The FAP transcription factor affects the fruiting body development and toughness of Flammulina filiformis by regulating the ROS signaling.
INTRODUCTION High toughness in Flammulina filiformis fruiting bodies severely restricts consumption. Mechanical strength shows a significant positive correlation with chitin content in cell walls, and understanding the regulatory mechanism of bZIP transcription factors in regulating this polysaccharide synthesis has become pivotal for overcoming quality improvement bottlenecks in medicinal-edible fungi, as mechanical properties directly determine post-harvest processing suitability and consumer acceptance. OBJECTIVES To screen key bZIP transcription factors regulating chitin synthesis in F. filiformis and elucidate their mechanism in modulating fruiting body development and toughness through ROS signaling. METHODS Spatial distribution analysis of chitin content and mechanical properties, bZIP family expression profiling (mycelium vs. stipe), yeast one-hybrid binding validation, construction of OE/ knockdown strains, ROS metabolic enzyme assays, H2O2/NAC treatments, and transcriptomic analysis. RESULTS fap expression in stipes was 9.36-39.70-fold higher than in mycelia (P < 0.01), aligning with chitin gradients; knockdown strains showed intracellular ROS increased to 508-526% of WT and 10-68% higher chitin in upper stipes, causing malformed fruiting bodies; whereas OE strains exhibited reduced ROS (MDA content decreased to 18-35% of WT), 18-32-fold enhanced POD activity, 9-18% reduced chitin in middle/lower stipes with decreased toughness, and normal fruiting body development; H2O2/NAC treatments directly induced chitin increase/decrease (P < 0.05), confirming the ROS-chitin regulatory axis; transcriptomics further revealed fap significantly modulates genes in carbon metabolism, amino acid biosynthesis, and ribosomal pathways. CONCLUSION FAP controls intracellular ROS levels by regulating ROS metabolic enzymes, thereby indirectly suppressing chitin synthesis and ultimately reducing mechanical strength in F. filiformis. This mechanism provides a novel scheme for texture improvement in edible fungi.