Regulatory Mechanisms of Bioactive Compound Biosynthesis in Polygonatum sibiricum Under Exogenous Salicylic Acid Treatment

Polygonatum sibiricum (P. sibiricum), rich in saponins, possesses extremely high medicinal value. However, inconsistent saponin levels in naturally grown P. sibiricum hinder its quality control assessments and industrial progress. In this study, we applied salicylic acid (SA) to P. sibiricum and measured the content changes of 11 saponins. Transcriptome sequencing was used to explore the molecular mechanism of saponin biosynthesis. Key saponin biosynthesis genes were identified and subsequently characterized through phylogenetic and structural analyses. The results showed that saponin contents changed significantly after SA treatment. We characterized six key gene families: SQLEs (squalene epoxidases, EC: 1.14.14.17), DXSs (1-deoxy-D-xylulose-5-phosphate synthases, EC: 2.2.1.7), FDPSs (farnesyl diphosphate synthases, EC: 2.5.1.1/2.5.1.10), CYP710As (cytochrome P450, family 710, subfamily A; sterol 22-desaturase, EC: 1.14.19.41), HMGCSs (3-hydroxy-3-methylglutaryl-CoA synthases, EC: 2.3.3.10), and SMT1s (sterol methyltransferase 1s, EC: 2.1.1.41), whose phylogenetic analysis revealed the unique evolutionary position of saponin biosynthesis genes. Furthermore, structural prediction and molecular docking revealed functional adaptations of SQLEs. In summary, our findings decipher the molecular mechanisms of SA-induced saponin biosynthesis in P. sibiricum, which can boost its medicinal value.