Enhancement of phenylpropanoid accumulation in tartary buckwheat hairy roots by overexpression of MYB transcription factors

Abstract

MYB transcription factors (TFs) play a vital role in the phenylpropanoid biosynthetic pathway. In the present study, we constructed an overexpression system for four R2R3-MYB TFs genes, namely FtMYB1, FtMYB2, FtMYB3, and FtMYB-Like in tartary buckwheat (Fagopyrum tataricum). FtMYBs were expressed in a tissue-specific manner: expression levels of FtMYB1, FtMYB2, FtMYB3, and FtMYB-Like were highest in the seed1, flower, root, and flower, respectively. FtMYBs under different stress conditions showed that FtMYB2 was highly expressed to MeJA followed by NaCl, ABA, and SA, whereas other FtMYBs does not show significant expression when compared to control. In order to investigate their function in the phenylpropanoid pathway, these genes were over-expressed in hairy roots of F. tataricum. Results showed that the genes responsible for the biosynthesis of phenylpropanoid, including FtPAL, Ft4CL, FtC4H, FtCHS, FtCHI, FtF3H, FtF3′H1, FtF3′H2, FtFLS2, and FtANS were markedly up-regulated in the transgenic lines compared with that in the control (β-glucuronidase) lines. However, FtFLS1 and FtDFR did not show any significant expression in FtMYB2 and FtMYB3 transgenic lines. The result of high-performance liquid chromatography also demonstrated that FtMYB1, FtMYB2, FtMYB3, and FtMYB-Like are likely to be involved in phenylpropanoid biosynthesis in F. tataricum, especially, in anthocyanin accumulation. This accumulation was found to be 2–fold higher in the transgenic lines than that in control lines. However, the FtMYB3 line did not show a significant accumulation of anthocyanin when compared with the other three MYB lines. Overall, these results demonstrated that the FtMYBs play a crucial role in secondary metabolism, especially FtMYB2 may act as important regulators of the environmental stress response in F. tataricum. Hence, this study provides novel insights regarding the functions of R2R3-MYB TFs in the regulatory network that controls phenylpropanoid accumulation in buckwheat.