PnMYB4 negatively modulates saponin biosynthesis in Panax notoginseng through interplay with PnMYB1

Abstract

Saponins are the main triterpenoid ingredients from Panax notoginseng, a well-known Chinese medicine, and are important sources for producing drugs to prevent and treat cerebrovascular and cardiovascular diseases. However, the transcriptional regulatory network of saponin biosynthesis in P. notoginseng is largely unknown. In the present study we demonstrated that one R2R3-MYB transcription factor, designated PnMYB4, acts as a repressor of saponin accumulation. Suppression of PnMYB4 in P. notoginseng calli significantly increased the saponin content and the expression level of saponin biosynthetic genes. PnMYB4 directly bound to the promoters of key saponin biosynthetic genes, including PnSS, PnSE, and PnDS, to repress saponin accumulation. PnMYB4 and the activator PnMYB1 could interacted with PnbHLH, which is a positive regulator of saponin biosynthesis, to modulate the biosynthesis of saponin. PnMYB4 competed with PnMYB1 for binding to PnbHLH, repressing activation of the promoters of saponin structural genes induced by the PnMYB1-PnbHLH complex. Our study reveals that a complex regulatory module of saponin biosynthesis is associated with positive and negative MYB transcriptional regulators and provides a theoretical basis for improving the content of saponins and efficacy of P. notoginseng.

Acknowledgements

This study was supported by Beijing Science and Technology Planning Project (Z201100005420005, China).

Author contributions

S.W. and X.(Xiaohui)W. conceived and designed the research. J.M. and Y.S. conducted experiments and wrote the manuscript. Y.H. and X.Z. cloned the genes of PnMYB4 and analyzed the expression levels of the genes involved in saponin biosynthesis. X.(Xin)W. and S.L. analyzed the content of saponins. G.H. and K.A. performed the localization of PnMYB4. D.H. collected Panax notoginseng samples.

Data availability

All relevant data and figures in this study can be found within the article and its supplementary materials. The raw RNA-seq data are available in NCBI and can be accessed with the accession numbers SAMN29967774 and SAMN29967775.

Conflict of interest

The authors have no conflict of interest to declare.

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