Silencing of the Mitochondrial Ascorbate Synthesizing Enzyme l-Galactono-1,4-Lactone Dehydrogenase Affects Plant and Fruit Development in Tomato

Abstract

L-Galactono-1,4-lactone dehydrogenase (EC 1.3.2.3) catalyzes the last step in the main pathway of vitamin C (L-ascorbic acid) biosynthesis in higher plants. In this study, we first characterized the spatial and temporal expression of SlGalLDH in several organs of tomato (Solanum lycopersicum) plants in parallel with the ascorbate content. P 35S :SlgalldhRNAi silenced transgenic tomato lines were then generated using an RNAi strategy to evaluate the effect of any resulting modification of the ascorbate pool on plant and fruit development. In all P 35S :SlgalldhRNAi plants with reduced SlGalLDH transcript and activity, plant growth rate was decreased. Plants displaying the most severe effects (dwarf plants with no fruit) were excluded from further analysis. The most affected lines studied exhibited up to an 80% reduction in SlGalLDH activity and showed a strong reduction in leaf and fruit size, mainly as a consequence of reduced cell expansion. This was accompanied by significant changes in mitochondrial function and altered ascorbate redox state despite the fact that the total ascorbate content remained unchanged. By using a combination of transcriptomic and metabolomic approaches, we further demonstrated that several primary, like the tricarboxylic acid cycle, as well as secondary metabolic pathways related to stress response were modified in leaves and fruit of P 35S :Slgalldh RNAi plants. When taken together, this work confirms the complexity of ascorbate regulation and its link with plant metabolism. Moreover, it strongly suggests that, in addition to ascorbate synthesis, GalLDH could play an important role in the regulation of cell growth-related processes in plants.

Mitochondrial Malate Dehydrogenase Lowers Leaf Respiration and Alters Photorespiration and Plant Growth in Arabidopsis

“…The report that antisense of mMDH can elevate ascorbate pool size in tomato leaves and increase GL-dependent ascorbate biosynthesis rate has been interpreted as linked to these respiratory chain connections and the redox poise of the mitochondrial matrix (Nunes-Nesi et al, 2005). It has been reported that the abundance and activity of GLDH is not well correlated with foliar ascorbate levels (Bartoli et al, 2005), although RNA interference and antisense suppression of the enzyme have previously been reported to greatly reduce cellular ascorbate pools (Tabata et al, 2001;Alhagdow et al, 2007). Interestingly, a recent report has shown the capacity for GLDH to be redox regulated, particularly by glutathionylation of a particular amino acid residue (Leferink et al, 2009).…”

Potato Snakin-1 Gene Silencing Affects Cell Division, Primary Metabolism, and Cell Wall Composition

“…Millar et al, (2003) reported that L-galatono-1,4 lactone-dehydrogenase (L-GalDH), the enzyme that catalyzes the last steps in ascorbate biosynthesis, is associated with complex I of the mitochondrial electron transport chain. In turn, Alhagdow et al (2007) described that tomato plants with reduced levels of L-GalDH have significant changes in mitochondrial function, show altered ascorbate redox state, and display severe defects in leaf growth as a consequence of reduced cell expansion. Ascorbate content has also been associated with cell division.…”

Tomato GDSL1 Is Required for Cutin Deposition in the Fruit Cuticle

“…A cherry tomato variety was used to generate transgenic plants (S. lycopersicum 'West Virginia 106'). In vitro culture and growth of transgenic plants were performed as previously indicated (Alhagdow et al, 2007).…”