Monoterpene synthases of loblolly pine (Pinus taeda) produce pinene isomers and enantiomers

The turpentine fraction of conifer oleoresin is a complex mixture of monote rpene olefins and plays important roles in defense and in the mediation of chemical communication between conifer hosts and insect predators. The ster eochemistry of the turpentine monoterpenes is critical in these interaction s, influencing host recognition, toxicity, and potency of derived pheromone s, and the stereochemical composition of these compounds lends insight into their biogenetic origin, with implications for the numbers and types of en zymes responsible and their corresponding genes. Analysis of the oleoresin from several tissues of loblolly pine (Pinus taeda) showed the derived turp entine to consist mainly of (+)-(3R:5R)-alpha-pinene and (-)(3S:5S)-beta-pi nene. Cell-free extracts from xylem tissue yielded three monoterpene syntha ses which together account for the monoterpene isomer and enantiomer conten t of the turpentine of this tissue. The major products of these enzymes, pr oduced from the universal precursor of monoterpenes, geranyl diphosphate, w ere shown to be (+)-alpha-pinene, (-)-alpha-pinene, and (-)-beta-pinene, re spectively. in most properties (molecular mass of similar to 60 kDa, K-m fo r geranyl diphosphate of 3 mu M, requirement for monovalent and divalent ca tions), these enzymes resemble other monoterpene synthases from conifer spe cies. (C) 1999 Academic Press.