Distinct Arabidopsis Responses to Two Generalist Caterpillar Species Differing in Host Breadth

In general, caterpillar herbivores with a narrow host preference (specialists) have evolved mechanisms to circumvent specific plant defenses. In contrast, caterpillars with a broader host range (generalists) may manipulate phytohormone pathways common to many plant species to attenuate induced defenses. Many studies have compared plant responses to specialist versus generalist caterpillars. In contrast, this study evaluates the induced response of Arabidopsis thaliana to two generalist caterpillar species, the cabbage looper, Trichoplusia ni, and the beet armyworm, Spodoptera exigua. Although both caterpillars are considered generalists, S. exigua has a broader plant host range, whereas T. ni prefers Brassicaceous plants. Our study shows that most responses to caterpillar herbivory, such as the jasmonate burst, are similar in plants attacked by either insect species; however, we do observe dynamic and temporal differences in specific responses. Expression of AtZAT10, a 12-oxo-phytodienoic acid-responsive gene, is only induced in response to T. ni damage. In comparison, only S. exigua herbivory activates the salicylic acid/NPR1-dependent pathway, as observed by the expression of the marker gene AtPR1. Even though both species induce AtPDF1.2 expression, we found caterpillar-specific temporal differences: T. ni herbivory results in sustained expression over time, whereas gene expression is sharply downregulated at 36 h in S. exigua-attacked plants. Although damage by these two caterpillar species induced AtMYB28 and AtMYB34 expression, specific short- and long-chain aliphatic and indolic glucosinolates accumulate only in response to S. exigua herbivory. These species-specific, plant-induced responses likely reflect differences in effectors found in caterpillar oral secretions.[Figure: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.