Biosynthesis of geranial, a potent aroma compound in ginger rhizome (<i>Zingiber officinale</i>): Molecular cloning and characterization of geraniol dehydrogenase

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Fresh ginger (<i>Zingiber officinale</i>) rhizome is characterized by a pleasant citrus aroma and pungent flavor. The majority of the aroma-contributing volatiles are monoterpenoids, especially geraniol derivatives such as geranial, geranyl acetate, geraniol and citronellol. In this study, we investigated the interconversion of geraniol derivatives by incorporation experiments using deuterium-labeled geraniol and geranyl acetate. GC-MS analysis revealed that the incorporated geraniol and geranyl acetate were transformed and detected as geranial, geraniol, geranyl acetate and citronellol; however, nerol and neral were hardly detected. Next, we isolated and characterized a cDNA encoding geraniol dehydrogenase (ZoGeDH) by expressed sequence tag database mining. Phylogenic analysis of <i>ZoGeDH</i> resulted in its categorization into the cinnamyl alcohol dehydrogenase (CAD) group, along with the previously reported <i>GeDHs</i> of sweet basil (<i>Ocimum basilicum</i>) and wild perilla (<i>P. setoyensis, P. citriodora, and P. frutescens</i>). The recombinant ZoGeDH catalyzed the NADP-dependent oxidation from geraniol to citral. Furthermore, its substrate specificity was the highest for geraniol and nerol, while that for cinnamyl alcohol was 32% of the activity observed for geraniol. The expression levels of <i>ZoGeDH</i> in various ginger plant tissues were in accordance with the accumulation of geranial, except in old rhizome.

Journal

  • Plant Biotechnology

    Plant Biotechnology 31(5), 525-534, 2014

    Japanese Society for Plant Cell and Molecular Biology

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