Abstract
Many plant secondary metabolites show strong antimicrobial activities and cytotoxicity. They are potentially also toxic to plants but plants producing those active compounds seem to be insensitive to their own metabolites, suggesting that they have a species-specific detoxification mechanism. Cultured cells of Coptis japonica, which produce a yellow isoquinoline alkaloid berberine and accumulate it in the vacuole, have strong berberine tolerance, where as it is highly toxic to plants that do not produce berberine. In order to clarify the detoxification mechanism for own secondary metabolite, we tried to isolate berberine tolerant genes using C. japonica cell culture system as a model. To isolate those genes, a yeast functional screening using a cDNA library constructed with a shuttle vector was performed. One cDNA clone, which conferred clear berberine tolerance, encoded a galactinol synthase (CjGolS). The accumulation level of berberine in CjGolS-expressing yeast was less than 40% compared to the control.
