• Open Access

Transgenic rice seed synthesizing diverse flavonoids at high levels: a new platform for flavonoid production with associated health benefits

Authors

  • Yuko Ogo,

    1. Transgenic Crop Research and Development Centre, National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki, Japan
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  • Kenjiro Ozawa,

    1. Transgenic Crop Research and Development Centre, National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki, Japan
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  • Tsutomu Ishimaru,

    1. Rice Physiology Research Team, National Institute of Crop Science (NICS), National Agricultural and Food Research Organization (NARO), Tsukuba, Ibaraki, Japan
    Current affiliation:
    1. Biological Resources and Post-harvest Division, Japan International Research Center for Agricultural Sciences (JIRCAS), Tsukuba, Ibaraki, Japan
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  • Tsugiya Murayama,

    1. Department of Microbiology and Immunology, Hokuriku University, Kanazawa, Japan
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  • Fumio Takaiwa

    Corresponding author
    • Transgenic Crop Research and Development Centre, National Institute of Agrobiological Sciences (NIAS), Tsukuba, Ibaraki, Japan
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Correspondence (tel +81 298 38 8397; e-mail takaiwa@nias.affrc.go.jp)

Summary

Flavonoids possess diverse health-promoting benefits but are nearly absent from rice, because most of the genes encoding enzymes for flavonoid biosynthesis are not expressed in rice seeds. In the present study, a transgenic rice plant producing several classes of flavonoids in seeds was developed by introducing multiple genes encoding enzymes involved in flavonoid synthesis, from phenylalanine to the target flavonoids, into rice. Rice accumulating naringenin was developed by introducing phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS) genes. Rice producing other classes of flavonoids, kaempferol, genistein, and apigenin, was developed by introducing, together with PAL and CHS, genes encoding flavonol synthase/flavanone-3-hydroxylase, isoflavone synthase, and flavone synthases, respectively. The endosperm-specific GluB-1 promoter or embryo- and aleurone-specific 18-kDa oleosin promoters were used to express these biosynthetic genes in seed. The target flavonoids of naringenin, kaempferol, genistein, and apigenin were highly accumulated in each transgenic rice, respectively. Furthermore, tricin was accumulated by introducing hydroxylase and methyltransferase, demonstrating that modification to flavonoid backbones can be also well manipulated in rice seeds. The flavonoids accumulated as both aglycones and several types of glycosides, and flavonoids in the endosperm were deposited into PB-II-type protein bodies. Therefore, these rice seeds provide an ideal platform for the production of particular flavonoids due to efficient glycosylation, the presence of appropriate organelles for flavonoid accumulation, and the small effect of endogenous enzymes on the production of flavonoids by exogenous enzymes.

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