Poster: Membrane Transport

Abs # 1204: CjMDR1 is a novel plant ABC transporter involved in influx of benzylisoquinoline alkaloid, berberine

Presenter:	Shitan, Nobukazu , shitan@kais.kyoto-u.ac.jp
Authors	Shitan, Nobukazu  (A)   Bazin, Ingrid  (B)   Ueda, Kazumitsu  (A)   Sato, Fumihiko  (A)   Forestier, Cyrille  (B)   Yazaki, Kazufumi  (C)
Affiliations:	(A): Laboratory of Molecular & Cellular Biology, Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University (B): CEA-CNRS, Cadarache (C): Laboratory of Gene Expression, Wood Research Institute, Kyoto University

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 specifically observed in root tissues, which suggests that berberine synthesized in the root is transported to the rhizome to be highly accumulated. Our previous attempts to identify the transporter of berberine in C. japonica cells suggested that an ABC protein is involved in berberine transport in this plant ¹⁾. Based on this idea, we isolated Cjmdr1 (Coptis japonica multidrug resistance 1) as a potential berberine transporter from C. japonica cells using RT-PCR. Cjmdr1 was expressed preferentially in the rhizome, where berberine is highly accumulated compared to other organs ²⁾. Functional analysis of Cjmdr1 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 oocytes. 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 functions as an ABC transporter. Conventional membrane separation methods showed that CjMDR1 was localized in the plasma membrane of C. japonica cells. These findings strongly suggest that CjMDR1 is involved in the translocation of berberine from the root to the rhizome ³⁾. ¹⁾ Sakai, K. et al., (2002) J. Exp. Bot. 53, 1879. ²⁾ Yazaki, K. et al., (2001) J. Exp. Bot. 52, 877. ³⁾ Shitan, N. et al., (2003) Proc. Natl. Acad. Sci. U S A. 100, 751.