Chitosan functionalized with Colobanthus quitensis metabolites enhances botryticidal activity and defense priming in Arabidopsis

Botrytis cinerea causes gray mold in many crops, and resistance to synthetic fungicides highlights the need for biologically derived alternatives. We developed an enzymatic approach in which tyrosinase grafts phenolic metabolites from the Antarctic plant Colobanthus quitensis onto chitosan, generating a stable bioactive conjugate (Chitosan–Cq). Spectroscopic analysis and density functional theory predominantly support Michael-type addition to chitosan amino groups, consistent with the covalent incorporation of quinone-derived aromatics. Chitosan–Cq showed markedly enhanced antifungal performance. In vitro , it inhibited ~90% of B. cinerea mycelial growth at 10 mg/mL, whereas non-functionalized chitosan reached only ~20–30% under the same conditions. In planta, preventive spray application of Chitosan–Cq to leaves of Arabidopsis thaliana reduced gray mold lesion area by ~60–70% and limited fungal spread, while maintaining photosynthetic performance close to healthy controls. No chlorosis, necrosis, or growth penalties were detected in non-infected plants treated with Chitosan–Cq, indicating negligible phytotoxicity. Mechanistic assays showed that Chitosan–Cq induces early oxidative stress and membrane damage in B. cinerea and primes host defenses in A. thaliana. Treated plants displayed higher expression of defense-related PR genes and coordinated shifts in salicylic acid, jasmonic acid, abscisic acid, and characteristic priming metabolites (pipecolic acid, N-hydroxypipecolic acid, azelaic acid, glycerol-3-phosphate). Overall, tyrosinase-functionalized chitosan carrying native extremophile phenolics simultaneously suppresses fungal growth and establishes a systemic primed state in the host without detectable fitness cost, supporting its potential as a scalable biocontrol input for crop protection.