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Berlin Brandenburg

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  • 1
    Language: English
    In: Proceedings of the National Academy of Sciences of the United States of America, 20 December 2011, Vol.108(51), pp.20820-5
    Description: By homology with the unique plastid terminal oxidase (PTOX) found in plants, two genes encoding oxidases have been found in the Chlamydomonas genome, PTOX1 and PTOX2. Here we report the identification of a knockout mutant of PTOX2. Its molecular and functional characterization demonstrates that it encodes the oxidase most predominantly involved in chlororespiration in this algal species. In this mutant, the plastoquinone pool is constitutively reduced under dark-aerobic conditions, resulting in the mobile light-harvesting complexes being mainly, but reversibly, associated with photosystem I. Accordingly, the ptox2 mutant shows lower fitness than wild type when grown under phototrophic conditions. Single and double mutants devoid of the cytochrome b(6)f complex and PTOX2 were used to measure the oxidation rates of plastoquinols via PTOX1 and PTOX2. Those lacking both the cytochrome b(6)f complex and PTOX2 were more sensitive to light than the single mutants lacking either the cytochrome b(6)f complex or PTOX2, which discloses the role of PTOX2 under extreme conditions where the plastoquinone pool is overreduced. A model for chlororespiration is proposed to relate the electron flow rate through these alternative pathways and the redox state of plastoquinones in the dark. This model suggests that, in green algae and plants, the redox poise results from the balanced accumulation of PTOX and NADPH dehydrogenase.
    Keywords: Arabidopsis Proteins -- Metabolism ; Chlamydomonas -- Enzymology ; Oxidoreductases -- Metabolism
    ISSN: 00278424
    E-ISSN: 1091-6490
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  • 2
    Language: English
    In: The Journal of biological chemistry, 09 November 2018, Vol.293(45), pp.17559-17573
    Description: The supramolecular organization of membrane proteins (MPs) is sensitive to environmental changes in photosynthetic organisms. Isolation of MP supercomplexes from the green algae , which are believed to contribute to cyclic electron flow (CEF) between the cytochrome complex (Cyt- ) and photosystem...
    Keywords: Chlamydomonas ; Cytochrome B6f Complex ; Electron Transfer Complex ; Membrane Protein ; Photosynthesis ; Protein Cross-Linking ; Chlamydomonas Reinhardtii -- Enzymology ; Cytochrome B6f Complex -- Metabolism ; Photosystem I Protein Complex -- Metabolism
    E-ISSN: 1083-351X
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  • 3
    Language: English
    In: The Journal of biological chemistry, 27 March 2015, Vol.290(13), pp.8666-76
    Description: Photosynthetic microalgae are exposed to changing environmental conditions. In particular, microbes found in ponds or soils often face hypoxia or even anoxia, and this severely impacts their physiology. Chlamydomonas reinhardtii is one among such photosynthetic microorganisms recognized for its unusual wealth of fermentative pathways and the extensive remodeling of its metabolism upon the switch to anaerobic conditions. As regards the photosynthetic electron transfer, this remodeling encompasses a strong limitation of the electron flow downstream of photosystem I. Here, we further characterize the origin of this limitation. We show that it stems from the strong reducing pressure that builds up upon the onset of anoxia, and this pressure can be relieved either by the light-induced synthesis of ATP, which promotes the consumption of reducing equivalents, or by the progressive activation of the hydrogenase pathway, which provides an electron transfer pathway alternative to the CO2 fixation cycle.
    Keywords: Anaerobic Glycolysis ; Chlamydomonas ; Electron Transfer ; Hydrogenase ; Oxidation-Reduction (Redox) ; Photosynthesis ; Adenosine Triphosphate -- Metabolism ; Chlamydomonas Reinhardtii -- Metabolism ; Chloroplasts -- Metabolism ; Hydrogen -- Metabolism ; Nadp -- Metabolism ; Oxygen -- Metabolism
    E-ISSN: 1083-351X
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  • 4
    Language: English
    In: The Journal of biological chemistry, 12 April 2013, Vol.288(15), pp.10672-83
    Description: Zinc is an essential nutrient because of its role in catalysis and in protein stabilization, but excess zinc is deleterious. We distinguished four nutritional zinc states in the alga Chlamydomonas reinhardtii: toxic, replete, deficient, and limited. Growth is inhibited in zinc-limited and zinc-toxic cells relative to zinc-replete cells, whereas zinc deficiency is visually asymptomatic but distinguished by the accumulation of transcripts encoding ZIP family transporters. To identify targets of zinc deficiency and mechanisms of zinc acclimation, we used RNA-seq to probe zinc nutrition-responsive changes in gene expression. We identified genes encoding zinc-handling components, including ZIP family transporters and candidate chaperones. Additionally, we noted an impact on two other regulatory pathways, the carbon-concentrating mechanism (CCM) and the nutritional copper regulon. Targets of transcription factor Ccm1 and various CAH genes are up-regulated in zinc deficiency, probably due to reduced carbonic anhydrase activity, validated by quantitative proteomics and immunoblot analysis of Cah1, Cah3, and Cah4. Chlamydomonas is therefore not able to grow photoautotrophically in zinc-limiting conditions, but supplementation with 1% CO2 restores growth to wild-type rates, suggesting that the inability to maintain CCM is a major consequence of zinc limitation. The Crr1 regulon responds to copper limitation and is turned on in zinc deficiency, and Crr1 is required for growth in zinc-limiting conditions. Zinc-deficient cells are functionally copper-deficient, although they hyperaccumulate copper up to 50-fold over normal levels. We suggest that zinc-deficient cells sequester copper in a biounavailable form, perhaps to prevent mismetallation of critical zinc sites.
    Keywords: Carbon Dioxide -- Metabolism ; Cation Transport Proteins -- Metabolism ; Chlamydomonas Reinhardtii -- Metabolism ; Copper -- Metabolism ; Homeostasis -- Physiology ; Zinc -- Metabolism
    ISSN: 00219258
    E-ISSN: 1083-351X
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  • 5
    Language: English
    In: Electrochimica Acta, 10 May 2017, Vol.236, pp.337-342
    Description: Oxygenic photosynthesis is the process used by plants, cyanobacteria or algae to convert the solar energy into a chemical one from the carbon dioxide reduction and water oxidation. In the past years, many strategies were implemented to take benefits from the overall low yield of this process to extract photosynthetic electrons and thus produce a sustainable photocurrent. In practice, electrochemical tools were involved and the principle of electrons harvestings was related to the step of electron transfer between the photosynthetic organism and a collecting electrode. In this context, works involving an algae population in suspension were rather scarce and rather focus on the grafting of the photosynthetic machinery at the electrode surface. Based on our previous works, we report here the implementation of an electrochemical set-up at the preparative scale to produce photocurrents. An algae suspension, i.e. an intact biological system to ensure culture and growth, was involved in presence of a centimeter-sized carbon gauze as the collecting electrode. The spectroelectrochemical cell contains 16 mL of suspension of a mutant with an appropriate mediator (2,6-DCBQ). Under these conditions, stable photocurrents were recorded over 1 h whose magnitude depends on the quinone concentration and the light illumination.
    Keywords: Photosynthesis ; Quinones ; Electrochemistry ; Chlamydomonas Reinhardtii Algae ; Photosystem II ; Photocurrent ; Engineering ; Chemistry
    ISSN: 0013-4686
    E-ISSN: 1873-3859
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  • 6
    Language: English
    In: Nucleic acids research, 13 October 2017, Vol.45(18), pp.10783-10799
    Description: In Chlamydomonas reinhardtii, regulation of chloroplast gene expression is mainly post-transcriptional. It requires nucleus-encoded trans-acting protein factors for maturation/stabilization (M factors) or translation (T factors) of specific target mRNAs. We used long- and small-RNA sequencing to generate a detailed map of the transcriptome. Clusters of sRNAs marked the 5' end of all mature mRNAs. Their absence in M-factor mutants reflects the protection of transcript 5' end by the cognate factor. Enzymatic removal of 5'-triphosphates allowed identifying those cosRNA that mark a transcription start site. We detected another class of sRNAs derived from low abundance transcripts, antisense to mRNAs. The formation of antisense sRNAs required the presence of the complementary mRNA and was stimulated when translation was inhibited by chloramphenicol or lincomycin. We propose that they derive from degradation of double-stranded RNAs generated by pairing of antisense and sense transcripts, a process normally hindered by the traveling of the ribosomes. In addition, chloramphenicol treatment, by freezing ribosomes on the mRNA, caused the accumulation of 32-34 nt ribosome-protected fragments. Using this 'in vivo ribosome footprinting', we identified the function and molecular target of two candidate trans-acting factors.
    Keywords: Transcriptome ; Chlamydomonas Reinhardtii -- Genetics ; RNA, Chloroplast -- Metabolism ; RNA, Small Untranslated -- Metabolism
    ISSN: 03051048
    E-ISSN: 1362-4962
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  • 7
    In: Traffic, December 2016, Vol.17(12), pp.1322-1328
    Description: Primary endosymbiosis, which gave rise to mitochondria or chloroplasts, required successful targeting of a number of proteins from the host cytosol to the endosymbiotic organelles. A survey of studies published in separate fields of biological research over the past 40 years argues for an antimicrobial origin of targeting peptides. It is proposed that mitochondria and chloroplast derive from microbes that developed a resistance strategy to antimicrobial peptides that consisted in their rapid internalization and proteolytic disposal by microbial peptidases. Primary endosymbiosis, which gave rise to mitochondria or chloroplasts, required successful targeting of a number of proteins from the host cytosol to the endosymbiotic organelles. A survey of studies published in separate fields of biological research over the past 40 years argue for an antimicrobial origin of targeting peptides. It is proposed that mitochondria and chloroplast derive from microbes that developed a resistance strategy to antimicrobial peptides that consisted in their rapid internalization and proteolytic disposal by microbial peptidases.
    Keywords: Antimicrobial Peptide ; Chloroplast ; Endosymbiosis ; Organelles ; Mitochondria ; Targeting Peptide
    ISSN: 1398-9219
    E-ISSN: 1600-0854
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  • 8
    Language: English
    In: Plant physiology, February 2016, Vol.170(2), pp.821-40
    Description: The remarkable capability of photosystem II (PSII) to oxidize water comes along with its vulnerability to oxidative damage. Accordingly, organisms harboring PSII have developed strategies to protect PSII from oxidative damage and to repair damaged PSII. Here, we report on the characterization of the THYLAKOID ENRICHED FRACTION30 (TEF30) protein in Chlamydomonas reinhardtii, which is conserved in the green lineage and induced by high light. Fractionation studies revealed that TEF30 is associated with the stromal side of thylakoid membranes. By using blue native/Deriphat-polyacrylamide gel electrophoresis, sucrose density gradients, and isolated PSII particles, we found TEF30 to quantitatively interact with monomeric PSII complexes. Electron microscopy images revealed significantly reduced thylakoid membrane stacking in TEF30-underexpressing cells when compared with control cells. Biophysical and immunological data point to an impaired PSII repair cycle in TEF30-underexpressing cells and a reduced ability to form PSII supercomplexes after high-light exposure. Taken together, our data suggest potential roles for TEF30 in facilitating the incorporation of a new D1 protein and/or the reintegration of CP43 into repaired PSII monomers, protecting repaired PSII monomers from undergoing repeated repair cycles or facilitating the migration of repaired PSII monomers back to stacked regions for supercomplex reassembly.
    Keywords: Chlamydomonas Reinhardtii -- Metabolism ; Photosystem II Protein Complex -- Metabolism
    ISSN: 00320889
    E-ISSN: 1532-2548
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  • 9
    Language: English
    In: PLoS ONE, 01 January 2015, Vol.10(3), p.e0118987
    Description: To address possible cell-to-cell heterogeneity in growth dynamics of isogenic cell populations of Chlamydomonas reinhardtii, we developed a millifluidic drop-based device that not only allows the analysis of populations grown from single cells over periods of a week, but is also able to sort and collect drops of interest, containing viable and healthy cells, which can be used for further experimentation. In this study, we used isogenic algal cells that were first synchronized in mixotrophic growth conditions. We show that these synchronized cells, when placed in droplets and kept in mixotrophic growth conditions, exhibit mostly homogeneous growth statistics, but with two distinct subpopulations: a major population with a short doubling-time (fast-growers) and a significant subpopulation of slowly dividing cells (slow-growers). These observations suggest that algal cells from an isogenic population may be present in either of two states, a state of restricted division and a state of active division. When isogenic cells were allowed to propagate for about 1000 generations on solid agar plates, they displayed an increased heterogeneity in their growth dynamics. Although we could still identify the original populations of slow- and fast-growers, drops inoculated with a single progenitor cell now displayed a wider diversity of doubling-times. Moreover, populations dividing with the same growth-rate often reached different cell numbers in stationary phase, suggesting that the progenitor cells differed in the number of cell divisions they could undertake. We discuss possible explanations for these cell-to-cell heterogeneities in growth dynamics, such as mutations, differential aging or stochastic variations in metabolites and macromolecules yielding molecular switches, in the light of single-cell heterogeneities that have been reported among isogenic populations of other eu- and prokaryotes.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 10
    Language: English
    In: BBA - Bioenergetics, July 2013, Vol.1827(7), pp.834-842
    Description: is a species of red algae that grows on rocks from the middle intertidal into the subtidal zones of the North Atlantic coasts. As such, it has to cope with strongly variable abiotic conditions. Here we studied the response of the photosynthetic apparatus of this red alga to illumination. We found that, as previously described in the case of the unicellular alga (E. Delphin et al., Plant Physiol. 118 (1998) 103–113), a single multi-turnover saturating pulse of light is sufficient to induce a strong quenching of fluorescence. To elucidate the mechanisms underlying this fluorescence quenching, we combined room temperature and 77 K fluorescence measurements with absorption spectroscopy to monitor the redox state of the different electron carriers in the chain. In addition, we studied the dependence of these various observables upon the excitation wavelength. This led us to identify energy spill-over from Photosystem II to Photosystem I rather than a qE-type non-photochemical quenching as the major source of fluorescence quenching that develops upon a series of 200 ms pulses of saturating light results, in line with the conclusion of Ley and Butler (Biochim. Biophys. Acta 592 (1980) 349–363) from their studies of the unicellular red alga . In addition, we show that the onset of this spill-over is triggered by the reduction of the plastoquinone pool.
    Keywords: Photosynthesis ; Red Algae ; Chondrus Crispus ; Chlorophyll Fluorescence ; Spill-Over ; Plastoquinone Pool ; Chemistry
    ISSN: 0005-2728
    E-ISSN: 1879-2650
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