title: Involvement of CjMDR1, a plant multidrug-resistance-type ATP-binding cassette protein, in alkaloid transport in Coptis japonica.
abstract: Alkaloids comprise one of the largest groups of plant secondary metabolites. Berberine, a benzylisoquinoline alkaloid, is preferentially accumulated in the rhizome of Coptis japonica, a ranunculaceous plant, whereas gene expression for berberine biosynthetic enzymes has been observed specifically in root tissues, which suggests that berberine synthesized in the root is transported to the rhizome, where there is high accumulation. We recently isolated a cDNA encoding a multidrug-resistance protein (MDR)-type ATP-binding cassette (ABC) transporter (Cjmdr1) from berberine-producing cultured C. japonica cells, which is highly expressed in the rhizome. Functional analysis of Cjmdr1 by using a Xenopus oocyte expression system showed that CjMDR1 transported berberine in an inward direction, resulting in a higher accumulation of berberine in Cjmdr1-injected oocytes than in the control. Typical inhibitors of ABC proteins, such as vanadate, nifedipine, and glibenclamide, as well as ATP depletion, clearly inhibited this CjMDR1-dependent berberine uptake, suggesting that CjMDR1 functioned as an ABC transporter. Conventional membrane separation methods showed that CjMDR1 was localized in the plasma membrane of C. japonica cells. In situ hybridization indicated that Cjmdr1 mRNA was expressed preferentially in xylem tissues of the rhizome. These findings strongly suggest that CjMDR1 is involved in the translocation of berberine from the root to the rhizome.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Nobukazu
authors.initials: N
authors.lastname: Shitan
authors.forename: Ingrid
authors.initials: I
authors.lastname: Bazin
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Dan
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Obata
authors.forename: Koji
authors.initials: K
authors.lastname: Kigawa
authors.forename: Kazumitsu
authors.initials: K
authors.lastname: Ueda
authors.forename: Fumihiko
authors.initials: F
authors.lastname: Sato
authors.forename: Cyrille
authors.initials: C
authors.lastname: Forestier
authors.forename: Kazufumi
authors.initials: K
authors.lastname: Yazaki
mesh_terms: D001599:Berberine / Q000378:metabolism*; D001692:Biological Transport; D002462:Cell Membrane / Q000737:chemistry; D002478:Cells, Cultured; D039323:Coptis / Q000378:metabolism*; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D013379:Substrate Specificity
chemical_list: C432805:CJMDR1 protein, Coptis japonica; D010940:Plant Proteins; D012333:RNA, Messenger; D001599:Berberine