title: A monogalactosyldiacylglycerol synthase found in the green sulfur bacterium Chlorobaculum tepidum reveals important roles for galactolipids in photosynthesis.
abstract: Monogalactosyldiacylglycerol (MGDG), which is conserved in almost all photosynthetic organisms, is the most abundant natural polar lipid on Earth. In plants, MGDG is highly accumulated in the chloroplast membranes and is an important bulk constituent of thylakoid membranes. However, precise functions of MGDG in photosynthesis have not been well understood. Here, we report a novel MGDG synthase from the green sulfur bacterium Chlorobaculum tepidum. This enzyme, MgdA, catalyzes MGDG synthesis using UDP-Gal as a substrate. The gene encoding MgdA was essential for this bacterium; only heterozygous mgdA mutants could be isolated. An mgdA knockdown mutation affected in vivo assembly of bacteriochlorophyll c aggregates, suggesting the involvement of MGDG in the construction of the light-harvesting complex called chlorosome. These results indicate that MGDG biosynthesis has been independently established in each photosynthetic organism to perform photosynthesis under different environmental conditions. We complemented an Arabidopsis thaliana MGDG synthase mutant by heterologous expression of MgdA. The complemented plants showed almost normal levels of MGDG, although they also had abnormal morphological phenotypes, including reduced chlorophyll content, no apical dominance in shoot growth, atypical flower development, and infertility. These observations provide new insights regarding the importance of regulated MGDG synthesis in the physiology of higher plants.
authors.affiliation: Center for Biological Resources and Informatics, Tokyo Institute of Technology, Yokohama 226-8501, Japan. shmasuda@bio.titech.ac.jp
authors.forename: Shinji
authors.initials: S
authors.lastname: Masuda
authors.forename: Jiro
authors.initials: J
authors.lastname: Harada
authors.forename: Makio
authors.initials: M
authors.lastname: Yokono
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Yuzawa
authors.forename: Mie
authors.initials: M
authors.lastname: Shimojima
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Murofushi
authors.forename: Hironori
authors.initials: H
authors.lastname: Tanaka
authors.forename: Hanako
authors.initials: H
authors.lastname: Masuda
authors.forename: Masato
authors.initials: M
authors.lastname: Murakawa
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Haraguchi
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Hideya
authors.initials: H
authors.lastname: Yuasa
authors.forename: Masato
authors.initials: M
authors.lastname: Noguchi
authors.forename: Hirozo
authors.initials: H
authors.lastname: Oh-Oka
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tamiaki
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000033:anatomy & histology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D019414:Chlorobi / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000502:physiology*; D002736:Chloroplasts / Q000378:metabolism / Q000648:ultrastructure; D038983:Galactolipids / Q000096:biosynthesis*; D005700:Galactosyltransferases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D010641:Phenotype; D010788:Photosynthesis / Q000502:physiology*; D010802:Phylogeny; D030821:Plants, Genetically Modified; D016415:Sequence Alignment
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; D038983:Galactolipids; C009909:monogalactosyldiacylglycerol; D005700:Galactosyltransferases; C109990:1,2-diacylglycerol 3-beta-galactosyltransferase