Molecular Mechanism During Mycelium Subculture Degeneration of <i>Volvariella volvacea</i>

Periodic mycelial subculture is a method commonly used for the storage of edible mushrooms, but excessive subculturing can lead to the degeneration of strains. In this study, the <i>Volvariella volvacea</i> strain V971(M0) was successively subcultured on PDA medium every 4 days, and one generation of strains was preserved every 4 months. Thus, five generations of subcultured strains (M1–M5) were obtained after 20 months of mycelial subculturing, their production traits were determined, and transcriptomic analysis was performed using RNA-seq; the differentially expressed genes were verified via RT-qPCR. The results showed that as the number of subcultures increased, the diameter of the mycelium and biological efficiency gradually decreased; in addition, the time in which the primordium formed increased and the production cycle was lengthened, while strains M4 and M5 lacked the ability to produce fruiting bodies. There were 245 differentially expressed genes between the M1–M5 and M0 strains, while the highest number of differentially expressed genes was between M3 and M0, at 1439; the smallest number of differentially expressed genes was between M2 and M0, at 959. GO enrichment analysis showed that the differentially expressed genes were mainly enriched in metabolic processes, organelle components, and catalytic activities. KEGG enrichment analysis showed that the differentially expressed genes were mainly enriched in metabolic pathways. The further annotation of differentially expressed genes showed that 39, 24, and 24 differentially expressed genes were related to substrate degradation, amino acid synthesis and metabolism, and reactive oxygen species metabolism, respectively. The downregulation of the related differentially expressed genes would lead to the excessive accumulation of reactive oxygen species, inhibit nutrient absorption and energy acquisition, and lead to the degradation of <i>V. volvacea</i>. These findings could form a theoretical basis for the degeneration mechanism of <i>V. volvacea,</i> and also provide a basis for the molecular function study of the genes related to strain degradation.