Functional analysis of the pathways for 2-Cys peroxiredoxin reduction in Arabidopsis thaliana chloroplasts.

Photosynthesis is a process that inevitably produces reactive oxygen species, such as hydrogen peroxide, which is reduced by chloroplast-localized detoxification mechanisms one of which involves 2-Cys peroxiredoxins (2-Cys Prxs). Arabidopsis chloroplasts contain two very similar 2-Cys Prxs (denoted A and B). These enzymes are reduced by two pathways: NADPH thioredoxin reductase C (NTRC), which uses NADPH as source of reducing power; and plastidial thioredoxins (Trxs) coupled to photosynthetically reduced ferredoxin of which Trx chi is the most efficient reductant in vitro.

The quaternary structure of NADPH thioredoxin reductase C is redox-sensitive.

NADPH thioredoxin reductase C (NTRC) is a chloroplast enzyme able to conjugate NADPH thioredoxin reductase (NTR) and thioredoxin (TRX) activities for the efficient reduction of 2-Cys peroxiredoxin (2-Cys PRX). Because NADPH can be produced in chloroplasts during darkness, NTRC plays a key role for plant peroxide detoxification during the night. Here, it is shown that the quaternary structure of NTRC is highly dependent on its redox status.

NTRC new ways of using NADPH in the chloroplast.

Despite being the primary source of energy in the biosphere, photosynthesis is a process that inevitably produces reactive oxygen species. Chloroplasts are a major source of hydrogen peroxide production in plant cells; therefore, different systems for peroxide reduction, such as ascorbate peroxidase and peroxiredoxins (Prxs), are found in this organelle. Most of the reducing power required for hydrogen peroxide reduction by these systems is provided by Fd reduced by the photosynthetic electron transport chain; hence, the function of these systems is highly dependent on light.

Rice NTRC is a high-efficiency redox system for chloroplast protection against oxidative damage.

One of the mechanisms plants have developed for chloroplast protection against oxidative damage involves a 2-Cys peroxiredoxin, which has been proposed to be reduced by ferredoxin and plastid thioredoxins, Trx x and CDSP32, the FTR/Trx pathway. We show that rice (Oryza sativa) chloroplast NADPH THIOREDOXIN REDUCTASE (NTRC), with a thioredoxin domain, uses NADPH to reduce the chloroplast 2-Cys peroxiredoxin BAS1, which then reduces hydrogen peroxide. The presence of both NTR and Trx-like domains in a single polypeptide is absolutely required for the high catalytic efficiency of NTRC.

A novel NADPH thioredoxin reductase, localized in the chloroplast, which deficiency causes hypersensitivity to abiotic stress in Arabidopsis thaliana.

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.