title: The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis.
abstract: The ability of plants to adapt to changing light conditions depends on a protein kinase network in the chloroplast that leads to the reversible phosphorylation of key proteins in the photosynthetic membrane. Phosphorylation regulates, in a process called state transition, a profound reorganization of the electron transfer chain and remodeling of the thylakoid membranes. Phosphorylation governs the association of the mobile part of the light-harvesting antenna LHCII with either photosystem I or photosystem II. Recent work has identified the redox-regulated protein kinase STN7 as a major actor in state transitions, but the nature of the corresponding phosphatases remained unknown. Here we identify a phosphatase of Arabidopsis thaliana, called PPH1, which is specifically required for the dephosphorylation of light-harvesting complex II (LHCII). We show that this single phosphatase is largely responsible for the dephosphorylation of Lhcb1 and Lhcb2 but not of the photosystem II core proteins. PPH1, which belongs to the family of monomeric PP2C type phosphatases, is a chloroplast protein and is mainly associated with the stroma lamellae of the thylakoid membranes. We demonstrate that loss of PPH1 leads to an increase in the antenna size of photosystem I and to a strong impairment of state transitions. Thus phosphorylation and dephosphorylation of LHCII appear to be specifically mediated by the kinase/phosphatase pair STN7 and PPH1. These two proteins emerge as key players in the adaptation of the photosynthetic apparatus to changes in light quality and quantity.
authors.affiliation: Department of Plant Biology, University of Geneva, 1211 Genève 4, Switzerland.
authors.forename: Alexey
authors.initials: A
authors.lastname: Shapiguzov
authors.forename: Björn
authors.initials: B
authors.lastname: Ingelsson
authors.forename: Iga
authors.initials: I
authors.lastname: Samol
authors.forename: Charles
authors.initials: C
authors.lastname: Andres
authors.forename: Felix
authors.initials: F
authors.lastname: Kessler
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Rochaix
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Vener
authors.forename: Michel
authors.initials: M
authors.lastname: Goldschmidt-Clermont
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D004579:Electron Transport; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D015151:Immunoblotting; D018613:Microscopy, Confocal; D009154:Mutation; D010749:Phosphoprotein Phosphatases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D045332:Photosystem II Protein Complex / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013050:Spectrometry, Fluorescence; D020524:Thylakoids / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C497212:STN7 protein, Arabidopsis; C463465:AHG3 protein, Arabidopsis; D010749:Phosphoprotein Phosphatases