Defensive resin biosynthesis in conifers

Tree killing bark beetles and their vectored fungal pathogens are the most destructive agents of conifer forests worldwide. Conifers defend against at tack by the constitutive and inducible production of oleoresin, a complex m ixture of mono-, sesqui-, and diterpenoids that accumulates at the wound si te to kill invaders and both flush and seal the injury. Although toxic to t he bark beetle and fungal pathogen, oleoresin also plays a central role in the chemical ecology of these boring insects, from host selection to pherom one signaling and tritrophic level interactions. The biochemistry of oleore sin terpenoids is reviewed, and the regulation of production of this unusua l plant secretion is described in the context of bark beetle infestation dy namics with respect to the function of the turpentine and rosin components. Recent advances in the molecular genetics of terpenoid biosynthesis provid e evidence for the evolutionary origins of oleoresin and permit considerati on of genetic engineering strategies to improve conifer defenses as a compo nent of modern forest biotechnology.