title: Antisense inhibition of the plastidial glucose-6-phosphate/phosphate translocator in Vicia seeds shifts cellular differentiation and promotes protein storage.
abstract: The glucose-6-phosphate/phosphate translocator (GPT) acts as an importer of carbon into the plastid. Despite the potential importance of GPT for storage in crop seeds, its regulatory role in biosynthetic pathways that are active during seed development is poorly understood. We have isolated GPT1 from Vicia narbonensis and studied its role in seed development using a transgenic approach based on the seed-specific legumin promoter LeB4. GPT1 is highly expressed in vegetative sink tissues, flowers and young seeds. In the embryo, localized upregulation of GPT1 at the onset of storage coincides with the onset of starch accumulation. Embryos of transgenic plants expressing antisense GPT1 showed a significant reduction (up to 55%) in the specific transport rate of glucose-6-phosphate as determined using proteoliposomes prepared from embryos. Furthermore, amyloplasts developed later and were smaller in size, while the expression of genes encoding plastid-specific translocators and proteins involved in starch biosynthesis was decreased. Metabolite analysis and stable isotope labelling demonstrated that starch biosynthesis was also reduced, although storage protein biosynthesis increased. This metabolic shift was characterized by upregulation of genes related to nitrogen uptake and protein storage, morphological variation of the protein-storing vacuoles, and a crude protein content of mature seeds of transgenics that was up to 30% higher than in wild-type. These findings provide evidence that (1) the prevailing level of GPT1 abundance/activity is rate-limiting for the synthesis of starch in developing seeds, (2) GPT1 exerts a controlling function on assimilate partitioning into storage protein, and (3) GPT1 is essential for the differentiation of embryonic plastids and seed maturation.
authors.affiliation: Leibniz-Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstr. 3, 06466 Gatersleben, Germany.
authors.forename: Hardy
authors.initials: H
authors.lastname: Rolletschek
authors.forename: Thuy H
authors.initials: TH
authors.lastname: Nguyen
authors.forename: Rainer E
authors.initials: RE
authors.lastname: Häusler
authors.forename: Twan
authors.initials: T
authors.lastname: Rutten
authors.forename: Cornelia
authors.initials: C
authors.lastname: Göbel
authors.forename: Ivo
authors.initials: I
authors.lastname: Feussner
authors.forename: Ruslana
authors.initials: R
authors.lastname: Radchuk
authors.forename: Annegret
authors.initials: A
authors.lastname: Tewes
authors.forename: Bernhard
authors.initials: B
authors.lastname: Claus
authors.forename: Christian
authors.initials: C
authors.lastname: Klukas
authors.forename: Ute
authors.initials: U
authors.lastname: Linemann
authors.forename: Hans
authors.initials: H
authors.lastname: Weber
authors.forename: Ulrich
authors.initials: U
authors.lastname: Wobus
authors.forename: Ljudmilla
authors.initials: L
authors.lastname: Borisjuk
mesh_terms: D017920:Antiporters / Q000378:metabolism*; D016375:Antisense Elements (Genetics); D002454:Cell Differentiation / Q000502:physiology*; D003001:Cloning, Molecular; D015536:Down-Regulation; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D019298:Glucose-6-Phosphate / Q000378:metabolism; D050356:Lipid Metabolism; D010710:Phosphates / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000378:metabolism; D018087:Plastids / Q000378:metabolism* / Q000648:ultrastructure; D011401:Promoter Regions, Genetic; D012639:Seeds / Q000166:cytology / Q000378:metabolism*; D013213:Starch / Q000378:metabolism; D031306:Vicia / Q000166:cytology / Q000235:genetics / Q000378:metabolism*
chemical_list: D017920:Antiporters; D016375:Antisense Elements (Genetics); D010710:Phosphates; D010940:Plant Proteins; D019298:Glucose-6-Phosphate; D013213:Starch