Additional evidence against jasmonate-induced jasmonate induction hypothesis

• The positive feedback loop hypothesis for jasmonate biosynthesis was challenged.
• Coronalon, a mimic of (+)-7-iso-jasmonoyl-L-isoleucine was used for treatments.
• Jasmonate-responsive genes were successfully induced by coronalon.
• Neither jasmonic acid nor jasmonoyl-L-isoleucine accumulated upon treatment.
• The positive feedback loop hypothesis for jasmonate biosynthesis is not tenable.

Jasmonates are phytohormones involved in development and stress reactions. The most prominent jasmonate is jasmonic acid, however, the bioactive jasmonate is (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile). Biosynthesis of jasmonates is long time known; compartmentalization, enzymes and corresponding genes are well studied. Because all genes encoding these biosynthetic enzymes are jasmonate inducible, a hypothesis of jasmonate-induced-jasmonate-biosynthesis is widely accepted. Here, this hypothesis was revisited by employing the synthetic JA-Ile mimic coronalon to intact and wounded leaves, which excludes structural cross-contamination with endogenous jasmonates. At an effective concentration that induced various jasmonate-responsive genes in Arabidopsis, neither accumulation of endogenous jasmonic acid, JA-Ile, nor of their hydroxylated metabolites was detected. Results indicate that in spite of jasmonate-induced biosynthetic gene expression, no jasmonate biosynthesis/accumulation takes place supporting a post-translational regulation.