Transcriptome Sequencing to Identify Candidate Genes for Mycelium Period Metabolism of Chinese Caterpillar Mushroom, Ophiocordyceps sinensis (Ascomycetes), Exposed to Light Treatment

The Chinese caterpillar mushroom, Ophiocordyceps sinensis, is rare in traditional Chinese herbal medicine. It was reported that the development of ascospores in sexual stage of Chinese Cordyceps requires certain UV irradiation, but whether light has effect on the asexual stage of O. sinensis is unclear. It is important and necessary to identify the candidate genes involved in asexual stages (mycelium period) metabolism of O. sinensis exposed to light treatment. In this study, the isolated and purified monoascospore strains from O. sinensis were treated with 10 days light (L10) and dark as control. Transcriptome sequencing (RNA-seq) was conducted to investigate the effect of light treatment on O. sinensis at the gene level and the changes in various metabolic pathways. The results showed that the colony surface was covered with villous aerial hyphae with a yellow circular mycelium ribbon in the center of the colony, and the content of polysaccharides, urea, adenosine, and cordycepin were significantly enhanced by L10 treatment. Kyoto Encyclopedia of Genes and Genomes (KEGG) functional annotation analysis showed that cell structure and catalytic metabolism were the significant items classified, and crucial genes affecting the anabolic pathways of polysaccharides, urea, adenosine, and cordycepin were also identified. In addition, the important roles of photoreceptor genes CRYD, WC-1, and FRQ were verified by combined analysis of qRT-PCR and transcriptome sequencing. Collectively, this study would be helpful to better understand the influence of light on the asexual stage of Chinese Cordyceps and provide a preliminary light treatment reference for Cordyceps artificial cultivation.