2.1.1.116 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 2.1.1.116 additional information localization of seven biosynthetic enzymes to the sieve elements, unique, cell type-specific biosynthesis of benzylisoquinoline alkaloids in the opium poppy 670561 2.1.1.116 additional information the fragment A11A1 with increased expression in Papaver somniferum plants compared to other Papaver species shows the highest homology (75% identity on protein level) to the 4'-OMT from Coptis japonica 676691