title: Inducible knockdown of MONOGALACTOSYLDIACYLGLYCEROL SYNTHASE1 reveals roles of galactolipids in organelle differentiation in Arabidopsis cotyledons.
abstract: Monogalactosyldiacylglycerol (MGDG) is the major lipid constituent of thylakoid membranes and is essential for chloroplast biogenesis in plants. In Arabidopsis (Arabidopsis thaliana), MGDG is predominantly synthesized by inner envelope-localized MONOGALACTOSYLDIACYLGLYCEROL SYNTHASE1 (MGD1); its knockout causes albino seedlings. Because of the lethal phenotype of the null MGD1 mutant, functional details of MGDG synthesis at seedling development have remained elusive. In this study, we used an inducible gene-suppression system to investigate the impact of MGDG synthesis on cotyledon development. We created transgenic Arabidopsis lines that express an artificial microRNA targeting MGD1 (amiR-MGD1) under the control of a dexamethasone-inducible promoter. The induction of amiR-MGD1 resulted in up to 75% suppression of MGD1 expression, although the resulting phenotypes related to chloroplast development were diverse, even within a line. The strong MGD1 suppression by continuous dexamethasone treatment caused substantial decreases in galactolipid content in cotyledons, leading to severe defects in the formation of thylakoid membranes and impaired photosynthetic electron transport. Time-course analyses of the MGD1 suppression during seedling germination revealed that MGDG synthesis at the very early germination stage is particularly important for chloroplast biogenesis. The MGD1 suppression down-regulated genes associated with the photorespiratory pathway in peroxisomes and mitochondria as well as those responsible for photosynthesis in chloroplasts and caused high expression of genes for the glyoxylate cycle. MGD1 function may link galactolipid synthesis with the coordinated transcriptional regulation of chloroplasts and other organelles during cotyledon greening.
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan (S.F., K.K., H.W.);PRESTO (Y.N.) and CREST (H.W.), JST, Kawaguchi, Saitama 332-0012, Japan; andInstitute of Plant and Microbial Biology, Academia Sinica, Nankang, Tapei 11529, Taiwan (Y.N.).
authors.forename: Sho
authors.initials: S
authors.lastname: Fujii
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan (S.F., K.K., H.W.);PRESTO (Y.N.) and CREST (H.W.), JST, Kawaguchi, Saitama 332-0012, Japan; andInstitute of Plant and Microbial Biology, Academia Sinica, Nankang, Tapei 11529, Taiwan (Y.N.) kkobayashi@bio.c.u-tokyo.ac.jp nakamura@gate.sinica.edu.tw.
authors.forename: Koichi
authors.initials: K
authors.lastname: Kobayashi
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan (S.F., K.K., H.W.);PRESTO (Y.N.) and CREST (H.W.), JST, Kawaguchi, Saitama 332-0012, Japan; andInstitute of Plant and Microbial Biology, Academia Sinica, Nankang, Tapei 11529, Taiwan (Y.N.) kkobayashi@bio.c.u-tokyo.ac.jp nakamura@gate.sinica.edu.tw.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Nakamura
authors.affiliation: Department of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan (S.F., K.K., H.W.);PRESTO (Y.N.) and CREST (H.W.), JST, Kawaguchi, Saitama 332-0012, Japan; andInstitute of Plant and Microbial Biology, Academia Sinica, Nankang, Tapei 11529, Taiwan (Y.N.).
authors.forename: Hajime
authors.initials: H
authors.lastname: Wada
mesh_terms: D017360:Arabidopsis / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D018548:Cotyledon / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D004579:Electron Transport; D038983:Galactolipids / Q000235:genetics / Q000378:metabolism*; D005700:Galactosyltransferases / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D055785:Gene Knockdown Techniques; D010788:Photosynthesis; D018515:Plant Leaves / Q000254:growth & development; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D036226:Seedlings / Q000235:genetics / Q000254:growth & development / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D038983:Galactolipids; C009909:monogalactosyldiacylglycerol; D002734:Chlorophyll; D003907:Dexamethasone; D005700:Galactosyltransferases; C528622:MGD1 protein, Arabidopsis