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 H2O2, 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.
Carbon dioxide is commonly used as one of the significant environmental factors to control pileus expansion during mushroom cultivation. However, the pileus expansion mechanism related to CO2 is still unknown. In this study, the young fruiting bodies of a popular commercial mushroom Flammulina filiformis were cultivated under different CO2 concentrations. In comparison to the low CO2 concentration (0.05%), the pileus expansion rates were significantly lower under a high CO2 concentration (5%). Transcriptome data showed that the up-regulated genes enriched in high CO2 concentration treatments mainly associated with metabolism processes indicated that the cell metabolism processes were active under high CO2 conditions. However, the gene ontology (GO) categories and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways associated with cell division processes contained down-regulated genes at both 12 h and 36 h under a high concentration of CO2. Transcriptome and qRT-PCR analyses demonstrated that a high CO2 concentration had an adverse effect on gene expression of the ubiquitin–proteasome system and cell cycle–yeast pathway, which may decrease the cell division ability and exhibit an inhibitory effect on early pileus expansion. Our research reveals the molecular mechanism of inhibition effects on early pileus expansion by elevated CO2, which could provide a theoretical basis for a CO2 management strategy in mushroom cultivation.
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