Identification of indole glucosinolate breakdown products with antifeedant effects on <i>Myzus persicae</i> (green peach aphid)

<jats:title>Summary</jats:title><jats:p>The cleavage of glucosinolates by myrosinase to produce toxic breakdown products is a characteristic insect defense of cruciferous plants. Although green peach aphids (<jats:italic>Myzus persicae</jats:italic>) are able to avoid most contact with myrosinase when feeding from the phloem of <jats:italic>Arabidopsis thaliana</jats:italic>, indole glucosinolates are nevertheless degraded during passage through the insects. A defensive role for indole glucosinolates is suggested by the observation that <jats:italic>atr1D</jats:italic> mutant plants, which overproduce indole glucosinolates, are more resistant to <jats:italic>M. persicae</jats:italic>, whereas <jats:italic>cyp79B2 cyp79B3</jats:italic> double mutants, which lack indole glucosinolates, succumb to <jats:italic>M. persicae</jats:italic> more rapidly. Indole glucosinolate breakdown products, including conjugates formed with ascorbate, glutathione and amino acids, are elevated in the honeydew of <jats:italic>M. persicae</jats:italic> feeding from <jats:italic>atr1D</jats:italic> mutant plants, but are absent when the aphids are feeding on <jats:italic>cyp79B2 cyp79B3</jats:italic> double mutants. <jats:italic>M. persicae</jats:italic> feeding from wild‐type plants and myrosinase‐deficient <jats:italic>tgg1 tgg2</jats:italic> double mutants excrete a similar profile of indole glucosinolate‐derived metabolites, indicating that the breakdown is independent of these foliar myrosinases. Artificial diet experiments show that the reaction of indole‐3‐carbinol, a breakdown product of indol‐3‐ylmethylglucosinolate, with ascorbate, glutathione and cysteine produces diindolylmethylcysteines and other conjugates that have antifeedant effects on <jats:italic>M. persicae</jats:italic>. Therefore, the post‐ingestive breakdown of indole glucosinolates provides a defense against herbivores such as aphids that can avoid glucosinolate activation by plant myrosinases.</jats:p>