐untreated conditions, V‐PPase‐overexpressing leaves showed a drop in photosynthetic capacity, plasma membrane depolarization and eventual leaf necrosis. Salt, however, rescued NbVHP‐hyperactive cells from cell death. Furthermore, a salt‐induced rise in V‐PPase but not of V‐ATPase pump currents was detected in nontransformed plants.The results indicate that under normal growth conditions, plants need to regulate the V‐PPase pump activity to avoid hyperactivity and its negative feedback on cell viability. Nonetheless, V‐PPase proton pump function becomes increasingly important under salt stress for generating the pH gradient necessary for vacuolar proton‐coupled Na+ sequestration.

Chinese wheat mosaic virus‐derived vsiRNA‐20 can regulate virus infection in wheat through inhibition of vacuolar‐ (H+)‐PPase induced cell death

“…It is well‐known that the canonical role of plant VPs is to facilitate the sequestration of sodium (Na + ) into vacuoles in plant. Functions of VP in many plant species, including Arabidopsis thaliana , Suaeda salsa , wheat ( Triticum aestivum ), tobacco and rice, have been studied extensively (Gaxiola et al , ; Gao et al , ; Guo et al , ; Brini et al , ; Zhang et al , ; Graus et al , ). Results of these studies indicate that VP is a protein with multiple roles, and one or more of these roles act(s) to improve plant defense against various abiotic stresses through enhancing plant development.…”

“…It is possible that V‐ATPase and VP play different roles in plant development (Krebs et al , ). A more recent report indicates that the VP proton pump activity can adapt to cellular demands and the rapid increase of operating pump numbers lead to a cell death phenotype in N. benthamiana leaves (Graus et al , ). Our results agree with this report and indicate that the PPi hydrolysis activity is higher in those plants overexpressing TaVP‐HA than that in the control plants (Fig.…”

“…Overexpression of TaVP increased PPi hydrolysis, leading to plant cell death Previous studies have shown that overexpression of VP in plant cells causes plasma membrane depolarization and then cell death due mainly to PPi hydrolysis rather than vacuolar acidification (Ferjani et al, 2011;Graus et al, 2018). To investigate the function of TaVP on PPi hydrolysis, we transiently overexpressed TaVP-HA in N. benthamiana leaves through agro-infiltration.…”

“…New Phytologist thaliana, Suaeda salsa, wheat (Triticum aestivum), tobacco and rice, have been studied extensively (Gaxiola et al, 2001;Gao et al, 2006;Guo et al, 2006;Brini et al, 2007;Zhang et al, 2011;Graus et al, 2018). Results of these studies indicate that VP is a protein with multiple roles, and one or more of these roles act(s) to improve plant defense against various abiotic stresses through enhancing plant development.…”

“…In plant, there are three distinct membrane H + -pumps that can generate pH gradients: the P-type (H + )-ATPase in plasma membrane to export H + from cells (Serrano, 1993); the vacuolar (H + )-ATPase (V-ATPase) complexes that are encoded by ≥ 26 genes and can acidify vacuoles and other intracellular trafficking compartments (Strompen et al, 2005); and the vacuolar (H + )-PPases (VPs) that are single subunit proteins and can generate H + gradients in endomembrane compartments using PPi (Zhen et al, 1997). Expression of the VP gene can be upregulated by various abiotic stresses, including low nutrient, drought, cold, heat, heavy metal and salinity stresses (Gaxiola et al, 2001;Han et al, 2005;Queiros et al, 2009;Kabala et al, 2014;Wehner et al, 2015;Graus et al, 2018). Previous studies have shown that overexpression of VP genes can enhance drought and/or salinity stress tolerance in plants, including Arabidopsis thaliana, Suaeda salsa, wheat (Triticum aestivum) and Nicotiana benthamiana (Gaxiola et al, 2001;Gao et al, 2006;Guo et al, 2006;Brini et al, 2007;Graus et al, 2018).…”