Chromosome doubling drives saponin enrichment in Aralia elata (Miq.) Seem: Multi-omics dissection of terpenoid biosynthesis regulation in tetraploid germplasm

Aralia elata (Miq.) Seem, a medicinal plant rich in pentacyclic triterpenoid saponins, was subjected to colchicine-induced chromosome doubling to develop novel tetraploid germplasms for industrial crop improvement. The optimal induction condition was 0.02% colchicine for 3 days, achieving a 17.26% success rate. Tetraploid plants, confirmed by flow cytometry, exhibited significant morphological alterations, including a dwarf stature, thicker stems, larger and darker leaves, and expanded stomata. Physiologically, tetraploids demonstrated enhanced baseline photosynthetic efficiency, with a net photosynthetic rate up to 1.6-fold higher (4.15 vs. 2.59 μmol·m⁻²·s⁻¹) than that of diploids. Crucially, total flavonoid and saponin concentrations were substantially elevated in tetraploids, increasin by 2.26- and 1.32-fold, respectively. Transcriptome sequencing identified 779 differentially expressed genes (DEGs) in tetraploids, predominantly enriched in secondary metabolite biosynthesis and terpenoid metabolism pathways. Concurrent metabolomic profiling revealed 16 significantly altered terpenoids, with a notable increase in several oleanane-type triterpenoid saponins. An integrated correlation analysis linked this saponin accumulation to 24 key terpene biosynthesis genes (from β-AS, P450, and UGT families), revealing strong positive correlations (|r| > 0.9) between gene expression and metabolite levels. This study successfully established superior tetraploid A. elata germplasms with enhanced biomass and bioactive compound production, providing foundational insights into the transcriptional regulation underlying saponin biosynthesis in polyploids.