Characterization and Phylogenetic Analysis of the Mitochondrial Genome of Shiraia bambusicola Reveals Special Features in the Order of Pleosporales

Shiraia bambusicola P. Henn. is a pathogenic fungus of bamboo, and its fruiting bodies are regarded as folk medicine. We determined and analyzed its complete mitochondrial DNA sequence (circular DNA molecule of 39,030 bp, G + C content of 25.19%). It contains the typical genes encoding proteins involved in electron transport and coupled oxidative phosphorylation (nad1-6 and nad4L, cob and cox1-3), one ATP synthase subunit (atp6), 4 hypothetical proteins, and two genes for large and small rRNAs (rnl and rns). There is a set of 32 tRNA genes comprising all 20 amino acids, and these genes are evenly distributed on the two strands. Phylogenetic analyses based on concatenated mitochondrial proteins indicated that S. bambusicola clustered with members of the order Pleosporales, which is in agreement with previous results. The gene arrangements of Dothideomycetes species contained three regions of gene orders partitioned in their mitochondrial genomes, including block 1 (nad6-atp6), block 2 (nad1-cox3) and block 3 (genes around rns). S. bambusicola displayed unique special features that differed from the other Pleosporales species, especially in the coding regions around rns (trnR-trnY). Moreover, a comparison of gene orders in mitochondrial genomes from Pezizomycotina revealed that although all encoded regions are located on the same strand in most Pezizomycotina mtDNAs, genes from Dothideomycetes species had different orientations, as well as diverse positions and colocalization of genes (such as cox3, cox1-cox2 and nad2-nad3); these distinctions were regarded as class-specific features. Interestingly, two incomplete copies of the atp6 gene were found on different strands of the mitogenomic DNA, a finding that has not been observed in the other analyzed fungal species. In our study, mitochondrial genomes from Dothideomycetes species were comprehensively analyzed for the first time, including many species that have not appeared in previous reports.