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1: J Biol Chem. 2002 Sep 6;277(36):32923-9. Epub 2002 May 31.
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Transport of UDP-galactose in plants. Identification and functional characterization of AtUTr1, an Arabidopsis thaliana UDP-galactos/UDP-glucose transporter.

Norambuena L, Marchant L, Berninsone P, Hirschberg CB, Silva H, Orellana A.

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.

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.

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PMID: 12042319 [PubMed - indexed for MEDLINE]