title: Thioredoxins Play a Crucial Role in Dynamic Acclimation of Photosynthesis in Fluctuating Light.
abstract: Sunlight represents the energy source for photosynthesis and plant growth. When growing in the field, plant photosynthesis has to manage strong fluctuations in light intensities. Regulation based on the thioredoxin (Trx) system is believed to ensure light-responsive control of photosynthetic reactions in the chloroplast. However, direct evidence for a role of this system in regulating dynamic acclimation of photosynthesis in fluctuating conditions is largely lacking. In this report we show that the ferredoxin-dependent Trxs m1 and m2 as well as the NADPH-dependent NTRC are both indispensable for photosynthetic acclimation in fluctuating light intensities. Arabidopsis mutants with combined deficiency in Trxs m1 and m2 show wild-type growth and photosynthesis under constant light condition, while photosynthetic parameters are strongly modified in rapidly alternating high and low light. Two independent trxm1m2 mutants show lower photosynthetic efficiency in high light, but surprisingly significantly higher photosynthetic efficiency in low light. Our data suggest that a main target of Trx m1 and m2 is the NADP-malate dehydrogenase involved in export of excess reductive power from the chloroplast. The decreased photosynthetic efficiency in the high-light peaks may thus be explained by a reduced capacity of the trxm1m2 mutants in the rapid light activation of this enzyme. In the ntrc mutant, dynamic responses of non-photochemical quenching of excitation energy and plastoquinone reduction state both were strongly attenuated in fluctuating light intensities, leading to a massive decrease in PSII quantum efficiency and a specific decrease in plant growth under these conditions. This is likely due to the decreased ability of the ntrc mutant to control the stromal NADP(H) redox poise. Taken together, our results indicate that NTRC is indispensable in ensuring the full range of dynamic responses of photosynthesis to optimize photosynthesis and maintain growth in fluctuating light, while Trxs m1 and m2 are indispensable for full activation of photosynthesis in the high-light periods but negatively affect photosynthetic efficiency in the low-light periods of fluctuating light.
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Ina
authors.initials: I
authors.lastname: Thormählen
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Department 3, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
authors.forename: Arkadiusz
authors.initials: A
authors.lastname: Zupok
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Department 3, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
authors.forename: Josephin
authors.initials: J
authors.lastname: Rescher
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Leger
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Weissenberger
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Groysman
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany.
authors.forename: Anne
authors.initials: A
authors.lastname: Orwat
authors.affiliation: Institute of Plant Sciences Paris Saclay (IPS2), UMR 9213/UMR1403, Université Paris Sud, CNRS, INRA, Université d'Evry, Université Paris Diderot, Sorbonne Paris Cité, Bâtiment 630, 91405 Orsay, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Chatel-Innocenti
authors.affiliation: Institute of Plant Sciences Paris Saclay (IPS2), UMR 9213/UMR1403, Université Paris Sud, CNRS, INRA, Université d'Evry, Université Paris Diderot, Sorbonne Paris Cité, Bâtiment 630, 91405 Orsay, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Issakidis-Bourguet
authors.affiliation: Max-Planck-Institut für Molekulare Pflanzenphysiologie, Department 3, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Armbruster
authors.affiliation: Department Biologie I, Ludwig-Maximilians-Universität München, Grosshaderner Straße 2-4, 82152 Martinsried, Germany. Electronic address: geigenberger@bio.lmu.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Geigenberger
mesh_terms: D000064:Acclimatization; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D054479:Chloroplast Thioredoxins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D008027:Light; D050538:Malate Dehydrogenase (NADP+) / Q000378:metabolism; D009154:Mutation; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000502:physiology* / Q000528:radiation effects; D013880:Thioredoxin-Disulfide Reductase / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D054479:Chloroplast Thioredoxins; D002734:Chlorophyll; D050538:Malate Dehydrogenase (NADP+); C000612940:NTRC protein, Arabidopsis; D013880:Thioredoxin-Disulfide Reductase
keywords: NTRC; arabidopsis; chloroplast; light signalling; redox regulation; thioredoxin