A Plant-Based Platform for the Production of Bark Beetle Pheromones

Bark beetle species of the genera Ips and Dendroctonus represent a threat to forests in both North America and Europe. Under normal circumstances, these beetles recycle dying trees into nutrients, but under certain conditions, growing populations can overcome healthy tree defenses and cause severe economic loss in forestry. The most economically relevant bark beetle species communicate with aggregation pheromones such as ipsdienol, cis-verbenol and trans-verbenol. These pheromones are currently used in synthetic baits as part of control strategies for bark beetles, although their chemical synthesis makes them expensive to use. Here, we explore the possibility of producing bark beetle pheromones in plant factories, since these compounds can be derived from isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) from the mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathways in plants. By the combined expression of enzymes from plants and bark beetles, we show that Arabidopsis thaliana can produce the intermediates β-myrcene (ipsdienol biosynthesis pathway) and α-pinene (verbenol biosynthesis pathway). Furthermore, we were able to produce the final products cis-verbenol and trans-verbenol in stably transformed Arabidopsis, without the addition of external substrates. Finally, we achieved the production of verbenone, an anti-aggregation pheromone derived from verbenol, which deters bark beetles from a host. These results are an important step towards using plants as biofactories for a cheaper and greener production of pheromones and repellent components for artificial baits.