title: Intrinsically unstructured phosphoprotein TSP9 regulates light harvesting in Arabidopsis thaliana.
abstract: Thylakoid-soluble phosphoprotein of 9 kDa, TSP9, is an intrinsically unstructured plant-specific protein [Song, J., et al. (2006) Biochemistry 45, 15633-15643] with unknown function but established associations with light-harvesting proteins and peripheries of both photosystems [Hansson, M., et al. (2007) J. Biol. Chem. 282, 16214-16222]. To investigate the function of this protein, we used a combination of reverse genetics and biochemical and fluorescence measurement methods in Arabidopsis thaliana. Differential gene expression analysis of plants with a T-DNA insertion in the TSP9 gene using an array of 24000 Arabidopsis genes revealed disappearance of high light-dependent induction of a specific set of mostly signaling and unknown proteins. TSP9-deficient plants had reduced levels of in vivo phosphorylation of light-harvesting complex II polypeptides. Recombinant TSP9 was phosphorylated in light by thylakoid membranes isolated from the wild-type and mutant plants lacking STN8 protein kinase but not by the thylakoids deficient in STN7 kinase, essential for photosynthetic state transitions. TSP9-lacking mutant and RNAi plants with downregulation of TSP9 showed reduced ability to perform state transitions. The nonphotochemical quenching of chlorophyll fluorescence at high light intensities was also less efficient in the mutant compared to wild-type plants. Blue native electrophoresis of thylakoid membrane protein complexes revealed that TSP9 deficiency increased relative stability of photosystem II dimers and supercomplexes. It is concluded that TSP9 regulates plant light harvesting acting as a membrane-binding protein facilitating dissociation of light-harvesting proteins from photosystem II.
authors.affiliation: Department of Clinical and Experimental Medicine, Linköping University, SE-581 85 Linköping, Sweden.
authors.forename: Rikard
authors.initials: R
authors.lastname: Fristedt
authors.forename: Inger
authors.initials: I
authors.lastname: Carlberg
authors.forename: Agnieszka
authors.initials: A
authors.lastname: Zygadlo
authors.forename: Mirva
authors.initials: M
authors.lastname: Piippo
authors.forename: Markus
authors.initials: M
authors.lastname: Nurmi
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Henrik Vibe
authors.initials: HV
authors.lastname: Scheller
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Vener
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D018527:Hydroponics; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008970:Molecular Weight; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D020524:Thylakoids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; D010750:Phosphoproteins; D045332:Photosystem II Protein Complex; D011994:Recombinant Proteins