Effects of β-1,6-Glucan Synthase Gene (<i>FfGS6</i>) Overexpression on Stress Response and Fruit Body Development in <i>Flammulina filiformis</i>.

β-1, 6-glucan synthase is a key enzyme of β-1, 6-glucan synthesis, which plays a vital role in the cell wall cross-linking of fungi. However, the role of the β-1, 6-glucan synthase gene in the development of the fruiting body and the stress response of macrofungi is largely unknown. In this study, four overexpression transformants of the β-1, 6-glucan synthase gene (<i>FfGS6</i>) were successfully obtained, and gene function was studied in <i>Flammulina filiformis</i>. The overexpression of <i>FfGS6</i> can increase the width of mycelium cells and improve the tolerance ability under mechanical injury and oxidative stress. Moreover, <i>FfGS6</i> gene expression fluctuated in up-regulation during the recovery process of mycelium injury but showed a negative correlation with H₂O₂ concentration. Fruiting body phenotype tests showed that mycelia's recovery ability after scratching improved when the <i>FfGS6</i> gene was overexpressed. However, primordia formation and the stipe elongation ability were significantly inhibited. Our findings indicate that <i>FfGS6</i> is involved in regulating mycelial cell morphology, the mycelial stress response, and fruit body development in <i>F. filiformis</i>.