Defense-related
terpenoid biosynthesis in conifers is a dynamic process closely associated with specialized anatomical structures that allows conifers to cope with attack from many potential pests and pathogens. The constitutive and inducible
terpenoid defense of conifers involves several hundred different
monoterpenes,
sesquiterpenes and
diterpenes. Changing arrays of these many compounds are formed from the general
isoprenoid pathway by activities of large gene families for two classes of
enzymes, the
terpene synthases and the
cytochrome P450-dependent
monooxygenases of the CYP720B group. Extensive studies have been conducted on the genomics, proteomics and molecular biochemical characterization of these
enzymes. Many of the conifer
terpene synthases are multi-product
enzymes, and the
P450 enzymes of the CYP720B group are promiscuous in catalyzing multiple oxidations, along homologous series of
diterpenoids, from a broad spectrum of substrates. The
terpene synthases and CYP720B genes respond to authentic or simulated insect attack with increased transcript levels,
protein abundance and
enzyme activity. The constitutive and induced oleoresin
terpenoids for conifer defense accumulate in preformed cortical resin ducts and in xylem
trauma-associated resin ducts. Formation of these resin ducts de novo in the cambium zone and developing xylem, following insect attack or treatment of trees with
methyl jasmonate, is a unique feature of the induced defense of long-lived conifer trees.