Abstract
Alkaloids comprise a large group of plant secondary metabolites. We have been studying the molecular mechanism of alkaloid transport using berberine, an isoquinoline alkaloid, as a model in Coptis japonica. Since the involvement of an ABC protein in berberine transport was suggested in cultured C. japonica cells, we isolated a cDNA encoding a multidrug-resistance protein-type ABC protein (Cjmdr1) from the cells. The functional analysis using Xenopus oocytes showed that CjMDR1 transported berberine in an inward direction. Typical inhibitors of ABC proteins, such as vanadate, as well as ATP depletion clearly inhibited this CjMDR1-dependent berberine uptake. In intact plants, Cjmdr1 was preferentially expressed in the rhizome, where berberine was highly accumulated, whereas genes of berberine biosynthetic enzymes were specifically expressed in the root. These findings strongly suggest that CjMDR1 is involved in the translocation of berberine from the root to the rhizome.
