Posttranslational Influence of NADPH-Dependent Thioredoxin Reductase C on Enzymes in Tetrapyrrole Synthesis

• Published in: Plant physiology (Bethesda) Vol. 162; no. 1; pp. 63 - 73
• Main Authors: Richter, Andreas S., Peter, Enrico, Rothbart, Maxi, Schlicke, Hagen, Toivola, Jouni, Rintamäki, Eevi, Grimm, Bernhard
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01-05-2013
• Subjects: Arabidopsis - enzymology; Arabidopsis - genetics; Arabidopsis - metabolism; Arabidopsis Proteins - genetics; Arabidopsis Proteins - metabolism; BIOCHEMISTRY AND METABOLISM; Biological and medical sciences; Biosynthesis; Chloroplasts; Chloroplasts - enzymology; Chloroplasts - genetics; Chloroplasts - metabolism; Enzymes; Fundamental and applied biological sciences. Psychology; Gene Expression Regulation, Plant; Light; Methyltransferases; NADP - genetics; NADP - metabolism; Oxidation-Reduction; Peroxiredoxins; Physiological regulation; Plant Leaves - enzymology; Plant Leaves - genetics; Plant Leaves - metabolism; Plant physiology and development; Plants; Plastids; Plastids - enzymology; Plastids - genetics; Plastids - metabolism; Proteins; Protoporphyrins - genetics; Protoporphyrins - metabolism; Seedlings; Seedlings - enzymology; Seedlings - genetics; Seedlings - metabolism; Tetrapyrroles; Tetrapyrroles - genetics; Tetrapyrroles - metabolism; Thioredoxin; Thioredoxin-Disulfide Reductase - chemistry; Thioredoxin-Disulfide Reductase - genetics; Thioredoxin-Disulfide Reductase - metabolism; Thioredoxins - genetics; Thioredoxins - metabolism; NADPH; Oxidoreductases; Plant physiology; Thioredoxin; Enzyme; Reductase
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.113.217141

The NADPH-dependent thioredoxin reductase C (NTRC) is involved in redox-related regulatory processes in chloroplasts and nonphotosynthetic active plastids. Together with 2-cysteine peroxiredoxin, it forms a two-component peroxide-detoxifying system that acts as a reductant under stress conditions. NTRC stimulates in vitro activity of magnesium protoporphyrin IX monomethylester (MgPMME) cyclase, most likely by scavenging peroxides. Reexamination of tetrapyrrole intermediate levels of the Arabidopsis (Arabidopsis thaliana) knockout ntrc reveals lower magnesium protoporphyrin IX (MgP) and MgPMME steadystate levels, the substrate and the product of MgP methyltransferase (CHLM) preceding MgPMME cyclase, while MgP strongly accumulates in mutant leaves after 5-aminolevulinic acid feeding. The ntrc mutant has a reduced capacity to synthesize 5-aminolevulinic acid and reduced CHLM activity compared with the wild type. Although transcript levels of genes involved in chlorophyll biosynthesis are not significantly altered in 2-week-old ntrc seedlings, the contents of glutamyl-transfer RNA reductasel (GluTR1) and CHLM are reduced. Bimolecular fluorescence complementation assay confirms a physical interaction of NTRC with GluTRl and CHLM. While ntrc contains partly oxidized CHLM, the wild type has only reduced CHLM. As NTRC also stimulates CHLM activity in vitro, it is proposed that NTRC has a regulatory impact on the redox status of conserved cysteine residues of CHLM. It is hypothesized that a deficiency of NTRC leads to a lower capacity to reduce cysteine residues of GluTR1 and CHLM, affecting the stability and, thereby, altering the activity in the entire tetrapyrrole synthesis pathway.