The PPH 1 phosphatase is

The ability of plants to adapt to changing light conditions depends on a protein kinase network in the chloroplast which 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 single 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 la rgely 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. DOI: https://doi.org/10.1073/pnas.0913810107 Posted at the Zurich Open Repository and Archive, University of Zurich ZORA URL: https://doi.org/10.5167/uzh-80910 Accepted Version Originally published at: Shapiguzov, A; Ingelsson, B; Samol, I; Andres, C; Kessler, F; Rochaix, J -D; Vener, A V; GoldschmidtClermont, M (2010). The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis. Proceedings of the National Academy of Sciences of the United States of America, 107(10):4782-4787. DOI: https://doi.org/10.1073/pnas.0913810107 The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis Alexey Shapiguzov , Björn Ingelsson , Iga Samol, Charles Andres, Felix Kessler, Jean-David Rochaix, Alexander V. Vener and Michel Goldschmidt-Clermont +: These authors contributed equally to this work. 1: Departments of Plant Biology and of Molecular Biology, University of Geneva, Quai E. Ansermet 30, 1211 Genève 4, Switzerland 2: Department of Clinical and Experimental Medicine, Linköping University, SE-581 85 Linköping, Sweden 3: University of Neuchâtel, Institute of Biology, Rue Emile Argand 11, CP 158, 2009 Neuchâtel, Switzerland 4: Permanent address: Institute of Plant Physiology, Russian Academy of Sciences, Botanicheskaya 35, 127276 Moscow, Russia.