Abscisic acid is essential for rewiring of jasmonic acid-dependent defenses during herbivory

Jasmonic acid (JA) is an important plant hormone in the regulation of defenses against chewing herbivores and necrotrophic pathogens. In Arabidopsis thaliana, the JA response pathway consists of two antagonistic branches that are regulated by MYC- and ERF-type transcription factors, respectively. The role of abscisic acid (ABA) and ethylene (ET) in the molecular regulation of the MYC/ERF antagonism during plant-insect interactions is still unclear. Here, we show that production of ABA induced in response to leaf-chewing Pieris rapae caterpillars is required for both the activation of the MYC-branch and the suppression of the ERF-branch during herbivory. Exogenous application of ABA suppressed ectopic ERF-mediated PDF1.2 expression in 35S::ORA59 plants. Moreover, the GCC-box promoter motif, which is required for JA/ET-induced activation of the ERF-branch genes ORA59 and PDF1.2, was targeted by ABA. Application of gaseous ET counteracted activation of the MYC-branch and repression of the ERF-branch by P. rapae, but infection with the ET-inducing necrotrophic pathogen Botrytis cinerea did not. Accordingly, P. rapae performed equally well on B. cinerea-infected and control plants, whereas activation of the MYC-branch resulted in reduced caterpillar performance. Together, these data indicate that upon feeding by P. rapae, ABA is essential for activating the MYC-branch and suppressing the ERF-branch of the JA pathway, which maximizes defense against caterpillars.