FIGURE 6.

(A) Active site phylogeny of putative VviTPS-b proteins from the diploid genomes and functionally characterized enzymes (outer labels) were used to predict the carbocation cascades that proceed from geranyl diphosphate (GPP), as shown in (B). The dark green branches represent enzymes that can utilize both GPP and farnesyl diphosphate (FPP), functioning as single product enzymes to form the monoterpene ocimene or the sesquiterpene (E,E)-alpha-farnesene, respectively. The pink branch is represented by a single product enzyme that proceeds through either the geranyl and/or linalyl cations, with a concerted protonation and deprotonation cascade to form the acyclic monoterpene alcohol limonene. Deprotonation of the geranyl and/or linalyl cations will result in the formation of the acyclic monoterpene ocimene, shown by the blue branch. The light green branch is represented by a multiproduct monoterpene synthase with a cascade proceeding from the linalyl cation to produce acyclic terpenes with a 1,6 ring-closure required to form the terpinyl carbocation and subsequent cyclic terpenes. The yellow branch represents multiproduct enzymes that produce only cyclic monoterpenes, with the gray branch representing a clade without a functional enzyme.