Plant Physiol. 2010 Jan 13. [Epub ahead of print]
Center for Integrative Genomics, University of Lausanne, Genopode Building, 1015 Lausanne, Switzerland; Department of Biology, Indiana University, Bloomington, 47405, USA; Molecular Plant Physiology and Biophysics, Julius-von-Sachs Institute for Biosciences, Biocenter, Wurzburg University, Julius-von-Sachs-Platz 2, D-97082 Wurzburg, Germany; Department of Biology, Faculty of Science, Kyushu University, Ropponmatsu, Fukuoka 810-8560, Japan; Department of Plant Biology, University of Geneva, 30 Quai Ernest Ansermet, 1211 Geneva 4, Switzerland; Institute of Plant Biology, University of Zurich, Zolliker Strasse 107, 8008 Zurich, Switzerland.
In Arabidopsis thaliana (L.), the blue light photoreceptors phototropins (phot1 and phot2) fine-tune the photosynthetic status of the plant by controlling several important adaptive processes in response to environmental light variations. These processes include stem and petiole phototropism (leaf positioning), leaf flattening, stomatal opening, and chloroplast movements. The PHYTOCHROME KINASE SUBSTRATE (PKS) protein family comprises four members in Arabidopsis (PKS1 to PKS4). PKS1 is a novel phot1 signaling element during phototropism as it interacts with phot1 and the important signaling element NON-PHOTOTROPIC HYPOCOTYL 3 (NPH3), and is required for normal phot1-mediated phototropism. In this study, we have analyzed more globally the role of three PKS members (PKS1, 2 and 4). Systematic analysis of mutants reveals that PKS2 (and to a lesser extent PKS1) act in the same subset of phot-controlled responses as NPH3, namely leaf flattening and positioning. PKS1, PKS2 and NPH3 co-immunoprecipitate with both phot1-GFP and phot2-GFP in leaf extracts. Genetic experiments position PKS2 within phot1 and phot2 pathways controlling leaf positioning and leaf flattening, respectively. NPH3 can act in both phot1 and phot2 pathways, and synergistic interactions observed between pks2 and nph3 mutants suggest complementary roles of PKS2 and NPH3 during phot signaling. Finally, several observations further suggest that PKS2 may regulate leaf flattening and positioning by controlling auxin homeostasis. Together with previous findings, our results indicate that the PKS proteins represent an important family of phot-signaling proteins.