Constitutive transcriptomic reprogramming underlies differential resistance of Flammulina velutipes to Pseudomonas...

Pseudomonas tolaasii, the causal agent of brown blotch disease, impairs not only fruiting body quality but also early mycelial development in Flammulina velutipes. However, the molecular basis underlying strain-dependent resistance at the vegetative stage remains poorly understood. In this study, we compared a resistant strain (S2595) and a susceptible strain (S2506) using dual-culture confrontation assays, scanning electron microscopy (SEM), and comparative transcriptome profiling with three biological replicates per condition. Under mock conditions, both strains exhibited comparable mycelial growth, indicating no intrinsic growth advantage. Upon bacterial challenge, however, S2595 maintained significantly higher relative growth and displayed reduced bacterial attachment compared to S2506. Transcriptome analysis revealed that resistance in S2595 is associated with constitutive up-regulation of 634 genes primarily involved in redox regulation, oxidoreductase activity, and cell wall integrity, rather than pathogen-induced transcriptional reprogramming (only 25-31 inducible DEGs). In contrast, a substantial set of constitutively differentially expressed genes was detected between S2595 and S2506 under basal conditions. Functional enrichment analysis indicated that genes up-regulated in S2595 were mainly associated with redox regulation, oxidoreductase activity, and cell wall-related processes, whereas several transmembrane transporter and vitamin-binding genes were expressed at lower levels. These transcriptional patterns suggest that resistance in S2595 may be associated with a pre-established defense-related homeostatic state rather than extensive pathogen-induced reprogramming. Collectively, our findings provide transcriptomic evidence supporting the contribution of constitutive defense signatures to strain-dependent resilience in F. velutipes, offering candidate markers for breeding disease-resistant cultivars.