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

## TL;DR

A fungus called Fusarium pseudonygamai helps another fungus, Ophiocordyceps sinensis, transform more efficiently, which is important for making Chinese cordyceps medicine.

## Contribution

The study reveals that microbiota-derived metabolites, especially mannitol, significantly enhance the transformation of O. sinensis blastospores into hyphae.

## Key findings

- Fusarium pseudonygamai supernatant increased O. sinensis transformation rates by 31.6% in 8 days.
- Mannitol from F. pseudonygamai promotes transformation and modulates biosynthesis genes like M1PDH and MDH.
- Early upregulation of genes like CYC1, hmp, gedE, and fahA supports fungal development during transformation.

## Abstract

Chinese cordyceps, a highly valued traditional medicine, is formed when the fungal parasite Ophiocordyceps sinensis infects an underground caterpillar (Thitarodes). 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 O. sinensis 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 Thitarodes xiaojinensis larvae, this study investigates the role of host microbiota in enhancing O. sinensis blastospore transformation under in vitro conditions. Cultured supernatant of Fusarium pseudonygamai associated with T. xiaojinensis 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 CYC1, hmp, gedE, and fahA), supporting the cellular reprogramming required for fungal development. Additionally, mannitol isolated from F. pseudonygamai culture acted as a key promoter of transformation. Further functional assays confirmed that modulation of mannitol biosynthesis genes (M1PDH and MDH) 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 O. sinensis transformation, offering potential strategies to improve artificial cultivation of Chinese cordyceps.