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.

中文翻译：

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RNA测序分析揭示PgbHLH28是桔梗茉莉酸甲酯诱导的皂苷积累的关键调节因子


Platycodon grandiflorus (Jacq.) A. DC 以其皂苷含量而闻名，可以预防和治疗脑血管疾病和 COVID-19。茉莉酸甲酯 (MeJA) 的应用可增强植物中三萜皂苷的生物合成。然而，大花杨中 MeJA 诱导的皂苷生物合成的潜在分子机制仍然未知。在本研究中，外源施用 100 μmol/L MeJA 被认为是促进皂苷积累的最佳选择。 RNA测序分析表明PgbHLH28基因是皂苷积累过程中响应MeJA的关键调节因子。 PgbHLH28在大花中的过表达增加了皂苷含量，而PgbHLH28的沉默显着抑制了皂苷合成，表明PgbHLH28作为皂苷生物合成的正调节因子。酵母单杂交和双荧光素酶测定表明，PgbHLH28 直接与 PgHMGR2 和 PgDXS2 的启动子结合以激活基因表达。 PgHMGR2和PgDXS2转化促进皂苷积累，而这些基因的沉默抑制皂苷生物合成。本研究确定，MeJA 通过诱导 PgbHLH28 基因表达并激活参与皂苷生物合成的下游基因（PgHMGR2 和 PgDXS2）来促进 P. grandiflorus 中皂苷的积累。总之，阐明了 MeJA 处理后控制皂苷生物合成的复杂调控网络，为提高大花大花皂苷含量和生物合成功效提供了理论基础。