title: MAG4/Atp115 is a golgi-localized tethering factor that mediates efficient anterograde transport in Arabidopsis.
abstract: Seed storage proteins are synthesized on rough endoplasmic reticulum (ER) in a precursor form and then are transported to protein storage vacuoles (PSVs) where they are converted to their mature form. To understand the mechanisms by which storage proteins are transported, we screened Arabidopsis maigo mutants to identify those that abnormally accumulate storage protein precursors. Here we describe a new maigo mutant, maigo 4 (mag4), that abnormally accumulates the precursors of two major storage proteins, 12S globulin and 2S albumin, in dry seeds. Electron microscopy revealed that mag4 seed cells abnormally develop a large number of novel structures that exhibit a highly electron-dense core. Some of these structures were surrounded by ribosomes. Immunogold analysis suggests that the electron-dense core is an aggregate of 2S albumin precursors and that 12S globulins are localized around the core. The MAG4 gene was identified as At3g27530, and the MAG4 protein has domains homologous to those found in bovine vesicular transport factor p115. MAG4 molecules were concentrated at cis-Golgi stacks. Our findings suggest that MAG4 functions in the transport of storage protein precursors from the ER to the Golgi complex in plants. In addition, the mag4 mutant exhibits a dwarf phenotype, suggesting that MAG4 is involved in both the transport of storage proteins and in plant growth and development.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.forename: Junpei
authors.initials: J
authors.lastname: Takagi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Koumoto
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
mesh_terms: D055516:2S Albumins, Plant / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D003001:Cloning, Molecular; D018870:Endoplasmic Reticulum, Rough / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism*; D000077614:Golgi Matrix Proteins; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D021381:Protein Transport; D018749:RNA, Plant / Q000235:genetics; D012639:Seeds / Q000254:growth & development / Q000648:ultrastructure; D033921:Vesicular Transport Proteins
chemical_list: D055516:2S Albumins, Plant; D029681:Arabidopsis Proteins; D002352:Carrier Proteins; D000077614:Golgi Matrix Proteins; D018749:RNA, Plant; D033921:Vesicular Transport Proteins; C091580:vesicular transport factor p115