Integrated transcriptome, metabolome and activity-guided fractionation of Parnassia wightiana Wall. reveal its insecticidal potential.

BACKGROUND: Parnassia wightiana Wall. (P. wightiana) is a traditional medicinal herb with demonstrated potential for developing eco-friendly botanical insecticides, but its insecticidal properties remain underexplored. METHODS: Here, we systematically evaluated the insecticidal activities of different plant tissues through integrated bioactivity assays and metabolomic profiling. Combining bioactivity-guided fractionation with transcriptomic analysis, we identified bioactive insecticidal compounds and elucidated key genes involved in secondary metabolite biosynthesis. RESULTS: Bioassays revealed that root extracts exhibited the highest insecticidal efficacy against third-instar Mythimna separata (M. separata) larvae, with a median lethal concentration (LC50) of 19.659 mg/mL. Integrated multi-omics analysis showed significant enrichment of terpenoid biosynthesis pathways in roots, including diterpenoid, sesquiterpenoid, triterpenoid, terpene backbone, and monoterpenoid metabolism. Notably, terpene synthase (TPS) substrates (Z, Z-FPP, Z,E-FPP, and E, E-FPP) were identified as critical precursors in terpenoid anabolism, with TPS-a subfamily genes potentially playing pivotal roles in synthesizing bioactive sesquiterpenes. Through bioactivity-guided isolation, we characterized Celahin B as a potent insecticidal sesquiterpenoid, showing remarkable toxicity against M. separata larvae (LC50 = 116.642 µg/mL). CONCLUSIONS: These findings advance our understanding of insecticidal metabolite biosynthesis in P. wightiana and provide a foundation for metabolic engineering of insecticidal compounds, and development of novel biopesticides with reduced environmental impact.