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 O(2)(−) and H(2)O(2) exhibit opposite gradient distributions in the stipe, with higher O(2)(−) levels in the elongation region (ER), and higher H(2)O(2) levels in the stable region (SR). Moreover, NADPH-oxidase-encoding genes are up-regulated in the ER, have a function in producing O(2)(−), and positively regulate stipe elongation. Genes encoding manganese superoxide dismutase (MnSOD) are up-regulated in the SR, have a function in producing H(2)O(2,) and negatively regulate stipe elongation. Altogether, our data demonstrate that ROS (O(2)(−)/H(2)O(2)) redistribution mediated by NADPH oxidase and MnSODs is linked to the gradient elongation of the F. filiformis stipe.