title: Light-dependent regulation of ascorbate in tomato by a monodehydroascorbate reductase localized in peroxisomes and the cytosol.
abstract: Ascorbate is a powerful antioxidant in plants, and its levels are an important quality criteria in commercial species. Factors influencing these levels include environmental variations, particularly light, and the genetic control of its biosynthesis, recycling and degradation. One of the genes involved in the recycling pathway encodes a monodehydroascorbate reductase (MDHAR), an enzyme catalysing reduction of the oxidized radical of ascorbate, monodehydroascorbate, to ascorbate. In plants, MDHAR belongs to a multigene family. Here, we report the presence of an MDHAR isoform in both the cytosol and peroxisomes and show that this enzyme negatively regulates ascorbate levels in Solanum lycopersicum (tomato). Transgenic lines overexpressing MDHAR show a decrease in ascorbate levels in leaves, whereas lines where MDHAR is silenced show an increase in these levels in both fruits and leaves. Furthermore, the intensity of these differences is light dependent. The unexpected effect of this MDHAR on ascorbate levels cannot be explained by changes in the expression of Smirnoff-Wheeler pathway genes, or the activity of enzymes involved in degradation (ascorbate peroxidase) or recycling of ascorbate (dehydroascorbate reductase and glutathione reductase), suggesting a previously unidentified mechanism regulating ascorbate levels.
authors.affiliation: INRA, UR1052, Génétique et amélioration des fruits et légumes, Domaine St Maurice, Allée des Chênes, Montfavet, France.
authors.forename: Noé
authors.initials: N
authors.lastname: Gest
authors.forename: Cécile
authors.initials: C
authors.lastname: Garchery
authors.forename: Hélène
authors.initials: H
authors.lastname: Gautier
authors.forename: Ana
authors.initials: A
authors.lastname: Jiménez
authors.forename: Rebecca
authors.initials: R
authors.lastname: Stevens
mesh_terms: D001205:Ascorbic Acid / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology; D005638:Fruit / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008027:Light; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D020675:Peroxisomes / Q000201:enzymology*; D018515:Plant Leaves / Q000378:metabolism
chemical_list: D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); D001205:Ascorbic Acid