Insoluble cell wall polysaccharide from Kluyveromyces marxianus enhances postharvest pear resistance against blue mold

Superior blue mold inhibition by K. marxianus NCWP versus S. cerevisiae ’s. • Unique rough, folded surface microstructure of the β-glucan NCWP. • Enhanced pear antioxidant capacity and early defense response activation. • Transcriptome revealed K. marxianus NCWP activation of hormone and immune pathways. • Coordinated upregulation of defense genes underpinning boosted pear resistance. Yeast cell wall polysaccharides represent a green and effective strategy for inducing fruit disease resistance, although their underlying mechanisms remain to be fully elucidated. This study investigated the efficacy and defense mechanisms of insoluble cell wall polysaccharides (NCWP) derived from Kluyveromyces marxianus in enhancing pear resistance against Penicillium expansum . Structural analysis revealed that K. marxianus NCWP is a β-glucan characterized by rough, folded, and protuberant surface morphology. This distinctive microstructure was associated with a stronger inhibitory effect on blue mold in pear fruit compared to the smoother NCWP from Saccharomyces cerevisiae . Treatment with K. marxianus NCWP triggered early defense responses, including a reactive oxygen species (ROS) burst, increased activities of antioxidant and defense-related enzymes, and upregulation of the corresponding genes. It also promoted endogenous γ-aminobutyric acid (GABA) accumulation and activated the GABA shunt pathway. Transcriptomic analysis further demonstrated that NCWP significantly induced jasmonic acid, abscisic acid, and ethylene signaling pathways, and upregulated pattern-triggered immunity (PTI)-related genes such as MKK5, PTI5 , and WRKY1 . Collectively, these findings indicate that K. marxianus NCWP enhances fruit resistance by concurrently activating immune signaling, hormone pathways, and metabolic defense processes, providing new insights into the mode of action of yeast-derived resistance inducers.