Diversity and Variability of Terpenoid Defences in Conifers: Molecular Genetics, Biochemistry and Evolution of the Terpene Synthase Gene Family in Grand Fir ( Abies Grandis )

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Abstract
This review focuses on the molecular genetics, biochemistry and evolution of terpenoid synthases relevant to terpenoid defences in conifers. In grand fir (Abies grandis) biosynthesis of terpenoids of the three classes of monoterpenes, sesquiterpenes and diterpenes is inducible t y stem wounding at the level of gene activation and increase of enzyme activity of the respective terpene synthases. The monoterpene, sesquiterpene and diterpene synthases utilize prenyl diphosphates of appropriate size as substrates to generate the large diversity of carbon skeletons characteristic of the terpenoid resin of conifers. A large and diverse gene family of grand fir terpene synthases has been cloned and cDNAs arc actively expressed in Escherichia coli for enzyme characterization. The monophyletic group of grand fir monoterpene, sesquiterpene and diterpene synthases represents both constitutively expressed and inducible genes encoding single product and multiple product enzymes. Several events of gene duplication and functional specialization of new synthases occurred during the evolution of terpenoid biosynthesis in grand fir, and gave rise to the enormous diversity and variability of this ancient and successful plant defence against herbivores and pathogens. The review concludes with a perspective of the biotechnological applications of terpenoid synthases for the genetic engineering of agricultural crops and forest trees.