5.3.2. Heterologous expression
As noted above, C. acuminate is a camptothecin-producing plant in
which geraniol is the biosynthetic precursor of secologanin and
camptothecin. A heterologous host strategy may be useful to gain a more
detailed understanding of camptothecin biosynthesis to enable improved
production to improve its production by employing genetic engineering
approaches. In this regard, genes from C. roseus encoding
strictosidine synthase and geraniol 10-hydroxylase (G10H ), were
transformed into Ophiorrhiza pumila hairy roots.
Co-overexpression of both genes enhances camptothecin production by 56%
in comparison to non-transgenic lines and expression of the single
gene(s) in the heterologous host (Cui et
al., 2015). Microbial organisms are multipurpose heterologous hosts for
pharmaceutically important natural products through metabolic
engineering of their biosynthetic pathways
(Morrone et al., 2010). Expression of the
geraniol synthase gene from C. acuminate for geraniol production
has successfully been achieved. Heterologous expression of geraniol
synthase gene with optimization condition in recombinant E. coliproduces 48.5 mg/l geraniol. This yield was higher than using transgenic
tobacco and yeasts (Chen et al., 2016).
Likewise, co-overexpression of strictosidine synthases (STR ) and
geraniol 10-hydroxylase (G10H ) genes from C. roseusinduced a 56% increase in camptothecin (CPT) production
(Cui et al., 2015) (Table 4 ).