High acyl gellan oligosaccharides trigger jasmonic acid-mediated immunity in Arabidopsis thaliana: Structural characterization and defense activation

The search for sustainable alternatives to chemical pesticides has intensified with growing environmental and food safety concerns. This study introduces high acyl gellan oligosaccharides (HAGO), derived from acid hydrolysis of microbial polysaccharides, as a novel plant immune inducer that selectively activates jasmonic acid (JA)-mediated defense pathways in Arabidopsis thaliana. Structural analysis confirmed HAGO as a hetero-oligosaccharide mixture (tri-to pentasaccharides) retaining acyl and carboxyl functional groups critical for immune recognition. In planta assays demonstrated that 100 mg/L HAGO pretreatment reduced Pseudomonas syringae pv. tomato DC3000 colonization by 42.6% and disease severity by 11.9%, which was not related to direct antibacterial effects. Mechanistic studies revealed a biphasic defense response: an initial reactive oxygen species (ROS) burst, followed by sustained upregulation of catalase (+22.16%) and phenylalanine ammonia-lyase (+33.6%) activities to mitigate oxidative stress, alongside malondialdehyde (+295%) accumulation as a lipid peroxidation marker. Crucially, HAGO exclusively activated the JA pathway, evidenced by 9.08-fold induction of PDF1.2 and 378% JA accumulation, while salicylic acid signaling remained unaltered. These findings establish HAGO as a structurally distinct elicitor that primes JA-dependent immunity through conserved ROS signaling and enzymatic detoxification. This work advances the development of polysaccharide-based, eco-friendly crop protection molecules and highlights the potential of acyl-modified oligosaccharides in immune induction strategies.