Conclusion:
Herbivory by S. exigua does not elicit ethylene pathway in M. truncatula .
Induction of defense responses in M. truncatula against caterpillar herbivory with intact spinneret is different from caterpillar with impaired spinneret. Effectors in caterpillar labial saliva could induce oxidative stress, induce the expression of antagonistic SAR pathway and hence suppress the induction of TI in M. truncatula . However, there was no difference in the expression of the studied defense related genes in plants after herbivory by normal or cauterized caterpillars.
An ethylene is a pleiotropic hormone involved in different physiological and developmental processes (Wang et al., 2002). By comparing the effects of herbivory with and without labial salivary secretion in wild type M. truncatula verses ethylene insensitive, skl mutant, we showed that ethylene could be involved in one response but not in other after herbivory. Ethylene was involved in the suppressive effect of defense protein due to normal caterpillar herbivory, it seemed to regulate glutathione as well as accelerate the induction of oxidative stress in plants. Ethylene had no role in the suppression of MtRCA , a gene involved in primary metabolism, after caterpillar herbivory but it is involved in suppression of regulatory genes, MtRPK and MtRFP. It is also found that ethylene regulates the expression of MtSTR in M. truncatula.