Developmental stage-specific gene expression profiling for a medicinal fungus Cordyceps militaris

The caterpillar fungus Cordyceps militaris is a well-known traditional Chinese medicine that has been shown to have immunostimulatory and anticancer activities. Molecular and genetic studies of Cordyceps spp. are still limited. In this study, we sequenced >5000 clones from four cDNA libraries representing different asexual and sexual developmental stages of C. militaris. The resulting 1341 unigenes were assembled into 454 contigs and 887 singletons. Transcriptional differences were considerable with only 2.1% of unigenes being detected in all libraries. Gene ontology mapping revealed divergent transcriptional patterns among the libraries. Thus, the fungus differentially upregulated more genes for cell metabolism, energy metabolism and stress responses during asexual compared to sexual development. In particular, the transcriptional profiles were found to be different between fruit-bodies produced on rice medium and silkworm pupae. However, both libraries were enriched in transcripts for cell wall structures, i.e. 38.72 and 26.35% of unigenes transcribed by rice medium and pupae induced fruit-bodies, respectively. This is consistent with the morphological changes associated with sexual development. Our data will provide a starting point for future molecular studies of this promising resource of medicinal products. Further study with high-throughput sequencing techniques is still required for whole-genome transcriptome analysis of this fungus.