Untargeted Metabolome-Transcriptome Joint Analysis Reveals Oxypaeoniflorin Biosynthetic Candidate Genes in Paeonia ostii 'Fengdan' Fruit Pods.

Paeonia ostii 'Fengdan' is an important woody ornamental crop that integrates ornamental value with practical applications in oil production and traditional medicine. The fruit pods of tree peony are rich in terpenoids, flavonoids, and phenolic acids which are valuable secondary metabolites yet frequently discarded as waste. Oxypaeoniflorin is a significant terpenoid secondary metabolite in tree peony; however, the temporal accumulation pattern of oxypaeoniflorin in tree peony fruit pods and the molecular mechanisms governing its biosynthesis remain incompletely understood. In this study, fruit pods of P. ostii 'Fengdan' were used as experimental materials. Samples from seven developmental stages (from 25 to 109 days after pollination) were collected and subjected to integrated analysis using non-targeted metabolomics and transcriptomics approaches. A total of 1740 metabolites were identified through metabolomic profiling, among which 105 common differentially accumulated metabolites were screened. Oxypaeoniflorin was identified as the target metabolite, exhibiting a dynamic accumulation pattern from stage 25 DAP to 109 DAP and reaching its peak level at stage 81 DAP. Through integrated weighted gene co-expression network analysis (WGCNA) and Mfuzz clustering, two candidate genes associated with oxypaeoniflorin biosynthesis were identified: ZEP and UGT73B4. Based on integrated multi-omics analysis, this study elucidated the temporal accumulation pattern and the underlying regulatory mechanisms of oxypaeoniflorin biosynthesis, which provides a theoretical basis for the high-value utilization of tree peony fruit pods and further studies on monoterpenoid glycoside biosynthesis.