TERPENOID-BASED DEFENSES IN CONIFERS - CDNA CLONING, CHARACTERIZATION, AND FUNCTIONAL EXPRESSION OF WOUND-INDUCIBLE (E)-ALPHA-BISABOLENE SYNTHASE FROM GRAND FIR (ABIES GRANDIS)

(E)-alpha-Bisabolene synthase is one of two wound-inducible sesquiterp ene synthases of grand fir (Abies grandis), and the olefin product of this cyclization reaction is considered to be the precursor in Abies s pecies of todomatuic acid, juvabione, and related insect juvenile horm one mimics. A cDNA encoding (E)-alpha-bisabolene synthase was isolated from a wound-induced-grand fir stem library by a PCR-based strategy a nd was functionally expressed in Escherichia coli and shown to produce (E)-alpha-bisabolene as the sole product from farnesyl diphosphate. T he expressed synthase has a deduced size of 93.8 kDa and a pI of 5.03, exhibits other properties typical of sesquiterpene synthases, and res embles in sequence other terpenoid synthases with the exception of a l arge aminoterminal insertion, corresponding to Pro(81)-Val(296). Biosy nthetically prepared (E)-alpha-[H-3]bisabolene was converted to todoma tuic acid in induced grand fir cells, and the time course of appearanc e of bisabolene synthase mRNA was shown by Northern hybridization to l ag behind that of mRNAs responsible for production of induced oleoresi n monoterpenes. These results suggest that induced (E)-alpha-bisabolen e biosynthesis constitutes part of a defense response targeted to inse ct herbivores, add possibly fungal pathogens, that is distinct from in duced oleoresin monoterpene production.