Molecular Mechanisms Underlying Phenotypic Degeneration in Cordyceps militaris: Insights from Transcriptome Reanalysis and Osmotic Stress Studies

Phenotypic degeneration is a well-known phenomenon in fungi, yet the underlying mechanisms remain poorly understood. Cordyceps militaris, a valuable medicinal fungus with therapeutic potential and known bioactive compounds, is vulnerable to degeneration, which is a concern for producers. However, the causes of this process are still unclear. To shed light on the molecular mechanisms responsible for phenotypic degeneration in C. militaris, we isolated two strains with different abilities to form fruiting bodies. Our observations revealed that the degenerated strain had reduced ability to develop fruiting bodies, limited radial expansion, and increased spore density. We also conducted a transcriptome reanalysis and identified dysregulation of genes involved in the MAPK signaling pathway in the degenerate strain. Our RT-qPCR results showed lower expression of genes associated with sexual development and upregulation of genes linked to asexual sporulation in the degenerate strain compared to the wild-type strain. We also found dysregulation of genes involved in glycerol synthesis and MAPK regulation. Additionally, we discovered that osmotic stress reduced radial growth but increased conidia sporulation and glycerol accumulation in both strains, and hyperosmotic stress inhibited fruiting body formation in all neutralized strains. These findings suggest that the MAPK signaling pathway is dysregulated in the degenerate strain and the high-osmolarity glycerol and spore formation modules may be continuously activated, while the pheromone response and filamentous growth cascades may be downregulated. Overall, our study provides valuable insights into the mechanisms underlying C. militaris degeneration and identifies potential targets for future studies aimed at improving cultivation practices.