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The PPH1 phosphatase is specifically involved in LHCII dephosphorylation and state transitions in Arabidopsis
University of Geneva, Switzerland.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
University of Geneva, Switzerland.
University of Neuchatel, Switzerland.
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2010 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 107, no 10, 4782-4787 p.Article in journal (Refereed) Published
Abstract [en]

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 tobe 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.

Place, publisher, year, edition, pages
2010. Vol. 107, no 10, 4782-4787 p.
Keyword [en]
Photosynthesis, PP2C phosphatases, thylakoid, plastid
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-54602DOI: 10.1073/pnas.0913810107ISI: 000275368400053OAI: diva2:305998
Available from: 2010-03-26 Created: 2010-03-26 Last updated: 2012-04-18Bibliographically approved
In thesis
1. Reversible modifications of chloroplast proteins and assessment of their functions
Open this publication in new window or tab >>Reversible modifications of chloroplast proteins and assessment of their functions
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxygenic photosynthesis is the process of solar energy conversion into chemical energy in the form of carbohydrates. This event is carried out by plants, algae and cyanobacteria and represents the starting point of the food chain in which most organisms are fed. Due to never-ending changes in the surrounding environment, these photoautotrophic organisms have evolved different acclimatizing strategies to optimize photosynthesis. Many of these fine-tuning mechanisms are dependent on reversible modifications of proteins on a post-translational level. In my research I have been focused on such reversible modifications of proteins in the organelle where photosynthesis takes place – the chloroplast – using the model plant Arabidopsis thaliana.

Within chloroplasts, light-driven reactions of photosynthesis are catalyzed by several multi-subunit protein complexes in the thylakoid membrane. Proteins need to be folded properly in order to function correctly. A rate-limiting step of protein folding is the isomerization of the peptide bond around proline, a step that is catalyzed by enzymes possessing peptidyl-prolyl cis-trans isomerase (PPIase) activity. Within the thylakoid lumen, only two proteins have been found to possess PPIase activity, FKBP13 and CYP20-2. Both these enzymes belong to a protein superfamily called immunophilins - ubiquitous proteins attributed with several different functions. By characterization of Arabidopsis mutants lacking FKBP13 and CYP20-2 I found that PPIase activity is a dispensable function of immunophilins in the thylakoid lumen.

A common post-translational modification of chloroplast proteins is phosphorylation. Protein phosphorylation alters protein functions and is a reversible mechanism utilized by plants for rapid acclimation to changes in the incident light. These events require the action of kinases and phosphatases that either add or remove phosphate groups on proteins, respectively. I have characterized mutants deficient in protein phosphatases responsible for dephosphorylation of thylakoid proteins. These phosphatases, PPH1 and PBCP, represent key players in acclimation of the photosynthetic machinery to changes in light quality/quantity. In addition, I discovered that phosphorylation of pTAC16, a protein associated with the chloroplast gene-expression machinery, depends on the presence of STN7; a light-regulated protein kinase located in the thylakoid membrane. This finding could provide a link between the redox state of the photosynthetic apparatus and chloroplast gene expression.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 67 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1296
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-76727 (URN)978-­‐91-­‐7519-­‐952-­‐8 (ISBN)
Public defence
2012-05-16, Eken, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2012-08-21Bibliographically approved

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