Enhanced Proton Translocating Pyrophosphatase Activity Improves Nitrogen Use Efficiency in Romaine Lettuce      

Abstract

Plant nitrate (NO 32 ) acquisition depends on the combined activities of root high-and low-affinity NO 3 2 transporters and the proton gradient generated by the plasma membrane H + -ATPase. These processes are coordinated with photosynthesis and the carbon status of the plant. Here, we present the characterization of romaine lettuce (Lactuca sativa 'Conquistador') plants engineered to overexpress an intragenic gain-of-function allele of the type I proton translocating pyrophosphatase (H + -PPase) of Arabidopsis (Arabidopsis thaliana). The proton-pumping and inorganic pyrophosphate hydrolytic activities of these plants are augmented compared with control plants. Immunohistochemical data show a conspicuous increase in H + -PPase protein abundance at the vasculature of the transgenic plants. Transgenic plants displayed an enhanced rhizosphere acidification capacity consistent with the augmented plasma membrane H + -ATPase proton transport values, and ATP hydrolytic capacities evaluated in vitro. These transgenic lines outperform control plants when challenged with NO 3 2 limitations in laboratory, greenhouse, and field scenarios. Furthermore, we report the characterization of a lettuce LsNRT2.1 gene that is constitutive up-regulated in the transgenic plants. Of note, the expression of the LsNRT2.1 gene in control plants is regulated by NO 3 2 and sugars. Enhanced accumulation of 15 N-labeled fertilizer by transgenic lettuce compared with control plants was observed in greenhouse experiments. A negative correlation between the level of root soluble sugars and biomass is consistent with the strong root growth that characterizes these transgenic plants.

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). Nevertheless, the role of H + ‐PPase‐induced Fe uptake is unknown.…”

“…Enhanced rhizosphere acidification by increased PM‐H + ‐ATPase activity is strongly associated with up‐regulated H + ‐PPase activity, as demonstrated by the IbVP1 overexpressing sweet potato under normal and Fe‐deficient conditions (Figures 3 and 7) consistent with other reports (Paez‐Valencia et al ., 2013; Yang et al ., 2007). Changes in the rhizosphere represent a central mechanism in plant mineral nutrition, contributing to nutrient solubility and proton‐motive force (Li et al ., 2015; Palmgren, 2001; Palmgren, 1998; Santi and Schmidt, 2009; Zhu et al ., 2009).…”

“…Up‐regulation of H + ‐PPase expression and activity has been reported in plants grown under abiotic stress conditions such as chilling, anoxia, mineral deficiency and salt stress (Maeshima, 2000). Up‐regulated H + ‐PPases induce plant tolerance to various stresses, such as drought, high salinity, and N and Pi deprivation (Arif et al ., 2013; Paez‐Valencia et al ., 2013; Yang et al ., 2007). It also affects auxin and sugar transport and accumulation during root and shoot growth (Gaxiola et al ., 2012; Khadilkar et al ., 2016; Li et al ., 2005; Pasapula et al ., 2011; Pizzio et al ., 2015).…”

Arabidopsis Type I Proton-Pumping Pyrophosphatase Expresses Strongly in Phloem, Where It Is Required for Pyrophosphate Metabolism and Photosynthate Partitioning

“…A second batch of plants grown several months earlier gave similar cDNA expression and fresh weight values; *, P # 0.05; **, P # 0.01; and ***, P # 0.0001. Yang et al, 2007;Bao et al, 2008;Lv et al, 2008;Pasapula et al, 2011;Arif et al, 2013;Paez-Valencia et al, 2013;Schilling et al, 2014). Some of these transgenic plants also have enhanced rhizosphere acidification capacity and nutrient use efficiencies (Yang et al, 2007;Pei et al, 2012;Undurraga et al, 2012;Paez-Valencia et al, 2013;Li et al, 2014).…”

“…Pizzio, and K. Regmi, unpublished data). In addition to salt and drought tolerance, increased shoot and root biomass and yield, enhanced root acidification, and improved nutrient use efficiencies were also reported (Yang et al, 2007(Yang et al, , 2014Lv et al, 2008;Pasapula et al, 2011;Pei et al, 2012;Arif et al, 2013;Paez-Valencia et al, 2013;Li et al, 2014;Schilling et al, 2014;Wang et al, 2014). These phenotypes are not well explained by the traditional model of type I H + -PPases operating solely on the vacuole to energize the tonoplast (Martinoia et al, 2007).…”