New insights into the reduction systems of plastidial thioredoxins point out the unique properties of thioredoxin z from Arabidopsis

Bohrer, Anne-Sophie; Massot, Vincent; Innocenti, Gilles; Reichheld, Jean‐Philippe; Issakidis‐Bourguet, Emmanuelle; Vanacker, Hélène

doi:10.1093/jxb/ers283

Cited by 55 publications

(73 citation statements)

References 43 publications

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“…7 and Fig. S8D), the Trx-z redox state in vivo could not be determined in this study, at least partly due to the low expression level in mature leaves (40,52,56) and the smeared nature of the protein band in the immunoblotting analysis (Figs. S8B and S9C).…”

Section: Cooperative Redox Regulation By the Ftr/trx And Ntrc Pathwaymentioning

confidence: 85%

Two distinct redox cascades cooperatively regulate chloroplast functions and sustain plant viability

Yoshida

Hisabori

2016

Proc. Natl. Acad. Sci. U.S.A.

120

182

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The thiol-based redox regulation system is believed to adjust chloroplast functions in response to changes in light environments. A redox cascade via the ferredoxin-thioredoxin reductase (FTR)/thioredoxin (Trx) pathway has been traditionally considered to serve as a transmitter of light signals to target enzymes. However, emerging data indicate that chloroplasts have a complex redox network composed of diverse redox-mediator proteins and target enzymes. Despite extensive research addressing this system, two fundamental questions are still unresolved: How are redox pathways orchestrated within chloroplasts, and why are chloroplasts endowed with a complicated redox network? In this report, we show that NADPH-Trx reductase C (NTRC) is a key redox-mediator protein responsible for regulatory functions distinct from those of the classically known FTR/Trx system. Target screening and subsequent biochemical assays indicated that NTRC and the Trx family differentially recognize their target proteins. In addition, we found that NTRC is an electron donor to Trx-z, which is a key regulator of gene expression in chloroplasts. We further demonstrate that cooperative control of chloroplast functions via the FTR/Trx and NTRC pathways is essential for plant viability. Arabidopsis double mutants impaired in FTR and NTRC expression displayed lethal phenotypes under autotrophic growth conditions. This severe growth phenotype was related to a drastic loss of photosynthetic performance. These combined results provide an expanded map of the chloroplast redox network and its biological functions.T o preserve the integrity and efficiency of photosynthesis and other metabolic reactions, chloroplast enzymes need to be flexibly and appropriately controlled in response to changes in light environments. The photosynthetic electron transport chain in the chloroplast thylakoid membrane converts light energy into chemical energy, which is captured and stored in ATP and NADPH. These molecules are primarily consumed by the Calvin-Benson cycle in the stroma, but part of the reducing power is used for other metabolic reactions in chloroplasts (e.g., nitrogen and sulfur metabolism). One pathway for the reducing power is the redox cascade, mediated by ferredoxin-thioredoxin reductase (FTR) and thioredoxin (Trx). In this system, FTR receives reducing power from the light-driven photosynthetic electron transport chain via ferredoxin and then donates the reducing power to Trx. A reduced form of Trx subsequently transfers reducing power to target proteins through a dithiol-disulfide exchange reaction, allowing the targets to modulate the enzymatic activities. The redox cascade via the FTR/Trx pathway provides the basis for thiol-based redox regulation in chloroplasts and ensures light-responsive control of chloroplast functions (1, 2).The FTR/Trx pathway has been considered the only pathway regulating redox reactions in chloroplasts. Information about its target proteins has also been limited to a specific set of lightactivated enzymes, such as some enzy...

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Section: Cooperative Redox Regulation By the Ftr/trx And Ntrc Pathwaymentioning

confidence: 85%

Two distinct redox cascades cooperatively regulate chloroplast functions and sustain plant viability

Yoshida

Hisabori

2016

Proc. Natl. Acad. Sci. U.S.A.

120

182

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“…6). Although CHLM was not identified as a target of TRX-dependent reduction, it could be speculated that the loss of a specific redox regulator can at least partially be compensated by other redox modulators (Bohrer et al, 2012;Luo et al, 2012;Thormählen et al, 2013). In principle, similar AMS experiments with GluTR indicated a larger amount of reduced GluTR in wild-type extracts in comparison with ntrc, but GluTR in nonreducing conditions migrates in high-M r molecular polymeric aggregates, which disappeared only when protein extracts were reduced with DTT (Supplemental Fig.…”

Section: Ntrc Is a Posttranslational Regulator Of Chl Biosynthesismentioning

confidence: 99%

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

Richter

Peter²,

Rothbart³

et al. 2013

Plant Physiology

115

112

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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 reductase1 (GluTR1) and CHLM are reduced. Bimolecular fluorescence complementation assay confirms a physical interaction of NTRC with GluTR1 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.During the last decades, almost all enzymes of tetrapyrrole biosynthesis and their complex network of transcriptional regulation have been comprehensively studied (Tanaka et al., 2011). These studies revealed a complex control of the expression of genes encoding enzymes in the light-regulated chlorophyll (Chl)-synthesizing branch of tetrapyrrole metabolism. In brief, 5-aminolevulinic acid (ALA) is synthesized in a transfer RNA (tRNA) GLU -mediated pathway, and eight molecules of ALA are ultimately converted in a series of enzymatic steps to protoporphyrin IX. The polymeric magnesium (Mg) chelatase complex consisting of the three different subunits CHLH, CHLI, and CHLD directs protoporphyrin IX into the Mg branch of tetrapyrrole biosynthesis. Methylation of magnesium protoporphyrin (MgP) by MgP methyltransferase (CHLM) at the C13 of pyrrole ring C initiates the formation of the typical fifth ring. The product of this step, magnesium protoporphyrin monomethylester (MgPMME), is then converted to divinyl protochlorophyllide (PChlide) by an oxidative cyclase complex. NADPH:protochlorophyllide oxidoreductase (POR) synthesizes chlorophyllide (Chlide). PChlide and Chlide are most likely the main substrates of a divinyl reductase that reduces the C7-C8 double bond, forming a monovinyl product. The two final steps of Chl a and b synthesis are likely ...

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“…Its catalytic unit is a homodimer, transferring electrons from NTR to Trx domains via intersubunit pathways . In vitro studies suggest that NTRC is a Trx with its own Trx reductase, because it has not been shown to interact with other free Trxs (Pérez-Ruiz et al, 2006;Bohrer et al, 2012).In chloroplasts, Trxs are reduced via Fdx-Trx reductase in a light-dependent manner, using photosynthetic electrons provided by Fdx. The Fdx-Trx system with Trxs f and m was originally discovered as a mechanism for the regulation of the Calvin-Benson cycle, ATP synthesis, and NADPH export in response to light-dark changes (Buchanan et al, 1979;Buchanan, 1980).…”

mentioning

confidence: 99%

“…Because most of these effects were operational in the dark, this suggests a role of NTRC to regulate these pathways independently of light. In addition to the NADPH-dependent NTRC system, 2-Cys Prx and AGPase have also been found to be regulated by the light-dependent Fdx-Trx system with Trx x (Collin et al, 2003;Bohrer et al, 2012) and Trx f1 (Thormählen et al, 2013), respectively. However, little is known on the interrelation of lightand NADPH-dependent chloroplast redox systems in regulating these targets.…”

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confidence: 99%

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Thioredoxin f1 and NADPH-dependent thioredoxin reductase C have overlapping functions in regulating photosynthetic metabolism and plant growth in response to varying light conditions

et al. 2015

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Two different thiol redox systems exist in plant chloroplasts, the ferredoxin-thioredoxin (Trx) system, which depends on ferredoxin reduced by the photosynthetic electron transport chain and, thus, on light, and the NADPH-dependent Trx reductase C (NTRC) system, which relies on NADPH and thus may be linked to sugar metabolism in the dark. Previous studies suggested, therefore, that the two different systems may have different functions in plants. We now report that there is a previously unrecognized functional redundancy of Trx f1 and NTRC in regulating photosynthetic metabolism and growth. In Arabidopsis (Arabidopsis thaliana) mutants, combined, but not single, deficiencies of Trx f1 and NTRC led to severe growth inhibition and perturbed light acclimation, accompanied by strong impairments of Calvin-Benson cycle activity and starch accumulation. Light activation of key enzymes of these pathways, fructose-1,6-bisphosphatase and ADP-glucose pyrophosphorylase, was almost completely abolished. The subsequent increase in NADPH-NADP + and ATP-ADP ratios led to increased nitrogen assimilation, NADP-malate dehydrogenase activation, and light vulnerability of photosystem I core proteins. In an additional approach, reporter studies show that Trx f1 and NTRC proteins are both colocalized in the same chloroplast substructure. Results provide genetic evidence that light-and NADPH-dependent thiol redox systems interact at the level of Trx f1 and NTRC to coordinately participate in the regulation of the Calvin-Benson cycle, starch metabolism, and growth in response to varying light conditions. Reversible disulfide bond formation between two Cys residues regulates structure and function of many proteins in diverse organisms (Cook and Hogg, 2013). Thiol disulfide exchange is controlled by thioredoxins (Trxs), which are small proteins containing a redoxactive disulfide group in their active site (Holmgren, 1985;Baumann and Juttner, 2002). The latter can be reduced to a dithiol by Trx reductases using NADPH or ferredoxin (Fdx) as electron donors. Due to their low redox midpoint potential, reduced Trxs are able to reductively cleave disulfide bonds in many target proteins and, thus, modulate their functions.Plants contain the most versatile Trx system found in all organisms with respect to the multiplicity of different isoforms and reduction systems (Buchanan and Balmer, 2005;Nikkanen and Rintamäki, 2014;Geigenberger and Fernie, 2014). The Arabidopsis (Arabidopsis thaliana) genome contains a complex family of Trxs, including up to 20 different isoforms grouped into seven subfamilies (Schürmann and Buchanan, 2008;Dietz and Pfannschmidt, 2011). Trxs f1-2, m1-4, x, y1-2, and z are located exclusively in the chloroplast, and Trx o is located exclusively in the mitochondria, while the eight Trx h representatives are distributed between the cytosol, nucleus, endoplasmic reticulum, and mitochondria (Meyer et al., 2012). The different Trxs can be reduced by two different redox systems, dependent on Fdx and Fdx-Trx reductase in the chlorop...

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New insights into the reduction systems of plastidial thioredoxins point out the unique properties of thioredoxin z from Arabidopsis

Cited by 55 publications

References 43 publications

Two distinct redox cascades cooperatively regulate chloroplast functions and sustain plant viability

Two distinct redox cascades cooperatively regulate chloroplast functions and sustain plant viability

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

Thioredoxin f1 and NADPH-dependent thioredoxin reductase C have overlapping functions in regulating photosynthetic metabolism and plant growth in response to varying light conditions

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