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Identification of a Photosystem II Phosphatase Involved in Light Acclimation in Arabidopsis
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Department of Botany and Plant Biology and Department of Molecular Biology, University of Geneva, 30 quai E. Ansermet, 1211 Genève 4, Switzerland.
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2012 (English)In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 24, no 6, 2596-2609 p.Article in journal (Refereed) Published
Abstract [en]

Reversible protein phosphorylation plays a major role in the rapid acclimation of the photosynthetic apparatus to changes in light. Two paralogous kinases phosphorylate subsets of thylakoid membrane proteins. STN7 phosphorylates LHCII, the light harvesting antenna of photosystem II (PSII), to balance the activity of the two photosystems through state transitions. STN8 which is mainly involved in phosphorylation of PSII influences folding of the thylakoid membranes and repair of PSII after photo-damage. The rapid reversibility of these acclimatory responses requires the action of protein phosphatases.

In a reverse genetic screen we have identified the chloroplast PP2C phosphatase, PBCP (PHOTOSYSTEM II CORE PHOSPHATASE), which is required for efficient dephosphorylation of PSII. Its targets identified by immunoblotting and mass spectrometry largely coincide with those of the kinase STN8. The recombinant phosphatase is active in vitro on a synthetic substrate or on isolated thylakoids. Thylakoid folding and degradation of D1 after photo-damage are affected in the absence of PBCP, while its over-expression alters the kinetics of state transitions. PBCP and STN8 form an antagonistic kinase and phosphatase pair whose substrate specificity and physiological function are distinct from those of STN7 and the counteracting phosphatase PPH1 (TAP38), but their activities may overlap to some degree.

Place, publisher, year, edition, pages
2012. Vol. 24, no 6, 2596-2609 p.
National Category
Natural Sciences
URN: urn:nbn:se:liu:diva-76725DOI: 10.3410/f.717847818.793153384ISI: 000306919300027OAI: diva2:516428

On the day of the defence date the title of the article was The role of PHOTOSYSTEM II CORE PHOSPHATASE in light acclimation of photosynthesis in Arabidopsis.

Funding agencies| (RTD Plant Growth in a Changing Environment)||Swiss National Foundation|3100AO-11771231003A_133089/1|FP7 Marie-Curie Initial Training Network (ITN) COSI|ITN 2008 GA 215-174|EMBO postdoctoral fellowship||Swedish Research Council|2008-5490|

Available from: 2012-04-18 Created: 2012-04-18 Last updated: 2012-08-30Bibliographically 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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