title: Deletion of PsbM in tobacco alters the QB site properties and the electron flow within photosystem II.
abstract: Photosystem II, the oxygen-evolving complex of photosynthetic organisms, includes an intriguingly large number of low molecular weight polypeptides, including PsbM. Here we describe the first knock-out of psbM using a transplastomic, reverse genetics approach in a higher plant. Homoplastomic Delta psbM plants exhibit photoautotrophic growth. Biochemical, biophysical, and immunological analyses demonstrate that PsbM is not required for biogenesis of higher order photosystem II complexes. However, photosystem II is highly light-sensitive, and its activity is significantly decreased in Delta psbM, whereas kinetics of plastid protein synthesis, reassembly of photosystem II, and recovery of its activity are comparable with the wild type. Unlike wild type, phosphorylation of the reaction center proteins D1 and D2 is severely reduced, whereas the redox-controlled phosphorylation of photosystem II light-harvesting complex is reversely regulated in Delta psbM plants because of accumulation of reduced plastoquinone in the dark and a limited photosystem II-mediated electron transport in the light. Charge recombination in Delta psbM measured by thermoluminescence oscillations significantly differs from the 2/6 patterns in the wild type. A simulation program of thermoluminescence oscillations indicates a higher Q(B)/Q(-)(B) ratio in dark-adapted mutant thylakoids relative to the wild type. The interaction of the Q(A)/Q(B) sites estimated by shifts in the maximal thermoluminescence emission temperature of the Q band, induced by binding of different herbicides to the Q(B) site, is changed indicating alteration of the activation energy for back electron flow. We conclude that PsbM is primarily involved in the interaction of the redox components important for the electron flow within, outward, and backward to photosystem II.
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Pavan
authors.initials: P
authors.lastname: Umate
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Serena
authors.initials: S
authors.lastname: Schwenkert
authors.affiliation: Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel-Aviv University, 69978 Ramat-Aviv, Tel-Aviv, Israel.
authors.forename: Izhar
authors.initials: I
authors.lastname: Karbat
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Cristina Dal
authors.initials: CD
authors.lastname: Bosco
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Lada
authors.initials: L
authors.lastname: Mlcòchová
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Volz
authors.affiliation: Minerva Avron, Even-Ari Center of Photosynthesis Research, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
authors.forename: Hagit
authors.initials: H
authors.lastname: Zer
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany.
authors.forename: Reinhold G
authors.initials: RG
authors.lastname: Herrmann
authors.affiliation: Department of Biological Chemistry, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
authors.forename: Itzhak
authors.initials: I
authors.lastname: Ohad
authors.affiliation: Department of Biology I, Botany, Ludwig-Maximilians-University, Menzingerstrasse 67, 80638 Munich, Germany. Electronic address: joerg.meurer@lrz.uni-muenchen.de.
authors.forename: Jörg
authors.initials: J
authors.lastname: Meurer
mesh_terms: D001665:Binding Sites / Q000235:genetics; D004579:Electron Transport / Q000235:genetics; D017353:Gene Deletion; D045332:Photosystem II Protein Complex / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D030821:Plants, Genetically Modified; D021122:Protein Subunits / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D011809:Quinones / Q000737:chemistry / Q000378:metabolism*; D014026:Nicotiana / Q000235:genetics* / Q000378:metabolism / Q000502:physiology
chemical_list: D045332:Photosystem II Protein Complex; D021122:Protein Subunits; D011809:Quinones