Herbivore-Induced Defense Response in a Model Legume. Two-Spotted Spider Mites Induce Emission of (E)-b-Ocimene and Transcript Accumulation of (E)-b-Ocimene Synthase in Lotus japonicus

Indirect defense of plants against herbivores often involves the induced emission of volatile infochemicals including terpenoids that attract natural enemies of the herbivores. We report the isolation and characterization of a terpene synthase cDNA (LjEbOS) from a model legume, Lotus japonicus. Recombinant LjEbOS enzyme produced (E)-b-ocimene (98%) and its Z-isomer (2%). Transcripts of LjEbOS were induced in L. japonicus plants infested with two-spotted spider mites (Tetranychus urticae), coinciding with increasing emissions of (E)-b-ocimene as well as other volatiles, (Z)-3-hexenyl acetate and (E)-4,8dimethyl-1,3,7-nonatriene, by the infested plants. We suggest that LjEbOS is involved in the herbivore-induced indirect defense response of spider mite-infested L. japonicus via de novo formation and emission (E)-b-ocimene. Mechanical wounding of the leaves or application of alamethicin (ALA), a potent fungal elicitor of plant volatile emission, also induced transiently increased levels of LjEbOS transcripts in L. japonicus. However, wounding or ALA did not result in elevated release of (E)-bocimene. Differences in volatile emissions after herbivory, mechanical wounding, or treatment with ALA suggest that neither a single mechanical wounding event nor ALA simulate the effect of herbivore activity and indicate that herbivore-induced emission of (E)-b-ocimene in L. japonicus involves control mechanisms in addition to up-regulation of LjEbOS transcripts.