Biosynthesis of Jasmonates from Linoleic Acid by the Fungus Fusarium oxysporum Fusarium oxysporum . Evidence for a Novel Allene Oxide Cyclase

摘要

Abstract Fusarium oxysporum f. sp . tulipae (FOT) secretes (+)‐7‐ iso ‐jasmonoyl‐( S )‐isoleucine ((+)‐JA‐Ile) to the growth medium together with about 10 times less 9,10‐dihydro‐(+)‐7‐ iso ‐JA‐Ile. Plants and fungi form (+)‐JA‐Ile from 18:3n‐3 via 12‐oxophytodienoic acid (12‐OPDA), which is formed sequentially by 13 S ‐lipoxygenase, allene oxide synthase (AOS), and allene oxide cyclase (AOC). Plant AOC does not accept linoleic acid (18:2n‐6)‐derived allene oxides and dihydrojasmonates are not commonly found in plants. This raises the question whether 18:2n‐6 serves as the precursor of 9,10‐dihydro‐JA‐Ile in Fusarium , or whether the latter arises by a putative reductase activity operating on the n‐3 double bond of (+)‐JA‐Ile or one of its precursors. Incubation of pentadeuterated (d 5 ) 18:3n‐3 with mycelia led to the formation of d 5 ‐(+)‐JA‐Ile whereas d 5 ‐9,10‐dihydro‐JA‐Ile was not detectable. In contrast, d 5 ‐9,10‐dihydro‐(+)‐JA‐Ile was produced following incubation of [17,17,18,18,18‐ 2 H 5 ]linoleic acid (d 5 ‐18:2n‐6). Furthermore, 9( S ),13 (S )‐12‐oxophytoenoic acid, the 15,16‐dihydro analog of 12‐OPDA, was formed upon incubation of unlabeled or d 5 ‐18:2n‐6. Appearance of the α‐ketol, 12‐oxo‐13‐hydroxy‐9‐octadecenoic acid following incubation of unlabeled or [ 13 C 18 ]‐labeled 13( S )‐hydroperoxy‐9( Z ),11( E )‐octadecadienoic acid confirmed the involvement of AOS and the biosynthesis of the allene oxide 12,13( S )‐epoxy‐9,11‐octadecadienoic acid. The lack of conversion of this allene oxide by AOC in higher plants necessitates the conclusion that the fungal AOC is distinct from the corresponding plant enzyme.