Molecular mechanisms underlying phenotypic degeneration in Cordyceps militaris: insights from transcriptome reanalysis and osmotic stress studies

Phenotypic degeneration in Cordyceps militaris poses a significant concern for producers, yet the mechanisms underlying this phenomenon remain elusive. To address this concern, we isolated two strains that differ in their abilities to form fruiting bodies. Our observations revealed that the degenerated strain lost the capacity to develop fruiting bodies, exhibited limited radial expansion, increased spore density, and elevated intracellular glycerol levels. Transcriptome reanalysis uncovered dysregulation of genes involved in the MAPK signaling pathway in the degenerate strain. Our RT-qPCR results demonstrated reduced expression of sexual development genes, along with upregulation of genes involved in asexual sporulation, glycerol synthesis, and MAPK regulation, when compared to the wild-type strain. Additionally, we discovered that osmotic stress reduced radial growth but increased conidia sporulation and glycerol accumulation in all strains. Furthermore, hyperosmotic stress inhibited fruiting body formation in all neutralized strains. These findings indicate dysregulation of the MAPK signaling pathway, the possibility of the activation of the high-osmolarity glycerol and spore formation modules, as well as the downregulation of the pheromone response and filamentous growth cascades in the degenerate strain. Overall, our study sheds light on the mechanisms underlying Cordyceps militaris degeneration and identifies potential targets for improving cultivation practices.