title: Control of STN7 transcript abundance and transient STN7 dimerisation are involved in the regulation of STN7 activity.
abstract: Reversible phosphorylation of LHCII, the light-harvesting complex of photosystem II, controls its migration between the two photosystems (state transitions), and serves to adapt the photosynthetic machinery of plants and green algae to short-term changes in ambient light conditions. The thylakoid kinase STN7 is required for LHCII phosphorylation and state transitions in vascular plants. Regulation of STN7 levels occurs at the post-translational level, depends on the thylakoid redox state, and might involve reversible autophosphorylation. Here, we have analysed the effects of different light conditions and chemical inhibitors on the abundance of STN7 transcripts and their products. This analysis was performed in wild-type Arabidopsis thaliana plants, in several photosynthetic mutants, and in lines overexpressing STN7 (oeSTN7) or expressing mutant variants of STN7 carrying single or double cysteine-serine exchanges. It was found that accumulation of the STN7 protein is also controlled at the level of transcript abundance. Under certain conditions, exposure to high light or far-red light treatment, the relative decreases in LHCII phosphorylation can be attributed to decreases in STN7 abundance. Nevertheless, inhibitor experiments showed that redox control of LHCII kinase activity persists in oeSTN7 plants. STN7 dimers were found in oeSTN7 plants and in lines with single cysteine-serine exchanges, indicating that dimerisation involves disulphide bridges. We speculate that transient STN7 dimerisation is required for STN7 activity, and that the altered dimerisation behaviour of oeSTN7 plants might be responsible for the unusually high phosphorylation of LHCII in the dark found in this genotype.
authors.affiliation: Department Biology I, Ludwig-Maximilians-University Munich (LMU), Plant Molecular Biology (Botany), Großhaderner Strasse 2, Planegg-Martinsried, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wunder
authors.forename: Qiuping
authors.initials: Q
authors.lastname: Liu
authors.forename: Elena
authors.initials: E
authors.lastname: Aseeva
authors.forename: Vera
authors.initials: V
authors.lastname: Bonardi
authors.forename: Dario
authors.initials: D
authors.lastname: Leister
authors.forename: Mathias
authors.initials: M
authors.lastname: Pribil
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism; D045346:Cytochrome b6f Complex / Q000235:genetics / Q000378:metabolism; D004220:Disulfides / Q000378:metabolism; D004229:Dithiothreitol; D004237:Diuron; D004789:Enzyme Activation; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D010766:Phosphorylation; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; D004220:Disulfides; D045342:Light-Harvesting Protein Complexes; D045332:Photosystem II Protein Complex; D012333:RNA, Messenger; D012694:Serine; D045346:Cytochrome b6f Complex; D004237:Diuron; D017346:Protein Serine-Threonine Kinases; C497212:STN7 protein, Arabidopsis; D003545:Cysteine; D004229:Dithiothreitol