18 糸状菌のアブシシン酸生合成経路-新しい直接経路の可能性

概要

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Abscisic acid (ABA) in higher plants is biosynthesized by the indirect pathway via carotenoids. However, the biosynthetic pathway of ABA in fungi remains unclear. Two pathways, the direct pathway via farnesyl diphosphate and the indirect pathway, have been proposed for Cercospora. We investigated the biosynthetic pathway of ABA in a fungus, Botrytis cinerea, by a feeding experiment with ^<18>O_2. The result showed that C-1,1 and 4' of ABA were labeled by ^<18>O, which was not coincident with the positions expected not only from the direct pathway but also from the indirect one. Precise analyses of the mycelia extract showed that the fungi did not produce carotenoids except for a very small amount of phytoene, but produced C15 metabolites, 2E-farnesa-2,4,6,10-tetraene and 2Z-farnesa-2,4,6,10-tetraene. These findings led us to propose a new direct pathway; farnesyl diphosphate is reduced at C-1 to give 2E-farnesa-2,4,6,10-tetraene, after isomerization to 2Z-farnesa-2,4,6,10-tetraene, it is converted to ionylideneethane, and ionylideneethane is oxidized by monooxygenase with molecular oxygen to give ABA. C. cruenta produced 2E-farnesa-2,4,6,10-tetraene and 2Z-γ-ionylideneethane, suggesting that the new direct pathway occurred in this fungus also.
植物化学調節学会の論文
2002-10-31