Abstract
Thioredoxins (TRXs) are protein oxidoreductases that control the structure and function of cellular proteins by cleavage of a disulphide bond between the side chains of two cysteine residues. Oxidized thioredoxins are reactivated by thioredoxin reductases (TR) and a TR-dependent reduction of TRXs is called a thioredoxin system. Thiol-based redox regulation is an especially important mechanism to control chloroplast proteins involved in biogenesis, in regulation of light harvesting and distribution of light energy between photosystems, in photosynthetic carbon fixation and other biosynthetic pathways, and in stress responses of plants. Of the two plant plastid thioredoxin systems, the ferredoxin-dependent system relays reducing equivalents from photosystem I via ferredoxin and ferredoxin-thioredoxin reductase (FTR) to chloroplast proteins, while NADPH-dependent thioredoxin reductase (NTRC) forms a complete thioredoxin system including both reductase and thioredoxin domains in a single polypeptide. Chloroplast thioredoxins transmit environmental light signals to biochemical reactions, which allows fine tuning of photosynthetic processes in response to changing environmental conditions. In this paper we focus on the recent reports on specificity and networking of chloroplast thioredoxin systems and evaluate the prospect of improving photosynthetic performance by modifying the activity of thiol regulators in plants.This article is part of the themed issue ‘Enhancing photosynthesis in crop plants: targets for improvement'.
Highlights
Photosynthesis comprises light-driven reactions in thylakoid membranes producing NADPH and ATP, and a CO2 fixation pathway storing the energy captured by light reactions into sugar phosphates
NADPH-dependent thioredoxin reductase (NTRC), TRXf, and TRXm interact with the same biosynthetic enzymes, and the antioxidative system based on peroxiredoxins is maintained by TRXx, y, and NTRC [11 –17]
We have shown that the high accumulation of oxidized 2-Cys-PRXs in Arabidopsis leaves lacking functional NTRC correlates with the oxidation of redoxregulated Calvin–Benson enzymes [17], suggesting that oxidized 2-Cys-PRXs may act as a general oxidizing loop for redox-regulated enzymes in the chloroplast [39]
Summary
Photosynthesis comprises light-driven reactions in thylakoid membranes producing NADPH and ATP, and a CO2 fixation pathway storing the energy captured by light reactions into sugar phosphates. The discovery of the chloroplast NADPH-dependent thioredoxin system (NTRC) [6] and novel TRX types [7] has indicated that in addition to light, chloroplast TRX systems control chloroplast development, respond to fluctuations in light intensity, transfer signals between chloroplast compartments and are involved in antioxidant networks (reviewed in [2 –4,8–10]). Another intriguing issue is that some chloroplast proteins are targets of several TRXs. For example, NTRC, TRXf, and TRXm interact with the same biosynthetic enzymes, and the antioxidative system based on peroxiredoxins is maintained by TRXx, y, and NTRC [11 –17]. We review the prospect of improving photosynthetic performance by modifying the activity of chloroplast TRX systems based on the recent reports on the interaction, networking and overlapping functions of TRXs
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