The complete mitochondrial genome of a medicinal fungus, Tolypocladium ophioglossoides

The complete mitochondrial genome of Ophiocordyceps gracilis and its comparison with related species

In this study, the complete mitochondrial genome of O. gracilis was sequenced and assembled before being compared with related species. As the second largest mitogenome reported in the family Ophiocordycipitaceae, the mitogenome of O. gracilis (voucher OG201301) is a circular DNA molecule of 134,288 bp that contains numerous introns and longer intergenomic regions. UCA was detected as anticodon in tRNA-Sec of O. gracilis, while comparative mitogenome analysis of nine Ophiocordycipitaceae fungi indicated that the order and contents of PCGs and rRNA genes were considerably conserved and could descend from a common ancestor in Ophiocordycipitaceae. In addition, the expansion of mitochondrial organization, introns, gene length, and order of O. gracilis were determined to be similar to those of O. sinensis, which indicated common mechanisms underlying adaptive evolution in O. gracilis and O. sinensis. Based on the mitochondrial gene dataset (15 PCGs and 2 RNA genes), a close genetic relationship between O. gracilis and O. sinensis was revealed through phylogenetic analysis. This study is the first to investigate the molecular evolution, phylogenetic pattern, and genetic structure characteristics of mitogenome in O. gracilis. Based on the obtained results, the mitogenome of O. gracilis can increase understanding of the genetic diversity and evolution of cordycipitoid fungi.

A Comparative Analyses of the Complete Mitochondrial Genomes of Fungal Endosymbionts in Sogatella furcifera, White-Backed Planthoppers

Sogatella furcifera Horvath, commonly known as the white-backed planthoppers (WBPH), is an important pest in East Asian rice fields. Fungal endosymbiosis is widespread among planthoppers in the infraorder Fulgoromorpha and suborder Auchenorrhyncha. We successfully obtained complete mitogenome of five WBPH fungal endosymbionts, belonging to the Ophiocordycipitaceae family, from next-generation sequencing (NGS) reads obtained from S. furcifera samples. These five mitogenomes range in length from 55,390 bp to 55,406 bp, which is shorter than the mitogenome of the fungal endosymbiont found in Ricania speculum, black planthoppers. Twenty-eight protein-coding genes (PCGs), 12 tRNAs, and 2 rRNAs were found in the mitogenomes. Two single-nucleotide polymorphisms, two insertions, and three deletions were identified among the five mitogenomes, which were fewer in number than those of four species of Ophiocordycipitaceae, Ophiocordyceps sinensis, Hirsutella thompsonii, Hirsutella rhossiliensis, and Tolypocladium inflatum. Noticeably short lengths (up to 18 bp) of simple sequence repeats were identified in the five WBPH fungal endosymbiont mitogenomes. Phylogenetic analysis based on conserved PCGs across 25 Ophiocordycipitaceae mitogenomes revealed that the five mitogenomes were clustered with that of R. speculum, forming an independent clade. In addition to providing the full mitogenome sequences, obtaining complete mitogenomes of WBPH endosymbionts can provide insights into their phylogenetic positions without needing to isolate the mtDNA from the host. This advantage is of value to future studies involving fungal endosymbiont mitogenomes.

Mitogenome of Tolypocladium guangdongense

Tolypocladium guangdongense is a high-value edible fungus with various medicinal and food safety properties. However, its evolutionary and genetic information is still limited. Mitochondrial genomes are potential models for molecular evolution and phylogenetic studies. In this study, we sequenced the complete mitogenome of T. guangdongense, demonstrating circular sequence of 46,102 bp, containing 14 standard protein-coding genes (PCGs), 2 ribosomal RNA subunit genes, and 28 tRNA genes. Phylogenetic analysis based on mitochondrial genes indicated that T. guangdongense was clustered into the Tolypocladium genus with high support value, based on the core PCG dataset. In addition, rps3 is also a suitable marker in the phylogenetic analysis in Hypocreales. Gene rearrangement analysis indicated that the gene order of PCGs was highly consistent in Hypocreales, and tRNA rearrangement events occurred in most species of Hypocreales; however, the rearrangement rates were not taxonomically correlated. Divergence time estimation based on the old fossil record and previous reports revealed that T. guangdongense originated approximately in the middle Cenozoic (42 Mya, 95% highest posterior density interval: 43-116) with the Tolypocladium genus differentiation. Our results provided more mitogenomic information of T. guangdongense and shed new insights into evolution of the Tolypocladium genus. KEY POINTS: • The general and unique features of T. guangdongense mitogenome are firstly reported. • Phylogenetic analysis further verified the taxonomic status of T. guangdongense. • Divergence time estimation provides more evolutionary information of T. guangdongense.

Genomic analyses reveal low mitochondrial and high nuclear diversity in the cyclosporin-producing fungus Tolypocladium inflatum

Mitochondrial DNA is generally regarded to evolve faster than nuclear DNA in animals, whereas if this is also true in fungi remains unclear. Herein, we annotate the first complete mitochondrial genome (mitogenome) of the cyclosporin-producing fungus Tolypocladium inflatum and report the genome-wide sequence variations among five isolates originating from distantly separated localities. We found that T. inflatum has among the most compact of fungal mitogenomes; its 25 kb DNA molecule encodes all standard fungal mitochondrial genes and harbors only one intron. Transcriptional analyses validated the expression of most conserved genes. We found several uncommon repetitive elements and evidence of gene transfer from the mitochondrion to the nucleus. Phylogenetic analyses confirmed the placement of T. inflatum in the fungal order Hypocreales although there was uncertainty on its family-level affiliation. Comparative genomic analyses among the five isolates identified an overall lower level of intraspecific variation in mitogenomes than in nuclear genomes; however, both the nuclear and mitochondrial genomes revealed similar isolate relationships, not correlating with geographic sources of these isolates. Our study shed new insights into the evolution of the medicinally important ascomycete T. inflatum.

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.