Given that most TPS form
multiple products from a single substrate, and given that
these products are often modified by the action of additional
enzymes such as P450 mono-oxygenases, the number of
terpenoids found in any given plant species is likely to
exceed the number of TPS genes present. Comparative and
functional genomics studies, in particular of the large gene
family of TPS, which is key in generating the structural
diversity of plant terpenoids, have also provided new
insights into evolutionary events of repeated gene duplication
and subsequent neo-functionalization, as well as the
role of allelic variations for new terpenoid biosyntheses (e.g.
Keeling et al., 2008; Ko¨ llner et al., 2004; Martin et al., 2004;
Xu et al., 2007).