Transcriptomic insights into the role of CmLec4 in infection and development of Cordyceps militaris.

Entomopathogenic fungi are a diverse group of ascomycetes that infect insects and form fruiting bodies, with over 1,000 species reported globally. Among them, Cordyceps militaris has long been valued in East Asia as a traditional medicinal resource, reflecting its recognized pharmacological potential. However, the molecular basis of host recognition and infection in this species remains poorly understood. Our previous work identified a novel chitin-binding lectin, CmLec4, in C. militaris, and functional studies revealed that this protein delays host pupal emergence and that disruption of the cmlec4 gene reduces fruiting body formation, suggesting a crucial role of CmLec4 in infection and development. To clarify the molecular functions of cmlec4 throughout its life cycle, we performed transcriptomic analyses using cmlec4 knockout strains. Phenotypic evaluation showed that the mutants exhibited lower infection efficiency than the wild-type. RNA-Seq profiling revealed significant transcriptional changes during both early infection and fruiting body formation stages, including altered expression of genes encoding LysM domain-containing proteins, chitinases, and glucosidases-key factors in fungal adhesion, host cell wall degradation, and nutrient acquisition. Additionally, downregulation of tyrosine metabolism-related enzymes implied that CmLec4 may also influence secondary metabolism associated with virulence. Collectively, these findings indicate that CmLec4 functions as a multifunctional lectin, coordinating host recognition, metabolic regulation, and pathogenic development in C. militaris. While the biological functions of lectins have long been overlooked, this study provides a deeper understanding of how they contribute to infection and development in entomopathogenic fungi.