title: Interactions between co-expressed Arabidopsis sucrose transporters in the split-ubiquitin system.
abstract: BACKGROUND
  The Arabidopsis genome contains nine sucrose transporter paralogs falling into three clades: SUT1-like, SUT2 and SUT4. The carriers differ in their kinetic properties. Many transport proteins are known to exist as oligomers. The yeast-based split ubiquitin system can be used to analyze the ability of membrane proteins to interact.
  
  
  RESULTS
  Promoter-GUS fusions were used to analyze the cellular expression of the three transporter genes in transgenic Arabidopsis plants. All three fusion genes are co-expressed in companion cells. Protein-protein interactions between Arabidopsis sucrose transporters were tested using the split ubiquitin system. Three paralogous sucrose transporters are capable of interacting as either homo- or heteromers. The interactions are specific, since a potassium channel and a glucose transporter did not show interaction with sucrose transporters. Also the biosynthetic and metabolizing enzymes, sucrose phosphate phosphatase and sucrose synthase, which were found to be at least in part bound to the plasma membrane, did not specifically interact with sucrose transporters.
  
  
  CONCLUSIONS
  The split-ubiquitin system provides a powerful tool to detect potential interactions between plant membrane proteins by heterologous expression in yeast, and can be used to screen for interactions with membrane proteins as baits. Like other membrane proteins, the Arabidopsis sucrose transporters are able to form oligomers. The biochemical approaches are required to confirm the in planta interaction.
authors.affiliation: Plant Physiology, Zentrum für Molekularbiologie der Pflanzen (ZMBP), Universität Tübingen, Auf der Morgenstelle1, D-72076 Tübingen, Germany. waltraud@bmb.sdu.dk
authors.forename: Waltraud X
authors.initials: WX
authors.lastname: Schulze
authors.forename: Anke
authors.initials: A
authors.lastname: Reinders
authors.forename: John
authors.initials: J
authors.lastname: Ward
authors.forename: Sylvie
authors.initials: S
authors.lastname: Lalonde
authors.forename: Wolf B
authors.initials: WB
authors.lastname: Frommer
mesh_terms: D029681:Arabidopsis Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005966:Glucuronidase / Q000096:biosynthesis / Q000235:genetics; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D025941:Protein Interaction Mapping; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000378:metabolism; D025801:Ubiquitin / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C078729:sucrose transport protein, plant; D005966:Glucuronidase