title: State transitions revisited-a buffering system for dynamic low light acclimation of Arabidopsis.
abstract: The mobile part of the light-harvesting chlorophyll (chl) a/b protein complex (LHCII), composed of the Lhcb1 and Lhcb2 proteins, is the basic unit of chloroplast state transitions--the short term tuning system in balancing the excitation energy between Photosystem (PS) II and PSI. State transitions are catalysed by the thylakoid associated STN7 kinase, and we show here that besides the phosphorylation of the Lhcb1 and Lhcb2 proteins, also the phosphorylation of Lhcb4.2 (CP29) is under the control of the STN7 kinase. Upon growth of Arabidopsis WT and stn7 mutant plants under low and moderate light conditions, the WT plants favoured state 2 whereas stn7 was locked in state 1. The lack of the STN7 kinase and state transitions in stn7 also modified the thylakoid protein contents upon long-term low light acclimation resulting, for example, in low Lhcb1 and in elevated Lhca1 and Lhca2 protein amounts as compared to WT. Adjustments of thylakoid protein contents probably occurred at post-transcriptional level since the DNA microarray experiments from each growth condition did not reveal any significant differences between stn7 and WT transcriptomes. The resulting high Lhcb2/Lhcb1 ratio in stn7 upon growth at low light was accompanied by lower capacity for NPQ than in WT. On the contrary, higher amounts of PsbS in stn7 under moderate and high light growth conditions resulted in higher NPQ compared to WT and consequently also in a protection of PSII against photoinhibition. STN7 kinase and the state transitions are suggested to have a physiological significance for dynamic acclimation to low but fluctuating growth light conditions. They are shown to function as a buffering system upon short high light illumination peaks by shifting the thylakoids from state 2 to state 1 and thereby down regulating the induction of stress-responsive genes, a likely result from transient over-reduction of PSI acceptors.
authors.affiliation: Plant Physiology and Molecular Biology, Department of Biology, University of Turku, FIN-20014 Turku, Finland.
authors.forename: Mikko
authors.initials: M
authors.lastname: Tikkanen
authors.forename: Tikkanen
authors.initials: T
authors.lastname: Mikko
authors.forename: Mirva
authors.initials: M
authors.lastname: Piippo
authors.forename: Piippo
authors.initials: P
authors.lastname: Mirva
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.forename: Suorsa
authors.initials: S
authors.lastname: Marjaana
authors.forename: Sari
authors.initials: S
authors.lastname: Sirpiö
authors.forename: Sirpiö
authors.initials: S
authors.lastname: Sari
authors.forename: Paula
authors.initials: P
authors.lastname: Mulo
authors.forename: Mulo
authors.initials: M
authors.lastname: Paula
authors.forename: Julia
authors.initials: J
authors.lastname: Vainonen
authors.forename: Vainonen
authors.initials: V
authors.lastname: Julia
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Vener
authors.forename: Vener
authors.initials: V
authors.lastname: Alexander
authors.forename: Yagut
authors.initials: Y
authors.lastname: Allahverdiyeva
authors.forename: Allahverdiyeva
authors.initials: A
authors.lastname: Yagut
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.forename: Aro
authors.initials: A
authors.lastname: Eva-Mari
mesh_terms: D000222:Adaptation, Physiological; D017360:Arabidopsis / Q000502:physiology / Q000528:radiation effects*; D015153:Blotting, Western; D004591:Electrophoresis, Polyacrylamide Gel; D008027:Light; D013058:Mass Spectrometry; D020411:Oligonucleotide Array Sequence Analysis; D010748:Phosphopeptides / Q000378:metabolism; D010766:Phosphorylation; D013050:Spectrometry, Fluorescence
chemical_list: D010748:Phosphopeptides