title: A guanine nucleotide exchange factor for Rab5 proteins is essential for intracellular transport of the proglutelin from the Golgi apparatus to the protein storage vacuole in rice endosperm.
abstract: Rice (Oryza sativa) glutelins are synthesized on the endoplasmic reticulum as a precursor, which are then transported via the Golgi to protein storage vacuoles (PSVs), where they are proteolytically processed into acidic and basic subunits. The glutelin precursor mutant6 (glup6) accumulates abnormally large amounts of proglutelin. Map-base cloning studies showed that glup6 was a loss-of-function mutant of guanine nucleotide exchange factor (GEF), which activates Rab GTPase, a key regulator of membrane trafficking. Immunofluorescence studies showed that the transport of proglutelins and α-globulins to PSV was disrupted in glup6 endosperm. Secreted granules of glutelin and α-globulin were readily observed in young glup6 endosperm, followed by the formation of large dilated paramural bodies (PMBs) containing both proteins as the endosperm matures. The PMBs also contained membrane biomarkers for the Golgi and prevacuolar compartment as well as the cell wall component, β-glucan. Direct evidence was gathered showing that GLUP6/GEF activated in vitro GLUP4/Rab5 as well as several Arabidopsis (Arabidopsis thaliana) Rab5 isoforms to the GTP-bound form. Therefore, loss-of-function mutations in GEF or Rab5 disrupt the normal transport of proglutelin from the Golgi to PSVs, resulting in the initial extracellular secretion of these proteins followed, in turn, by the formation of PMBs. Overall, our results indicate that GLUP6/GEF is the activator of Rab5 GTPase and that the cycling of GTP- and GDP-bound forms of this regulatory protein is essential for the intracellular transport of proglutelin and α-globulin from the Golgi to PSVs and in the maintenance of the general structural organization of the endomembrane system in rice seeds.
authors.affiliation: Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Fukuda
authors.forename: Liuying
authors.initials: L
authors.lastname: Wen
authors.forename: Mio
authors.initials: M
authors.lastname: Satoh-Cruz
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawagoe
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Nagamura
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Okita
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Washida
authors.forename: Aya
authors.initials: A
authors.lastname: Sugino
authors.forename: Sonoko
authors.initials: S
authors.lastname: Ishino
authors.forename: Yoshizumi
authors.initials: Y
authors.lastname: Ishino
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ogawa
authors.forename: Mariko
authors.initials: M
authors.lastname: Sunada
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueda
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kumamaru
mesh_terms: D002874:Chromosome Mapping; D056625:Endosperm / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D005816:Genetic Complementation Test; D005983:Glutens / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D046529:Microscopy, Electron, Transmission; D009154:Mutation; D012275:Oryza / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics; D014617:Vacuoles / Q000235:genetics / Q000378:metabolism*; D020696:rab5 GTP-Binding Proteins
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D010940:Plant Proteins; D011498:Protein Precursors; D005983:Glutens; D020696:rab5 GTP-Binding Proteins