Revisiting ethylene metabolism: Identification of an ethylene glycol-glucose conjugate reveals active ethylene metabolism in Populus

In many plant species, the role of ethylene as a phytohormone signal has been well-studied, yet its direct metabolism in planta has received less attention. Consequently, this gap constrains our understanding of the full impact ethylene has on plant systems. During multiple evaluations of resilience in Populus spp., we detected an unidentified metabolite with plausible links to ethylene. In this study, we structurally characterize and identify this molecule as an ethylene glycol glucose conjugate (EGGC). Ethylene-perturbation experiments revealed EGGC abundance is positively correlated with endogenous ethylene production, supporting EGGC as an ethylene-derived metabolite. Stable-isotope labeled EGGC supplied to the media was detected in stem/leaf tissue, indicating long-distance translocation of the compound. These studies also revealed enzymatic conversion in stem/leaf tissue of EGGC to ethylene glycol (EG), with EG levels maintained and accompanied by shifts in downstream metabolites (i.e., glycolic acid and oxalic acid). These results suggest that EGGC participates in active metabolism rather than serves as a waste product. Collectively, the findings reported in this study demonstrate that EGGC is a biomarker of whole-plant ethylene production and position it as a tool for monitoring ethylene-associated stress responses.