GENOMIC ORGANIZATION OF PLANT TERPENE SYNTHASES AND MOLECULAR EVOLUTIONARY IMPLICATIONS

Institute of Biological Chemsitry, Washington State University, P.O. Box 646340, Pullman, WA 99164-6340 USA

Terpenoids are the largest, most diverse class of plant natural products with numerous functional roles such as hormones, photosynthetic pigments, electron carriers, structural components of membranes; they also serve plant-plant and plant-insect communication. The first committed step of terpenoid biosynthesis is the cyclization of a prenyl diphosphate substrate, geranyl diphosphate (GPP), farnesyl diphosphate (FPP), or geranylgeranyl diphosphate (GGPP), catalyzed by the monoterpene (C₁₀), sesquiterpene (C₁₅), and diterpene synthases (C₂₀), respectively. Over 30 plant terpenoid synthases (cyclases) have been cloned and characterized to date. Herein, we report the genomic DNA sequence isolation and analysis of 5 conifer terpene cyclases, beta-pinene (C₁₀), (E)-alpha-bisabolene (C₁₅), delta-selinene (C₁₅), and abietadiene synthases (C₂₀) from Abies grandis,and taxadiene synthase (C₂₀) from Taxus brevifolia. Genome organization of these gymnosperm terpene synthases was analyzed and compared to nine characterized angiosperm terpene synthases and to eight Arabidopsis thaliana,putative terpene synthase genomic sequences. Based upon intron/exon structure, a pattern was observed which distinguishes diterpene synthases, containing 12-14 introns, from monoterpene and sesquiterpene synthases, containing 6-9 introns. The intron phase of six core introns, (I, VI, IX, X, XI, and XII) are conserved among all terpene synthase genome sequences analyzed. This preliminary study provides a model with which thorough analysis of genome organization of an enzyme family can complement protein phylogenetic studies to make evolutionary inferences.