title: Transport of UDP-galactose in plants. Identification and functional characterization of AtUTr1, an Arabidopsis thaliana UDP-galactos/UDP-glucose transporter.
abstract: The synthesis of non-cellulosic polysaccharides and glycoproteins in the plant cell Golgi apparatus requires UDP-galactose as substrate. The topology of these reactions is not known, although the orientation of a plant galactosyltransferase involved in the biosynthesis of galactomannans in fenugreek is consistent with a requirement for UDP-galactose in the lumen of the Golgi cisternae. Here we provide evidence that sealed, right-side-out Golgi vesicles isolated from pea stems transport UDP-galactose into their lumen and transfer galactose, likely to polysaccharides and other acceptors. In addition, we identified and cloned AtUTr1, a gene from Arabidopsis thaliana that encodes a multitransmembrane hydrophobic protein similar to nucleotide sugar transporters. Northern analysis showed that AtUTr1 is indeed expressed in Arabidopsis. AtUTr1 is able to complement the phenotype of MDCK ricin-resistant cells; a mammalian cell line deficient in transport of UDP-galactose into the Golgi. In vitro assays using a Golgi-enriched vesicle fraction obtained from Saccharomyces cerevisiae expressing AtUTr1-MycHis is able to transport UDP-galactose but also UDP-glucose. AtUTr1- MycHis does not transport GDP-mannose, GDP-fucose, CMP-sialic acid, UDP-glucuronic acid, or UDP-xylose when expressed in S. cerevisiae. AtUTr1 is the first transporter described that is able to transport UDP-galactose and UDP-glucose. Thus AtUTr1 may play an important role in the synthesis of glycoconjugates in Arabidopsis that contain galactose and glucose.
authors.affiliation: Department of Biology, Faculty of Sciences and the Millenium Institute in Cell Biology and Biotechnology, University of Chile, Las Palmeras 3425, Nuñoa, Casilla 653, Santiago, Chile.
authors.forename: Lorena
authors.initials: L
authors.lastname: Norambuena
authors.forename: Lorena
authors.initials: L
authors.lastname: Marchant
authors.forename: Patricia
authors.initials: P
authors.lastname: Berninsone
authors.forename: Carlos B
authors.initials: CB
authors.lastname: Hirschberg
authors.forename: Herman
authors.initials: H
authors.lastname: Silva
authors.forename: Ariel
authors.initials: A
authors.lastname: Orellana
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D015152:Blotting, Northern; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004285:Dogs; D018745:Genome, Plant; D006056:Golgi Apparatus / Q000378:metabolism; D050356:Lipid Metabolism; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry*; D018532:Pisum sativum; D010802:Phylogeny; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014531:Uridine Diphosphate Galactose / Q000378:metabolism*; D014532:Uridine Diphosphate Glucose / Q000378:metabolism; D000099237:UDP-Galactose Translocators
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D026901:Membrane Transport Proteins; D009004:Monosaccharide Transport Proteins; D014531:Uridine Diphosphate Galactose; D014532:Uridine Diphosphate Glucose; D000099237:UDP-Galactose Translocators; C466998:UTr1 protein, Arabidopsis