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See detailChlamydomonas can play a role in the study of a heteroplasmic human mitochondrial mutation
Larosa, Véronique ULg; Coosemans, Nadine ULg; Bonnefoy, Nathalie et al

Scientific conference (2011)

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See detailCharacterization of a knock-down mutant deficient for isocitrate lyase in Chlamydomonas reinhardtii
Remacle, Claire ULg

in Microorganisms for bio-fuel production from sunlight, ESF conference (2011)

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See detail3D-reconstruction and overall topology of the dimeric mitochondrial ATP synthase of the colorless alga Polytomella sp
González-Halphen, Diego; Vázquez-Acevedo, Myriam; Cano-Estrada, Araceli et al

in Biochimica et Biophysica Acta (BBA) - Bioenergetics (2010, July), 1797(Supplement 1), 32

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See detailAtypical subunit composition of the chlorophycean mitochondrial F1FO ATP synthase and role of Asa7 protein in stability and oligomycin resistance of the enzyme.
Lapaille, Marie; Escobar-Ramirez, Adelma; Degand, Hervé et al

in Molecular Biology and Evolution (2010), 27(7), 1630-1644

Background. In yeast, mammals, and land plants, mitochondrial F(1)F(O) ATP synthase (complex V) is a remarkable enzymatic machinery which comprises about 15 conserved subunits. Peculiar among eukaryotes ... [more ▼]

Background. In yeast, mammals, and land plants, mitochondrial F(1)F(O) ATP synthase (complex V) is a remarkable enzymatic machinery which comprises about 15 conserved subunits. Peculiar among eukaryotes, complex V from Chlamydomonadales algae (order of chlorophycean class) has an atypical subunit composition of its peripheral stator and dimerization module, with 9 subunits of unknown evolutionary origin (Asa subunits). In vitro, this enzyme exhibits an increased stability of its dimeric form, and in vivo, Chlamydomonas reinhardtii cells are insensitive to oligomycins, which are potent inhibitors of proton translocation through the F(O) moiety. Methodology/Principal Findings. In this work, we showed that the atypical features of the Chlamydomonadales complex V enzyme are shared by the other chlorophycean orders. By biochemical and in silico analyses, we detected several atypical Asa subunits in Scenedesmus obliquus (Sphaeropleales) and Chlorococcum ellipsoideum (Chlorococcales). In contrast, Complex V has a canonical subunit composition in other classes of Chlorophytes (Trebouxiophyceae, Prasinophyceae, and Ulvophyceae) as well as in Streptophytes (land plants) and in Rhodophytes (red algae). Growth, respiration and ATP levels in Chlorophyceae were also barely affected by oligomycin concentrations that affect representatives of the other classes of Chlorophytes. We finally studied the function of the Asa7 atypical subunit by using RNA interference in C. reinhardtii. Although the loss of Asa7 subunit has no impact on cell bioenergetics or mitochondrial structures, it destabilizes in vitro the enzyme dimeric form and renders growth, respiration and ATP level sensitive to oligomycins. Conclusions/Significance. Altogether, our results suggest that the loss of canonical components of the Complex V stator happened at the root of chlorophycean lineage and was accompanied by the recruitment of novel polypeptides. Such a massive modification of Complex V stator features might have conferred novel properties, including the stabilization of the enzyme dimeric form and the shielding of the proton channel. In these respects, we discuss an evolutionary scenario for F(1)F(O) ATP synthase in the whole green lineage (i.e. Chlorophyta and Streptophyta). [less ▲]

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See detail(Functionnal) analysis of hydrogen production in Chlamydomonas reinhardtii mitochondrial mutants
Lecler, Renaud ULg; Godaux, Damien ULg; Hamilton, Christopher ULg et al

Poster (2010, June 27)

Mitochondrial Chlamydomonas mutants for respiratory complexes present a decreased dark respiration and apparent yield of photosynthetic linear electron flow. They accumulate reducing power such as NAD(P)H ... [more ▼]

Mitochondrial Chlamydomonas mutants for respiratory complexes present a decreased dark respiration and apparent yield of photosynthetic linear electron flow. They accumulate reducing power such as NAD(P)H and show lower levels of ATP. Under restrictive conditions, like sulfur depletion and anoxia, Chlamydomonas is able to produce hydrogen towards the activation of a chloroplatic O2-sensitive Fe-hydrogenase which catalyses the reduction of electrons to H2. In this study we used an adapted Melis protocol to analyse hydrogen evolution of mitochondrial mutants. For this aim a simple-flask system was built with gaz collecting tubes. A parallel flask was used for GC analyses. [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 detailLoss of mitochondrial ATP synthase subunit beta (Atp2) alters mitochondrial and chloroplastic function and morphology in Chlamydomonas.
Lapaille, M.; Thiry, Marc ULg; Perez, E. et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797

Mitochondrial F(1)F(O) ATP synthase (Complex V) catalyses ATP synthesis from ADP and inorganic phosphate using the proton-motive force generated by the substrate-driven electron transfer chain. In this ... [more ▼]

Mitochondrial F(1)F(O) ATP synthase (Complex V) catalyses ATP synthesis from ADP and inorganic phosphate using the proton-motive force generated by the substrate-driven electron transfer chain. In this work, we investigated the impact of the loss of activity of the mitochondrial enzyme in a photosynthetic organism. In this purpose, we inactivated by RNA interference the expression of the ATP2 gene, coding for the catalytic subunit beta, in the green alga Chlamydomonas reinhardtii. We demonstrate that in the absence of beta subunit, complex V is not assembled, respiratory rate is decreased by half and ATP synthesis coupled to the respiratory activity is fully impaired. Lack of ATP synthase also affects the morphology of mitochondria which are deprived of cristae. We also show that mutants are obligate phototrophs and that rearrangements of the photosynthetic apparatus occur in the chloroplast as a response to ATP synthase deficiency in mitochondria. Altogether, our results contribute to the understanding of the yet poorly studied bioenergetic interactions between organelles in photosynthetic organisms. [less ▲]

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See detailSubunit-subunit interactions and overall topology of the dimeric mitochondrial ATP synthase of Polytomella sp.
Cano-Estrada, A.; Vazquez-Acevedo, M.; Villavicencio-Queijeiro, A. et al

in Biochimica et Biophysica Acta-Bioenergetics (2010), 1797

Mitochondrial F(1)F(0)-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 ... [more ▼]

Mitochondrial F(1)F(0)-ATP synthase of chlorophycean algae is a dimeric complex of 1600kDa constituted by 17 different subunits with varying stoichiometries, 8 of them conserved in all eukaryotes and 9 that seem to be unique to the algal lineage (subunits ASA1-9). Two different models proposing the topological assemblage of the nine ASA subunits in the ATP synthase of the colorless alga Polytomella sp. have been put forward. Here, we readdressed the overall topology of the enzyme with different experimental approaches: detection of close vicinities between subunits based on cross-linking experiments and dissociation of the enzyme into subcomplexes, inference of subunit stoichiometry based on cysteine residue labelling, and general three-dimensional structural features of the complex as obtained from small-angle X-ray scattering and electron microscopy image reconstruction. Based on the available data, we refine the topological arrangement of the subunits that constitute the mitochondrial ATP synthase of Polytomella sp. [less ▲]

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See detailKnock-down of the COX3 and COX17 gene expression of cytochrome c oxidase in the unicellular green alga Chlamydomonas reinhardtii.
Remacle, Claire ULg; Coosemans, Nadine ULg; Jans, Frédéric ULg et al

in Plant Molecular Biology (2010), 74(3), 223-2363

The COX3 gene encodes a core subunit of mitochondrial cytochrome c oxidase (complex IV) whereas the COX17 gene encodes a chaperone delivering copper to the enzyme. Mutants of these two genes were isolated ... [more ▼]

The COX3 gene encodes a core subunit of mitochondrial cytochrome c oxidase (complex IV) whereas the COX17 gene encodes a chaperone delivering copper to the enzyme. Mutants of these two genes were isolated by RNA interference in the microalga Chlamydomonas. The COX3 mRNA was completely lacking in the cox3-RNAi mutant and no activity and assembly of complex IV were detected. The cox17-RNAi mutant presented a reduced level of COX17 mRNA, a reduced activity of the cytochrome c oxidase but no modification of its amount. The cox3-RNAi mutant had only 40% of the wild-type rate of dark respiration which was cyanide-insensitive. The mutant presented a 60% decrease of H(2)O(2) production in the dark compared to wild type, which probably accounts for a reduced electron leakage by respiratory complexes III and IV. In contrast, the cox17-RNAi mutant showed no modification of respiration and of H(2)O(2) production in the dark but a two to threefold increase of H(2)O(2) in the light compared to wild type and the cox3-RNAi mutant. The cox17-RNAi mutant was more sensitive to cadmium than the wild-type and cox3-RNAi strains. This suggested that besides its role in complex IV assembly, Cox17 could have additional functions in the cell such as metal detoxification or Reactive Oxygen Species protection or signaling. Concerning Cox3, its role in Chlamydomonas complex IV is similar to that of other eukaryotes although this subunit is encoded in the nuclear genome in the alga contrary to the situation found in all other organisms. [less ▲]

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See detailF1FO ATP synthase mutants in Chlamydomonas: Stability and oligomycin resistance mediated by atypical Asa7 protein; interaction between chloroplastic and mitochondrial bioenergetics
Lapaille, Marie ULg; Escobar-Ramírez, Adelma; Degand, Hervé et al

in Biochimica et Biophysica Acta (BBA) - Bioenergetics (2010), 1797(Supplement 1), 29

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See detailCharacterization of complex I mutants in Chlamydomonas reinhardtii : Role of structural subunits and identification of assembly factors.
Larosa, Véronique ULg; Barbieri, Rosario; Bonnefoy, Nathalie et al

Scientific conference (2009)

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See detailThe ARG9 Gene Encodes the Plastid-Resident N-Acetyl Ornithine Aminotransferase in the Green Alga Chlamydomonas reinhardtii
Remacle, Claire ULg; Cline, Sara; Boutaffala, Layla ULg et al

in Eukaryotic Cell (2009), 8(9), 1460-1463

Here we report the characterization of the Chlamydomonas reinhardtii gene ARG9, encoding the plastid resident N-acetyl ornithine aminotransferase, which is involved in arginine synthesis. Integration of ... [more ▼]

Here we report the characterization of the Chlamydomonas reinhardtii gene ARG9, encoding the plastid resident N-acetyl ornithine aminotransferase, which is involved in arginine synthesis. Integration of an engineered ARG9 cassette in the plastid chromosome of the nuclear arg9 mutant restores arginine prototrophy. This suggests that ARG9 could be used as a new selectable marker for plastid transformation. [less ▲]

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See detailSteady-state levels of imported tRNAs in Chlamydomonas mitochondria are correlated with both cytosolic and mitochondrial codon usages
Vinogradova, Elizaveta; Salinas, Thalia; Cognat, Valerie et al

in Nucleic Acids Research (2009), 37(5), 1521-1528

The mitochondrial genome of Chlamydomonas reinhardtii only encodes three expressed tRNA genes, thus most mitochondrial tRNAs are likely imported. The sharing of tRNAs between chloroplasts and mitochondria ... [more ▼]

The mitochondrial genome of Chlamydomonas reinhardtii only encodes three expressed tRNA genes, thus most mitochondrial tRNAs are likely imported. The sharing of tRNAs between chloroplasts and mitochondria has been speculated in this organism. We first demonstrate that no plastidial tRNA is present in mitochondria and that the mitochondrial translation mainly relies on the import of nucleus-encoded tRNA species. Then, using northern analysis, we show that the extent of mitochondrial localization for the 49 tRNA isoacceptor families encoded by the C. reinhardtii nuclear genome is highly variable. Until now the reasons for such variability were unknown. By comparing cytosolic and mitochondrial codon usage with the sub-cellular distribution of tRNAs, we provide unprecedented evidence that the steady-state level of a mitochondrial tRNA is linked not only to the frequency of the cognate codon in mitochondria but also to its frequency in the cytosol, then allowing optimal mitochondrial translation. [less ▲]

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See detailOxidative phosphorylation: Building blocks and related components
Cardol, Pierre ULg; Figueroa, Francisco; Remacle, Claire ULg et al

in Stern, David; Harris, Elizabeth; Witman, George (Eds.) The Chlamydomonas Sourcebook 3-vol set, 1-3 (2009)

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