Preparation and Functional Characterization of Konjac Glucomannan Oligosaccharide as an Immunomodulator Against <i>Pst</i> DC3000 in <i>Arabidopsis thaliana</i>

Plant-derived oligosaccharides are promising ecofriendly elicitors of plant immunity. In this study, a β-1,4-mannanase (<i>Pp</i>ManA) from <i>Paenibacillus polymyxa</i> was characterized with broad pH stability, relatively low-temperature activity, and high specificity for konjac glucomannan (KGM), efficiently producing KGM oligosaccharides (KGMOS, DP 2-13). Treatment with KGMOS (10-50 mg/L) enhanced <i>Arabidopsis</i> resistance against <i>Pseudomonas syringae</i> pv <i>tomato</i> DC3000 (<i>Pst</i> DC3000), reducing bacterial colonization and disease symptoms while suppressing pathogen-responsive genes. KGMOS elevated H₂O₂ and NO levels and up-regulated SA- and JA-responsive genes. During infection, KGMOS activated both pathways, increasing hormone levels and defense gene expression. Genetic studies using SA-deficient (<i>NahG</i>) and JA-deficient (<i>jar1</i>) mutants showed attenuated resistance, with higher bacterial counts and severe symptoms versus those of wild-type plants under KGMOS treatment. These results demonstrate that KGMOS triggers immunomodulation via coordinated SA/JA signaling, offering a sustainable alternative to chemical pesticides for crop protection.