Reactive Oxygen Species Distribution Involved in Stipe Gradient Elongation in the Mushroom Flammulina filiformis

The mushroom stipe raises the pileus above the substrate into a suitable position for dispersing spores. The stipe elongates at different speeds along its length, with the rate of elongation decreasing in a gradient from the top to the base. However, the molecular mechanisms underlying stipe gradient elongation are largely unknown. Here, we used the model basidiomycete mushroom Flammulina filiformis to investigate the mechanism of mushroom stipe elongation and the role of reactive oxygen species (ROS) signaling in this process. Our results show that O₂^- and H₂O₂ exhibit opposite gradient distributions in the stipe, with higher O₂^- levels in the elongation region (ER), and higher H₂O₂ levels in the stable region (SR). Moreover, NADPH-oxidase-encoding genes are up-regulated in the ER, have a function in producing O₂^-, and positively regulate stipe elongation. Genes encoding manganese superoxide dismutase (MnSOD) are up-regulated in the SR, have a function in producing H₂O_2, and negatively regulate stipe elongation. Altogether, our data demonstrate that ROS (O₂^-/H₂O₂) redistribution mediated by NADPH oxidase and MnSODs is linked to the gradient elongation of the F. filiformis stipe.