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A Protein Phosphorylation Threshold for Functional Stacking of Plant Photosynthetic Membranes
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine. Linköping University, Faculty of Health Sciences.
Linköping University, Department of Clinical and Experimental Medicine, Cell Biology. Linköping University, Faculty of Health Sciences.
2010 (English)In: PLOS ONE, ISSN 1932-6203, Vol. 5, no 6Article in journal (Refereed) Published
Abstract [en]

Phosphorylation of photosystem II (PSII) proteins affects macroscopic structure of thylakoid photosynthetic membranes in chloroplasts of the model plant Arabidopsis. In this study, light-scattering spectroscopy revealed that stacking of thylakoids isolated from wild type Arabidopsis and the mutant lacking STN7 protein kinase was highly influenced by cation (Mg++) concentrations. The stacking of thylakoids from the stn8 and stn7stn8 mutants, deficient in STN8 kinase and consequently in light-dependent phosphorylation of PSII, was increased even in the absence of Mg++. Additional PSII protein phosphorylation in wild type plants exposed to high light enhanced Mg++-dependence of thylakoid stacking. Protein phosphorylation in the plant leaves was analyzed during day, night and prolonged darkness using three independent techniques: immunoblotting with anti-phosphothreonine antibodies; Diamond ProQ phosphoprotein staining; and quantitative mass spectrometry of peptides released from the thylakoid membranes by trypsin. All assays revealed dark/night-induced increase in phosphorylation of the 43 kDa chlorophyll-binding protein CP43, which compensated for decrease in phosphorylation of the other PSII proteins in wild type and stn7, but not in the stn8 and stn7stn8 mutants. Quantitative mass spectrometry determined that every PSII in wild type and stn7 contained on average 2.5 +/- 0.1 or 1.4 +/- 0.1 phosphoryl groups during day or night, correspondingly, while less than every second PSII had a phosphoryl group in stn8 and stn7stn8. It is postulated that functional cation-dependent stacking of plant thylakoid membranes requires at least one phosphoryl group per PSII, and increased phosphorylation of PSII in plants exposed to high light enhances stacking dynamics of the photosynthetic membranes.

Place, publisher, year, edition, pages
Public Library of Science (PLoS) , 2010. Vol. 5, no 6
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-57385DOI: 10.1371/journal.pone.0010963ISI: 000278380500009OAI: diva2:325571
Original Publication: Rikard Fristedt, Pontus Granath and Alexander Vener, A Protein Phosphorylation Threshold for Functional Stacking of Plant Photosynthetic Membranes, 2010, PLOS ONE, (5), 6. Copyright: Public Library of Science (PLoS) Available from: 2010-06-18 Created: 2010-06-18 Last updated: 2010-11-26
In thesis
1. Regulatory Functions of Protein Phosphorylation in Plant Photosynthetic Membranes
Open this publication in new window or tab >>Regulatory Functions of Protein Phosphorylation in Plant Photosynthetic Membranes
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Oxygenic photosynthesis is the process in plants, algae and cyanobacteria which converts light energy from the sun into carbohydrates and at the same time produces oxygen from water. Both carbohydrates and oxygen are essential to sustain life on earth. Sunlight is thus a necessity for life, but it can also cause severe problems for photosynthetic organisms, which have evolved several remarkable acclimation systems to cope with light fluctuations in the environment. In higher plants the light driven reactions of photosynthesis proceed in the chloroplast thylakoid membranes highly organized into stacked regions of grana and interconnecting stroma  lamellae. The grana structure is thought to provide functional benefits in the processes of acclimation of the photosynthetic apparatus, particularly in the quality control of photosystem II (PSII) were photodamaged PSII is repaired in a stepwise manner. These processes in the thylakoid membranes were suggested to be regulated by reversible phosphorylation of several proteins in PSII and in its light harvesting antennae complexes (LHCII). Two thylakoid protein kinases, called STN8 and STN7, have been previously identified as responsible for the phosphorylation of PSII and LHCII, respectively. However, molecular mechanisms and the exact functions of these protein phosphorylation events remained largely unknown.

In this thesis research I have demonstrated that the PSII protein phosphorylation is needed for the maintenance of the thylakoid structure in Arabidopsis thaliana chloroplasts. A big part of the work on characterization of proteins and their phosphorylation has been done using novel mass spectrometry techniques, and we further developed a label-free method for quantitative studies of protein phosphorylation. The phosphorylation of PSII proteins was found to be diurnal regulated and required for maintenance of the cation-dependent functional stacking of the thylakoid membranes. This phosphorylation was further shown to be important for the regulated turnover of the D1 protein of PSII.

Phosphorylation of the plant specific TSP9 protein was found to be dependent on STN7 kinase, and plants deficient in TSP9 showed reduced ability to perform the photosynthetic state transitions and to execute thermal dissipation of excess light energy under high light conditions. I also accomplished characterization of the protein phosphorylation in thylakoids from Arabidopsis plants subjected to high light treatment and discovered STN7-dependent phosphorylation of the antenna protein CP29 required for the adaptive disassembly of PSII supercomplexes in conditions of high light stress.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 42 p.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1212
National Category
Medical and Health Sciences
urn:nbn:se:liu:diva-62303 (URN)978-91-7393-301-8 (ISBN)
Public defence
2010-12-17, Linden, Hälsouniversitetet, Campus US, Linköpings universitet, Linköping, 13:00 (English)
Available from: 2010-11-26 Created: 2010-11-26 Last updated: 2010-11-26Bibliographically approved

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