Supplementing the axenic culture with easily available plant
extracts as a rich source of precursor(s) and/or elicitor(s) for CPT
biosynthesis can be a cost effective strategy to enhance CPT production
in the impeded strain of F. solani. Strictosidine is not
unique to CPT biosynthesis but is actually the precursor to over
1800 different monoterpene indole alkaloids (Sachin et al., 2013).
Hence, in an attempt to enhance the CPT yield in the axenic culture
of F. solani MTCC 9668, ethanolic extracts of C. roseus leaves were
used as a presumable source of strictosidine and other precursor
molecules for CPT biosynthesis. The plant is an ornamental shrub
which grows like a weed in the tropics and is the source of about
130 different monoterpene indole alkaloids (but not CPT), all of
which use strictosidine as a precursor (van Der Heijden et al.,
2004). Moreover, the leaf extract of C. roseus was expected to play
a dual role as the strictosidine in the leaf extracts could be taken up
by the culture as a precursor, while the cytotoxic alkaloids including
vincristine and vinblastine might trigger stress responses in the fungus by acting as elicitors thereby increasing the biosynthesis of defence related compounds like CPT.