title: MAIGO5 functions in protein export from Golgi-associated endoplasmic reticulum exit sites in Arabidopsis.
abstract: Plant cells face unique challenges to efficiently export cargo from the endoplasmic reticulum (ER) to mobile Golgi stacks. Coat protein complex II (COPII) components, which include two heterodimers of Secretory23/24 (Sec23/24) and Sec13/31, facilitate selective cargo export from the ER; however, little is known about the mechanisms that regulate their recruitment to the ER membrane, especially in plants. Here, we report a protein transport mutant of Arabidopsis thaliana, named maigo5 (mag5), which abnormally accumulates precursor forms of storage proteins in seeds. mag5-1 has a deletion in the putative ortholog of the Saccharomyces cerevisiae and Homo sapiens Sec16, which encodes a critical component of ER exit sites (ERESs). mag mutants developed abnormal structures (MAG bodies) within the ER and exhibited compromised ER export. A functional MAG5/SEC16A-green fluorescent protein fusion localized at Golgi-associated cup-shaped ERESs and cycled on and off these sites at a slower rate than the COPII coat. MAG5/SEC16A interacted with SEC13 and SEC31; however, in the absence of MAG5/SEC16A, recruitment of the COPII coat to ERESs was accelerated. Our results identify a key component of ER export in plants by demonstrating that MAG5/SEC16A is required for protein export at ERESs that are associated with mobile Golgi stacks, where it regulates COPII coat turnover.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Junpei
authors.initials: J
authors.lastname: Takagi
authors.forename: Luciana
authors.initials: L
authors.lastname: Renna
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Koumoto
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.forename: Giovanni
authors.initials: G
authors.lastname: Stefano
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Fukao
authors.forename: Maki
authors.initials: M
authors.lastname: Kondo
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
authors.forename: Federica
authors.initials: F
authors.lastname: Brandizzi
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D030821:Plants, Genetically Modified; D021381:Protein Transport / Q000502:physiology; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D033921:Vesicular Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D011993:Recombinant Fusion Proteins; C517555:SEC16A protein, human; C547881:SEC24 protein, Arabidopsis; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins