Monoterpenes induce the heat shock response in Arabidopsis

Monoterpenes are common constituents of essential oils produced by plants. Although it has been reported that monoterpenes enhanced the heat tolerance of plants, the mechanism has not been elucidated. Here, we tested whether 13 monoterpenes promoted the heat shock response (HSR) in Arabidopsis. To assess the HSR-inducing activity of monoterpenes, we produced transgenic Arabidopsis, which has the beta-glucuronidase gene driven by the promoter of a small heat shock protein (HSP17.6C-CI) gene. Results indicated that two monocyclic and four bicyclic monoterpenes showed HSR-inducing activities using the reporter gene system. In particular, (-)-perillaldehyde, which is a monocyclic monoterpene, demonstrated the most potent HSR-inducing activity. (-)-Perillaldehyde significantly inhibited the reduction of chlorophyll content by heat shock in Arabidopsis seedlings. Our previous study indicated that chemical HSR inducers such as geldanamycin and sanguinarine inhibited the activity of plant chaperones in vitro. (-)-Perillaldehyde also inhibited chaperone activity, indicating that it might promote the expression of heat shock protein genes by inhibiting chaperones in the plant cell.