title: Evidence for sequential action of Rab5 and Rab7 GTPases in prevacuolar organelle partitioning.
abstract: GTPases of the Rab5 and Rab7 families were shown to control vacuolar sorting but their specific subcellular localization is controversial in plants. Here, we show that both the canonical as well as the plant-specific Rab5 reside at the newly discovered 'late prevacuolar compartment' (LPVC) while Rab7 partitions to the vacuolar membrane when expressed at low levels. Higher expression levels of wild-type Rab5 GTPases but not Rab7 lead to dose-dependent inhibition of biosynthetic vacuolar transport. In the case of Ara6, this included aberrant co-localization with markers for earlier post-Golgi compartments including the trans-Golgi network. However, nucleotide-free mutants of all three GTPases (Rha1, Ara6 and Rab7) cause stronger dose-dependent inhibition of vacuolar sorting. In addition, nucleotide-free Rha1 led to a later maturation defect and co-localization of markers for the prevacuolar compartment (PVC) and the LPVC. The corresponding Rab7 mutant strongly inhibited vacuolar delivery without merging of PVC and LPVC markers. Evidence for functional differentiation of the Rab5 family members is underlined by the fact that mutant Rha1 expression can be suppressed by increasing wild-type Rha1 levels while mutant Ara6 specifically titrates the nucleotide exchange factor Vps9. A model describing the sequential action of Rab5 and Rab7 GTPases is presented in the light of the current observations.
authors: Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds, LS2 9JT, UK.
authors: Francesca
authors: F
authors: Bottanelli
authors: David C
authors: DC
authors: Gershlick
authors: Jürgen
authors: J
authors: Denecke
mesh_terms: D003600:Cytosol / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D008561:Membrane Fusion / Q000502:physiology; D008954:Models, Biological; D009154:Mutation / Q000502:physiology; D019441:Plant Epidermis / Q000166:cytology*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011523:Protoplasts / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D014162:Transfection / Q000379:methods; D014617:Vacuoles / Q000378:metabolism; D000516:alpha-Amylases / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000090802:rab7 GTP-Binding Proteins; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D008164:Luminescent Proteins; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D000090802:rab7 GTP-Binding Proteins; C075978:rab5 protein, Nicotiana tabacum; D000516:alpha-Amylases; D020691:rab GTP-Binding Proteins