Loliolide, a Carotenoid Metabolite, Is a Potential Endogenous Inducer of Herbivore Resistance.

Jasmonic acid (JA) plays an important role in the induction of herbivore resistance in many plants. However, JA-independent herbivore resistance has been suggested. An herbivore-resistance-inducing substance was isolated from -infected tobacco () leaves in which a hypersensitive response (HR) was induced and identified as loliolide, which has been identified as a β-carotene metabolite. When applied to tomato () leaves, loliolide decreased the survival rate of the two-spotted spider mite, , egg deposition by the same pest, and the survival rate of larvae of the common cutworm without exhibiting toxicity against these herbivores. Endogenous loliolide levels increased not only with an infestation by larvae, but also with the exogenous application of their oral secretions in tomato. A microarray analysis identified cell-wall-associated defense genes as loliolide-responsive tomato genes, and exogenous JA application did not induce the expression of these genes. - (), an Arabidopsis () mutant with a point mutation in a key gene of the β-carotene metabolic pathway, exhibited the decreased accumulation of endogenous loliolide and increased susceptibility to infestation by the western flower thrip (). A pretreatment with loliolide decreased susceptibility to thrips in the JA-insensitive Arabidopsis mutant - Exogenous loliolide did not restore reduced electrolyte leakage in in response to a HR-inducing bacterial strain. These results suggest that loliolide functions as an endogenous signal that mediates defense responses to herbivores, possibly independently of JA, at least in tomato and Arabidopsis plants.