Evidence for regulation of resistance in Arabidopsis to Egyptian cotton worm by salicylic and jasmonic acid signaling pathways

Signaling cross-talk between wound- and pathogen-response pathways influences resistance of plants to insects and disease. To elucidate potential interactions between salicylic acid (SA) and jasmonic acid (JA) defense pathways, we exploited the availability of characterized mutants of Arabidopsis thaliana (L.) Heynh. and monitored resistance to Egyptian cotton worm (Spodoptera littoralis Boisd.; Lepidoptera: Noctuidae). This generalist herbivore is sensitive to induced plant defense pathways and is thus a useful model for a mechanistic analysis of insect resistance. As expected, treatment of wild-type Arabidopsis with JA enhanced resistance to Egyptian cotton worm. Conversely, the coil mutant, with a deficiency in the JA response pathway, was more susceptible to Egyptian cotton worm than wild-type Arabidopsis. By contrast, the npr1 mutant, with defects in systemic disease resistance, exhibited enhanced resistance to Egyptian cotton worm. Pretreatment with SA significantly reduced this enhanced resistance of npr1 plants but had no influence on the resistance of wild-type plants. However, exogenous SA reduced the amount of JA that Egyptian cotton worm induced in both npr1 mutant and wild-type plants. Thus, this generalist herbivore engages two different induced defense pathways that interact to mediate resistance in Arabidopsis.