A sugar chain-dependent two-component chemical defense in <i>Hedera helix</i> reveals substrate-driven β-glucosidase evolution in Apiales.

Abstract

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 <i>Hedera helix</i> 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 <i>Nicotiana benthamiana</i> 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.