title: Serine and threonine residues of plant STN7 kinase are differentially phosphorylated upon changing light conditions and specifically influence the activity and stability of the kinase.
abstract: STN7 kinase catalyzes the phosphorylation of the globally most common membrane proteins, the light-harvesting complex II (LHCII) in plant chloroplasts. STN7 itself possesses one serine (Ser) and two threonine (Thr) phosphosites. We show that phosphorylation of the Thr residues protects STN7 against degradation in darkness, low light and red light, whereas increasing light intensity and far red illumination decrease phosphorylation and induce STN7 degradation. Ser phosphorylation, in turn, occurs under red and low intensity white light, coinciding with the client protein (LHCII) phosphorylation. Through analysis of the counteracting LHCII phosphatase mutant tap38/pph1, we show that Ser phosphorylation and activation of the STN7 kinase for subsequent LHCII phosphorylation are heavily affected by pre-illumination conditions. Transitions between the three activity states of the STN7 kinase (deactivated in darkness and far red light, activated in low and red light, inhibited in high light) are shown to modulate the phosphorylation of the STN7 Ser and Thr residues independently of each other. Such dynamic regulation of STN7 kinase phosphorylation is crucial for plant growth and environmental acclimation.
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, FI-20520, Finland.
authors.forename: Andrea
authors.initials: A
authors.lastname: Trotta
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, FI-20520, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, FI-20520, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Rantala
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Gothenburg, 405 30, Sweden.
authors.forename: Björn
authors.initials: B
authors.lastname: Lundin
authors.affiliation: Molecular Plant Biology, Department of Biochemistry, University of Turku, Turku, FI-20520, Finland. evaaro@utu.fi.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D008027:Light; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D013912:Threonine; D012694:Serine; D017346:Protein Serine-Threonine Kinases; C497212:STN7 protein, Arabidopsis
keywords: Arabidopsis thaliana; STN7; light-harvesting complex; phosphoproteomics; selected reaction monitoring