Cells of Catharanthus roseus (L.) G. Don were
genetically engineered to over-express the enzymes
strictosidine synthase (STR; EC 4.3.3.2) and tryptophan
decarboxylase (TDC; EC 4.1.1.28), which catalyze key
steps in the biosynthesis of terpenoid indole alkaloids
(TIAs). The cultures established after Agrobacteriummediated transformation showed wide phenotypic diversity, re¯ecting the complexity of the biosynthetic
pathway. Cultures transgenic for Str consistently
showed tenfold higher STR activity than wild-type
cultures, which favored biosynthetic activity through
the pathway. Two such lines accumulated over
200 mg á L)1 of the glucoalkaloid strictosidine and/or
strictosidine-derived TIAs, including ajmalicine, catharanthine, serpentine, and tabersonine, while maintaining
wild-type levels of TDC activity. Alkaloid accumulation
by highly productive transgenic lines showed considerable instability and was strongly in¯uenced by culture
conditions, such as the hormonal composition of the
medium and the availability of precursors. High transgene-encoded TDC activity was not only unnecessary
for increased productivity, but also detrimental to the
normal growth of the cultures. In contrast, high STR
activity was tolerated by the cultures and appeared to be
necessary, albeit not su cient, to sustain high rates of
alkaloid biosynthesis. We conclude that constitutive
over-expression of Str is highly desirable for increased
TIA production. However, given its complexity, limited
intervention in the TIA pathway will yield positive
results only in the presence of a favorable epigenetic
environment.info:eu-repo/semantics/publishedVersio
