AtGH3.10 is another jasmonic acid‐amido synthetase in Arabidopsis thaliana.

SUMMARY: Jasmonoyl‐isoleucine (JA‐Ile) is a key signaling molecule that activates jasmonate‐regulated flower development and the wound stress response. For years, JASMONATE RESISTANT1 (JAR1) has been the sole jasmonoyl‐amino acid synthetase known to conjugate jasmonic acid (JA) to isoleucine, and the source of persisting JA‐Ile in jar1 knockout mutants has remained elusive until now. Here we demonstrate through recombinant enzyme assays and loss‐of‐function mutant analyses that AtGH3.10 functions as a JA‐amido synthetase. Recombinant AtGH3.10 could conjugate JA to isoleucine, alanine, leucine, methionine, and valine. The JA‐Ile accumulation in the gh3.10–2 jar1‐11 double mutant was nearly eliminated in the leaves and flower buds while its catabolism derivative 12OH‐JA‐Ile was undetected in the flower buds and unwounded leaves. Residual levels of JA‐Ile, JA‐Ala, and JA‐Val were nonetheless detected in gh3.10–2 jar1‐11, suggesting the activities of similar promiscuous enzymes. Upon wounding, the accumulation of JA‐Ile and 12OH‐JA‐Ile and the expression of JA‐responsive genes OXOPHYTODIENOIC ACID REDUCTASE3 and JASMONATE ZIM‐DOMAIN1 observed in WT, gh3.10–1, and jar1‐11 leaves were effectively abolished in gh3.10–2 jar1‐11. Additionally, an increased proportion of undeveloped siliques associated with retarded stamen development was observed in gh3.10–2 jar1‐11. These findings conclusively show that AtGH3.10 contributes to JA‐amino acid biosynthesis and functions partially redundantly with AtJAR1 in sustaining flower development and the wound stress response in Arabidopsis. Significance Statement: The identity of an enzyme that functions similarly to JASMONATE RESISTANT1 in conjugating jasmonic acid (JA) to amino acids has been unknown for years. Our study reveals that AtGH3.10 is the long‐sought jasmonoyl‐amido synthetase in Arabidopsis that contributes to the biosynthesis of bioactive JA‐isoleucine and other JA‐amido conjugates necessary for JA‐mediated processes like the wound stress response and flower development. [ABSTRACT FROM AUTHOR]