title: Increased expression of a phloem membrane protein encoded by NHL26 alters phloem export and sugar partitioning in Arabidopsis.
abstract: The complex process of phloem sugar transport involves symplasmic and apoplasmic events. We characterized Arabidopsis thaliana lines ectopically expressing a phloem-specific gene encoding NDR1/HIN1-like26 (NHL26), a putative membrane protein. NHL26 overexpressor plants grew more slowly than wild-type plants, accumulated high levels of carbohydrates in mature leaves, and had a higher shoot biomass, contrasting with slower root growth and a lower seed yield. Similar effects were observed when NHL26 was overexpressed in companion cells, under the control of a companion cell-specific promoter. The soluble sugar content of the phloem sap and sink organs was lower than that in the wild type, providing evidence of a sugar export defect. This was confirmed in a phloem-export assay with the symplastic tracer carboxyfluorescein diacetate. Leaf sugar accumulation was accompanied by higher organic acid, amino acid, and protein contents, whereas analysis of the metabolite profile of phloem sap exudate revealed no change in amino acid or organic acid content, indicating a specific effect on sugar export. NHL26 was found to be located in the phloem plasmodesmata and the endoplasmic reticulum. These findings reveal that NHL26 accumulation affects either the permeability of plasmodesmata or sugar signaling in companion cells, with a specific effect on sugar export.
authors.affiliation: Unité Mixte de Recherche 1318, Institut Jean-Pierre Bourgin, Institut National de la Recherche Agronomique-AgroParisTech, F-78000 Versailles, France.
authors.forename: Françoise
authors.initials: F
authors.lastname: Vilaine
authors.forename: Pavel
authors.initials: P
authors.lastname: Kerchev
authors.forename: Gilles
authors.initials: G
authors.lastname: Clément
authors.forename: Brigitte
authors.initials: B
authors.lastname: Batailler
authors.forename: Thibaud
authors.initials: T
authors.lastname: Cayla
authors.forename: Laurence
authors.initials: L
authors.lastname: Bill
authors.forename: Lionel
authors.initials: L
authors.lastname: Gissot
authors.forename: Sylvie
authors.initials: S
authors.lastname: Dinant
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D050260:Carbohydrate Metabolism / Q000235:genetics*; D016000:Cluster Analysis; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D018613:Microscopy, Confocal; D046529:Microscopy, Electron, Transmission; D008958:Models, Molecular; D009154:Mutation; D020411:Oligonucleotide Array Sequence Analysis; D052585:Phloem / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D030821:Plants, Genetically Modified; D031425:Plasmodesmata / Q000378:metabolism / Q000648:ultrastructure; D011487:Protein Conformation; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D029681:Arabidopsis Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; C585919:NHL26 protein, Arabidopsis