Mechanisms of plant stress adaptation and physiological regulation induced by olive by-product–derived elicitors

Olive mill waste (OMW) is produced in substantial quantities during oil extraction, and its uncontrolled dispersion can disrupt ecosystems because of its complex and highly reactive organic composition. Intriguingly, these by-products constitute a potential source of bioactive compounds which function as natural elicitors of plant immunity(1–3). Despite their promise, industrial applications are limited due to unsustainability of chemical solvents and low technology readiness. This study is an integral part of the OLinWASTE Horizon Europe initiative(4), which aims to establish a zero-emission system for the management of olive mill waste, reduce soil pollution and optimise resource efficiency. The project involves the development of sustainable extraction and separation processes to recover biocompounds from olive mill wastes. The fractions were chemically characterised for their glycan–phenolic profiles. Physiological and molecular analyses revealed that selected fractions activate key hallmarks of plant innate immunity, including the induction of defence-related gene expression, the activation of mitogen-activated protein kinases (MAPKs), and the accumulation of hydrogen peroxide (H₂O₂). Importantly, these immune responses were accompanied by the maintenance of normal plant growth, indicating a priming effect rather than a growth–defence trade-off. Overall, these results demonstrate that OMW-derived bioactive fractions can modulate plant stress physiology by triggering immune signalling pathways associated with enhanced stress resilience. This approach provides a sustainable strategy for improving crop performance under environmental stress, while supporting circular agriculture and reducing dependency on chemical pesticides.