A genetic engineering approach to improve the carbon fixation in C3 plants by reducing the flux through the photorespiratory pathway. Consequences of the expression of novel activities in chloroplasts of A. thaliana
Zusammenfassung der Projektergebnisse
Transgenic lines expressing the GMK pathway had a higher fresh and dry weight, displayed higher photosynthetic capacities, and showed higher glycine/serine ratios than the wild-type (Fahnenstich 2008; manuscript in preparation). In this way, a cycle was created which resulted in an increased efficiency of CO2 assimilation. This approach also indicated that it is possible to reduce metabolic fluxes through the photorespiratory pathway in A. thaliana by introducing a biochemical CO2 concentrating mechanism in the chloroplasts. At the same time plants expressing the new proposed pathway (GDH-MS plants) were produced and characterized at the molecular level. Further characterization of these plants at the biochemical and physiological levels is being conducted. A. thaliana overexpressing glycolate oxidase (GO plants) were the basis for both proposed pathways. The characterization of the GO plants indicated that the antioxidant machinery of chloroplasts is swamped by the light-induced production of H2O2 in these plants and that its accumulation is responsible for the observed GO phenotype, i.e. retarded development, yellowish rosettes, impaired photosynthetic performance and development of oxidative stress lesions under photorespiratory condition. Moreover, the changes in transcript levels and activities of known oxidative stress responsive components prompt us to propose the GO lines as an inducible system to study oxidative stress phenomena. Finally, the amount of H2O2 produced in the GO plants could be controlled by changing the conditions of growth, thus making the GO plants a challenging model to study the action of plastid-produced H2O2 as a signal molecule. A. thaliana plants overexpressing the C4-maize NADP-ME presented a light regimedependent pale green phenotype with decreased biomass production and photosynthetic competence. Moreover, dark-induced senescence progressed more rapidly in MEm plants compared to the wild type. The data revealed that the phenotype of the MEm plants is a consequence of accelerated carbon-starvation due to extremely low levels of malate and fumarate that are not sufficient to support metabolism and carbon export after sugar depletion under short day/long night conditions. In this way, malate and fumarate emerge as importani forms of fixed carbon that are rapidly consumed during the night period to sustain metabolism in A. thaliana. The double transformants TSS-TSR showed resistance to salt and cold stress. Metabolic profile analysis indicated that proline could bet the cause of this resistance. Further work on the causes of salts and cold resistance is being conducted.
Projektbezogene Publikationen (Auswahl)
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(2007) Alteration of organic acid metabolism in Arabidopsis thaliana overexpressing the maize C4-NADP-malic enzyme causes accelerated senescence during extended darkness. Plant Physiol. 145, 640-652
Fahnenstich H, Saigo M, Niessen M, Zanor MI, Andreo CS, Fernie AR, Drincovich MF, Flügge UI, Maurino VG
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(2008) Arabidopsis thaliana NADP-malic enzyme isoforms: high degree of identity but clearly distinct properties. Plant Mol. Biol. 67, 231-242
Gerrard Wheeler MC, Arias CL, Tronconi MA, Maurino VG, Andreo CS, Drincovich MF
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(2008) Arabidopsis thaliana overexpressing glycolate oxidase in chloroplasts: H2O2-induced changes in primary metabolic pathways. Plant Signal. Behav, 3, 1122-1125
Fahnenstich H, Flügge U-I, Maurino VG
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(2008) C4 decarboxylases. Different solutions for the same biochemical problem: provision of CO2 in the bundle sheath cells. In: C4 photosynthesis and related CO2 concentrating mechanisms; Advances in Photosynthesis and Respiration (AlPH) Series. Editor: Govindjee S
Drincovich MF, Lara MV, Maurino VG, Andreo CS
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(2008) Experimental systems to assess the effects of reactive oxygen species in plant tissues. Plant Signal. Behav. 3, 919-924
Maurino VG, Flügge UI
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(2008) Generation of H2O2 in chloroplasts of Arabidopsis thaliana overexpressing glycolate oxidase as an inducible system to study oxidative stress. Plant Physiol. 148, 719-729
Fahnenstich H, Scarpeci TE, Valle EM, Flügge Ul, Maurino VG
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(2008) Improving salt tolerance. A plant cell comprising enzymatic activities for converting glyoxylate to glycerate. Reference number: EP 08160030.6
Maurino VG and Flügge U-I
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(2008) Malate and fumarate emerge as key players in primary metabolism: Arabidopsis thaliana overexpressing C4-NADP-ME offer a way to manipulate the levels of malate and to analyse the physiological consequences. In: Photosynthesis. Energy from the Sun (Allen JF, Gantt E, Golbeck JH and Osmond B, eds). Springer-Verlag, Heidelberg, Germany
Fahnenstich H, Saigo M, Andreo CS, Drincovich MF, Flügge UI, Maurino VG
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(2008) Means for improving agrobiological traits in a plant by providing a plant cell comprising in its chloroplasts enzymatic activities for converting glycolate into malate. Reference number: EP08151759.1
Maurino VG and Flügge U-I
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(2008) Structure-function relationship studies of the four Arabidopsis thaliana NADP-malic enzyme isoforms. In: Photosynthesis. Energy from the Sun. (Allen JF, Gantt E, Golbeck JH and Osmond B, eds). Springer-Verlag, Heidelberg, Germany
Gerrard Wheeler MA, Arias CL, Tronconi MA, Maurino VG, Andreo CS, Drincovich MF
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(2009) Arabidopsis thaliana Malic enzymes: six isoforms just involved in malate degradation? Plant Science
Maurino VG, Gerrard Wheeler MC, Andreo CS, Drincovich MF
