Resin-based defenses in conifers

Bark beetle infestation and associated fungal infection are a serious disea se problem in conifer species. Conifers have evolved elaborate, constitutiv e and inducible, terpene-based defense mechanisms to deter insect pests and their symbiotic fungal pathogens. This process involves the secretion of o leoresin, a complex mixture of monoterpenes, sesquiterpenes and diterpenoid acids. Induced oleoresinosis in grand fir (Abies grandis) provides a model system for studying the regulation of defensive terpene biosynthesis and f or identifying relevant genes. The ecological relationships between conifer s, beetle pests, beetle predators and fungal pathogens present several poss ible avenues for manipulating oleoresin composition to improve tree resista nce. Possible examples include chemically disguising the host, adding toxin s and altering the levels of pheromone precursors, attractants for predator s or hormone mimics to disrupt insect development. Strategies and prospects for generating transgenic conifers with increased defense capability are d iscussed.