Abstract
Soybean seeds contain substantial amount of diverse triterpenoid saponins that influence the seed quality, although little is known about the physiologic functions of saponins in plants. We now describe the modification of saponin biosynthesis by RNA interference (RNAi)-mediated gene silencing targeted to β-amyrin synthase, a key enzyme in the synthesis of a common aglycon of soybean saponins. We identified two putative β-amyrin synthase genes in soybean that manifested distinct expression patterns with regard to developmental stage and tissue specificity. Given that one of these genes, GmBAS1, was expressed at a much higher level than the other (GmBAS2) in various tissues including the developing seeds, we constructed two RNAi vectors that encode self-complementary hairpin RNAs corresponding to the distinct regions of GmBAS1 under the control of a seed-specific promoter derived from the soybean gene for the α′ subunit of the seed storage protein β-conglycinin. These vectors were introduced independently into soybean. Six independent transgenic lines exhibited a stable reduction in seed saponin content, with the extent of saponin deficiency correlating with the β-amyrin synthase mRNA depletion. Although some transgenic lines produced seeds almost devoid of saponins, no abnormality in their growth was apparent and the antioxidant activity of their seeds was similar to that of control seeds. These results suggest that saponins are not required for seed development and survival, and that soybean seeds may therefore be amenable to the modification of triterpenoid saponin content and composition through molecular biologic approaches.
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Acknowledgments
We thank Chigen Tsukamoto (Iwate University, Japan) for the saponin standard, comments on the manuscript, and advice, as well as Mieko Kudo, Sayuri Noguchi, and Hiromi Mori for technical assistance. This work was supported by the Program for Promotion of Basic and Applied Researches for Innovations in Bio-oriented Industry (BRAIN) as well as, in part, by a grant from the Ministry of Agriculture, Forestry, and Fisheries of Japan (Genomics for Agricultural Innovation, GMZ-1004) and by the Fuji Foundation for Protein Research (Osaka, Japan).
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Takagi, K., Nishizawa, K., Hirose, A. et al. Manipulation of saponin biosynthesis by RNA interference-mediated silencing of β-amyrin synthase gene expression in soybean. Plant Cell Rep 30, 1835–1846 (2011). https://doi.org/10.1007/s00299-011-1091-1
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DOI: https://doi.org/10.1007/s00299-011-1091-1