Endophytic Bacteria Enterobacter cloacae PN7 Promotes Biosynthesis and Accumulation of Saponins in Panax notoginseng.

Panax notoginseng is an important Chinese medicinal plant. Saponins are the major bioactive secondary metabolites with a wide range of medicinal and commercial value in P. notoginseng, so it is crucial to develop environmentally friendly methods to increase their production. The symbiotic relationship between endophytic bacteria and host plants offers a sustainable approach to enhance secondary metabolite biosynthesis. In this study, it was reported that the co-cultivation of an endophytic bacterium Enterobacter cloacae PN7, isolated from P. notoginseng and its host plant could greatly promote saponin accumulation in the root of seedlings. After six days of PN7 treatment, the total saponin concentration reached 21.64 mg/g, representing a 2.01-fold increase over the control. Transcriptome sequencing revealed that PN7 induction upregulated key genes in the saponin biosynthetic pathway (including DXS, HMGR, PMK, DS, CYP450, and GTs), modulated 253 plant hormone signaling genes (such as those related to JA, ETH, and ABA), and affected 284 transcription factor genes and 47 ABC transporter genes. Co-expression network analysis identified DEGs related to plant hormone signaling, transcription factors, and ABC transporters in saponin biosynthesis and distribution. The results suggested that JA signaling, mediated by transcription factors, such as bHLH and MYBs, and its interaction with ETH, played crucial roles in saponin biosynthesis. Additionally, potential ABC transporter candidates involved in saponin transport were identified. This study highlights the role of endophytic bacteria in enhancing saponin production in P. notoginseng and opens avenues for further research on microbial-plant interactions in secondary metabolite production.