Biosynthesis of Oxylipins by Rhizoctonia solani Rhizoctonia solani with Allene Oxide and Oleate 8 S S ,9 S S ‐Diol Synthase Activities

摘要

Abstract Oxylipin biosynthesis by fungi is catalyzed by both the lipoxygenase (LOX) family and the linoleate diol synthase (LDS) family of the peroxidase‐cyclooxygenase superfamily. Rhizoctonia solani , a pathogenic fungus, infects staple crops such as potato and rice. The genome predicts three genes with 9–13 introns, which code for tentative dioxygenase (DOX)–cytochrome P450 fusion enzymes of the LDS family, and one gene, which might code for a 13‐LOX. The objective was to determine whether mycelia or nitrogen powder of mycelia oxidized unsaturated C 18 fatty acids to LDS‐ or LOX‐related metabolites. Mycelia converted 18:2 n ‐6 to 8 R ‐hydroxy‐9 Z ,12 Z ‐octadecadienoic acid and to an α‐ketol, 9 S ‐hydroxy‐10‐oxo‐12 Z ‐octadecenoic acid. In addition to these metabolites, nitrogen powder of mycelia oxidized 18:2 n ‐6 to 9 S ‐hydroperoxy‐10 E , 12 Z ‐octadecadienoic, and 13 S ‐hydroperoxy‐9 Z ,11 E ‐octadecadienoic acids; the latter was likely formed by the predicted 13‐LOX. 18:1 n ‐9 was transformed into 8 S ‐hydroperoxy‐9 Z ‐octadecenoic and into 8 S ,9 S ‐dihydroxy‐10 E ‐octadecenoic acids, indicating the expression of 8,9‐diol synthase. The allene oxide, 9 S (10)epoxy‐10,12 Z ‐octadecadienoic acid, is unstable and decomposes rapidly to the α‐ketol above, indicating biosynthesis by 9 S ‐DOX‐allene oxide synthase. This allene oxide and α‐ketol are also formed by potato stolons, which illustrates catalytic similarities between the plant host and fungal pathogen.