Regulatory Mechanisms of Salinity-Induced Triterpenoid Saponin Biosynthesis in Cyclocarya paliurus Seedling Revealed by Integrated Multi-Omics Analysis and Molecular Docking

Soil salinity is a major environmental constraint limiting plant productivity and modulating secondary metabolism. Triterpenoid saponins play crucial roles in plant stress adaptation, yet their biosynthetic regulation in Cyclocarya paliurus under salt stress remains poorly understood. This research integrated transcriptomic and metabolomic analyses to investigate triterpenoid saponin metabolism in C. paliurus leaves at four NaCl concentrations and two sampling times. Salt stress altered ion homeostasis, suppressed growth, and induced distinct triterpenoid saponins accumulation patterns, with cyclocaric acid B and oleanolic acid showing significant increases. Weighted gene co-expression network analysis identified two modules significantly correlated with triterpenoid saponin accumulation and highlighted transcription factors including WRKY18, bHLH121, ERF4, and ERF1 as regulators of key biosynthetic genes (DXS, SQS, and HMGR). Molecular docking further validated these regulatory interactions, demonstrating that bHLH35, MYC2, ERF113, and MED26B form stable complexes with target gene promoters through extensive hydrogen-bond networks. These findings elucidate the regulatory framework of triterpenoid saponin metabolism under salinity and provide a foundation for molecular breeding and cultivation of C. paliurus in saline regions.