Background: Superoxide dismutases (SODs, EC 1.15.1.1) are defense proteins that can be used as sweepers to clear reactive oxygen species (ROS). They have been widely studied in the plant. Intensive research demonstrates that SOD plays an essential role in plants. However, in Pleurotus ostreatus, the function and regulatory pathway of SOD in the growth and development and the abiotic stress response have not been clear. Results: In this study, three MnSOD-encoding genes of the P. ostreatus CCMSSC00389 strain were cloned and identified. Mnsod1, Mnsod2, and Mnsod3 were interrupted by 3, 7, and 2 introns, and encoded proteins of 204, 220, and 344 amino acids, respectively. By comparing the relative expression of three MnSOD-encoding genes in mycelia, the results showed that the gene with the highest primary expression was Mnsod1. Subsequently, the function of P. ostreatus Mnsod1 was explored by overexpression (OE) and RNA interference (RNAi). The results showed that during the growth and development of P. ostreatus, MnSOD1 protein increased gradually from mycelia to the fruiting body, but decreased in spores. The change of Mnsod1 transcription level was not consistent with the changing trend of MnSOD1 protein. Further studies showed that during primordia formation, the expression of Mnsod1 gradually increased, reaching a peak at 48 h, and the transcription level was 2.05-folds compared to control. H₂O₂ content progressively accumulated during the formation of primordia, and its change trend was similar to that of Mnsod1 transcription. OE-Mnsod1-1 and OE-Mnsod1-21 strains accelerated the formation of primordia. The results suggested that Mnsod1 may participate in the formation rate of P. ostreatus primordium by regulating the signal molecule H₂O₂. In addition, OE-Mnsod1-1 and OE-Mnsod1-21 strains shortened the mycelial recovery time after heat stress and improved the tolerance of the strains to 2.5 mM and 5 mM H₂O₂, which showed that Mnsod1 was involved in the response of P. ostreatus mycelium to heat stress. Conclusions: This study indicates that Mnsod1 plays an active role in the formation of P. ostreatus primordia and the response to abiotic stress.

Pleurotus ostreatus is the third largest cultivated species in China’s edible mushroom industry; however, its agricultural cultivation method is easily affected by high-temperature environments. To understand the response mechanism of mycelia to heat stress, the mycelia of P. ostreatus, which had been grown at 28 °C for 4 days, were subjected to heat stress at 32 °C and 36 °C for 2 days, followed by RNA-seq analysis. These results indicate that, under heat stress, mycelial growth was significantly inhibited, the cell membrane was disrupted, the cell walls became thicker, and chitinase and β-1,3-glucanase activities decreased. Transcriptome analysis revealed 2118 differentially expressed genes (DEGs) under 36 °C heat stress, and 458 DEGs were identified under 32 °C heat stress. A total of 328 DEGs were upregulated or downregulated under heat stress at 36 °C and 32 °C. The functional enrichment analysis of these genes revealed significant enrichment in genes related to hydrogen peroxide metabolism, oxidoreductase activity, ATP hydrolysis, and cell wall structure composition. There was a total of 80 DEGs specific to heat stress at 32 °C, and they were significantly enriched in catalase activity, the cell wall, the aminoglycan catabolic process, and oxidoreductase activity. However, 817 DEGs specific to heat stress at 36 °C were significantly enriched in the cell wall, integral components of the membrane, and oxidoreductase activity. The identification of cell wall-related genes revealed that hydrophobic proteins, Cerato plateau proteins, laccases, and glycoside hydrolases may respond to stress. The results of qRT-PCR for cell wall-related genes are consistent with the RNA-seq data. This study revealed several potential candidate genes for high-temperature thermal response, laying the foundation for the study of the thermal response mechanism of P. ostreatus.

Morchella importuna polysaccharide (MIP) has been proven to have obvious hypoglycemic effects on mice with type 2 diabetes (T2DM). This study looked at the functional and rheological characteristics of MIP, and investigated the effects of MIP on the human fecal microbiota through in vitro fermentation experiments. The outcomes demonstrate the excellent oil-holding capacity, emulsifying, foaming, and rheological characteristics of MIP. After salivary gastrointestinal digestion, the Mw of MIP decreased from 398.2 kDa and 21.5 kDa to 21.9 kDa and 11.7 kDa. By 16S rRNA sequencing of bacteria fermented in vitro, it was found that MIP did not improve the richness and diversity of intestinal microorganisms, but it may exert an anti-T2DM function by significantly increasing the relative abundance of Firmicutes and promoting Ruminococcaceae_UCG_014, Bacteroides, and Blautia proliferation. Escherichia-Shigella could also be inhibited to improve the intestinal microenvironment. In addition, the fermentation of MIP increased the total short-chain fatty acid (SCFA) concentration from 3.23 mmol/L to 39.12 mmol/L, and the propionic acid content increased significantly. In summary, MIP has excellent processing performance and is expected to exert potential anti-T2DM activity through the human intestinal microbiota, which has broad market prospects.