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See detailLack of isocitrate lyase in Chlamydomonas leads to changes in carbon metabolism and in the response to oxidative stress under mixotrophic growth.
Plancke, Charlotte; Vigeolas, Hélène ULg; Hohner, Ricarda et al

in The Plant journal : for cell and molecular biology (2014), 77(3), 404-417

Isocitrate lyase is a key enzyme of the glyoxylate cycle. This cycle plays an essential role in cell growth on acetate, and is important for gluconeogenesis as it bypasses the two oxidative steps of the ... [more ▼]

Isocitrate lyase is a key enzyme of the glyoxylate cycle. This cycle plays an essential role in cell growth on acetate, and is important for gluconeogenesis as it bypasses the two oxidative steps of the tricarboxylic acid (TCA) cycle in which CO2 is evolved. In this paper, a null icl mutant of the green microalga Chlamydomonas reinhardtii is described. Our data show that isocitrate lyase is required for growth in darkness on acetate (heterotrophic conditions), as well as for efficient growth in the light when acetate is supplied (mixotrophic conditions). Under these latter conditions, reduced acetate assimilation and concomitant reduced respiration occur, and biomass composition analysis reveals an increase in total fatty acid content, including neutral lipids and free fatty acids. Quantitative proteomic analysis by 14 N/15 N labelling was performed, and more than 1600 proteins were identified. These analyses reveal a strong decrease in the amounts of enzymes of the glyoxylate cycle and gluconeogenesis in parallel with a shift of the TCA cycle towards amino acid synthesis, accompanied by an increase in free amino acids. The decrease of the glyoxylate cycle and gluconeogenesis, as well as the decrease in enzymes involved in beta-oxidation of fatty acids in the icl mutant are probably major factors that contribute to remodelling of lipids in the icl mutant. These modifications are probably responsible for the elevation of the response to oxidative stress, with significantly augmented levels and activities of superoxide dismutase and ascorbate peroxidase, and increased resistance to paraquat. [less ▲]

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See detailCharacterization of algae to produce biofuels
Vigeolas, Hélène ULg

Scientific conference (2012, August 27)

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See detailFunctional analysis of hydrogen photoproduction in respiratory-deficient mutants of Chlamydomonas reinhardtii
Lecler, Renaud ULg; Godaux, Damien ULg; Vigeolas, Hélène ULg et al

in International Journal of Hydrogen Energy (2011), 36

In this paper, mitochondrial mutants of Chlamydomonas reinhardtii defective for respiratory complex I (NADH:ubiquinone oxidoreductase), complex III (ubiquinol cytochrome c oxidoreductase) and both ... [more ▼]

In this paper, mitochondrial mutants of Chlamydomonas reinhardtii defective for respiratory complex I (NADH:ubiquinone oxidoreductase), complex III (ubiquinol cytochrome c oxidoreductase) and both complexes I and III were analyzed for H2 photoproduction. Several parameters were followed during the S-deficiency stage and the anaerobic stage leading to H2 photoproduction. At the early aerobic S-deficiency stage, starch and neutral lipids accumulated in all strains but their amount was significantly decreased in mutants compared to wild type. During the H2 photoproduction process, whereas starch content strongly decreased in all strains, neutral lipid amount remained nearly unchanged, suggesting that starch degraded by glycolysis is the preferential substrate for energy production during anaerobiosis. The mutants displayed a decrease in H2 photoproduction correlating to the number of active mitochondrial proton-pumping sites lost in the strains. Our results thus highlight the critical role of oxidative phosphorylation during the first (aerobic) stage of S-starvation when carbon resources are accumulated. [less ▲]

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See detailNon-symbiotic hemoglobin-2 leads to an elevated energy state and to a combined increase in polyunsaturated fatty acids and total oil content when over-expressed in developing seeds of transgenic Arabidopsis plants.
Vigeolas, Hélène ULg; Huhn, D.; Geigenberger, P.

in Plant Physiology (2011)

Non-symbiotic hemoglobins are ubiquitously expressed in plants and divided into two different classes based on gene-expression pattern and oxygen binding-properties. Most of the published research has ... [more ▼]

Non-symbiotic hemoglobins are ubiquitously expressed in plants and divided into two different classes based on gene-expression pattern and oxygen binding-properties. Most of the published research has been on the function of class-1 hemoglobins. To investigate the role of class-2 hemoglobins, transgenic Arabidopsis plants were generated over-expressing Arabidopsis hemoglobin-2 (AHb2) under the control of a seed-specific promoter. Over-expression of AHb2 led to a 40% increase in the total fatty acid content of developing and mature seeds in three subsequent generations. This was mainly due to an increase in the poly-unsaturated C18:2 (omega-6) linoleic and C18:3 (omega-3) alpha-linolenic acids. Moreover, AHb2 over-expression led to an increase in the C18:2/C18:1 and C18:3/C18:2 ratios as well as in the C18:3 content in mol% of total fatty acids and in the unsaturation/saturation index of total seed lipids. The increase in fatty-acid content was mainly due to a stimulation of the rate of triacylglycerol synthesis which was attributable to a 3-fold higher energy state and a 2-fold higher sucrose content of the seeds. Under low external oxygen, AHb2 over-expression maintained an up to 5-fold higher energy state and prevented fermentation. This is consistent with AHb2 over-expression results in improved oxygen availability within developing seeds. In contrast to this, over-expression of class-1 hemoglobin did not lead to any significant increase in the metabolic performance of the seeds. Results provide evidence for a specific function of class-2 hemoglobin in seed oil production and in promoting the accumulation of poly-unsaturated fatty acids by facilitating oxygen supply in developing seeds. [less ▲]

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See detailSucrose non-fermenting kinase 1 (SnRK1) coordinates metabolic and hormonal signals during pea cotyledon growth and differentiation.
Radchuk, Ruslana; Emery, R J Neil; Weier, Diana et al

in Plant Journal (The) (2010), 61(2), 324-38

Seed development passes through developmental phases such as cell division, differentiation and maturation: each have specific metabolic demands. The ubiquitous sucrose non-fermenting-like kinase (SnRK1 ... [more ▼]

Seed development passes through developmental phases such as cell division, differentiation and maturation: each have specific metabolic demands. The ubiquitous sucrose non-fermenting-like kinase (SnRK1) coordinates and adjusts physiological and metabolic demands with growth. In protoplast assays sucrose deprivation and hormone supplementation, such as with auxin and abscisic acid (ABA), stimulate SnRK1-promoter activity. This indicates regulation by nutrients: hormonal crosstalk under conditions of nutrient demand and cell proliferation. SnRK1-repressed pea (Pisum sativum) embryos show lower cytokinin levels and deregulation of cotyledonary establishment and growth, together with downregulated gene expression related to cell proliferation, meristem maintenance and differentiation, leaf formation, and polarity. This suggests that at early stages of seed development SnRK1 regulates coordinated cotyledon emergence and growth via cytokinin-mediated auxin transport and/or distribution. Decreased ABA levels and reduced gene expression, involved in ABA-mediated seed maturation and response to sugars, indicate that SnRK1 is required for ABA synthesis and/or signal transduction at an early stage. Metabolic profiling of SnRK1-repressed embryos revealed lower levels of most organic and amino acids. In contrast, levels of sugars and glycolytic intermediates were higher or unchanged, indicating decreased carbon partitioning into subsequent pathways such as the tricarbonic acid cycle and amino acid biosynthesis. It is hypothesized that SnRK1 mediates the responses to sugar signals required for early cotyledon establishment and patterning. As a result, later maturation and storage activity are strongly impaired. Changes observed in SnRK1-repressed pea seeds provide a framework for how SnRK1 communicates nutrient and hormonal signals from auxins, cytokinins and ABA to control metabolism and development. [less ▲]

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See detailManipulating seed quality traits in pea (Pisum sativum L.) for improved feed and food
Vigeolas, Hélène ULg; Domoney, Claire; Charlton, A. et al

in Grain Legumes (2009), 52

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See detailCombined metabolomic and genetic approaches reveal a link between the polyamine pathway and albumin 2 in developing pea seeds.
Vigeolas, Hélène ULg; Chinoy, Catherine; Zuther, Ellen et al

in Plant Physiology (2008), 146(1), 74-82

Several legume seed proteins that are potentially allergenic, poorly digested by farm animals, and/or have undesirable functional properties, have been described. One of these is the albumin protein in ... [more ▼]

Several legume seed proteins that are potentially allergenic, poorly digested by farm animals, and/or have undesirable functional properties, have been described. One of these is the albumin protein in pea (Pisum sativum) called PA2. A naturally occurring mutant line that lacks PA2 has been exploited in studies to determine the biological function of this nonstorage protein in seed development. The mutant, which has a small seed, a tall plant phenotype, and lacks most of the PA2-encoding genes, has been crossed with a standard cultivar, 'Birte,' which contains PA2 to give rise to a recombinant inbred (RI) population. An F(3) line carrying the mutation and having a short plant phenotype has been used to generate backcross (BC) lines with 'Birte.' Despite having a lower albumin content, seeds from the mutant parent and RI lines lacking PA2 have an equivalent or higher seed nitrogen content. Metabolite profiling of seeds revealed major differences in amino acid composition and polyamine content in the two parent lines. This was investigated further in BC lines, where the effects of differences in seed size and plant height between the two parents were eliminated. Here, differences in polyamine synthesis were maintained as was a difference in total seed protein between the BC line lacking PA2 and 'Birte.' Analysis of enzyme activities in the pathways of polyamine synthesis revealed that the differences in spermidine content were attributable to changes in the overall activities of spermidine synthase and arginine decarboxylase. Although the genes encoding spermidine synthase and PA2 both localized to the pea linkage group I, the two loci were shown not to be closely linked and to have recombined in the BC lines. A distinct locus on linkage group III contains a gene that is related to PA2 but expressed predominantly in flowers. The results provide evidence for a role of PA2 in regulating polyamine metabolism, which has important functions in development, metabolism, and stress responses in plants. [less ▲]

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See detailVERFAHREN ZUR VERÄNDERUNG DES ATP-ADP-VERHÄLTNISSES IN ZELLEN
Vigeolas, Hélène ULg; Zank, thorsten; Oswald, Oliver et al

Patent (2007)

(FR) L'invention concerne un procédé de modification du rapport ATP/ADP dans une cellule, un tissu, un organe, un micro-organisme ou une plante par modification de l'activité d'une protéine à hème dans la ... [more ▼]

(FR) L'invention concerne un procédé de modification du rapport ATP/ADP dans une cellule, un tissu, un organe, un micro-organisme ou une plante par modification de l'activité d'une protéine à hème dans la cellule. L'invention porte également sur l'application de ce procédé. [less ▲]

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See detailVERFAHREN ZUR ERHÖHUNG DES GESAMTÖLGELHALTES IN ÖLPFLANZEN
Vigeolas, Hélène ULg; Zank, Thorsten; Oswald, Oliver et al

Patent (2007)

DE) Die Erfindung betrifft Verfahren zur Erhöhung des Gesamtölgehaltes und/oder des Gehalts an Glycerol-3-Phosphat in transgenen Ölpflanzen, die mindestens 20 Gew-% Ölsäure bezogen auf den ... [more ▼]

DE) Die Erfindung betrifft Verfahren zur Erhöhung des Gesamtölgehaltes und/oder des Gehalts an Glycerol-3-Phosphat in transgenen Ölpflanzen, die mindestens 20 Gew-% Ölsäure bezogen auf den Gesamtfettsäuregehalt enthalten, bevorzugt in pflanzlichen Samen, durch Expression von Glycerol-3-phosphatdehydrogenasen (G3PDH) aus Hefen, bevorzugt aus Saccharomyces cerevisiae. Vorteilhaft wird das im Verfahren gewonnene Öl und/oder die freien Fettsäure Polymeren, Nahrungsmitteln, Futtermitteln, Kosmetika, Pharmazeutika oder Produkten mit industriellen Anwendungen zugesetzt. [less ▲]

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See detailThe metabolome of developing pea seeds
Vigeolas, Hélène ULg

Conference (2007)

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See detailIncreasing seed oil content in oil-seed rape (Brassica napus L.) by over-expression of a yeast glycerol-3-phosphate dehydrogenase under the control of a seed-specific promoter.
Vigeolas, Hélène ULg; Waldeck, Peter; Zank, Thorsten et al

in Plant Biotechnology Journal (2007), 5(3), 431-41

Previous attempts to manipulate oil synthesis in plants have mainly concentrated on the genes involved in the biosynthesis and use of fatty acids, neglecting the possible role of glycerol-3-phosphate ... [more ▼]

Previous attempts to manipulate oil synthesis in plants have mainly concentrated on the genes involved in the biosynthesis and use of fatty acids, neglecting the possible role of glycerol-3-phosphate supply on the rate of triacylglycerol synthesis. In this study, a yeast gene coding for cytosolic glycerol-3-phosphate dehydrogenase (gpd1) was expressed in transgenic oil-seed rape under the control of the seed-specific napin promoter. It was found that a twofold increase in glycerol-3-phosphate dehydrogenase activity led to a three- to fourfold increase in the level of glycerol-3-phosphate in developing seeds, resulting in a 40% increase in the final lipid content of the seed, with the protein content remaining substantially unchanged. This was accompanied by a decrease in the glycolytic intermediate dihydroxyacetone phosphate, the direct precursor of glycerol-3-phosphate dehydrogenase. The levels of sucrose and various metabolites in the pathway from sucrose to fatty acids remained unaltered. The results show that glycerol-3-phosphate supply co-limits oil accumulation in developing seeds. This has important implications for strategies that aim to increase the overall level of oil in commercial oil-seed crops for use as a renewable alternative to petrol. [less ▲]

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See detailMetabolic profiling in pea seeds
Vigeolas, Hélène ULg

Conference (2005)

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See detailSymbiotic leghemoglobins are crucial for nitrogen fixation in legume root nodules but not for general plant growth and development.
Ott, Thomas; van Dongen, Joost T; Gunther, Catrin et al

in Current Biology (2005), 15(6), 531-5

Hemoglobins are ubiquitous in nature and among the best-characterized proteins. Genetics has revealed crucial roles for human hemoglobins, but similar data are lacking for plants. Plants contain symbiotic ... [more ▼]

Hemoglobins are ubiquitous in nature and among the best-characterized proteins. Genetics has revealed crucial roles for human hemoglobins, but similar data are lacking for plants. Plants contain symbiotic and nonsymbiotic hemoglobins; the former are thought to be important for symbiotic nitrogen fixation (SNF). In legumes, SNF occurs in specialized organs, called nodules, which contain millions of nitrogen-fixing rhizobia, called bacteroids. The induction of nodule-specific plant genes, including those encoding symbiotic leghemoglobins (Lb), accompanies nodule development. Leghemoglobins accumulate to millimolar concentrations in the cytoplasm of infected plant cells prior to nitrogen fixation and are thought to buffer free oxygen in the nanomolar range, avoiding inactivation of oxygen-labile nitrogenase while maintaining high oxygen flux for respiration. Although widely accepted, this hypothesis has never been tested in planta. Using RNAi, we abolished symbiotic leghemoglobin synthesis in nodules of the model legume Lotus japonicus. This caused an increase in nodule free oxygen, a decrease in the ATP/ADP ratio, loss of bacterial nitrogenase protein, and absence of SNF. However, LbRNAi plants grew normally when fertilized with mineral nitrogen. These data indicate roles for leghemoglobins in oxygen transport and buffering and prove for the first time that plant hemoglobins are crucial for symbiotic nitrogen fixation. [less ▲]

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See detailA new substrate cycle in plants. Evidence for a high glucose-phosphate-to-glucose turnover from in vivo steady-state and pulse-labeling experiments with [13C]glucose and [14C]glucose.
Alonso, Ana Paula; Vigeolas, Hélène ULg; Raymond, Philippe et al

in Plant Physiology (2005), 138(4), 2220-32

Substrate (futile) cycling involving carbohydrate turnover has been widely reported in plant tissues, although its extent, mechanisms, and functions are not well known. In this study, two complementary ... [more ▼]

Substrate (futile) cycling involving carbohydrate turnover has been widely reported in plant tissues, although its extent, mechanisms, and functions are not well known. In this study, two complementary approaches, short and steady-state labeling experiments, were used to analyze glucose metabolism in maize (Zea mays) root tips. Unidirectional rates of synthesis for storage compounds (starch, Suc, and cell wall polysaccharides) were determined by short labeling experiments using [U-14C]glucose and compared with net synthesis fluxes to determine the rate of glucose production from these storage compounds. Steady-state labeling with [1-(13)C]glucose and [U-13C]glucose showed that the redistribution of label between carbon C-1 and C-6 in glucose is close to that in cytosolic hexose-P. These results indicate a high resynthesis flux of glucose from hexose-P that is not accounted for by glucose recycling from storage compounds, thus suggesting the occurrence of a direct glucose-P-to-glucose conversion. An enzyme assay confirmed the presence of substantial glucose-6-phosphatase activity in maize root tips. This new glucose-P-to-glucose cycle was shown to consume around 40% of the ATP generated in the cell, whereas Suc cycling consumes at most 3% to 6% of the ATP produced. The rate of glucose-P cycling differs by a factor of 3 between a maize W22 line and the hybrid maize cv Dea, and is significantly decreased by a carbohydrate starvation pretreatment. [less ▲]

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