Plant specialized metabolites are commonly stored in glycosylated forms within plant cells, with their homeostasis regulated by glycosyltransferases and β-glucosidases (BGLUs, also known as β-glucoside hydrolases (E.C.3.2.1.21)). Soyasaponins, the predominant triterpenoid compounds (C30) in soybean seeds, contain two sugar moieties attached at the C3 and C22 positions. While glycosyltransferases involved in soyasaponin biosynthesis have been well characterized, the role of BGLUs in soyasaponin homeostasis remains unclear. In this study, we identified GmSSBG1 (Soyasaponin β-glucosidase1; Glyma.07G258700) as a candidate gene potentially involved in soyasaponin homeostasis through gene to gene co-expression analysis. Biochemical assays demonstrated that GmSSBG1 specifically hydrolyzes arabinose residues at the C22 position of A0- and B0-series soyasaponins. Loss-of-function mutations in GmSSBG1 led to a significant accumulation of A0- and B0-series soyasaponins in mutant seeds, which correlated with a pronounced decrease in resistance to the soybean pod borer (Leguminivora glycinivorella). Our findings provide critical insights into the regulatory mechanisms underlying soyasaponin homeostasis and lay a theoretical foundation for molecular breeding strategies aimed at developing soybean lines with enhanced resistance to soybean pod borer, even to other insect pests.
