References of "Matagne, René-Fernand"
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See detailInactivation of genes coding for mitochondrial Nd7 and Nd9 complex I subunits in Chlamydomonas reinhardtii. Impact of complex I loss on respiration and energetic metabolism.
Massoz, Simon; Larosa, Véronique ULg; Plancke, Charlotte et al

in Mitochondrion (2013)

In Chlamydomonas, unlike in flowering plants, genes coding for Nd7 (NAD7/49kDa) and Nd9 (NAD9/30kDa) core subunits of mitochondrial respiratory-chain complex I are nucleus-encoded. Both genes possess all ... [more ▼]

In Chlamydomonas, unlike in flowering plants, genes coding for Nd7 (NAD7/49kDa) and Nd9 (NAD9/30kDa) core subunits of mitochondrial respiratory-chain complex I are nucleus-encoded. Both genes possess all the features that facilitate their expression and proper import of the polypeptides in mitochondria. By inactivating their expression by RNA interference or insertional mutagenesis, we show that both subunits are required for complex I assembly and activity. Inactivation of complex I impairs the cell growth rate, reduces the respiratory rate, leads to lower intracellular ROS production and lower expression of ROS scavenging enzymes, and is associated to a diminished capacity to concentrate CO2 without compromising photosynthetic capacity. [less ▲]

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See detailFunction of the Chloroplast Hydrogenase in the Microalga Chlamydomonas: The Role of Hydrogenase and State Transitions during Photosynthetic Activation in Anaerobiosis
Ghysels, Bart ULg; Godaux, Damien ULg; Matagne, René-Fernand ULg et al

in PLoS ONE (2013), 8(5), 64161

Like a majority of photosynthetic microorganisms, the green unicellular alga Chlamydomonas reinhardtii may encounter O2 deprived conditions on a regular basis. In response to anaerobiosis or in a ... [more ▼]

Like a majority of photosynthetic microorganisms, the green unicellular alga Chlamydomonas reinhardtii may encounter O2 deprived conditions on a regular basis. In response to anaerobiosis or in a respiration defective context, the photosynthetic electron transport chain of Chlamydomonas is remodeled by a state transition process to a conformation that favours the photoproduction of ATP at the expense of reductant synthesis. In some unicellular green algae including Chlamydomonas, anoxia also triggers the induction of a chloroplast-located, oxygen sensitive hydrogenase, which accepts electrons from reduced ferredoxin to convert protons into molecular hydrogen. Although microalgal hydrogen evolution has received much interest for its biotechnological potential, its physiological role remains unclear. By using specific Chlamydomonas mutants, we demonstrate that the state transition ability and the hydrogenase function are both critical for induction of photosynthesis in anoxia. These two processes are thus important for survival of the cells when they are transiently placed in an anaerobic environment. [less ▲]

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See detailA Chlamydomonas mutant locked in anaerobiosis
Ghysels, Bart ULg; Matagne, René-Fernand ULg; Franck, Fabrice ULg

Conference (2011, May)

The soil dwelling microalga Chlamydomonas reinhardtii most likely encounters transient periods of anaerobiosis in its natural environment, for instance at night time or when photosynthesis is turned down ... [more ▼]

The soil dwelling microalga Chlamydomonas reinhardtii most likely encounters transient periods of anaerobiosis in its natural environment, for instance at night time or when photosynthesis is turned down in response to macronutrient limitation. Anoxic conditions trigger state I to state II transition in C.r. and the induction of a chloroplast hydrogenase., which ability to accept electrons from reduced Fd results in a transient light driven H2 evolution. We present evidence that hydrogenase induction and state transitions are required for the induction of photosynthesis in anaerobiosis and therefore critical for this alga in order to survive transient anaerobic periods in the dark. In an anaerobic metabolic context the induction of photosynthesis is severely slowed down. The highly reduced state of the NAD(P) pools and the absence of O2 as electron sink hamper light driven reoxydation of the intersystem electron carriers while CO2 assimilation by the Calvin cycle is inhibited by ATP deficiency. We have seen that gradual increase of hydrogenase activity during anaerobiosis restores a PSI acceptor pool and leads to a reduction of the induction lag of oxygenic photosynthesis. A mutant HydEF devoid of hydrogenase maturation genes typically shows 3 to 4 times longer lag phases that the WT. State transitions provide another mechanism by which photosynthetic electron transport can be unlocked in anaerobic conditions. A state II conformation is known to stimulate photo-phosphorylation, and may therefore restore Calvin cycle activity in an ATP depleted metabolic context. We observed that an anaerobically adapted stt7 mutant locked in state I is only able to induce oxygenic photosynthesis upon hydrogenase expression. We therefore constructed a double mutant Stt7HydEF impaired of state transition ability and hydrogenase activity and found it to have lost the capacity of inducing photosynthesis in anaerobic conditions. [less ▲]

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See detailProteomic and functional characterization of a Chlamydomonas reinhardtii mutant lacking the mitochondrial alternative oxidase 1
Mathy, Grégory ULg; Cardol, Pierre ULg; Dinant, Monique et al

in Journal of Proteome Research (2010), 9

In the present work we have isolated by RNA interference and characterized at the functional and the proteomic levels a Chlamydomonas reinhardtii strain devoid of the mitochondrial alternative oxidase ... [more ▼]

In the present work we have isolated by RNA interference and characterized at the functional and the proteomic levels a Chlamydomonas reinhardtii strain devoid of the mitochondrial alternative oxidase (AOX). The AOX-deficient strain displays a doubling of the cell volume and biomass without any alteration of the generation time, a significantly higher ROS production, no change in total respiration rate, and a slight decrease of the photosynthesis efficiency. In order to identify the molecular adaptation underlying these phenotypical effects, we carried out a comparative proteomic study at the level of the mitochondrial and cellular soluble proteomes. Our results indicate a strong up-regulation of the ROS scavenging systems and important modifications of proteins involved in the primary metabolism, namely an increase of enzymes involved in anabolic pathways and a concomitant general down-regulation of enzymes of the main catabolic pathways. [less ▲]

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See detailImportance of the alternative pathway of respiration for avoidance of ROS production and for optimisation of photosynthesis in Chlamydomonas
Franck, Fabrice ULg; Dinant, M.; Cardol, Pierre ULg et al

Conference (2008, June)

The physiological function of the alternative pathway of respiration has been investigated by analysing two RNAi C.reinhardtii lines deprived of alternative oxidase protein (AOX1). Compared to wild-type ... [more ▼]

The physiological function of the alternative pathway of respiration has been investigated by analysing two RNAi C.reinhardtii lines deprived of alternative oxidase protein (AOX1). Compared to wild-type, AOX1- lines exhibited modified growth curves and reduced maximal cell density. These differences were more pronounced at high irradiance and in nitrate-containing medium (TAP NO3) rather than in ammonium-containing medium (TAP NH4). Although the alternative pathway was inactive, respiration was not significantly altered in transgenics. Light-saturation curves of O2-evolution were only slightly modified. However, non-photochemical quenching of fluorescence (NPQ) was strongly reduced. Further analysis showed that AOX1- transgenics present a reduced ability to promote the change in energy distribution between photosystems, known as state transition. This effect, which explains low NPQ in the light, was most pronounced in high-light cells cultivated in TAP NO3 medium. Moreover, AOX1- transgenics exhibited higher levels of intracellular peroxides, which suggests that inhibition of state transition might result from higher ROS production. In support of this hypothesis, addition of millimolar-range concentrations of H2O2 to wild-type inhibited the state transition promoted by the reduction of the plastoquinone pool in darkness. [less ▲]

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See detailIn Chlamydomonas, the Loss of Nd5 Subunit Prevents the Assembly of Whole Mitochondrial Complex I and Leads to the Formation of a Low Abundant 700 Kda Subcomplex
Cardol, Pierre ULg; Boutaffala, Layla ULg; Memmi, S. et al

in Biochimica et Biophysica Acta-Bioenergetics (2008), 1777

In the green alga Chlamydomonas reinhardtii, a mutant deprived of complex I enzyme activity presents a 1T deletion in the mitochondrial nd5 gene. The loss of the ND5 subunit prevents the assembly of the ... [more ▼]

In the green alga Chlamydomonas reinhardtii, a mutant deprived of complex I enzyme activity presents a 1T deletion in the mitochondrial nd5 gene. The loss of the ND5 subunit prevents the assembly of the 950 kDa whole complex I. Instead, a low abundant 700 kDa subcomplex, loosely associated to the inner mitochondrial membrane, is assembled. The resolution of the subcomplex by SDS-PAGE gave rise to 19 individual spots, sixteen having been identified by mass spectrometry analysis. Eleven, mainly associated to the hydrophilic part of the complex, are homologs to subunits of the bovine enzyme whereas five (including gamma-type carbonic anhydrase subunits) are specific to green plants or to plants and fungi. None of the subunits typical of the beta membrane domain of complex I enzyme has been identified in the mutant. This allows us to propose that the truncated enzyme misses the membrane distal domain of complex I but retains the proximal domain associated to the matrix arm of the enzyme. A complex I topology model is presented in the light of our results. Finally, a supercomplex most probably corresponding to complex I-complex III association, was identified in mutant mitochondria, indicating that the missing part of the enzyme is not required for the formation of the supercomplex. [less ▲]

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See detailND3 and ND4L subunits of mitochondrial complex I, both nucleus encoded in Chlamydomonas reinhardtii, are required for activity and assembly of the enzyme
Cardol, Pierre ULg; Lapaille, Marie ULg; Minet, P. et al

in Eukaryotic Cell (2006), 5(9), 1460-1467

Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants ... [more ▼]

Made of more than 40 subunits, the rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. In vascular plants, fungi, and animals, at least seven complex I subunits (ND1, -2, -3, -4, -4L, -5, and -6; ND is NADH dehydrogenase) are coded by mitochondrial genes. The role of these highly hydrophobic subunits in the enzyme activity and assembly is still poorly understood. In the unicellular green alga Chlamydomonas reinhardtii, the ND3 and ND4L subunits are encoded in the nuclear genome, and we show here that the corresponding genes, called NUO3 and NUO11, respectively, display features that facilitate their expression and allow the proper import of the corresponding proteins into mitochondria. In particular, both polypeptides show lower hydrophobicity compared to their mitochondrion-encoded counterparts. The expression of the NUO3 and NUO11 genes has been suppressed by RNA interference. We demonstrate that the absence of ND3 or ND4L polypeptides prevents the assembly of the 950-kDa whole complex I and suppresses the enzyme activity. The putative role of hydrophobic ND subunits is discussed in relation to the structure of the complex I enzyme. A model for the assembly pathway of the Chlamydomonas enzyme is proposed. [less ▲]

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See detailThe mitochondrial oxidative phosphorylation proteome of Chlamydomonas reinhardtii deduced from the genome sequencing project
Cardol, Pierre ULg; Gonzalez-Halphen, Diego; Reyes-Prieto, Adrian et al

in Plant Physiology (2005), 137(2), 447-459

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See detailHigher plant-like subunit composition of mitochondrial complex I from Chlamydomonas reinhardtii: 31 conserved components among eukaryotes
Cardol, Pierre ULg; Vanrobaeys, F.; Devreese, B. et al

in Biochimica et Biophysica Acta-Bioenergetics (2004), 1658(3), 212-224

The rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. Notably the bovine enzyme comprises up to 46 subunits ... [more ▼]

The rotenone-sensitive NADH:ubiquinone oxidoreductase (complex I) is the most intricate membrane-bound enzyme of the mitochondrial respiratory chain. Notably the bovine enzyme comprises up to 46 subunits, while 27 subunits could be considered as widely conserved among eukaryotic complex I. By combining proteomic and genomic approaches, we characterized the complex I composition from the unicellular green alga Chlamydomonas reinhardtii. After purification by blue-native polyacrylamide gel electrophoresis (BN-PAGE), constitutive subunits were analyzed by SDS-PAGE coupled to tandem mass spectrometry (MS) that allowed the identification of 30 proteins. We compared the known complex I components from higher plants, mammals, nematodes and fungi with this MS data set and the translated sequences from the algal genome project. This revealed that the Chlamydomonas complex I is likely composed of 42 proteins, for a total molecular mass of about 970 kDa. In addition to the 27 typical components, we have identified four new complex I subunit families (bovine ESSS, PFFD, B16.6, B12 homologues), extending the number of widely conserved eukaryote complex I components to 31. In parallel, our analysis showed that a variable number of subunits appears to be specific to each eukaryotic kingdom (animals, fungi or plants). Protein sequence divergence in these kingdom-specific sets is significant and currently we cannot exclude the possibility that homology between them exists, but has not yet been detected. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailImpact of a mutation in the mitochondrial LSU rRNA gene from Chlamydomonas reinhardtii on the activity and the assembly of respiratory-chain complexes
Remacle, Claire ULg; Gloire, Geoffrey ULg; Cardol, Pierre ULg et al

in Current Genetics (2004), 45(5), 323-330

Two substitutions A1090G and A1098C (together called the m mutation) located in the conserved GTPase domain of the mitochondrial LSU rRNA gene were recently shown to weakly compensate for the phenotypical ... [more ▼]

Two substitutions A1090G and A1098C (together called the m mutation) located in the conserved GTPase domain of the mitochondrial LSU rRNA gene were recently shown to weakly compensate for the phenotypical effect of a -1T frameshift mutation in the mitochondrial cox1 gene of C. reinhardtii. In order to analyze the impact of the m mutation on the mitochondrial translational machinery, a strain carrying the m mutation but wild-type for the cox1 gene was isolated. We found that the growth and the respiratory rate of the m mutant were affected and that the activities of complexes I, III, and IV, all containing mitochondria-encoded subunits, were lowered. In contrast the activities of complex II and of the alternative oxidase, both encoded exclusively by the nuclear genome, were not modified. The steady-state levels of complex I enzyme and of several components of the respiratory complexes I, III, and IV were also reduced in the mutant. We moreover showed that m did not suppress other frameshift or UGA stop mutations which affect mitochondrial genes. [less ▲]

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See detailPhotosynthesis and state transitions in mitochondrial mutants of Chlamydomonas reinhardtii affected in respiration
Cardol, Pierre ULg; Gloire, Geoffrey ULg; Havaux, M. et al

in Plant Physiology (2003), 133(4), 2010-2020

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I + III, and I + IV) of the respiratory chain. Oxygen evolution ... [more ▼]

Photosynthetic activities were analyzed in Chlamydomonas reinhardtii mitochondrial mutants affected in different complexes (I, III, IV, I + III, and I + IV) of the respiratory chain. Oxygen evolution curves showed a positive relationship between the apparent yield of photosynthetic linear electron transport and the number of active proton-pumping sites in mitochondria. Although no significant alterations of the quantitative relationships between major photosynthetic complexes were found in the mutants, 77 K fluorescence spectra showed a preferential excitation of photosystem I (PSI) compared with wild type, which was indicative of a shift toward state 2. This effect was correlated with high levels of phosphorylation of light-harvesting complex II polypeptides, indicating the preferential association of light-harvesting complex II with PSI. The transition to state 1 occurred in untreated wild-type cells exposed to PSI light or in 3-(3,4-dichlorophenyl)-1,1-dimethylurea-treated cells exposed to white light. In mutants of the cytochrome pathway and in double mutants, this transition was only observed in white light in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. This suggests higher rates of non-photochemical plastoquinone reduction through the chlororespiratory pathway, which was confirmed by measurements of the complementary area above the fluorescence induction curve in dark-adapted cells. Photo-acoustic measurements of energy storage by PSI showed a stimulation of PSI-driven cyclic electron flow in the most affected mutants. The present results demonstrate that in C. reinhardtii mutants, permanent defects in the mitochondrial electron transport chain stabilize state 2, which favors cyclic over linear electron transport in the chloroplast. [less ▲]

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See detailRegulation of the alternative oxidase Aox1 gene in Chlamydomonas reinhardtii. Role of the nitrogen source on the expression of a reporter gene under the control of the Aox1 promoter
Baurain, Denis ULg; Dinant, Monique; Coosemans, Nadine ULg et al

in Plant Physiology (2003), 131(3), 1418-1430

In higher plants, various developmental and environmental conditions enhance expression of the alternative oxidase (AOX), whereas its induction in fungi is mainly dependent on cytochrome pathway ... [more ▼]

In higher plants, various developmental and environmental conditions enhance expression of the alternative oxidase (AOX), whereas its induction in fungi is mainly dependent on cytochrome pathway restriction and triggering by reactive oxygen species. The AOX of the unicellular green alga Chlamydomonas reinhardtii is encoded by two different genes, the Aox1 gene being much more transcribed than Aox2. To analyze the transcriptional regulation of Aox1, we have fused its 1.4-kb promoter region to the promoterless arylsulfatase (Ars) reporter gene and measured ARS enzyme activities in transformants carrying the chimeric construct. We show that the Aox1 promoter is generally unresponsive to a number of known AOX inducers, including stress agents, respiratory inhibitors, and metabolites, possibly because the AOX activity is constitutively high in the alga. In contrast, the Aox1 expression is strongly dependent on the nitrogen source, being down-regulated by ammonium and stimulated by nitrate. Inactivation of nitrate reductase leads to a further increase of expression. The stimulation by nitrate also occurs at the AOX protein and respiratory levels. A deletion analysis of the Aox1 promoter region demonstrates that a short upstream segment (-253 to +59 with respect to the transcription start site) is sufficient to ensure gene expression and regulation, but that distal elements are required for full gene expression. The observed pattern of AOX regulation points to the possible interaction between chloroplast and mitochondria in relation to a potential increase of photogenerated ATP when nitrate is used as a nitrogen source. [less ▲]

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See detailImpact of mutations affecting ND mitochondria-encoded Subunits on the activity and assembly of complex I in chlamydomonas. Implication for the structural organization of the enzyme
Cardol, Pierre ULg; Matagne, René-Fernand ULg; Remacle, Claire ULg

in Journal of Molecular Biology (2002), 319(5), 1211-1221

The mitochondrial rotenone-sensitive NADH:ubiquinone oxidoreductase (complex 1) comprises more than 35 subunits, the majority of which are encoded by the nucleus. In Chlamydomonas reinhardtii, only five ... [more ▼]

The mitochondrial rotenone-sensitive NADH:ubiquinone oxidoreductase (complex 1) comprises more than 35 subunits, the majority of which are encoded by the nucleus. In Chlamydomonas reinhardtii, only five components (ND1, ND2, ND4, ND5 and ND6) are coded for by the mitochondrial genome. Here, we characterize two mitochondrial mutants (dum5 and dum17) showing strong reduction or inactivation of complex I activity: dum5 is a IT deletion in the 3' UTR of nd5 whereas dum17 is a IT deletion in the coding sequence of nd6. The impact of these mutations and of mutations affecting nd1, nd4 and nd4/nd5 genes on the assembly of complex I is investigated. After separation of the respiratory complexes by blue native (BN)-PAGE or sucrose gradient centrifugation, we demonstrate that the absence of intact ND1 or ND6 subunit prevents the assembly of the 850 kDa whole complex, whereas the loss of ND4 or ND4/ND5 leads to the formation of a subcomplex of 650 kDa present in reduced amount. The implications of our findings for the possible role of these ND subunits on the activity of complex I and for the structural organization of the membrane arm of the enzyme are discussed. In mitochondria from all the strains analyzed, we moreover detected a 160210 kDa fragment comprising the hydrophilic 49 kDa and 76 kDa subunits of the complex I peripheral arm and showing NADH dehydrogenase activity. (C) 2002 Elsevier Science Ltd. All rights reserved. [less ▲]

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