Light induces jasmonate‐isoleucine conjugation via OsJAR1 ‐dependent and ‐independent pathways in rice

The bioactive form of jasmonate is the conjugate of the amino acid isoleucine ( I le) with jasmonic acid ( JA ), which is biosynthesized in a reaction catalysed by the GH 3 enzyme JASMONATE RESISTANT 1 ( JAR 1). We examined the biochemical properties of OsJAR1 and its involvement in photomorphogenesis of rice ( O ryza sativa ). Os JAR 1 has a similar substrate specificities as its orthologue in A rabidopsis . However, osjar1 loss‐of‐function mutants did not show as severe coleoptile phenotypes as the JA ‐deficient mutants coleoptile photomorphogenesis 2 ( cpm2 ) and hebiba , which develop long coleoptiles in all light qualities we examined. Analysis of hormonal contents in the young seedling stage revealed that osjar1 mutants are still able to synthesize JA ‐ I le conjugate in response to blue light, suggesting that a redundantly active enzyme can conjugate JA and I le in rice seedlings. A good candidate for this enzyme is OsJAR2 , which was found to be able to catalyse the conjugation of JA with I le as well as with some additional amino acids. In contrast, if plants in the vegetative stage were mechanically wounded, the content of JA ‐ I le was severely reduced in osjar1 , demonstrating that OsJAR1 is the most important JA ‐ I le conjugating enzyme in the wounding response during the vegetative stage.