Mitochondrial genome of the nematode endoparasitic fungus Hirsutella vermicola reveals a high level of synteny in the family Ophiocordycipitaceae.

Ophiocordycipitaceae is a diverse fungal family comprising multiple ecologically, economically, medicinally, and culturally important fungal species; however, only four species of the family have available mitochondrial genomes (mitogenomes). In this study, the complete mitogenome of the nematode endoparasitic fungus Hirsutella vermicola in Ophiocordycipitaceae was sequenced, and a comparative mitogenomic analysis of Ophiocordycipitaceae was performed. We found that the 53,793-bp circular mitogenome of H. vermicola, except for standard fungal mitochondrial genes, harbors seven introns acquired possibly through lateral transfer from other fungi and three free-standing open reading frames (ORFs) coding for hypothetical proteins. Phylogenetic analysis based on concatenated mitochondrial protein sequences confirmed its placement in Ophiocordycipitaceae. Comparison on five mitogenomes of Ophiocordycipitaceae revealed great variation on their sizes, from 35.2 kb in Tolypocladium ophioglossoides to 157.5 kb in Ophiocordyceps sinensis, mainly due to variable numbers of introns (from 7 to 54) as well as variable lengths of intergenic regions. The five mitogenomes, however, are highly syntenic to each other in terms of gene order, the presence of an intronic ORF encoding ribosomal protein S3 within rnl, and the nad2/nad3 joining pattern. Our study is the first report of the mitogenome of H. vermicola and has facilitated the understanding of mitogenome evolution of Ophiocordycipitaceae.