title: Oxygenic photosynthesis without galactolipids.
abstract: The thylakoid membranes of oxygenic photosynthetic organisms are dominated by the galactolipids monogalactosyldiacylglycerol (MGDG) and digalactosyldiacylglycerol (DGDG). In cyanobacteria, MGDG is synthesized via monoglucosyldiacylglycerol (GlcDG). However, the putative epimerase involved in the conversion of GlcDG to MGDG has not been identified. Here we report the identification of the gene for the glucolipid epimerase (mgdE) by comparative genomic analysis. Knockout mutants of mgdE in Synechocystis sp. PCC 6803 lacked both MGDG and DGDG and accumulated GlcDG. The mutants did possess thylakoid membranes and showed normal maximal photosynthetic activity, albeit with reduced utilization of light energy. These results cast doubt on the long-standing belief that oxygenic photosynthesis is absolutely dependent on galactolipids.
authors.affiliation: Graduate School of Science, Shizuoka University, Shizuoka 422-8529, Japan; Research Institute of Electronics, Shizuoka University, Hamamatsu 432-8011, Japan; Precursory Research for Embryonic Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan; dkawai@ipc.shizuoka.ac.jp.
authors.forename: Koichiro
authors.initials: K
authors.lastname: Awai
authors.affiliation: Center for Biological Resources and Informatics, Tokyo Institute of Technology, Yokohama 226-8501, Japan; Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo 152-8551, Japan; Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Tokyo 102-0076, Japan; and.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
authors.affiliation: Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Tokyo 102-0076, Japan; and Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Tokyo 153-8902, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Sato
mesh_terms: D004926:Escherichia coli / Q000235:genetics; D038983:Galactolipids / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D010802:Phylogeny; D019998:Racemases and Epimerases / Q000378:metabolism; D046939:Synechocystis / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D038983:Galactolipids; D019998:Racemases and Epimerases; D010100:Oxygen
keywords: NAD(P)H-dependent oxidoreductase; chromatophore; cluster analysis; endosymbiosis; evolution of photosynthesis