Journal Article

NADPH-dependent thioredoxin system constitutes a functional backup for cytosolic glutathione reductase in Arabidopsis

Schwarzländer, Markus, Meyer, Andreas J, Hell, Rüdiger, Meyer, Yves, Wirtz, Markus, Sweetlove, Lee J, Reichheld, Jean-Philippe, Marty, Laurent, Siala, Wafi, Fricker, Mark D

2009

Overview

Tight control of cellular redox homeostasis is essential for protection against oxidative damage and for maintenance of normal metabolism as well as redox signaling events. Under oxidative stress conditions, the tripeptide glutathione can switch from its reduced form (GSH) to oxidized glutathione disulfide (GSSG), and thus, forms an important cellular redox buffer. GSSG is normally reduced to GSH by 2 glutathione reductase (GR) isoforms encoded in the Arabidopsis genome, cytosolic GR1 and GR2 dual-targeted to chloroplasts and mitochondria. Measurements of total GR activity in leaf extracts of wild-type and 2 gr1 deletion mutants revealed that [almost equal to]65% of the total GR activity is attributed to GR1, whereas [almost equal to]35% is contributed by GR2. Despite the lack of a large share in total GR activity, gr1 mutants do not show any informative phenotype, even under stress conditions, and thus, the physiological impact of GR1 remains obscure. To elucidate its role in plants, glutathione-specific redox-sensitive GFP was used to dynamically measure the glutathione redox potential (EGSH) in the cytosol. Using this tool, it is shown that EGSH in gr1 mutants is significantly shifted toward more oxidizing conditions. Surprisingly, dynamic reduction of GSSG formed during induced oxidative stress in gr1 mutants is still possible, although significantly delayed compared with wild-type plants. We infer that there is functional redundancy in this critical pathway. Integrated biochemical and genetic assays identify the NADPH-dependent thioredoxin system as a backup system for GR1. Deletion of both, NADPH-dependent thioredoxin reductase A and GR1, prevents survival due to a pollen lethal phenotype.

• Publisher: National Academy of Sciences,National Acad Sciences
• Subject: Arabidopsis / Arabidopsis - enzymology / Arabidopsis - genetics / Arabidopsis Proteins / Arabidopsis Proteins - genetics / Arabidopsis Proteins - metabolism / Arabidopsis thaliana / Biochemistry / Biochemistry, Molecular Biology / Biodiversity / Bioinformatics / Biological Sciences / Cell Cycle Proteins / Cell Cycle Proteins - genetics / Cell Cycle Proteins - metabolism / Cellular Biology / Computer Science / Cytosol / Cytosol - metabolism / enzyme activity / Enzymes / Fertility / Flowers & plants / Gametophytes / Gene Knockout Techniques / Genetics / Genomics / Genotype & phenotype / glutathione / Glutathione Disulfide / Glutathione Disulfide - metabolism / Glutathione Reductase / glutathione reductase (NADPH) / Glutathione Reductase - genetics / Glutathione Reductase - metabolism / glutathione-disulfide reductase / Leaves / Life Sciences / Metabolism / Molecular biology / Molecular Networks / Mutation / NADP / NADP (coenzyme) / NADP - metabolism / Oxidation / Oxidative stress / Phenotypes / Plant breeding / Plant extracts / Plants / Plants genetics / Pollen / Pollen - enzymology / Pollen - genetics / Populations and Evolution / Quantitative Methods / Redox potential / reduction / Structural Biology / Systematics, Phylogenetics and taxonomy / Thioredoxin / thioredoxin reductase / Thioredoxin-Disulfide Reductase / Thioredoxin-Disulfide Reductase - genetics / Thioredoxin-Disulfide Reductase - metabolism / Thioredoxins / Thioredoxins - metabolism / Vegetal Biology