Antifungal activity and function mechanisms of chitooligosaccharide against Gymnosporangium pleoporum, the pathogen causing rust in Juniperus przewalskii.

Juniperus przewalskii, a keystone species in China's ecologically fragile Sanjiangyuan region, faces severe threats from Gymnosporangium pleoporum rust. This study establishes chitooligosaccharides (COS) as potent antifungal agents against G. pleoporum, dose-dependently suppressing teliospore germination and viability. Integrated physiological analyses revealed COS-induced severe membrane damage evidenced by electrolyte leakage, soluble protein efflux, SEM-confirmed structural deformities, and elevated malondialdehyde indicating lipid peroxidation. Concurrently, COS triggered oxidative catastrophe via reactive oxygen species accumulation with suppression of antioxidant enzymes, while collapsing energy metabolism through adenosine triphosphate depletion and inhibition of electron transport chain enzymes. Transcriptomics identified concentration-dependent differential expression in energy metabolism pathways (glycolysis, oxidative phosphorylation, fatty acid degradation), alongside disrupted protein synthesis and redox homeostasis. Crucially, nine viability-correlated downregulated core genes, including putative orthologs for oxidative defense and aromatic amino acid biosynthesis, exhibited lineage-specific functions. Collectively, COS acts as a multi-target antifungal agent directly disrupting membrane integrity, redox homeostasis, and energy / protein metabolism in rust fungi, distinct from plant-induced resistance. This study establishes the scientific foundation for COS deployment against J. przewalskii rust disease, highlighting its eco-compatible potential through targeted exploitation of essential pathogen vulnerabilities. Furthermore, it positions COS as a cornerstone for precision forestry therapeutics that concurrently achieve pathogen suppression and ecological integrity preservation in vulnerable montane ecosystems.