showed a high homology to various plastid localized aromatic prenyltransferases
(Yazaki et al. 2009 ). Thus, it is likely that CsPT-1 accepts GPP from the MEP
pathway in plastids. In addition, CsPT-1 gene expression was distributed in
cannabinoid-producing tissues such as young leaves,flowers, and trichomes. These
results suggest that CsPT-1 is the essential GOT enzyme inC. sativa. As CsPT-1 is
responsible for producing the carbon skeleton of cannabinoids, the gene is, of
course, an invaluable tool for metabolic engineering to control the cannabinoid
content in plants. In addition, the structural aspect of CsPT-1 governing substrate
specificity is also of interest because GPP- and resorcylic acid-specific aromatic
prenyltransferases have rarely been identified to date (Yazaki et al. 2009 ; Munakata
et al. 2014 ), and will provide novel insights into the enzymology of
prenyltransferases.
Interesting chemical diversity is found inCannabis, specifically, a prenylogous
cannabinoid sesquicannabigerol with a farnesyl chain instead of a geranyl group,
was isolated from afiber-type (variety Carma) ofC. sativa(Pollastro et al. 2011 ).
This novel cannabinoid is also of interest from a biosynthetic point of view. A novel
and yet undiscovered prenyltransferase, might produce prenylogous cannabinoids,
because CsPT-1 is highly specific to GPP (Page and Boubakir 2011 ).
8.2.5 Olivetol Synthase, a Polyketide Synthase for OLA
Biosynthesis
Based on the substrate specificity of GOT, it became evident that OLA is thefirst
committed intermediate of cannabinoid production. OLA is a type of alkylresor-
cinol, and has been assumed to be biosynthesized via a polyketide pathway. In fact,
the^13 C incorporation experiments described above clearly demonstrated that the
alkylresorcinol moiety is derived from acetate units (Fellermeier et al. 2001 ). Thus,
a polyketide synthase has been proposed to catalyze the biosynthesis of OLA. In the
proposed reaction mechanism, OLA is synthesized from hexanoyl-CoA and three
molecules of malonyl-CoA via an aldol condensation of a tetraketide intermediate
to form a resorcylic acid structure (Dewick 2002 ).
Recent advances in the study on plant polyketide synthases have demonstrated
that various types of enzymes belong to the chalcone synthase superfamily, and
share high levels of sequence identity (Austin and Noel 2003 ; Abe and Morita
2010 ). Thus, in order to obtain the cDNA for OLA synthase, we performed
homology-based RT-PCR, and consequently obtained a novel cDNA encoding a
polyketide synthase fromC. sativa(Taura et al.2009b). The deduced primary
structure had relatively low (*60%) identity to the chalcone synthases, produced
by a prototypic plant polyketide synthase, implying that the cDNA encodes a novel
enzyme. However, the bacterially expressed recombinant enzyme did not synthe-
size OLA when incubated with hexanoyl-CoA and malonyl-CoA, whereas it pro-
duced olivetol (Fig.8.10a). Thus, we tentatively named this enzyme“olivetol
8 Cannabinoids: Biosynthesis and Biotechnological Applications 195