title: Guanine nucleotide exchange factor 2 for Rab5 proteins coordinated with GLUP6/GEF regulates the intracellular transport of the proglutelin from the Golgi apparatus to the protein storage vacuole in rice endosperm.
abstract: Rice glutelin polypeptides are initially synthesized on the endoplasmic reticulum (ER) membrane as a proglutelin, which are then transported to the protein storage vacuole (PSV) via the Golgi apparatus. Rab5 and its cognate activator guanine nucleotide exchange factor (GEF) are essential for the intracellular transport of proglutelin from the Golgi apparatus to the PSV. Results from previous studies showed that the double recessive type of glup4/rab5a and glup6/gef mutant accumulated much higher amounts of proglutelin than either parent line. The present study demonstrates that the double recessive type of glup4/rab5a and glup6/gef mutant showed not only elevated proglutelin levels and much larger paramural bodies but also reduced the number and size of PSVs, indicating a synergistic mutation effect. These observations led us to the hypothesis that other isoforms of Rab5 and GEF also participate in the intracellular transport of rice glutelin. A database search identified a novel guanine nucleotide exchange factor, Rab5-GEF2. Like GLUP6/GEF, Rab5-GEF2 was capable of activating Rab5a and two other Rab5 isoforms in in vitro GTP/GDP exchange assays. GEF proteins consist of the helical bundle (HB) domain at the N-terminus, Vps9 domain, and a C-terminal region. By the deletion analysis of GEFs, the HB domain was found essential for the activation of Rab5 proteins.
authors.affiliation: Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan Tobacco Research Institute, Chinese Academy of Agricultural Science, Qingdao 266101, China.
authors.forename: Liuying
authors.initials: L
authors.lastname: Wen
authors.affiliation: Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Masako
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: Graduated School of Science, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Mariko
authors.initials: M
authors.lastname: Sunada
authors.affiliation: Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Sonoko
authors.initials: S
authors.lastname: Ishino
authors.affiliation: Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan.
authors.forename: Yoshizumi
authors.initials: Y
authors.lastname: Ishino
authors.affiliation: Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340, USA.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Okita
authors.affiliation: Department of General Education, Yamaguchi Prefectural University, Yamaguchi 753-8502, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Ogawa
authors.affiliation: Graduated School of Science, University of Tokyo, Tokyo 113-0033, Japan Japan Science and Technology Agency (JST), PRESTO, Saitama 332-0012, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Ueda
authors.affiliation: Faculty of Agriculture, Kyushu University, Fukuoka 812-8581, Japan kumamaru@agr.kyushu-u.ac.jp.
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Kumamaru
mesh_terms: D056625:Endosperm; D005983:Glutens / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport / Q000235:genetics; D017422:Sequence Analysis, DNA; D014617:Vacuoles / Q000378:metabolism; D020696:rab5 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D010940:Plant Proteins; D005983:Glutens; D020696:rab5 GTP-Binding Proteins
keywords: Guanine nucleotide exchange factor; Rab5; helical bundle domain; in vitro GEF assay; intracellular transport; storage protein.