The language of methylation in genomics of eukaryotes

Revealing mitogenome-wide DNA methylation and RNA editing of three Ascomycotina fungi using SMRT sequencing

Beauveria bassiana, Cordyceps militaris and Ophiocordyceps sinensis (Ascomycotina) are traditional Chinese medicines. Here, mitogenomes of these three Ascomycotina fungi were sequenced and de-novo assembled using single-molecule real-time sequencing. The results showed that their complete mitogenomes were 31,258, 31,854 and 157,584 bp, respectively, with sequencing depth approximately 278,760×, 326,283× and 69,385×. Types of repeat sequences were mainly (AA)n, (AAT)n, (TA)n and (TATT)n. DNA methylation motifs were revealed in DNA modifications of these three fungi. We discovered new models of RNA editing through analysis of transcriptomes from B. bassiana and C. militaris. These data lay a solid foundation for further genetic and biological studies about these three fungi, especially for elucidating the mitogenome evolution and exploring the regulatory mechanism of adapting environment.

SMRT Sequencing Revealed Mitogenome Characteristics and Mitogenome-Wide DNA Modification Pattern in Ophiocordyceps sinensis

Single molecule, real-time (SMRT) sequencing was used to characterize mitochondrial (mt) genome of Ophiocordyceps sinensis and to analyze the mt genome-wide pattern of epigenetic DNA modification. The complete mt genome of O. sinensis, with a size of 157,539 bp, is the fourth largest Ascomycota mt genome sequenced to date. It contained 14 conserved protein-coding genes (PCGs), 1 intronic protein rps3, 27 tRNAs and 2 rRNA subunits, which are common characteristics of the known mt genomes in Hypocreales. A phylogenetic tree inferred from 14 PCGs in Pezizomycotina fungi supports O. sinensis as most closely related to Hirsutella rhossiliensis in Ophiocordycipitaceae. A total of 36 sequence sites in rps3 were under positive selection, with dN/dS >1 in the 20 compared fungi. Among them, 16 sites were statistically significant. In addition, the mt genome-wide base modification pattern of O. sinensis was determined in this study, especially DNA methylation. The methylations were located in coding and uncoding regions of mt PCGs in O. sinensis, and might be closely related to the expression of PCGs or the binding affinity of transcription factor A to mtDNA. Consequently, these methylations may affect the enzymatic activity of oxidative phosphorylation and then the mt respiratory rate; or they may influence mt biogenesis. Therefore, methylations in the mitogenome of O. sinensis might be a genetic feature to adapt to the cold and low PO2 environment at high altitude, where O. sinensis is endemic. This is the first report on epigenetic modifications in a fungal mt genome.