2.1.1.117 analysis transient RNA silencing of scoulerine 9-O-methyltransferase expression by double stranded RNA in Coptis japonica protoplasts. Utility of gene silencing based on in vitro synthesized dsRNA to study function and behavior of endogenous enzymes 658313 2.1.1.117 medicine a Saccharomyces cerevisiae strain is engineered to express seven heterologous enzymes (Papaper somniferum norcoclaurine 6-O-methyltransferase (Ps6OMT), Papaver somniferum 3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase 2 (Ps4'OMT), Papapver somniferum coclaurine N-methyltransferase (PsCNMT), Papaver somniferum berberine bridge enzyme (PsBBE), Thalictrum flavum scoulerine 9-O-methyltransferase (TfS9OMT), Thalictrum flavum canadine synthase (TfCAS), and Arabidopsis thaliana cytochrome P450 reductase 1 (CPR)), resulting in protoberberine alkaloid production from a simple benzylisoquinoline alkaloid precursor. A number of strategies are implemented to improve flux through the pathway, including enzyme variant screening, genetic copy number variation, and culture optimization. This leads to an over 70-fold increase in canadine titer up to 1.8 mg/l. Increased canadine titers enable extension of the pathway to produce berberine, a major constituent of several traditional medicines in a microbial host. This strain is viable at pilot scale 743234