Identification of an allene oxide synthase (CYP74C) that leads to formation of α-ketols from 9-hydroperoxides of linoleic and linolenic acid in below-ground organs of potato

Authors

  • Michael Stumpe,

    1. Department of Plant Biochemistry, Georg-August-University Göttingen, Albrecht-von-Haller-Institute for Plant Sciences, D-37077 Göttingen, Germany,
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  • Cornelia Göbel,

    1. Department of Plant Biochemistry, Georg-August-University Göttingen, Albrecht-von-Haller-Institute for Plant Sciences, D-37077 Göttingen, Germany,
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  • Kirill Demchenko,

    1. Laboratory of Anatomy and Morphology, Komarov Botanical Institute, Russian Academy of Sciences, Prof. Popov st. 2, 197376, St Petersburg, Russia, and
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  • Manuela Hoffmann,

    1. Martin-Luther-University, Institute for Plant and Cell Physiology, Weinbergweg 10, D-06120 Halle, Germany
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  • Ralf B. Klösgen,

    1. Martin-Luther-University, Institute for Plant and Cell Physiology, Weinbergweg 10, D-06120 Halle, Germany
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  • Katharina Pawlowski,

    1. Department of Plant Biochemistry, Georg-August-University Göttingen, Albrecht-von-Haller-Institute for Plant Sciences, D-37077 Göttingen, Germany,
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    • Present address: Department of Botany, Stockholm University, S-10691 Stockholm, Sweden.

  • Ivo Feussner

    Corresponding author
    1. Department of Plant Biochemistry, Georg-August-University Göttingen, Albrecht-von-Haller-Institute for Plant Sciences, D-37077 Göttingen, Germany,
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For correspondence (fax +49 551 39 5749; e-mail ifeussn@gwdg.de).

Summary

Allene oxide synthase (AOS) enzymes are members of the cytochrome P450 enzyme family, sub-family CYP74. Here we describe the isolation of three cDNAs encoding AOS from potato (StAOS1–3). Based on sequence comparisons, they represent members of either the CYP74A (StAOS1 and 2) or the CYP74C (StAOS3) sub-families. StAOS3 is distinguished from the other two AOS isoforms in potato by its high substrate specificity for 9-hydroperoxides of linoleic and linolenic acid, compared with 13-hydroperoxides, which are only poor substrates. The highest activity was shown with (9S,10E,12Z)-9-hydroperoxy-10,12-octadecadienoic acid (9-HPODE) as a substrate. This hydroperoxide was metabolized in vitro to α- and γ-ketols as well as to the cyclopentenone compound 10-oxo-11-phytoenoic acid. They represent hydrolysis products of the initial StAOS3 product 9,10-epoxyoctadecadienoic acid, an unstable allene oxide. By RNA gel hybridization blot analysis, StAOS3 was shown to be expressed in sprouting eyes, stolons, tubers and roots, but not in leaves. StAOS3 protein was found in all organs tested, but mainly in stems, stolons, sprouting eyes and tubers. As in vivo reaction products, the α-ketols derived from 9-hydroperoxides of linoleic and linolenic acid were only found in roots, tubers and sprouting eyes. Immunolocalization showed that StAOS3 was associated with amyloplasts and leucoplasts.

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