title: The Low Molecular Weight Protein PsaI Stabilizes the Light-Harvesting Complex II Docking Site of Photosystem I.
abstract: PsaI represents one of three low molecular weight peptides of PSI. Targeted inactivation of the plastid PsaI gene in Nicotiana tabacum has no measurable effect on photosynthetic electron transport around PSI or on accumulation of proteins involved in photosynthesis. Instead, the lack of PsaI destabilizes the association of PsaL and PsaH to PSI, both forming the light-harvesting complex (LHC)II docking site of PSI. These alterations at the LHCII binding site surprisingly did not prevent state transition but led to an increased incidence of PSI-LHCII complexes, coinciding with an elevated phosphorylation level of the LHCII under normal growth light conditions. Remarkably, LHCII was rapidly phosphorylated in ΔpsaI in darkness even after illumination with far-red light. We found that this dark phosphorylation also occurs in previously described mutants impaired in PSI function or state transition. A prompt shift of the plastoquinone (PQ) pool into a more reduced redox state in the dark caused an enhanced LHCII phosphorylation in ΔpsaI Since the redox status of the PQ pool is functionally connected to a series of physiological, biochemical, and gene expression reactions, we propose that the shift of mutant plants into state 2 in darkness represents a compensatory and/or protective metabolic mechanism. This involves an increased reduction and/or reduced oxidation of the PQ pool, presumably to sustain a balanced excitation of both photosystems upon the onset of light.
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Magdalena
authors.initials: M
authors.lastname: Plöchinger
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Salar
authors.initials: S
authors.lastname: Torabi
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Marjaana
authors.initials: M
authors.lastname: Rantala
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Mikko
authors.identifier: 0000-0002-2753-9597
authors.initials: M
authors.lastname: Tikkanen
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Marjaana
authors.identifier: 0000-0002-3821-0607
authors.initials: M
authors.lastname: Suorsa
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Poul-Erik
authors.identifier: 0000-0001-6524-7723
authors.initials: PE
authors.lastname: Jensen
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.).
authors.forename: Eva Mari
authors.identifier: 0000-0002-2922-1435
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Department of Biology I, Plant Molecular Biology, Ludwig-Maximilians-University Munich, 80638 Munich, Germany (M.P., S.T., J.M.); Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen, DK-1871 Frederiksberg C, Copenhagen, Denmark (P.-E.J.); and Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014 Turku, Finland (M.R., M.T., M.S., E.M.A.) meurer@bio.lmu.de.
authors.forename: Jörg
authors.identifier: 0000-0003-2973-9514
authors.initials: J
authors.lastname: Meurer
mesh_terms: D001665:Binding Sites / Q000235:genetics; D003624:Darkness; D004579:Electron Transport / Q000235:genetics / Q000528:radiation effects; D015151:Immunoblotting; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000235:genetics / Q000378:metabolism*; D008970:Molecular Weight; D009154:Mutation; D010084:Oxidation-Reduction / Q000528:radiation effects; D010766:Phosphorylation / Q000528:radiation effects; D010788:Photosynthesis / Q000235:genetics / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010971:Plastoquinone / Q000378:metabolism; D011485:Protein Binding; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D010940:Plant Proteins; D010971:Plastoquinone