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Elevated production of melatonin in transgenic rice seeds expressing rice tryptophan decarboxylase

Authors

  • Yeong Byeon,

    1. Department of Biotechnology, Interdisciplinary Program of Bioenergy and Biomaterials, Bioenergy Research Center, Chonnam National University, Gwangju, Korea
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  • Sangkyu Park,

    1. Department of Biotechnology, Interdisciplinary Program of Bioenergy and Biomaterials, Bioenergy Research Center, Chonnam National University, Gwangju, Korea
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  • Hyoung Yool Lee,

    1. Department of Biotechnology, Interdisciplinary Program of Bioenergy and Biomaterials, Bioenergy Research Center, Chonnam National University, Gwangju, Korea
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  • Young-Soon Kim,

    1. Department of Biotechnology, Interdisciplinary Program of Bioenergy and Biomaterials, Bioenergy Research Center, Chonnam National University, Gwangju, Korea
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  • Kyoungwhan Back

    Corresponding author
    1. Department of Biotechnology, Interdisciplinary Program of Bioenergy and Biomaterials, Bioenergy Research Center, Chonnam National University, Gwangju, Korea
    • Address reprint requests to Kyoungwhan Back,

      Department of Biotechnology, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 500-757, Korea.

      E-mail: kback@chonnam.ac.kr

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Abstract

A major goal of plant biotechnology is to improve the nutritional qualities of crop plants through metabolic engineering. Melatonin is a well-known bioactive molecule with an array of health-promoting properties, including potent antioxidant capability. To generate melatonin-rich rice plants, we first independently overexpressed three tryptophan decarboxylase isogenes in the rice genome. Melatonin levels were altered in the transgenic lines through overexpression of TDC1, TDC2, and TDC3; TDC3 transgenic seed (TDC3-1) had melatonin concentrations 31-fold higher than those of wild-type seeds. In TDC3 transgenic seedlings, however, only a doubling of melatonin content occurred over wild-type levels. Thus, a seed-specific accumulation of melatonin appears to occur in TDC3 transgenic lines. In addition to increased melatonin content, TDC3 transgenic lines also had enhanced levels of melatonin intermediates including 5-hydroxytryptophan, tryptamine, serotonin, and N-acetylserotonin. In contrast, expression levels of melatonin biosynthetic mRNA did not increase in TDC3 transgenic lines, indicating that increases in melatonin and its intermediates in these lines are attributable exclusively to overexpression of the TDC3 gene.

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