Exogenous ethephon treatment on the biosynthesis and accumulation of astragaloside IV in Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao

Abstract Background Astragaloside IV, a prominent secondary metabolite found in Astragalus membranaceus Bge. var. mongholicus (Bge.) Hsiao (A. membranaceus), serves as a crucial indicator of A. membranaceus quality. Ethylene, acting as an exogenous signal, plays a role in regulating secondary metabolism in plants. In this study, the application of ethephon (Eth) to hydroponically cultivated A. membranaceus was employed to investigate the biosynthesis of astragaloside IV in the roots, involving both content measurement and analysis of key gene expression. Results The results demonstrated that the significantly accumulation of astragaloside IV was observed on the 3rd day after 200 µmol·L− 1 Eth treatment, reaching 0.269%. Among the 10 key genes involved in astragaloside IV synthesis, HMGS, FPS, CAS, CYP88D6, and CYP93E3 were found to be insensitive to Eth. On the other hand, the expression levels of AACT, HMGR, IDI, and SS exhibited a significant increase at 12 hours under Eth treatment, followed by a notable decrease at 3rd day. Additionally, SE displayed a significant decrease at 12 hours and a subsequent increase in the 3rd day under Eth treatment. The expression level of FPS, HMGR, IDI, SS, and CYP93E3 exhibited significant negative correlations with astragaloside IV content, while expression level of SE displayed a significant positive correlation. Conclusions These findings suggest that exogenous Eth treatment can potentially influence the synthesis of astragaloside IV by modulating the expression of FPS, HMGR, IDI, SS, CYP93E3 and SE. This study provides a theoretical basis for utilizing molecular strategies to enhance the quality of A. membranaceus.