title: Structural and functional characterization of ferredoxin-NADP+-oxidoreductase using knock-out mutants of Arabidopsis.
abstract: In Arabidopsis thaliana, the chloroplast-targeted enzyme ferredoxin-NADP+-oxidoreductase (FNR) exists as two isoforms, AtLFNR1 and AtLFNR2, encoded by the genes At5g66190 and At1g20020, respectively. Both isoforms are evenly distributed between the thylakoids and soluble stroma, and they are separated by two-dimensional electrophoresis in four distinct spots, suggesting post-translational modification of both isoforms. To reveal the functional specificity of AtLFNR1, we have characterized the T-DNA insertion mutants with an interrupted At5g66190 gene. Absence of AtLFNR1 resulted in a reduced size of the rosette with pale green leaves, which was accompanied by a low content of chlorophyll and light-harvesting complex proteins. Also the photosystem I/photosystem II (PSI/PSII) ratio was significantly lower in the mutant, but the PSII activity, measured as the F(V)/F(M) ratio, remained nearly unchanged and the excitation pressure of PSII was lower in the mutants than in the wild type. A slow re-reduction rate of P700 measured in the mutant plants suggested that AtLFNR1 is involved in PSI-dependent cyclic electron flow. Impaired function of FNR also resulted in decreased capacity for carbon fixation, whereas nitrogen metabolism was upregulated. In the absence of AtLFNR1, we found AtLFNR2 exclusively in the stroma, suggesting that AtLFNR1 is required for membrane attachment of FNR. Structural modeling supports the formation of a AtLFNR1-AtLFNR2 heterodimer that would mediate the membrane attachment of AtLFNR2. Dimer formation, in turn, might regulate the distribution of electrons between the cyclic and linear electron transfer pathways according to environmental cues.
authors.affiliation: Laboratory Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Minna
authors.initials: M
authors.lastname: Lintala
authors.forename: Yagut
authors.initials: Y
authors.lastname: Allahverdiyeva
authors.forename: Heidi
authors.initials: H
authors.lastname: Kidron
authors.forename: Mirva
authors.initials: M
authors.lastname: Piippo
authors.forename: Natalia
authors.initials: N
authors.lastname: Battchikova
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.forename: Eevi
authors.initials: E
authors.lastname: Rintamäki
authors.forename: Tiina A
authors.initials: TA
authors.lastname: Salminen
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Paula
authors.initials: P
authors.lastname: Mulo
mesh_terms: D017360:Arabidopsis / Q000201:enzymology*; D005287:Ferredoxin-NADP Reductase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism*; D010641:Phenotype; D010788:Photosynthesis / Q000502:physiology; D030821:Plants, Genetically Modified; D020033:Protein Isoforms / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D020524:Thylakoids / Q000737:chemistry*; D014158:Transcription, Genetic
chemical_list: D020033:Protein Isoforms; D005287:Ferredoxin-NADP Reductase; D009584:Nitrogen