A Novel NADPH Thioredoxin Reductase, Localized in the Chloroplast, Which Deficiency Causes Hypersensitivity to Abiotic Stress in Arabidopsis thaliana

• Published in: The Journal of biological chemistry 2004-10, Vol.279 (42), p.43821-43827
• Main Authors: Serrato, Antonio Jesús, Pérez-Ruiz, Juan Manuel, Spínola, María Cristina, Cejudo, Francisco Javier
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Arabidopsis - enzymology; Arabidopsis - growth & development; Arabidopsis - physiology; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Base Sequence; Chloroplasts - enzymology; Conserved Sequence; DNA Primers; Humans; Molecular Sequence Data; Oryza - enzymology; Oryza sativa; Phylogeny; Reverse Transcriptase Polymerase Chain Reaction; Sequence Alignment; Sequence Deletion; Sequence Homology, Amino Acid; Thioredoxin-Disulfide Reductase - genetics; Thioredoxin-Disulfide Reductase - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M404696200

Plants contain three thioredoxin systems. Chloroplast thioredoxins are reduced by ferredoxin-thioredoxin reductase, whereas the cytosolic and mitochondrial thioredoxins are reduced by NADPH thioredoxin reductase (NTR). There is high similarity among NTRs from plants, lower eukaryotes, and bacteria, which are different from mammal NTR. Here we describe the OsNTRC gene from rice encoding a novel NTR with a thioredoxin-like domain at the C terminus, hence, a putative NTR/thioredoxin system in a single polypeptide. Orthologous genes were found in other plants and cyanobacteria, but not in bacteria, yeast, or mammals. Full-length OsNTRC and constructs with truncated NTR and thioredoxin domains were expressed in Escherichia coli as His-tagged polypeptides, and a polyclonal antibody specifically cross-reacting with the OsNTRC enzyme was raised. An in vitro activity assay showed that OsNTRC is a bifunctional enzyme with both NTR and thioredoxin activity but is not an NTR/thioredoxin system. Although the OsNTRC gene was expressed in roots and shoots of rice seedlings, the protein was exclusively found in shoots and mature leaves. Moreover, fractionation experiments showed that OsNTRC is localized to the chloroplast. An Arabidopsis NTRC knock-out mutant showed growth inhibition and hypersensitivity to methyl viologen, drought, and salt stress. These results suggest that the NTRC gene is involved in plant protection against oxidative stress.