Abstract:
Catharanthlls rosellS (L.) G Don is a commercially significant flower species and
in addition is the only source of the monoterpenoid indole alkaloids (MIA) vinblastine
and vincristine, which are key pharmaceutical compounds that are used to combat a
number of different cancers. Therefore, procurement of the antineoplastic agents is
difficult but essential procedure. Alternatively, CatharanthllS tissue cultures have been
investigated as a source of these agents; however they do not produce vindoline, which is
an obligate precursor to vinblastine and vincristine.
The interest in developing high MIA cultivars of Catharantlws rosellS has
prompted metabolic profiling studies to determine the variability of MIA accumulation of
existing flowering cultivars, with particular focus on the vindoline component ofthe
pathway. Metabolic profiling studies that used high performance liquid chromatography
of MIAs from seedlings and young leaf extracts from 50 different flowering cultivars
showed that, except for a single low vindoline cultivar (Vinca Mediterranean DP Orchid),
they all accumulate similar levels of MIAs. Further enzymatic studies with extracts from
young leaves and from developing seedlings showed that the low vindoline cultivar has a
IO-fold lower tabersonine-16-hydroxylase activity than those of CatharanthllS rosellS cv
Little Delicata. Additionally, studies aimed at metabolic engineering ofvindoline
bios}l1thesis in Catharanthus rosellS hairy root cultures have been performed by
expressing the last step in vindoline biosynthesis [Dcacetylvindoline-4-0-
acetyltransferase (DAT)]. Enzymatic profiling studies with transformed hairy roots have
confirmed that over-expressing DAT leads to lines with high levels of O-acetyltransferase
activity when compared to non-expressing hairy roots. One particular DA T over111
expressing hairy root culture (line 7) contained 200 times the OAT activity than leaves of
control lines. Additional MIA analyses revealed that DAT over-expressing hairy roots
have an altered alkaloid profile with significant variation in the accumulation of
h6rhammericine. Further analysis of transformed hairy root line 7 suggests a correlation
between the expression of OAT activity and h6rhammericine accumulation with root
maturation. These studies show that metabolic and selective enzymatic profiling can
enhance our ability to search for relevant MIA pathway mutants and that genetic
engineering with appropriate pathway genes shows promise as a tool to modify the MIA
profile of Catharanthus roseus.
