Metatranscriptomics analysis of the fruiting caterpillar fungus collected from the Qinghai-Tibetan plateau

The caterpillar fungus (i.e., the insect-fungus complex) is formed when the ghost moth ( Thitarodes spp.) larvae have been infected and killed by the fungus Ophiocordyceps sinensis . After finishing the genomics study of O. sinensis , we performed metatranscriptomics analysis of the caterpillar fungal samples collected from five places within the Qinghai-Tibetan Plateau. The fruiting-bodies were dissected for total RNA isolation and RNA-seq analysis. It was found that diversified microbial communities were present in different samples and interestingly, the mycoparasites Trichoderma spp. were found ubiquitously present in all samples. By mapping the reads to the genes encoded by O. sinensis , gene differential expression profiling revealed that the environmental gene expression patterns varied between samples but were correlated with the field altitudes from where the samples had been collected. In particular, the genes involved in sexuality and fruiting-body development controls were differentially expressed in different samples, indicating that the fungus might develop at varied stages at the sampling dates. The transposable elements (TEs) are expanded in the genome of O. sinensis . Our metatranscriptomics analysis demonstrated that massive transcriptions of the Class I type of retrotransposons and Class II type of DNA transposons were detected in all five samples. In addition to contributing to environmental adaptation, active expression of these TEs could drive the rapid evolution of fungal genomes.