title: Galactolipid synthesis in chloroplast inner envelope is essential for proper thylakoid biogenesis, photosynthesis, and embryogenesis.
abstract: The biogenesis of thylakoid membranes, an indispensable event for the photoautotrophic growth of plants, requires a significant increase in the level of the unique thylakoid membrane lipid monogalactosyldiacylglycerol (MGDG), which constitutes the bulk of membrane lipids in chloroplasts. The final step in MGDG biosynthesis occurs in the plastid envelope and is catalyzed by MGDG synthase. Here we report the identification and characterization of an Arabidopsis mutant showing a complete defect in MGDG synthase 1. The mutant seeds germinated as small albinos only in the presence of sucrose. The seedlings lacked galactolipids and had disrupted photosynthetic membranes, leading to the complete impairment of photosynthetic ability and photoautotrophic growth. Moreover, invagination of the inner envelope, which is not seen in mature WT chloroplasts, was observed in the mutant, supporting an old hypothesis that envelope invagination is a major event in early chloroplast biogenesis. In addition to the defective seedling phenotype, embryo development was arrested in the mutant, although seeds with impaired embryos could germinate heterotrophically. These results demonstrate the importance of galactolipids not only in photosynthetic growth but also in embryogenesis.
authors.affiliation: Graduate School of Bioscience and Biotechnology, Center for Biological Resources and Informatics, and Research Center for the Evolving Earth and Planets, Tokyo Institute of Technology, 4259-B-65 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Kobayashi
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Fukuda
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohta
mesh_terms: D017360:Arabidopsis / Q000196:embryology* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism; D047108:Embryonic Development; D038983:Galactolipids / Q000096:biosynthesis*; D018525:Germination; D007425:Intracellular Membranes / Q000378:metabolism*; D050356:Lipid Metabolism; D009154:Mutation; D010641:Phenotype; D010788:Photosynthesis; D018515:Plant Leaves / Q000166:cytology / Q000648:ultrastructure; D036226:Seedlings / Q000378:metabolism; D012639:Seeds / Q000378:metabolism; D020524:Thylakoids / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D038983:Galactolipids