Involved in the biosynthesis of jasmonic acid, a growth regulator that is implicated also as a signaling molecule in plant defense. Converts 13-hydroperoxylinolenic acid to 12,13-epoxylinolenic acid (By similarity). (13S)-hydroperoxy-(9Z,11E,15Z)-octadecatrienoate = (9Z,13S,15Z)-12,13-epoxyoctadeca-9,11,15-trienoate + H2O Lipid metabolism; oxylipin biosynthesis. Not expressed in dark-grown seedlings. Not induced by red (R) light, or abrasion in dark-grown seedlings. Belongs to the cytochrome P450 family.