Dissection of transcriptome and metabolome insights into the polyphyllin biosynthesis in Paris

Polyphyllins are significant medicinal compounds found in Paris species, with different polyphyllins fulfilling distinct medicinal roles. Although some genes involved in polyphyllin synthesis have been identified, further exploration of the genes in the polyphyllin synthesis pathway is necessary due to the extensive genome of Paris species. The content and composition of polyphyllins vary among different Paris species, and the variations in specific polyphyllin levels across these plants make them promising candidates for identifying metabolites and genes associated with the biosynthesis of specific polyphyllins.

In this study, we investigate the global metabolic and transcriptomic profiles of three types of Paris polyphylla var. yunnanensis (Franch.) Hand.-Mazz, one Paris fargesii Franch, and one Paris forrestii (Takht.) H. Li. The rhizome of P. polyphylla is rich in polyphyllin I and II, while P. forrestii is abundant in polyphyllin III, and P. fargesii contains high levels of polyphyllin VI, VII and H. The three Paris species exhibit distinct metabolomic and transcriptomic profiles. Through an integrated analysis of metabolic and transcriptomic data, along with a phylogenetic analysis of genes related to polyphyllin synthesis in Paris, we annotated a total of six 2,3-oxidosqualene cyclases (OSCs), 120 cytochrome P450s (CYPs), and 138 UDP glycosyltransferases (UGTs). Phylogenetic tree analysis of the obtained data assisted in refining the candidate gene pool for OSC, CYP, and UGT. Subsequently, we identified 6, 12, and 26 candidate genes for OSC, CYP, and UGT, respectively. Finally, by combining the analyses of metabolic and genetic differences, we identified a total of 17 candidate genes, including 2 CAS, 4 CYP, and 11 UGT.

P. fargesii and P. forrestii are candidate medicinal plants for the development and application of specific polyphyllins. Transcripts from the UGT91 subfamily in Paris may play dual roles, contributing to both the synthesis of polyphyllin II and the catabolism of polyphyllin V and VI. The homologous genes of PpUGT73CE1 may regulate the synthesis of polyphyllin VI in P. fargesii. This study provides new insights into the investigation of biosynthetic pathways in medicinal plants that lack gene clusters.