Ectropis obliqua-Induced Secondary Metabolites Are Regulated by Methyl Jasmonate in a Threshold-Dependent Manner

The jasmonic acid (JA) signaling pathway has been demonstrated to play a crucial role in plant defense against herbivorous insects. However, the relationship between Ectropis obliqua-induced defensive metabolites and the JA signaling pathway in tea plants remains poorly understood. In this study, we investigated seven key special metabolites, including p-coumaroylputrescine, feruloylputrescine, prunin, naringenin, and three monolignols, to address this knowledge gap. Epicatechin was selected as a positive control based on its well-documented regulation through the JA signaling pathway. Notably, the content of all selected compounds was significantly increased by E. obliqua infestation. Furthermore, exogenous application of high-dose methyl jasmonate (MeJA) induced the accumulation of six of the eight compounds, excluding p-coumaryl alcohol and sinapyl alcohol, whereas low-dose MeJA failed to elicit their accumulation. To confirm the results, we screened two bioactive molecules, D-allose and L-theanine, which significantly increased the endogenous JA levels at low concentrations. Interestingly, neither D-allose nor L-theanine triggered the biosynthesis of these defensive compounds. Additionally, D-allose-treated tea leaves had no significant effect on the performance of E. obliqua larvae. These findings demonstrate that the metabolic accumulation induced by E. obliqua is mediated through a high-threshold JA signaling cascade. This study provides novel insights into the relationship between plant resistance and JA signaling pathway, advancing our understanding of special metabolites mediated plant-insect interactions.