title: A previously unknown maltose transporter essential for starch degradation in leaves.
abstract: A previously unknown maltose transporter is essential for the conversion of starch to sucrose in Arabidopsis leaves at night. The transporter was identified by isolating two allelic mutants with high starch levels and very high maltose, an intermediate of starch breakdown. The mutations affect a gene of previously unknown function, MEX1. We show that MEX1is a maltose transporter that is unrelated to other sugar transporters. The severe mex1 phenotype demonstrates that MEX1is the predominant route of carbohydrate export from chloroplasts at night. Homologous genes in plants including rice and potato indicate that maltose export is of widespread significance.
authors.affiliation: Department of Metabolic Biology, John Innes Centre, Norwich NR4 7UH, UK.
authors.forename: Totte
authors.initials: T
authors.lastname: Niittylä
authors.forename: Gaëlle
authors.initials: G
authors.lastname: Messerli
authors.forename: Martine
authors.initials: M
authors.lastname: Trevisan
authors.forename: Jychian
authors.initials: J
authors.lastname: Chen
authors.forename: Alison M
authors.initials: AM
authors.lastname: Smith
authors.forename: Samuel C
authors.initials: SC
authors.lastname: Zeeman
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002736:Chloroplasts / Q000378:metabolism; D003001:Cloning, Molecular; D003433:Crosses, Genetic; D018076:DNA, Complementary; D017343:Genes, Plant; D005947:Glucose / Q000378:metabolism; D008320:Maltose / Q000378:metabolism*; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010641:Phenotype; D018515:Plant Leaves / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D013213:Starch / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D018076:DNA, Complementary; D009004:Monosaccharide Transport Proteins; D011993:Recombinant Fusion Proteins; D008320:Maltose; D013213:Starch; D005947:Glucose