Identification and characterization of a mitochondrial thioredoxin system in plants.
Plants possess two well described thioredoxin systems: a cytoplasmic system including several thioredoxins and an NADPH-dependent thioredoxin reductase and a specific chloroplastic system characterized by a ferredoxin-dependent thioredoxin reductase. On the basis of biochemical activities, plants also are supposed to have a mitochondrial thioredoxin system as described in yeast and mammals, but no gene encoding plant mitochondrial thioredoxin or thioredoxin reductase has been identified yet. We report the characterization of a plant thioredoxin system located in mitochondria. Arabidopsis thaliana genome sequencing has revealed numerous thioredoxin genes among which we have identified AtTRX-o1, a gene encoding a thioredoxin with a potential mitochondrial transit peptide. AtTRX-o1 and a second gene, AtTRX-o2, define, on the basis of the sequence and intron positions, a new thioredoxin type up to now specific to plants. We also have characterized AtNTRA, a gene encoding a protein highly similar to the previously described cytosolic NADPH-dependent thioredoxin reductase AtNTRB but with a putative presequence for import into mitochondria. Western blot analysis of A. thaliana subcellular and submitochondrial fractions and in vitro import experiments show that AtTRX-o1 and AtNTRA are targeted to the mitochondrial matrix through their cleavable N-terminal signal. The two proteins truncated to the estimated mature forms were produced in Escherichia coli; AtTRX-o1 efficiently reduces insulin in the presence of DTT and is reduced efficiently by AtNTRA and NADPH. Therefore, the thioredoxin and the NADPH-dependent thioredoxin reductase described here are proposed to constitute a functional plant mitochondrial thioredoxin system.
Laloi
C
C
Laboratoire Génome et Développement des Plantes, Unité Mixte de Recherche Centre National de la Recherche Scientifique 5096, Université de Perpignan, 52 Avenue de Villeneuve, F-66860 Perpignan, France.
Rayapuram
N
N
Chartier
Y
Y
Grienenberger
J M
JM
Bonnard
G
G
Meyer
Y
Y
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins; D001483:Base Sequence; D001692:Biological Transport; D018744:DNA, Plant; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D017343:Genes, Plant; D008928:Mitochondria / Q000378:metabolism*; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D013347:Subcellular Fractions; D054480:Thioredoxin h; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics* / Q000378:metabolism; D013879:Thioredoxins / Q000145:classification / Q000235:genetics* / Q000378:metabolism
C442832:ATO2 protein, Arabidopsis; C504905:ATTRX1 protein, Arabidopsis; D029681:Arabidopsis Proteins; D018744:DNA, Plant; D004792:Enzyme Precursors; D010455:Peptides; D010940:Plant Proteins; D011498:Protein Precursors; D054480:Thioredoxin h; D013879:Thioredoxins; D013880:Thioredoxin-Disulfide Reductase