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This article focuses on urban development in Conakry, the capital of the Republic of Guinea, to reflect on the progress and innovation represented by the increasingly widespread application of the World Bank’s international environmental and social standards with respect to the consideration of local stakeholders in governance processes. It also examines the paradoxical fact that, within the same territory, the variable application of those standards can create strong inequalities, particularly in the treatment of people involuntarily displaced by projects of public interest. This article underlines that the funding source of a project often determines whether international standards are adhered to. These differences in the consideration of people affected by projects may thus depend on criteria that are difficult for them to understand and are largely beyond their control.

International audience; Stomatal movements via the control of gas exchanges determine plant growth in relation to environmental stimuli through a complex signalling network involving reactive oxygen species that lead to post‐translational modifications of Cys and Met residues, and alter protein activity and/or conformation. Thiol‐reductases (TRs), which include thioredoxins, glutaredoxins (GRXs) and peroxiredoxins (PRXs), participate in signalling pathways through the control of Cys redox status in client proteins. Their involvement in stomatal functioning remains poorly characterized. By performing a mass spectrometry‐based proteomic analysis, we show that numerous thiol reductases, like PRXs, are highly abundant in guard cells. When investigating various Arabidopsis mutants impaired in the expression of TR genes, no change in stomatal density and index was noticed. In optimal growth conditions, a line deficient in cytosolic NADPH‐thioredoxin reductases displayed higher stomatal conductance and lower leaf temperature evaluated by thermal infrared imaging. In contrast, lines deficient in plastidial 2‐CysPRXs or type‐II GRXs exhibited compared to WT reduced conductance and warmer leaves in optimal conditions, and enhanced stomatal closure in epidermal peels treated with abscisic acid or hydrogen peroxide. Altogether, these data strongly support the contribution of thiol redox switches within the signalling network regulating guard cell movements and stomatal functioning.

Impact assessments and action plans are mandatory during the feasibility phases of mining projects, but are too often perceived as simple legal obligations to obtain development permits. However, these steps must be considered as planning tools for the implementation of a mining project over its entire duration. Adapting these performance standards to actual mining contexts and integrating operational requirements into these documents can simultaneously rationalise costs and optimise efficiency while providing genuine tools for project development. This positioning has the virtue of meeting the requirements of both national legislation and international standards as well as the operational requirements of the project, while optimising investments in all the prerequisites of the feasibility phases. Drawing on findings from research on and assessments of the mining sector in Guinea during 2011–2020, we explore the paradoxes that arise from the objectives of Environmental and Social Impact Assessment (ESIA) regulations and the constraints that they generate at each phase of mining project development. Based on our analysis, we suggest ways to use these standards to improve the integration of mining projects in their territories while respecting environmental and social sustainability.

L’importance de nouveaux projets d'exploitation miniere industrielle en Afrique a souleve de nombreuses questions a propos des synergies entre les secteurs prive et public dans le cadre du developpement de tels projets. Les relations adoptees par les societes minieres et les Etats et les inegalites entre les differents acteurs participent a creer le flou dans la relation public-prive et sa perception. A travers des travaux de recherche et d’expertise realises en Afrique de l’Ouest entre 2008 et 2019, nous reexaminons les roles et les responsabilites des differents acteurs dans la creation de synergies entre les secteurs prive et public. Nous explorerons les strategies deployees des deux cotes pour comprendre les interets qui influencent la mise en œuvre des politiques. Classification JEL : F23, G38, L72, M14, O13

International audience

The levels of methionine sulfoxide (MetO) and the abundances of methionine sulfoxide reductases (Msrs) were reported as important for the desiccation tolerance of Acer seeds. To determine whether the MetO/Msrs system is related to reactive oxygen species (ROS) and involved in the regulation of germination in orthodox and recalcitrant seeds, Norway maple and sycamore were investigated. Changes in water content, MetO content, the abundance of MsrB1 and MsrB2 in relation to ROS content and the activity of reductases depending on nicotinamide adenine dinucleotides were monitored. Acer seeds differed in germination speed&mdash, substantially higher in sycamore&mdash, hydration dynamics, levels of hydrogen peroxide, superoxide anion radicals (O2&bull, &minus, ) and hydroxyl radicals (&bull, OH), which exhibited peaks at different stages of germination. The MetO level dynamically changed, particularly in sycamore embryonic axes, where it was positively correlated with the levels of O2&bull, and the abundance of MsrB1 and negatively with the levels of &bull, OH and the abundance of MsrB2. The MsrB2 abundance increased upon sycamore germination, in contrast, it markedly decreased in Norway maple. We propose that the ROS&ndash, MetO&ndash, Msr redox system, allowing balanced Met redox homeostasis, participates in the germination process in sycamore, which is characterized by a much higher speed compared to Norway maple.

International audience; Two related tree species, Norway maple (Acer platanoides L.) and sycamore (Acer pseudoplatanus L.), produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. We compared the seeds of these two species to characterize the developmentally driven changes in the levels of peptide-bound methionine sulfoxide (MetO) and the abundance of methionine sulfoxide reductases (Msrs) B1 and B2, with respect to the cellular redox environment. Protein oxidation at the Met level was dynamic only in Norway maple seeds, and the reduced MsrB2 form was detected only in this species. Cell redox status, characterized by the levels of reduced and oxidized ascorbate, glutathione, and nicotinamide adenine dinucleotide (NAD)/phosphate (NADP), was clearly more reduced in the Norway maple seeds than in the sycamore seeds. Clear correlations between MetO levels, changes in water content and redox status were reported in orthodox Acer seeds. The abundance of Msrs was correlated in both species with redox determinants, mainly ascorbate and glutathione. Our data suggest that MsrB2 is associated with the acquisition of desiccation tolerance and that ascorbate might be involved in the redox pathway enabling the regeneration of Msr via intermediates that are not known yet.

Norway maple and sycamore produce desiccation-tolerant (orthodox) and desiccation-sensitive (recalcitrant) seeds, respectively. Drying affects reduction and oxidation (redox) status in seeds. Oxidation of methionine to methionine sulfoxide (MetO) and reduction via methionine sulfoxide reductases (Msrs) have never been investigated in relation to seed desiccation tolerance. MetO levels and the abundance of Msrs were investigated in relation to levels of reactive oxygen species (ROS) such as hydrogen peroxide, superoxide anion radical and hydroxyl radical (&bull, OH), and the levels of ascorbate and glutathione redox couples in gradually dried seeds. Peptide-bound MetO levels were positively correlated with ROS concentrations in the orthodox seeds. In particular, &bull, OH affected MetO levels as well as the abundance of MsrB2 solely in the embryonic axes of Norway maple seeds. In this species, MsrB2 was present in oxidized and reduced forms, and the latter was favored by reduced glutathione and ascorbic acid. In contrast, sycamore seeds accumulated higher ROS levels. Additionally, MsrB2 was oxidized in sycamore throughout dehydration. In this context, the three elements &bull, OH level, MetO content and MsrB2 abundance, linked together uniquely to Norway maple seeds, might be considered important players of the redox network associated with desiccation tolerance.

International audience

ZPR1 proteins belong to the C4-type of zinc finger coordinators known in animal cells to interact with other proteins and participate in cell growth and proliferation. In contrast, the current knowledge regarding plant ZPR1 proteins is very scarce. Here, we identify a novel potato nuclear factor belonging to this family and named StZPR1. StZPR1 is specifically expressed in photosynthetic organs during the light period, and the ZPR1 protein is located in the nuclear chromatin fraction. From modelling and experimental analyses, we reveal the StZPR1 ability to bind the circadian DNA cis motif 'CAACAGCATC', named CIRC and present in the promoter of the clock-controlled double B-box StBBX24 gene, the expression of which peaks in the middle of the day. We found that transgenic lines silenced for StZPR1 expression still display a 24 h period for the oscillation of StBBX24 expression but delayed by 4 h towards the night. Importantly, other BBX genes exhibit altered circadian regulation in these lines. Our data demonstrate that StZPR1 allows fitting of the StBBX24 circadian rhythm to the light period and provide evidence that ZPR1 is a novel clock-associated protein in plants necessary for the accurate rhythmic expression of specific circadian-regulated genes.

L’autosuffisance en riz est un mythe persistant en Republique de Guinee. Depuis l’epoque coloniale, cet objectif a ete continuellement repris par les differentes Republiques qui se sont succedees, au point d’etre encore encourage de nos jours par des bailleurs qui interviennent dans le developpement agricole. Cependant, le contexte mondialise, l’importation de riz d’Asie, l’organisation sociale locale, les itineraires techniques et les strategies economiques des menages rendent peu justifiable cette volonte. Cet article propose de mettre dans une perspective diachronique ces politiques et de les confronter aux realites locales pour questionner leur pertinence, en se basant sur un ensemble de travaux realises en Guinee Maritime entre 2003 et 2016.

Plant 2-Cys peroxiredoxins (2-CysPRXs) are abundant plastidial thiol-peroxidases involved in key signaling processes such as photosynthesis deactivation at night. Their functions rely on the redox status of their two cysteines and on the enzyme quaternary structure, knowledge of which remains poor in plant cells. Using ex vivo and biochemical approaches, we thoroughly characterized the 2-CysPRX dimer/monomer distribution, hyperoxidation level, and thiol content in Arabidopsis, barley, and potato in relation to the light cycle. Our data reveal that the enzyme hyperoxidization level and its distribution as a dimer and monomer vary through the light cycle in a species-dependent manner. A differential susceptibility to hyperoxidation was observed for the two Arabidopsis 2-CysPRX isoforms and among the proteins of the three species, and was associated to sequence variation in hyperoxidation resistance motifs. Alkylation experiments indicate that only a minor fraction of the 2-CysPRX pool carries one free thiol in the three species, and that this content does not change during the light period. We conclude that most plastidial 2-CysPRX forms are oxidized and propose that there is a species-dependent variability in their functions since dimer and hyperoxidized forms fulfill distinct roles regarding direct oxidation of partners and signal transmission.

Peroxiredoxins are ubiquitous thioredoxin-dependent peroxidases presumed to display, upon environmental constraints, a chaperone function resulting from a redox-dependent conformational switch. In this work, using biochemical and genetic approaches, we aimed to unravel the factors regulating the redox status and the conformation of the plastidial 2-Cys peroxiredoxin (2-Cys PRX) in plants. In Arabidopsis, we show that in optimal growth conditions, the overoxidation level mainly depends on the availability of thioredoxin-related electron donors, but not on sulfiredoxin, the enzyme reducing the 2-Cys PRX overoxidized form. We also observed that upon various physiological temperature, osmotic and light stress conditions, the overoxidation level and oligomerization status of 2-Cys PRX can moderately vary depending on the constraint type. Further, no major change was noticed regarding protein conformation in water-stressed Arabidopsis, barley and potato plants, whereas species-dependent up- and down-variations in overoxidation were observed. In contrast, both 2-Cys PRX overoxidation and oligomerization were strongly induced during a severe oxidative stress generated by methyl viologen. From these data, revealing that the oligomerization status of plant 2-Cys PRX does not exhibit important variation and is not tightly linked to the protein redox status upon physiologically relevant environmental constraints, the possible in planta functions of 2-Cys PRX are discussed.

Double B-box zinc finger (DBB) proteins are recently identified plant transcription regulators that participate in the response to sodium chloride-induced stress in arabidopsis plants. Little is known regarding their subcellular localization and expression patterns, particularly in relation to other osmotic constraints and the day/night cycle. This study investigated natural variations in the amount of a Solanum DBB protein, SsBBX24, during plant development, and also under various environmental constraints leading to cell dehydration in relation to the circadian clock and the time of day.SsBBX24 transcript and protein abundance in various organs of phytotron-grown Solanum tuberosum and S. sogarandinum plants were investigated at different time points of the day and under various osmotic constraints. The intracellular location of SsBBX24 was determined by western blot analysis of subcellular fractions.Western blot analysis of SsBBX24 protein revealed that it was located in the nucleus at the beginning of the light period and in the cytosol at the end, suggesting movement ('trafficking') during the light phase. SsBBX24 gene expression exhibited circadian cycling under control conditions, with the highest and lowest abundances of both transcript and protein occurring 8 and 18 h after dawn, respectively. Exposing Solanum plants to low temperature, salinity and polyethylene glycol (PEG), but not to drought, disturbed the circadian regulation of SsBBX24 gene expression at the protein level. SsBBX24 transcript and protein accumulated in Solanum plants in response to salt and PEG treatments, but not in response to low temperature or water deficit. Most interestingly, the time of the day modulated the magnitude of SsBBX24 expression in response to high salt concentration.The interplay between circadian rhythm and osmotic constraints in the regulation of the expression of a Solanum DBB transcriptional regulator is demonstrated. It is proposed that stress-dependent, post-transcriptional mechanisms alter the regulation by the circadian clock of the amount of SsBBX24.

Peroxiredoxins are ubiquitous thiol-dependent peroxidases for which chaperone and signaling roles have been reported in various types of organisms in recent years. In plants, the peroxidase function of the two typical plastidial 2-Cys peroxiredoxins (2-Cys PRX A and B) has been highlighted while the other functions, particularly in ROS-dependent signaling pathways, are still elusive notably due to the lack of knowledge of interacting partners. Using an ex vivo approach based on co-immunoprecipitation of leaf extracts from Arabidopsis thaliana wild-type and mutant plants lacking 2-Cys PRX expression followed by mass spectrometry-based proteomics, 158 proteins were found associated with 2-Cys PRXs. Already known partners like thioredoxin-related electron donors (Chloroplastic Drought-induced Stress Protein of 32kDa, Atypical Cysteine Histidine-rich Thioredoxin 2) and enzymes involved in chlorophyll synthesis (Protochlorophyllide OxidoReductase B) or carbon metabolism (Fructose-1,6-BisPhosphatase) were identified, validating the relevance of the approach. Bioinformatic and bibliographic analyses allowed the functional classification of the identified proteins and revealed that more than 40% are localized in plastids. The possible roles of plant 2-Cys PRXs in redox signaling pathways are discussed in relation with the functions of the potential partners notably those involved in redox homeostasis, carbon and amino acid metabolisms as well as chlorophyll biosynthesis.

ZPR1 proteins belong to the C4-type of zinc finger coordinators known in animal cells to interact with other proteins and participate in cell growth and proliferation. In contrast, the current knowledge regarding plant ZPR1 proteins is very scarce. Here, we identify a novel potato nuclear factor belonging to this family and named StZPR1. StZPR1 is specifically expressed in photosynthetic organs during the light period, and the ZPR1 protein is located in the nuclear chromatin fraction. From modelling and experimental analyses, we reveal the StZPR1 ability to bind the circadian DNA cis motif 'CAACAGCATC', named CIRC and present in the promoter of the clock-controlled double B-box StBBX24 gene, the expression of which peaks in the middle of the day. We found that transgenic lines silenced for StZPR1 expression still display a 24 h period for the oscillation of StBBX24 expression but delayed by 4 h towards the night. Importantly, other BBX genes exhibit altered circadian regulation in these lines. Our data demonstrate that StZPR1 allows fitting of the StBBX24 circadian rhythm to the light period and provide evidence that ZPR1 is a novel clock-associated protein in plants necessary for the accurate rhythmic expression of specific circadian-regulated genes.

Phosphatidylinositol transfer proteins (PITPs) include a large group of proteins implicated in the non-vesicular traffic of phosphatidylinositol (PI) between membranes. In yeast, the structure and function of the PITP Sec14-p protein have been well characterized. In contrast, the knowledge on plant PITP proteins is very scarce. In this work, we characterized a novel type of PITP protein in barley named HvSec14p and related to the yeast Sec14-p protein. Our data reveal that HvSec14p consists of only the Sec14p-domain structurally homologous to the yeast phosphoinositide binding domain. We show that HvSec14p expression is up-regulated at both transcript and protein levels at specific stages of development during seed formation and germination, and in leaves of a drought-tolerant barley genotype under osmotic constraints. Modeling analyses of the protein three-dimensional structure revealed its capacity to dock the phosphoinositides, PtdIns(3)P, PtdIns(4)P, PtdIns(5)P and PtdIns(3,5)P2. Consistently, the recombinant HvSec14p protein is able to bind in vitro most PIP types, the highest affinity being observed with PtdIns(3,5)P2. Based on the high gene expression at specific developmental stages and in drought-tolerant barley genotypes, we propose that HvSec14p plays essential roles in the biogenesis of membranes in expanding cells and in their preservation under osmotic stress conditions.

The arrival of mining investments in Guinea lead to an important influx of migrants and changes throughout the region. Under international and national regulations, mining companies are obliged to mitigate their negative impacts, including migration. Based on an analysis of several mining projects since 2008, we have assessed the contribution of mining companies to regional development and through that to the overall process of governing urban Africa. A common practice is to develop public–private collaboration by the creation of tools and guidelines for regional development. But this type of collaboration modifies the established balance of local power. Mining companies may be perceived as social agents instead of governments. There is also a risk that mining companies will make decisions that serve their own interests.

Methionine (Met) in proteins can be oxidized to two diastereoisomers of methionine sulfoxide, Met-S-O and Met-R-O, which are reduced back to Met by two types of methionine sulfoxide reductases (MSRs), A and B, respectively. MSRs are generally supplied with reducing power by thioredoxins. Plants are characterized by a large number of thioredoxin isoforms, but those providing electrons to MSRs in vivo are not known. Three MSR isoforms, MSRA4, MSRB1 and MSRB2, are present in Arabidopsis thaliana chloroplasts. Under conditions of high light and long photoperiod, plants knockdown for each plastidial MSR type or for both display reduced growth. In contrast, overexpression of plastidial MSRBs is not associated with beneficial effects in terms of growth under high light. To identify the physiological reductants for plastidial MSRs, we analyzed a series of mutants deficient for thioredoxins f, m, x or y. We show that mutant lines lacking both thioredoxins y1 and y2 or only thioredoxin y2 specifically display a significantly reduced leaf MSR capacity (-25%) and growth characteristics under high light, related to those of plants lacking plastidial MSRs. We propose that thioredoxin y2 plays a physiological function in protein repair mechanisms as an electron donor to plastidial MSRs in photosynthetic organs.

De nombreux travaux alimentent la reflexion sur le droit foncier des zones rurales en Afrique de l’Ouest. En Guinee, la reforme fonciere est d’actualite depuis plusieurs annees mais les differents evenements politiques de ces dernieres annees ont continuellement repousse le travail entame. Il n’en reste pas moins que le sujet demeure un enjeu d’actualite et sera un des chantiers du nouveau gouvernement. Nous proposons, dans cet article, grâce a une description precise du droit local, de reflechir sur les enjeux de la reforme et proposer des voies de faisabilite pour concilier la legalite avec les pratiques.

Vitamin E is a generic term for a group of lipid-soluble antioxidant compounds, the tocopherols and tocotrienols. While tocotrienols are considered as important vitamin E components in humans, with functions in health and disease, the protective functions of tocotrienols have never been investigated in plants, contrary to tocopherols. We took advantage of the strong accumulation of tocotrienols in leaves of double transgenic tobacco (Nicotiana tabacum) plants that coexpressed the yeast (Saccharomyces cerevisiae) prephenate dehydrogenase gene (PDH) and the Arabidopsis (Arabidopsis thaliana) hydroxyphenylpyruvate dioxygenase gene (HPPD) to study the antioxidant function of those compounds in vivo. In young leaves of wild-type and transgenic tobacco plants, the majority of vitamin E was stored in thylakoid membranes, while plastoglobules contained mainly δ-tocopherol, a very minor component of vitamin E in tobacco. However, the vitamin E composition of plastoglobules was observed to change substantially during leaf aging, with α-tocopherol becoming the major form. Tocotrienol accumulation in young transgenic HPPD-PDH leaves occurred without any significant perturbation of photosynthetic electron transport. Tocotrienols noticeably reinforced the tolerance of HPPD-PDH leaves to high light stress at chilling temperature, with photosystem II photoinhibition and lipid peroxidation being maintained at low levels relative to wild-type leaves. Very young leaves of wild-type tobacco plants turned yellow during chilling stress, because of the strongly reduced levels of chlorophylls and carotenoids, and this phenomenon was attenuated in transgenic HPPD-PDH plants. While sugars accumulated similarly in young wild-type and HPPD-PDH leaves exposed to chilling stress in high light, a substantial decrease in tocotrienols was observed in the transgenic leaves only, suggesting vitamin E consumption during oxygen radical scavenging. Our results demonstrate that tocotrienols can function in vivo as efficient antioxidants protecting membrane lipids from peroxidation.

The abundance of a single domain cyclophilin (CyP), designated as SsCyP, was investigated in Solanum sogarandinum and Solanum tuberosum plants during development and in response to various environmental constraints. We show that under control conditions, SsCyP is distributed throughout the plant but in an organ-specific manner. In both Solanum species, the highest protein levels are observed in transporting organs and in tubers, and substantial amounts are noticed in open flowers and in stamens. We also show that the SsCyP abundance in leaves strongly decreases with age. In in vitro-grown plantlets of S. sogarandinum, the SsCyP gene is induced by low temperature at the transcript level but not at the protein level, indicating that post-transcriptional mechanisms control SsCyP expression under cold conditions. In in vivo-grown Solanum plants, the organ-dependent SsCyP protein distribution and abundance are not modified by cold, drought, salinity and photooxidative treatments. In contrast, the protein abundance substantially decreases in all organs of Solanum plants subjected to heat shock. We conclude that the SsCyP protein acts mainly during development and does not belong to the group of stress-induced CyPs.

Summary Thellungiella halophila and Arabidopsis thaliana were irrigated with medium containing NaCl at various concentrations. The salt treatment resulted in a restriction of rosette biomass deposition in both species. In A. thaliana leaves, this inhibition was stronger than for T. halophila and was associated with strong inhibition of both leaf initiation and leaf expansion. At highest medium salinity, A. thaliana accumulated Na + and Cl − at higher levels than T. halophila , but similar leaf dehydration was observed in the two species. Proline accumulation, which increased with NaCl concentration, did not differentiate the two species. The magnitude of the electrolyte leakage and the level of lipid peroxidation (assessed through hydroxy fatty acid content) were modest in T. halophila and quite marked in A. thaliana . The detrimental effects of the salt on photosynthetic activity and stomatal conductance of A. thaliana leaves were much more important than in T. halophila leaves. The abundance of the CDSP32 thioredoxin, a critical component of the defence system against oxidative damage and lipid peroxidation, was found to be higher in T. halophila than in A. thaliana under control conditions and salt treatment. These results suggest that the rosette leaves of T. halophila exhibit more efficient protective mechanisms against Na + metabolic toxicity than those of A. thaliana .

The 2-cysteine peroxiredoxins (2-Cys-Prxs) are antioxidants that reduce peroxides through a thiol-based mechanism. During catalysis, these ubiquitous enzymes are occasionally inactivated by the substrate-dependent oxidation of the catalytic cysteine to the sulfinic acid (-SO2H) form, and are reactivated by reduction by sulfiredoxin (Srx), an enzyme recently identified in yeast and in mammal cells. In plants, 2-Cys-Prxs constitute the most abundant Prxs and are located in chloroplasts. Here we have characterized the unique Srx gene in Arabidopsis thaliana (AtSrx) from a functional point of view, and analyzed the phenotype of two AtSrx knockout (AtSrx-) mutant lines. AtSrx is a chloroplastic enzyme displaying sulfinic acid reductase activity, as shown by the ability of the recombinant AtSrx to reduce the overoxidized 2-Cys-Prx form in vitro, and by the accumulation of the overoxidized Prx in mutant lines lacking Srx in vivo. Furthermore, AtSrx mutants exhibit an increased tolerance to photooxidative stress generated by high light combined with low temperature. These data establish that, as in yeast and in mammals, plant 2-Cys-Prxs are subject to substrate-mediated inactivation reversed by Srx, and suggest that the 2-Cys-Prx redox status and sulfiredoxin are parts of a signaling mechanism participating in plant responses to oxidative stress.

International audience; Background: Increasing knowledge has been recently gained regarding the redox regulation of plant developmental stages. Scope of view: The current state of knowledge concerning the involvement of glutathione, glutaredoxins and thioredoxins in plant development is reviewed. Major conclusions: The control of the thiol redox status is mainly ensured by glutathione (GSH), a cysteine-containing tripeptide and by reductases sharing redox-active cysteines, glutaredoxins (GRXs) and thioredoxins (TRXs). Indeed, thiol groups present in many regulatory proteins and metabolic enzymes are prone to oxidation, ultimately leading to post-translational modifications such as disulfide bond formation or glutathionylation. This review focuses on the involvement of GSH, GRXs and TRXs in plant development. Recent studies showed that the proper functioning of root and shoot apical meristems depends on glutathione content and redox status, which regulate, among others, cell cycle and hormone-related processes. A critical role of GRXs in the formation of floral organs has been uncovered, likely through the redox regulation of TGA transcription factor activity. TRXs fulfill many functions in plant development via the regulation of embryo formation, the control of cell-to-cell communication, the mobilization of seed reserves, the biogenesis of chloroplastic structures, the metabolism of carbon and the maintenance of cell redox homeostasis. This review also highlights the tight relationships between thiols, hormones and carbon metabolism, allowing a proper development of plants in relation with the varying environment and the energy availability. General significance: GSH, GRXs and TRXs play key roles during the whole plant developmental cycle via their antioxidant functions and the redox-regulation of signaling pathways. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

International audience; Glutaredoxins (Grxs) are oxidoreductases structurally related to thioredoxins (Trxs). They have two major proposed biochemical roles, the reduction of disulfide bonds and the binding of iron-sulfur (Fe-S) clusters, both of which usually involve glutathione. In photosynthetic organisms, Grxs are distributed into six classes. Several Grxs from classes I and II can indeed exist either as apoforms which display deglutathionylation activity or as holoforms which bind Fe-S clusters. Using biochemical, spectroscopic and structural approaches, we have characterized four plastidial Grxs, showing that three of these can bind an Fe-S cluster. Site-directed mutagenesis experiments and resolution of the crystal structure of class I Grxs (GrxC5 and S12) revealed the critical role of some active site residues for cluster formation and for protein activity. The deglutathionylation activity of these two Grxs proceeds through a monothiol mechanism, which is important for the regeneration of the thiol-peroxidase and methionine sulfoxide reductase families. The two plastidial class II Grxs (GrxS14 and S16) can bind more labile Fe-S clusters that can serve for the maturation of other proteins as demonstrated by in vitro Fe-S cluster transfer experiments and by the complementation of a yeast strain deleted for the mitochondrial Grx5. Using binary yeast two hybrid and bimolecular fluorescence complementation experiments, we have shown that class II but not class I Grxs interact with plastidial BolA proteins, including SufE1, a sulfurtransferase required for the maturation of plastidial Fe-S proteins. Finally, using spectroscopic and structural approaches, we have determined that the Grx-BolA couples form two types of complexes involving distinct regions of both partners. Hence, we propose (i) that, based on its peculiar catalytic and thermodynamic properties, GrxS12 and potentially GrxC5 could rather act as oxidoreductases and/or redox sensors, and (ii) that GrxS14 and GrxS16 could participate to the maturation of iron-sulfur proteins either by being directly involved in Fe-S cluster trafficking or by having regulatory roles in particular via their interaction with BolA proteins.

Peroxiredoxins are ubiquitous thioredoxin-dependent peroxidases presumed to display, upon environmental constraints, a chaperone function resulting from a redox-dependent conformational switch. In this work, using biochemical and genetic approaches, we aimed to unravel the factors regulating the redox status and the conformation of the plastidial 2-Cys peroxiredoxin (2-Cys PRX) in plants. In Arabidopsis, we show that in optimal growth conditions, the overoxidation level mainly depends on the availability of thioredoxin-related electron donors, but not on sulfiredoxin, the enzyme reducing the 2-Cys PRX overoxidized form. We also observed that upon various physiological temperature, osmotic and light stress conditions, the overoxidation level and oligomerization status of 2-Cys PRX can moderately vary depending on the constraint type. Further, no major change was noticed regarding protein conformation in water-stressed Arabidopsis, barley and potato plants, whereas species-dependent up- and down-variations in overoxidation were observed. In contrast, both 2-Cys PRX overoxidation and oligomerization were strongly induced during a severe oxidative stress generated by methyl viologen. From these data, revealing that the oligomerization status of plant 2-Cys PRX does not exhibit important variation and is not tightly linked to the protein redox status upon physiologically relevant environmental constraints, the possible in planta functions of 2-Cys PRX are discussed.