RNA sequencing analysis reveals PgbHLH28 as the key regulator in response to methyl jasmonate-induced saponin accumulation in Platycodon grandiflorus

Abstract

Platycodon grandiflorus (Jacq.) A. DC, known for its saponin content, can potentially prevent and treat cerebrovascular diseases and COVID-19. Triterpenoid saponin biosynthesis in plants is enhanced by methyl jasmonate (MeJA) application. However, the underlying molecular mechanisms of MeJA-induced saponin biosynthesis remain unknown in P. grandiflorus. In the current study, exogenous application of 100 μmol/l MeJA was identified to be optimal for promoting saponin accumulation. RNA sequencing analysis demonstrated the PgbHLH28 gene as a key regulatory factor responding to MeJA during saponin accumulation. Overexpression of PgbHLH28 in P. grandiflorus increased saponin content, while silencing of PgbHLH28 significantly inhibited saponin synthesis, suggesting that PgbHLH28 acts as a positive regulator of saponin biosynthesis. Yeast one-hybrid and dual luciferase assays demonstrated that PgbHLH28 directly bound to the promoters of PgHMGR2 and PgDXS2 to activate gene expression. PgHMGR2 and PgDXS2 transformation promoted saponin accumulation, while silencing of these genes inhibited saponin biosynthesis. This study determined that MeJA promoted saponin accumulation in P. grandiflorus by inducing PgbHLH28 gene expression and activating downstream genes (PgHMGR2 and PgDXS2) involved in saponin biosynthesis. In conclusion, a complex regulatory network governing saponin biosynthesis following MeJA treatment was elucidated, offering a theoretical foundation for enhancing saponin content and biosynthesis efficacy in P. grandiflorus.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 31971700) and the Joint Guiding Project of Natural Science Foundation of Heilongjiang Province (No. LH2020C014). In addition, we thank MJEditor (www.mjeditor.com) for providing English editing services during the preparation of this manuscript.

Author contributions

D.C., W.Z., J.Z., and T.Y. conceived and designed the experiments. W.Z., Y.F., and W.J. performed the experiments. W.Z., J.Z., J.D., and P.G. performed the data analysis. W.Z. wrote the manuscript. All authors read and approved the final manuscript.

Data availability

The data presented in this study are available in the article or supplementary material. The raw RNA-seq data generated in this study are available in the NCBI-SRA database (PRJNA1032698). The sequences of PgbHLH28, PgDXS2 and PgHMGR2 are available in the NGDC database (C_AA057966.1- C_AA057968.1).

Conflict of interest statement

The authors have no conflicts of interest to declare.

Supplementary Data

Supplementary data is available at Horticulture Research online.

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