Overexpression of malate dehydrogenase in transgenic tobacco leaves: enhanced malate synthesis and augmented Al-resistance

Abstract

Numerous studies with transgenic plants have demonstrated that overexpression of enzymes related to organic acid metabolism under the control of CaMV 35S promoter increased organic acid exudation and Al-resistance. The synthesis of organic acids requires a large carbon skeleton supply from leaf photosynthesis. Thus, we produced transgenic tobacco overexpressing cytosolic malate dehydrogenase (MDH) cDNA from Arabidopsis thaliana (amdh) and the MDH gene from Escherichia coli (emdh), respectively, under the control of a leaf-specific light-inducible promoter (Rubisco small subunit promoter, PrbcS) in the present study. Our data indicated that an increase (120-130%) in MDH-specific activity in leaves led to an increase in malate content in the transgenic tobacco leaves and roots as well as a significant increase in root malate exudation compared with the WT plants under the acidic (pH 4.5) conditions irrespective of 300 lM Al 3? stress absence or presence. After being exposed to 25 lM Al 3? in a hydroponic solution, the transgenic plants exhibited stronger Al-tolerance than WT plants and the degree of A1 tolerance in the transgenic plants corresponded with the amount of malate secretion. When grown in an Al-stress perlite medium, the transgenic tobacco lines showed better growth than the WT plants. The results suggested that overexpression of MDH driven by the PrbcS promoter in transgenic plant leaves enhanced malate synthesis and improved Al-resistance.

Malate Synthesis and Secretion Mediated by a Manganese-Enhanced Malate Dehydrogenase Confers Superior Manganese Tolerance in Stylosanthes guianensis

“…5). Consistent with this, it has been demonstrated that malate synthesis has been increased through overexpression of cytoplasm-localized MDH in alfalfa (Medicago sativa) and tobacco (Nicotiana tabacum; Tesfaye et al, 2001;Wang et al, 2010). We found that SgMDH1 was also localized in the cytoplasm through the transient expression of SgMDH1 in Arabidopsis mesophyll protoplasts (Supplemental Fig.…”

On the role of the tricarboxylic acid cycle in plant productivity

“…Increasing organic acid exudation has been tested as a possible means to enhance Al tolerance; for example, through increasing the activities of the following enzymes: (i) citrate synthase (Barone et al 2008;Deng et al 2009;Han et al 2009); (ii) malate dehydrogenase (Tesfaye et al 2001;Wang et al 2010); (iii) malic enzyme (Sun et al 2014); (iv) pyruvate tolerance genes (such as Al-activated malate transporter 1 (AtALMT1) and multidrug and toxic compound extrusion 1 (AtMATE1)) could improve Al 3þ exclusion by associating with the exudation of organic acid (i.e., citrate, malate, or oxalate). In addition, ALS1 is implicated in Al 3þ sequestration in the vacuole after chelation of Al 3þ with OA in the cytosol.…”

Roles of Organic Acid Anion Secretion in Aluminium Tolerance of Higher Plants

“…Modulation of OA metabolism enhanced Al tolerance and secretion of citrate and/or malate in transgenic tobacco and papaya ( Carica papaya ) plants overexpressing a Pseudomonas aeruginosa CS [108], rape plants [58], and carrot ( Daucus carota ) cells [109] overexpressing a mitochondrial CS ( mCS ) from A. thaliana , Nicotiana benthamiana plants overexpressing an mCS from C. junos [24], tobacco plants overexpressing a cytosolic MDH from A. thaliana , an MDH from Escherichia coli [110] and a CS from rice mitochondria [111], alfalfa ( Medicago sativa ) plants overexpressing a alfalfa nodule-enhanced form of MDH ( neMDH ) [112], and tobacco plants overexpressing pyruvate phosphate dikinase ( PPDK , EC 2.7.9.1) gene from Mesembryanthemum crystallinum [113]. However, Delhaize et al showed that the expression of a P. aeruginosa CS in tobacco did not result in enhanced citrate accumulation or secretion, despite generating transgenic tobacco lines that expressed the CS protein at up to a 100-fold greater level than the previously described CSb lines [40, 108].…”

“…Overexpression of mitochondrial CS also resulted in increased citrate secretion and enhanced Al tolerance in A. thaliana [134], rape [58], N. benthamiana [24], and tobacco [111]. In tobacco, overexpression of cytosolic MDH genes from A. thaliana and from E. coli led to increased malate secretion and enhanced Al tolerance [110]. Zhang et al reported that overexpression of a C. junos MDH in tobacco conferred Al tolerance [135].…”