title: Biosynthesis of abscisic acid by the direct pathway via ionylideneethane in a fungus, Cercospora cruenta.
abstract: We examined the biosynthetic pathway of abscisic acid (ABA) after isopentenyl diphosphate in a fungus, Cercospora cruenta. All oxygen atoms at C-1, -1, -1', and -4' of ABA produced by this fungus were labeled with (18)O from (18)O(2). The fungus did not produce the 9Z-carotenoid possessing gamma-ring that is likely a precursor for the carotenoid pathway, but produced new sesquiterpenoids, 2E,4E-gamma-ionylideneethane and 2Z,4E-gamma-ionylideneethane, along with 2E,4E,6E-allofarnesene. The fungus converted these sesquiterpenoids labeled with (13)C to ABA, and the incorporation ratio of 2Z,4E-gamma-ionylideneethane was higher than that of 2E,4E-gamma-ionylideneethane. From these results, we concluded that C. cruenta biosynthesized ABA by the direct pathway via oxidation of ionylideneethane with molecular oxygen following cyclization of allofarnesene. This direct pathway via ionylideneethane in the fungus is consistent with that in Botrytis cinerea, except for the positions of double bonds in the rings of biosynthetic intermediates, suggesting that the pathway is common among ABA-producing fungi.
authors.affiliation: Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Inomata
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Hirai
authors.forename: Ryuji
authors.initials: R
authors.lastname: Yoshida
authors.forename: Hajime
authors.initials: H
authors.lastname: Ohigashi
mesh_terms: D000040:Abscisic Acid / Q000031:analogs & derivatives* / Q000096:biosynthesis* / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism; D003500:Cyclization; D005658:Fungi / Q000378:metabolism*; D008798:Mevalonic Acid / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D012717:Sesquiterpenes / Q000378:metabolism
chemical_list: D012717:Sesquiterpenes; C495492:ionylideneethane; D002338:Carotenoids; D000040:Abscisic Acid; D008798:Mevalonic Acid; D010100:Oxygen