1. Botanisches Institut, Department Biologie I, Ludwig-Maximilians-Universität, Menzinger Strasse 67, 80638 München, Germany
2. Abteilung für Pflanzenzüchtung und Genetik, Max-Planck-Institut für Züchtungsforschung, Carl-von-Linné-Weg 10, 50829 Köln, Germany
3. Fondazione Parco Tecnologico Padano, Via Albert Einstein Cascina Codazza, 26900 Lodi, Italy
4. Lehrstuhl für Pflanzenphysiologie, Friedrich-Schiller-Universität Jena, Dornburger Strasse 159, 07743 Jena, Germany
5. Institut für Biochemie der Pflanzen, Heinrich-Heine-Universität Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany
6. *These authors contributed equally to this work

Correspondence to: Dario Leister^1,2 Correspondence and requests for materials should be addressed to D.L. (Email: leister@lrz.uni-muenchen.de). Complete data sets are deposited at GEO (http://www.ncbi.nlm.nih.gov/geo/) under accession numbers GSE2620–GSE2622.

Abstract

Illumination changes elicit modifications of thylakoid proteins and reorganization of the photosynthetic machinery. This involves, in the short term, phosphorylation of photosystem II (PSII) and light-harvesting (LHCII) proteins. PSII phosphorylation is thought to be relevant for PSII turnover^{1, 2}, whereas LHCII phosphorylation is associated with the relocation of LHCII and the redistribution of excitation energy (state transitions) between photosystems^{3, 4}. In the long term, imbalances in energy distribution between photosystems are counteracted by adjusting photosystem stoichiometry^{5, 6}. In the green alga Chlamydomonas and the plant Arabidopsis, state transitions require the orthologous protein kinases STT7 and STN7, respectively^{7, 8}. Here we show that in Arabidopsis a second protein kinase, STN8, is required for the quantitative phosphorylation of PSII core proteins. However, PSII activity under high-intensity light is affected only slightly in stn8 mutants, and D1 turnover is indistinguishable from the wild type, implying that reversible protein phosphorylation is not essential for PSII repair. Acclimation to changes in light quality is defective in stn7 but not in stn8 mutants, indicating that short-term and long-term photosynthetic adaptations are coupled. Therefore the phosphorylation of LHCII, or of an unknown substrate of STN7, is also crucial for the control of photosynthetic gene expression.

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