title: GFS9/TT9 contributes to intracellular membrane trafficking and flavonoid accumulation in Arabidopsis thaliana.
abstract: Flavonoids are the most important pigments for the coloration of flowers and seeds. In plant cells, flavonoids are synthesized by a multi-enzyme complex located on the cytosolic surface of the endoplasmic reticulum, and they accumulate in vacuoles. Two non-exclusive pathways have been proposed to mediate flavonoid transport to vacuoles: the membrane transporter-mediated pathway and the vesicle trafficking-mediated pathway. No molecules involved in the vesicle trafficking-mediated pathway have been identified, however. Here, we show that a membrane trafficking factor, GFS9, has a role in flavonoid accumulation in the vacuole. We screened a library of Arabidopsis thaliana mutants with defects in vesicle trafficking, and isolated the gfs9 mutant with abnormal pale tan-colored seeds caused by low flavonoid accumulation levels. gfs9 is allelic to the unidentified transparent testa mutant tt9. The responsible gene for these phenotypes encodes a previously uncharacterized protein containing a region that is conserved among eukaryotes. GFS9 is a peripheral membrane protein localized at the Golgi apparatus. GFS9 deficiency causes several membrane trafficking defects, including the mis-sorting of vacuolar proteins, vacuole fragmentation, the aggregation of enlarged vesicles, and the proliferation of autophagosome-like structures. These results suggest that GFS9 is required for vacuolar development through membrane fusion at vacuoles. Our findings introduce a concept that plants use GFS9-mediated membrane trafficking machinery for delivery of not only proteins but also phytochemicals, such as flavonoids, to vacuoles.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Kyoto, 606-8502, Japan.
authors.forename: Takuji
authors.initials: T
authors.lastname: Ichino
authors.forename: Kentaro
authors.initials: K
authors.lastname: Fuji
authors.forename: Haruko
authors.initials: H
authors.lastname: Ueda
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Koumoto
authors.forename: Junpei
authors.initials: J
authors.lastname: Takagi
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Sasaki
authors.forename: Koh
authors.initials: K
authors.lastname: Aoki
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000502:physiology / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D005419:Flavonoids / Q000378:metabolism*; D035264:Flowers / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D012639:Seeds / Q000235:genetics / Q000502:physiology / Q000648:ultrastructure; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D029681:Arabidopsis Proteins; C000601312:At3g28430 protein, Arabidopsis; D005419:Flavonoids; D008565:Membrane Proteins
keywords: Arabidopsis thaliana; GFS9; Golgi apparatus; flavonoid; transparent testa; vacuole; vesicle trafficking