Genomic Hardwiring and Phenotypic Plasticity of Terpenoid-Based Defenses in Conifers

Abstract

Over evolutionary history, conifers have faced a myriad of threats from phloem- and xylem-feeding insects, defoliating insects, and fungal pathogens. Among the trees' defenses, terpenoids appear to play a major role by harming, disabling, deterring, repelling, or otherwise reducing the fitness of potential invaders. Each of the three classes of terpenoids in conifers, monoterpenes, sesquiterpenes, and diterpenes, are composed of a large number of representative compounds. In most cases, the presence of a particular terpenoid compound in the oleoresin or volatile emissions from a specific conifer can be accounted for by the expression of one of many committed terpene synthase (TPS) genes. However, while each TPS may produce one or a few major products, many produce a variety of minor products with relatively constant component ratios in the product blends. TPS genes exist in conifers in large and functionally diverse, yet monophyletic, gene families. Within these gene families, new biochemical functions of TPS appear to have evolved by gene duplication and changes in the amino acid sequence of the enzyme's active site. In addition, TPS genes may be differentially expressed prior to, during, and following attack by insects or pathogens. Thus, while the production of any particular terpenoid is hardwired into a conifer's genome, these trees have the capacity to change the mixture of terpenoids in oleoresin secretions and volatile emissions. Anatomical changes may also accompany induced terpenoid production, supplementing the plasticity of the molecular and biochemical events.

Do multiple herbivores maintain chemical diversity of Scots pine monoterpenes?

“…This variation is exemplified by the concentrations of single monoterpenes in the needles of trees sampled in the capercaillie study; the mean of the coefficients of variation of monoterpene concentrations calculated across the 42 trees was 57 per cent, in contrast to 11 per cent for needle nitrogen and 18 per cent for needle magnesium concentrations. Constitutive variation in monoterpenes within and between pine populations is genetically determined to a large degree [30][31][32][33]. All herbivore species studied here exert large impacts on Scots pine and all eat needle tissue.…”

Loblolly pine abietadienol/abietadienal oxidase PtAO (CYP720B1) is a multifunctional, multisubstrate cytochrome P450 monooxygenase

“…For example, limonene hydroxylase functions with both (ϩ)-and (Ϫ)-enantiomers of the monoterpene limonene (34), and the diterpene hydoxylase taxadiene 5␣-hydroxylase efficiently utilizes two different double-bond isomers of taxadiene (30). The relatively broad substrate profile of PtAO could have important biological and adaptive functions by generating structural diversity of terpenoid chemical defense in conifers (35). DRA biosynthesis involves initial formation of several different diterpene olefins from GGDP by activity of one or more diTPSs (6).…”

Emissions of BVOC from lodgepole pine in response to mountain pine beetle attack in high and low mortality forest stands

“…This tree exhibited by far the highest MT emission capacity and one of the highest SQT emission rates during the first sampling visit. By now it has been well documented that biotic stressors can enhance emissions of both MT and SQT (Huber et al, 2004;Duhl et al, 2008). Although stressinduced emissions bursts have also been observed following enclosure installation (e.g., Arey et al, 1995), all enclosures were allowed to equilibrate prior to sampling for a minimum of 16 h to minimize this risk.…”