Han Xiaoyang, Jie Yang, Deng Zixin, Yu Yi
Plants have evolved diverse chemical strategies to defend against herbivores and pathogens, yet the mechanisms underlying their origin and diversification remain unclear. Here, we identify a sugar chain–dependent triterpenoid saponin defense system in Hedera helix that exemplifies adaptive innovation in plant chemical defenses. Three glycosyltransferases sequentially assemble a glucose–glucose–rhamnose chain at the C-28 position of α-hederin to form the detoxified precursor hederacoside C. Upon tissue disruption, the β-glucosidase HhGH1 hydrolyzes the entire sugar chain, regenerating α-hederin, a potent hemolytic saponin. Reconstitution of this system in Nicotiana benthamiana conferred strong herbivore resistance, demonstrating its ecological functionality and portability. Intriguingly, comparative genomics and biochemical analysis revealed that β-glucosidases across Apiales diversified in response to triterpenoid glycosylation, illustrating how substrate-driven enzyme evolution and metabolic innovation together generate new adaptive defense strategies in plants.