Chemical Ecology & Phytochemistry-2006

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8 SCHMIDT, et al. Fig. 1.3: Symptoms of fungal infection in Norway spruce after massive inoculation with the blue-stain fungus Ceratocystis polonica. In areas that have been successfully colonized by the fungus the phloem and cambial areas are necrotic and the sapwood is blue-stained (arrowheads). The Search for Genes Encoding Short-Chain Isoprenyl Diphosphate Synthases- Branch-point Enzymes of Terpene Biosynthesis To study more precisely the function of induced terpene resins in defense, it is necessary to develop a method to manipulate terpene formation without affecting other possible defenses. For this purpose, we initiated a long-term study of the molecular biology of induced terpene biosynthesis in P. abies. The basic outline of terpene formation is well understood 14 (Fig. 1.4). The C 5 building blocks of all terpenes are synthesized via the mevalonate pathway (localized in the cytosol) from
INDUCED CHEMICAL DEFENSES IN CONIFERS 9 acetyl-CoA or via the methylerythritol phosphate pathway (localized in the plastids) from pyruvate and glyceraldehyde-3-phosphate. These pathways produce isopententyl diphosphate (IPP, C 5 ) and its isomer dimethylallyl diphosphate (DMAPP, C 5 ). IPP and DMAPP then condense in a series of reactions to form isoprenyl diphosphates of 10, 15, 20 or more carbon atoms. Next, these different length diphosphate intermediates undergo reactions catalyzed by terpene synthases (principally cyclizations) to form the parent carbon skeletons of the major terpene classes. The parent carbon skeletons in turn undergo a series of secondary reactions, largely oxidations or reductions, to form the enormous variety of terpenes found in plants. Acetyl-CoA Pyruvate Glyceraldehyde-3-phosphate MEVALONATE PATHWAY METHYLERYTHRITOL PHOSPHATE PATHWAY OPP OPP IPP (C 5 ) DMAPP (C 5 ) Isoprenyl diphosphate synthases 1xIPP 2xIPP 3xIPP GPP (C 10 ) Terpene synthases OPP MONOTERPENES (C 10 ) (-)/(+)-α/ß-pinene (-)-limonene ß-phellandrene FPP (C 15 ) OPP SESQUITERPENES (C 15 ) (E)-α-bisabolene (E)-ß-farnesene GGPP (C 20 ) OPP DITERPENES (C 20 ) levopimaric acid abietadiene Fig. 1.4: Outline of terpenoid biosynthesis from isopentenyl diphosphate (IPP) via dimethylallyl diphosphate (DMAPP), geranyl diphosphate (GPP), farnesyl diphosphate (FPP) and geranylgeranyl diphosphate (GGPP). These reactions are catalyzed by isoprenyl diphosphate synthases and terpene synthases. The major products of the monoterpene, sesquiterpene, and diterpene pathways that constitute the oleoresin of Picea abies are listed. The general precursor IPP is derived either from the plastidial methylerythritol phosphate (MEP) pathway or the cytosolic mevalonate pathway.
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