Conifer terpene synthases: Functions in induced plant defense, phylogenetic analyses, and molecular modelin

Terpenes and terpene biosynthesis play major roles in conifer secondary metabolism. Oleoresin, a combination of monoterpenes, sesquiterpenes and diterpenes, is produced by conifers in copious quantities and stored in specialized anatomical structures. These chemicals serve as toxic protectants and mechanical barriers against invading herbivores and pathogens. Norway spruce, Picea abies , is capable of constitutive and inducible terpene-based defenses. Following insect attack or biological elicitation, Norway spruce is induced to form traumatic resin ducts. The studies presented here describe the complex changes induced after methyl jasmonate (MeJA) treatment in this species. Terpene defenses are characterized in a tissue specific manner on anatomical, chemical, biochemical, and molecular levels. The formation of traumatic resin ducts in the developing xylem is initiated after MeJA treatment. Similarly, the accumulation of monoterpenes in both bark and wood and the accumulation of diterpenes in wood begin rapidly after MeJA treatment. Terpene accumulation is preceded temporally by the increase in GGPP synthase, monoterpene synthase (mono-TPS) and diterpene synthase (di-TPS) activities in wood. Mono-TPS and di-TPS transcripts increase in abundance in stem tissue and mono-TPS transcripts increase in foliage following MeJA treatment. MeJA treatment also induces the release of large amounts of volatile oxygenated monoterpenes and sesquiterpenes, compounds that are not emitted from untreated control plants. This emission of volatile terpenes coincides with a two-fold accumulation on terpenes in foliage and a five-fold increase in TPS activities. Ten Norway spruce TPS genes, involved in these constitutive and inducible defenses, were cloned, functionally expressed and characterized. This suite of TPS contains members of the mono-TPS, sesqui-TPS and di-TPS biochemical classes including several of previously not characterized functions. Furthermore, these TPS have provided a new basis to re-examine the phylogeny of the gymnosperm TPS-d subfamily and the TPS family overall. A model of gymnosperm TPS evolution is discussed as are some striking parallels between gymnosperm and angiosperm TPS evolution.