title: VvHT1 encodes a monosaccharide transporter expressed in the conducting complex of the grape berry phloem.
abstract: The accumulation of sugars in grape berries requires the co-ordinate expression of sucrose transporters, invertases, and monosaccharide transporters. A monosaccharide transporter homologue (VvHT1, Vitis vinifera hexose transporter 1) has previously been isolated from grape berries at the veraison stage, and its expression was shown to be regulated by sugars and abscisic acid. The present work investigates the function and localization of VvHT1. Heterologous expression in yeast indicates that VvHT1 encodes a monosaccharide transporter with maximal activity at acidic pH (pH 4.5) and high affinity for glucose (K(m)=70 muM). Fructose, mannose, sorbitol, and mannitol are not transported by VvHT1. In situ hybridization shows that VvHT1 transcripts are primarily found in the phloem region of the conducting bundles. Immunofluorescence and immunogold labelling experiments localized VvHT1 in the plasma membrane of the sieve element/companion cell interface and of the flesh cells. The expression and functional properties of VvHT1 suggests that it retrieves the monosaccharides needed to provide the energy necessary for cell division and cell growth at an early stage of berry development.
authors.affiliation: Unité Mixte de Recherches Centre National de la Recherche Scientifique 6161, Transport des Assimilats, Laboratoire de Physiologie, Biochimie et Biologie Moléculaire Végétales, Bâtiment Botanique, Université de Poitiers, Poitiers, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Vignault
authors.forename: Magali
authors.initials: M
authors.lastname: Vachaud
authors.forename: Birsen
authors.initials: B
authors.lastname: Cakir
authors.forename: David
authors.initials: D
authors.lastname: Glissant
authors.forename: Fabienne
authors.initials: F
authors.lastname: Dédaldéchamp
authors.forename: Michael
authors.initials: M
authors.lastname: Büttner
authors.forename: Rossitza
authors.initials: R
authors.lastname: Atanassova
authors.forename: Pierrette
authors.initials: P
authors.lastname: Fleurat-Lessard
authors.forename: Rémi
authors.initials: R
authors.lastname: Lemoine
authors.forename: Serge
authors.initials: S
authors.lastname: Delrot
mesh_terms: D001483:Base Sequence; D001692:Biological Transport; D003001:Cloning, Molecular; D017931:DNA Primers; D018506:Gene Expression Regulation, Plant; D017403:In Situ Hybridization; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D009005:Monosaccharides / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics*; D013402:Sugar Alcohols / Q000378:metabolism; D027843:Vitis / Q000235:genetics / Q000502:physiology*
chemical_list: D017931:DNA Primers; D009004:Monosaccharide Transport Proteins; D009005:Monosaccharides; D010940:Plant Proteins; D013402:Sugar Alcohols