Fusarium pseudonygamai Promotes Blastospore Transformation in Ophiocordyceps sinensis: Insights into Microbial Interaction and Key Mechanisms

Chinese cordyceps, a highly valued traditional medicine, is formed when the fungal parasite <i>Ophiocordyceps sinensis</i> infects an underground caterpillar (<i>Thitarodes</i>). This interaction progresses slowly, as the larvae have a long developmental period and the fungus requires several months to complete its growth. The medicinal fungus <i>O. sinensis</i> has a complex life cycle that requires successful transformation from blastospores to hyphae for the formation of Chinese cordyceps. Building on our previous identification of diverse microbial communities associated with <i>Thitarodes xiaojinensis</i> larvae, this study investigates the role of host microbiota in enhancing <i>O. sinensis</i> blastospore transformation under in vitro conditions. Cultured supernatant of <i>Fusarium pseudonygamai</i> associated with <i>T. xiaojinensis</i> larvae significantly increased transformation rates by 31.6% after 8 days. Transcriptomic profiling revealed early upregulation of genes involved in energy metabolism, stress response, detoxification, and hyphal morphogenesis (notably <i>CYC1</i>, <i>hmp</i>, <i>gedE</i>, and <i>fahA</i>), supporting the cellular reprogramming required for fungal development. Additionally, mannitol isolated from <i>F. pseudonygamai</i> culture acted as a key promoter of transformation. Further functional assays confirmed that modulation of mannitol biosynthesis genes (<i>M1PDH</i> and <i>MDH</i>) through chemical agonists and inhibitors directly influenced mannitol levels and transformation efficiency. Collectively, these results highlight the pivotal role of microbiota-derived metabolites, particularly mannitol, in regulating <i>O. sinensis</i> transformation, offering potential strategies to improve artificial cultivation of Chinese cordyceps.