Redox regulation of carbon storage and partitioning in response to light and sugars (original) (raw)
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Redox regulation of chloroplast metabolism
Plant Physiology, 2020
Regulation of enzyme activity based on thiol-disulfide exchange is a regulatory mechanism in which the protein disulfide reductase activity of thioredoxins (TRXs) plays a central role. Plant chloroplasts are equipped with a complex set of up to 20 TRXs and TRX-like proteins, the activity of which is supported by reducing power provided by photosynthetically reduced ferredoxin (FDX) with the participation of a FDX-dependent TRX reductase (FTR). Therefore, the FDX–FTR–TRXs pathway allows the regulation of redox-sensitive chloroplast enzymes in response to light. In addition, chloroplasts contain an NADPH-dependent redox system, termed NTRC, which allows the use of NADPH in the redox network of these organelles. Genetic approaches using mutants of Arabidopsis (Arabidopsis thaliana) in combination with biochemical and physiological studies have shown that both redox systems, NTRC and FDX-FTR-TRXs, participate in fine-tuning chloroplast performance in response to changes in light intensi...
Photosynthesis Research, 2004
The role of the ferredoxin:thioredoxin system in the reversible light activation of chloroplast enzymes by thioldisulfide interchange with thioredoxins is now well established. Recent fruitful collaboration between biochemists and structural biologists, reflected by the shared authorship of the paper, allowed to solve the structures of all of the components of the system, including several target enzymes, thus providing a structural basis for the elucidation of the activation mechanism at a molecular level. In the present Review, these structural data are analyzed in conjunction with the information that was obtained previously through biochemical and site-directed mutagenesis approaches. The unique 4Fe-4S cluster enzyme ferredoxin:thioredoxin reductase (FTR) uses photosynthetically reduced ferredoxin as an electron donor to reduce the disulfide bridge of different thioredoxin isoforms. Thioredoxins in turn reduce regulatory disulfides of various target enzymes. This process triggers conformational changes on these enzymes, allowing them to reach optimal activity. No common activation mechanism can be put forward for these enzymes, as every thioredoxin-regulated protein undergoes specific structural modifications. It is thus important to solve the structures of the individual target enzymes in order to fully understand the molecular mechanism of the redox regulation of each of them.
Photosynthesis: Regulation by redox signalling
Current Biology, 1995
Photosynthesis is light-driven redox chemistry. Molecular redox signalling, the coupling of gene expression to electron transfer, is now implicated in the adaptation of photosynthesis to variation in light quality and quantity. Photosynthesis is the conversion of light energy into chemical energy. The primary event is light-driven electron transfer-a redox reaction-and it sets in motion a chain of electron transfers upon which all life ultimately depends. The last decade has seen huge strides forward in understanding the hardware of photosynthesis. The structure of a reaction centre, where the primary redox reaction occurs, has been solved [1]. There are now also structures available for light-harvesting proteins of plant chloroplasts [2] and purple bacteria [3], which capture photons and feed the light energy to the photosynthetic reaction centres. A structural description of a complete photosynthetic unit is, it seems, on the horizon. Crystallography yields still photographs, whereas life is, almost by definition, dynamically responsive to environmental change. For example, the number of chlorophyll molecules that harvest light for each photosynthetic reaction centre is variable. This variability provides a gain control that is turned up to increase photosynthetic efficiency in dim light, and down to postpone destructive redox chemistry in bright light. An amplifier's gain control is not an optional extra, and regulation is not an afterthought to photosynthesis: it was built into the hardware from early in its evolution. The primary redox chemistry of photosynthesis would be useless or positively destructive without it. Recent work with Rhodobacter capsulatus [4,5] confirms this suspicion, and shows that redox control over photosynthesis genes is exerted by two new members of the growing family of two-component regulatory systems. RegA is a 'response regulator', phosphorylated on aspartate by transfer of a phosphate from its partner, RegB. RegB is a 'sensor kinase', and is autophosphorylated on a histidine residue under anaerobic conditions [4,5]. Mutations in either regA or regB prevent anaerobic induction of photosynthesis genes [4]. Reg thus works like Arc, the two-component redox regulatory system that mediates aerobic respiratory control in Escherichia coli [4,6].
Current Knowledge on Mechanisms Preventing Photosynthesis Redox Imbalance in Plants
Antioxidants, 2021
Photosynthesis includes a set of redox reactions that are the source of reducing power and energy for the assimilation of inorganic carbon, nitrogen and sulphur, thus generating organic compounds, and oxygen, which supports life on Earth. As sessile organisms, plants have to face continuous changes in environmental conditions and need to adjust the photosynthetic electron transport to prevent the accumulation of damaging oxygen by-products. The balance between photosynthetic cyclic and linear electron flows allows for the maintenance of a proper NADPH/ATP ratio that is adapted to the plant’s needs. In addition, different mechanisms to dissipate excess energy operate in plants to protect and optimise photosynthesis under adverse conditions. Recent reports show an important role of redox-based dithiol–disulphide interchanges, mediated both by classical and atypical chloroplast thioredoxins (TRXs), in the control of these photoprotective mechanisms. Moreover, membrane-anchored TRX-like...
Redox-Modulation of Chloroplast Enzymes
Plant Physiology, 1991
Assimilation of C, N, and S into organic compounds requires effective and flexible cooperation among the energy-converting, tightly coupled, thylakoid-bound processes and stromal metabolism. Fluctuations of light, temperature, and changing concentrations of the various reducible substrates pose unique regulatory problems to photoautotrophic plant cells. Covalent redox modification of enzyme proteins as mediated by the ferredoxin/thioredoxin-system is suited to provide short-term adaptation of various enzymatic activities in the chloroplast. This mode of regulation is based on the continuous turnover of interconvertible enzyme
Chloroplast Redox Regulatory Mechanisms in Plant Adaptation to Light and Darkness
Frontiers in Plant Science
Light is probably the most important environmental stimulus for plant development. As sessile organisms, plants have developed regulatory mechanisms that allow the rapid adaptation of their metabolism to changes in light availability. Redox regulation based on disulfide-dithiol exchange constitutes a rapid and reversible post-translational modification, which affects protein conformation and activity. This regulatory mechanism was initially discovered in chloroplasts when it was identified that enzymes of the Calvin-Benson cycle (CBC) are reduced and active during the day and become rapidly inactivated by oxidation in the dark. At present, the large number of redox-sensitive proteins identified in chloroplasts extend redox regulation far beyond the CBC. The classic pathway of redox regulation in chloroplasts establishes that ferredoxin (Fdx) reduced by the photosynthetic electron transport chain fuels reducing equivalents to the large set of thioredoxins (Trxs) of this organelle via the activity of a Fdx-dependent Trx reductase (FTR), hence linking redox regulation to light. In addition, chloroplasts harbor an NADPH-dependent Trx reductase with a joint Trx domain, termed NTRC. The presence in chloroplasts of this NADPH-dependent redox system raises the question of the functional relationship between NTRC and the Fdx-FTR-Trx pathways. Here, we update the current knowledge of these two redox systems focusing on recent evidence showing their functional interrelationship through the action of the thioldependent peroxidase, 2-Cys peroxiredoxin (2-Cys Prx). The relevant role of 2-Cys Prxs in chloroplast redox homeostasis suggests that hydrogen peroxide may exert a key function to control the redox state of stromal enzymes. Indeed, recent reports have shown the participation of 2-Cys Prxs in enzyme oxidation in the dark, thus providing an explanation for the long-lasting question of photosynthesis deactivation during the light-dark transition.
Redox-Modulation of Chloroplast Enzymes : A Common Principle for Individual Control
PLANT PHYSIOLOGY, 1991
Assimilation of C, N, and S into organic compounds requires effective and flexible cooperation among the energy-converting, tightly coupled, thylakoid-bound processes and stromal metabolism. Fluctuations of light, temperature, and changing concentrations of the various reducible substrates pose unique regulatory problems to photoautotrophic plant cells. Covalent redox modification of enzyme proteins as mediated by the ferredoxin/thioredoxin-system is suited to provide short-term adaptation of various enzymatic activities in the chloroplast. This mode of regulation is based on the continuous turnover of interconvertible enzyme
Annals of botany, 2009
Photosynthetic electron transport is performed by a chain of redox components that are electrochemically connected in series. Its efficiency depends on the balanced action of the photosystems and on the interaction with the dark reaction. Plants are sessile and cannot escape from environmental conditions such as fluctuating illumination, limitation of CO(2) fixation by low temperatures, salinity, or low nutrient or water availability, which disturb the homeostasis of the photosynthetic process. Photosynthetic organisms, therefore, have developed various molecular acclimation mechanisms that maintain or restore photosynthetic efficiency under adverse conditions and counteract abiotic stresses. Recent studies indicate that redox signals from photosynthetic electron transport and reactive oxygen species (ROS) or ROS-scavenging molecules play a central role in the regulation of acclimation and stress responses. The underlying signalling network of photosynthetic redox control is largely...