Mitochondrial inheritance in fungi

The complete mitochondrial genome of medicinally important wood-decaying fungus Tyromyces fissilis within the family Incrustoporiaceae, Polyporales

Tyromyces fissilis (Berk. & M.A.Curtis) Donk 1933, a globally renowned white-rot basidiomycete belonging to the Polyporales order, holds significant potential for lignin degradation, yet its mitochondrial genome has received comparatively little attention. Our study concentrates on a specimen designated T. fissilis NEFU_01, sourced from the Forest Botanical Garden in Heilongjiang Province, China. Utilizing next-generation sequencing (NGS) technology, we have successfully delineated the complete mitochondrial genome of this T. fissilis isolate. The genome is composed of 15 protein-coding genes (PCGs), an array of 24 transfer RNAs (tRNAs), and a pair of ribosomal RNAs (rRNAs), encompassing a total of 163,380 base pairs (bp). Additionally, the genome encodes 28 LAGLIDADG- and 10 GIY-YIG-homing endonucleases. The nucleotide composition is characterized by adenine (A) at 37.02%, cytosine (C) at 12.91%, guanine (G) at 13.04%, and thymine (T) at 37.03%, culminating in a GC content of 25.95%. Subsequently, we undertook a phylogenetic analysis, employing a dataset of 25 mitochondrial genomes to construct a phylogenetic tree. This research represents the first comprehensive foray into understanding the phylogenetic relationships of T. fissilis with its Basidiomycete kin, particularly its sister-group relationship with Phlebia radiata Fr. (1821), thereby laying a substantive groundwork for subsequent evolutionary and taxonomic studies within this mycological cohort.

Assembly and comparative analysis of the complete mitochondrial genome of Daedaleopsissinensis (Polyporaceae, Basidiomycota), contributing to understanding fungal evolution and ecological functions

Daedaleopsissinensis is a crucial wood-decaying fungus with significant lignocellulose-degrading ability, which plays a vital role in the material cycle and energy flow of forest ecosystems. However, the mitochondrial genome of D.sinensis has not yet been revealed. In the present study, the complete mitochondrial genome of D.sinensis was assembled and compared with related species. The mitochondrial genome spans 69,155 bp and has a GC content of 25.0%. It comprises 15 protein-coding genes (PCGs), 26 transfer RNA genes, two ribosomal RNA genes and one DNA polymerase gene (dpo). Herein, we characterised and analysed the codon preferences, variation and evolution of PCGs, repeats, intron dynamics, as well as RNA editing events in the D.sinensis mitochondrial genome. Further, a phylogenetic analysis of D.sinensis and the other 86 Basidiomycota species was performed using mitochondrial genome data. The results revealed that four species, D.confragosa, D.sinensis, D.nitida and Fomesfomentarius, were grouped in a closely-related cluster with high support values, indicating that a close phylogenetic relationship existed between Daedaleopsis and Fomes. This study reported on the initial assembly and annotation of the mitochondrial genome of D.sinensis, which greatly improved the knowledge of the fungus. These results contribute to the limited understanding of the mitochondrial repository of wood-decaying fungi, thereby laying the foundation for subsequent research on fungal evolution and ecological functions.

Mitochondrial Genomes from Fungal the Entomopathogenic Moelleriella Genus Reveals Evolutionary History, Intron Dynamics and Phylogeny

Members of the genus Moelleriella (Hypocreales, Clavicipitaceae) are insect pathogens with specificity for scale insects and whiteflies. However, no mitochondrial genomes are available for these fungi. Here, we assembled seven mitogenomes from M. zhongdongii, M. libera, M. raciborskii, M. gracilispora, M. oxystoma, Moelleriella sp. CGMCC 3.18909, and Moelleriella sp. CGMCC 3.18913, which varied in size from 40.8 to 95.7 Kb. Synteny and codon usage bias was relatively conserved, with the mitochondrial gene arrangement being completely homologous to the gene order of 21 other species within the Hypocreales. Nevertheless, significant intron polymorphism was observed between Moelleriella species. Evolutionary analyses revealed that all 15 core protein-coding genes had ka/ks < 1, indicating purifying selection pressure. Sequence variation within the mitochondrial ATP synthase F0 subunit 6 (atp6) gene showed the largest genetic distance, with the ATP synthase F0 subunit 9 (atp9) gene showing the smallest. Comparative analyses of mitogenomes revealed that introns were the primary factor contributing to the size variation in Moelleriella and, more broadly, within Hypocreales mitogenomes. Phylogenetic analyses indicated that the seven Moelleriella species examined form a well-supported clade, most closely related to Metarhizium. These data present the first mitogenomes from Moelleriella and further advance research into the taxonomy, origin, evolution, and genomics of Moelleriella.

Comparative Mitogenomics Analysis Revealed Evolutionary Divergence among Purpureocillium Species and Gene Arrangement and Intron Dynamics of Ophiocordycipitaceae

The species of Purpureocillium are cosmopolitan and multitrophic fungi that can infect a wide range of invertebrate hosts. This study reports the mitogenome of P. atypicola, a specialized spider pathogenic fungus. The 112,465 bp mitogenome encoded genes typically found in fungal mitogenomes, and a total of 52 introns inserted into seven genes. A comparison with three other Purpureocillium species revealed significant differences in length and intron number, primarily due to intron variation; however, there was no dynamic variation in the introns of the cox1 gene within the same species of the Purpureocillium genus. Different mitochondrial protein-coding genes showed variable degrees of genetic differentiation among these species, but they were all under purifying selection. Additionally, frequent intron loss or gain events were detected to have occurred during the evolution of the Ophiocordycipitaceae mitogenomes, yet the gene arrangement remains conserved. A phylogenetic analysis of the combined mitochondrial gene set gave identical and well-supported tree topologies. The estimated age of the crown of Ophiocordycipitaceae and Purpureocillium were around the Early Cretaceous period (127 Mya) and Late Cretaceous period (83 Mya), respectively. The results of this study advance our understanding of the genomics, evolution, and taxonomy of this important fungal group.

The complete mitochondrial genome of the basidiomycetous fungus, Tinctoporellus epimiltinus strain RS1

Tinctoporellus epimiltinus is widely known as a wood-decaying fungus. In the present study, we identified the complete mitochondrial genome of this species using next-generation sequencing technology. Our findings revealed that the genomic structure is a circular molecule with a size of 51,878 bp. Consistent with most Basidiomycota species, it consists of 14 core protein-coding genes, one ribosomal protein gene (rps3), 26 transfer RNA genes, and small and large ribosomal RNA (rns and rnl) genes. Seven additional open reading frames were identified. These included two sequences similar to DNA polymerases, an endonuclease-like sequence, and four hypothetical proteins. The mitochondrial genome exhibited a nucleotide composition of A (36.24%), C (12.04%), G (13.18%), and T (38.55%), resulting in a 25.21% GC content. A phylogenetic tree constructed using the combined mitochondrial gene dataset provided insight into the phylogenetic relationships of this species within the context of Basidiomycota and its members.

Evolution and maintenance of mtDNA gene content across eukaryotes

Across eukaryotes, most genes required for mitochondrial function have been transferred to, or otherwise acquired by, the nucleus. Encoding genes in the nucleus has many advantages. So why do mitochondria retain any genes at all? Why does the set of mtDNA genes vary so much across different species? And how do species maintain functionality in the mtDNA genes they do retain? In this review, we will discuss some possible answers to these questions, attempting a broad perspective across eukaryotes. We hope to cover some interesting features which may be less familiar from the perspective of particular species, including the ubiquity of recombination outside bilaterian animals, encrypted chainmail-like mtDNA, single genes split over multiple mtDNA chromosomes, triparental inheritance, gene transfer by grafting, gain of mtDNA recombination factors, social networks of mitochondria, and the role of mtDNA dysfunction in feeding the world. We will discuss a unifying picture where organismal ecology and gene-specific features together influence whether organism X retains mtDNA gene Y, and where ecology and development together determine which strategies, importantly including recombination, are used to maintain the mtDNA genes that are retained.

Distinguishing Sanghuangporus from sanghuang-related fungi: a comparative and phylogenetic analysis based on mitogenomes

The Chinese medicinal fungi "Sanghuang" have been long recognized for their significant and valued medicinal properties, as documented in ancient medical literature. However, in traditional folk medicine, various macrofungi sharing similar appearance, habitat, and therapeutic effects with Sanghuang were erroneously used. These Sanghuang-like fungi mainly belong to the Porodaedalea, Phellinus, and Inonotus genera within the Hymenochaetaceae family. Despite the establishment of the Sanghuangporus genus and the identification of multiple species, the emerging taxonomic references based on morphological, ITS, and mycelial structural features have been inadequate to differentiate Sanghuangporus and Sanghuang-like fungi. To address this limitation, this study presents the first comparative and phylogenetic analysis of Sanghuang-related fungi based on mitogenomes. Our results show that Sanghuangporus species show marked convergence in mitochondrial genomic features and form a distinct monophyletic group based on phylogenetic analyses of five datasets. These results not only deepen our understanding of Sanghuang-like fungi but also offer novel insights into their mitochondrial composition and phylogeny, thereby providing new research tools for distinguishing members of the Sanghuangporus genus. KEY POINTS: • Sanghuangporus, Inonotus, and Porodaedalea are monophyly in sanghuang-like species. • Mitogenome-based analysis exhibits high resolution in sanghuang-like genus. • The mitogenomes provide strong evidence for reclassifying Phellinus gilvus S12 as Sanghuangporus vaninii.

The complete mitochondrial genomes of five critical phytopathogenic Bipolaris species: features, evolution, and phylogeny

In the present study, three mitogenomes from the Bipolaris genus (Bipolaris maydis, B. zeicola, and B. oryzae) were assembled and compared with the other two reported Bipolaris mitogenomes (B. oryzae and B. sorokiniana). The five mitogenomes were all circular DNA molecules, with lengths ranging from 106,403 bp to 135,790 bp. The mitogenomes of the five Bipolaris species mainly comprised the same set of 13 core protein-coding genes (PCGs), two rRNAs, and a certain number of tRNAs and unidentified open reading frames (ORFs). The PCG length, AT skew and GC skew showed large variability among the 13 PCGs in the five mitogenomes. Across the 13 core PCGs tested, nad6 had the least genetic distance among the 16 Pleosporales species we investigated, indicating that this gene was highly conserved. In addition, the Ka/Ks values for all 12 core PCGs (excluding rps3) were < 1, suggesting that these genes were subject to purifying selection. Comparative mitogenomic analyses indicate that introns were the main factor contributing to the size variation of Bipolaris mitogenomes. The introns of the cox1 gene experienced frequent gain/loss events in Pleosporales species. The gene arrangement and collinearity in the mitogenomes of the five Bipolaris species were almost highly conserved within the genus. Phylogenetic analysis based on combined mitochondrial gene datasets showed that the five Bipolaris species formed well-supported topologies. This study is the first report on the mitogenomes of B. maydis and B. zeicola, as well as the first comparison of mitogenomes among Bipolaris species. The findings of this study will further advance investigations into the population genetics, evolution, and genomics of Bipolaris species.

Complete mitochondrial genome sequence of Aureoboletus raphanaceus (Boletales, Basidiomycota)

Aureoboletus raphanaceus is a member of boletoid mushroom, which is named after its distinctive radish smell. The mitochondrial genome and phylogenetic relationships with other boletes need to be investigated to gain a comprehensive understanding of it. In this study, we sequenced the mitochondrial genome of A. raphanaceus using next-generation sequencing technology and found that its mitochondrial genome is a circular DNA molecule measuring 42,157 bp. It consists of 15 core protein-coding genes, 27 transfer RNA genes, and two ribosomal RNA genes. The mitochondrial genome had a base composition of A (39.89%), C (11.06%), G (11.67%), and T (37.38%), with a GC content of 22.73%. A phylogenetic tree based on 22 mitochondrial genomes was constructed, which provided the first insights into the phylogenetic relationships of this species with related boletes.

Sex Without Sexes: Can the Cost of Finding a Mate Explain Diversity in Fungal Mating Systems?

Eukaryotes have evolved myriad ways of uniting gametes during sexual reproduction. A repeated pattern is the convergent evolution of a mating system with the fusion of larger gametes with smaller gametes (anisogamy) from that of fusion between morphologically identical gametes (isogamy). In anisogamous species, sexes are defined as individuals that produce only one gamete type. Although sexes abound throughout Eukarya, in fungi there are no biological sexes, because even in anisogamous species, individuals are hermaphroditic and produce both gamete types. For this reason, the term mating types is preferred over sexes, and, thus defined, only individuals of differing mating types can mate (homoallelic incompatibility). In anisogamous fungal species, there is scant evidence that there are more than two mating types, and this may be linked to genetic constraints, such as the use of mating types to determine the inheritance of cytoplasmic genomes. However, the mushroom fungi (Agaricomycetes) stand out as having both large numbers of mating types within a species, which will allow nearly all individuals to be compatible with each other, and reciprocal exchange of nuclei during mating, which will avoid cytoplasmic mixing and cyto-nuclear conflicts. Although the limitation of mating types to two in most fungi is consistent with the cyto-nuclear conflicts model, there are many facets of the Agaricomycete life cycle that also suggest they will demand a high outbreeding efficiency. Specifically, they are mostly obligately sexual and outcrossing, inhabit complex competitive niches, and display broadcast spore dispersal. Subsequently, the Agaricomycete individual pays a high cost to being choosy when encountering a mate. Here, I discuss the costs of mate finding and choice and demonstrate how most fungi have multiple ways of reducing these costs, which can explain why mating types are mostly limited to two per species. Nevertheless, it is perplexing that fungi have not evolved multiple mating types on more occasions nor evolved sexes. The few exceptions to these rules suggest that it is dictated by both molecular and evolutionary constraints.

Mitogenome Variations in a Global Population of Aspergillus fumigatus

Aspergillus fumigatus is a ubiquitous, critical priority human fungal pathogen. Despite its clinical importance, there is limited knowledge regarding the variations of the genome within mitochondria, the powerhouse organelle within eukaryotic cells. In this study, we leveraged publicly available, raw, whole genome sequence data isolates from 1939 to investigate the variations in the mitochondrial genomes of A. fumigatus. These isolates were isolated from 22 countries on six continents, as well as from outer space and from within the International Space Station. In total, our analysis revealed 39 mitochondrial single nucleotide polymorphisms (mtSNPs) within this global sample, and, together, these 39 mtSNPs grouped the 1939 isolates into 79 mitochondrial multilocus genotypes (MLGs). Among the 79 MLGs, 39 were each distributed in at least two countries and 30 were each shared by at least two continents. The two most frequent MLGs were also broadly distributed: MLG11 represented 420 isolates from 11 countries and four continents and while MLG79 represented 418 isolates from 18 countries and five continents, consistent with long-distance dispersals of mitogenomes. Our population genetic analyses of the mtSNPs revealed limited differentiation among continental populations, but highly variable genetic differences among national populations, largely due to localized clonal expansions of different MLGs. Phylogenetic analysis and Discriminant Analysis of Principal Components of mtSNPs suggested the presence of at least three mitogenome clusters. Linkage disequilibrium, Index of Association, and phylogenetic incompatibility analyses collectively suggested evidence for mitogenome recombination in natural populations of A. fumigatus. In addition, sequence read depth analyses revealed an average ratio of ~20 mitogenomes per nuclear genome in this global population, but the ratios varied among strains within and between certain geographic populations. Together, our results suggest evidence for organelle dynamics, genetic differentiation, recombination, and both widespread and localized clonal expansion of the mitogenomes in the global A. fumigatus population.

The First Five Mitochondrial Genomes for the Family Nidulariaceae Reveal Novel Gene Rearrangements, Intron Dynamics, and Phylogeny of Agaricales

The family Nidulariaceae, consisting of five genera including Cyathus, is a unique group of mushrooms commonly referred to as bird's nest fungi due to their striking resemblance to bird's nests. These mushrooms are considered medicinal mushrooms in Chinese medicine and have received attention in recent years for their anti-neurodegenerative properties. However, despite the interest in these mushrooms, very little is known about their mitochondrial genomes (mitogenomes). This study is the first comprehensive investigation of the mitogenomes of five Nidulariaceae species with circular genome structures ranging in size from 114,236 bp to 129,263 bp. Comparative analyses based on gene content, gene length, tRNA, and codon usage indicate convergence within the family Nidulariaceae and heterogeneity within the order Agaricales. Phylogenetic analysis based on a combined mitochondrial conserved protein dataset provides a well-supported phylogenetic tree for the Basidiomycetes, which clearly demonstrates the evolutionary relationships between Nidulariaceae and other members of Agaricales. Furthermore, phylogenetic inferences based on four different gene sets reveal the stability and proximity of evolutionary relationships within Agaricales. These results reveal the uniqueness of the family Nidulariaceae and its similarity to other members of Agaricales; provide valuable insights into the origin, evolution, and genetics of Nidulariaceae species; and enrich the fungal mitogenome resource. This study will help to expand the knowledge and understanding of the mitogenomes in mushrooms.

Insight into the evolutionary and domesticated history of the most widely cultivated mushroom Agaricus bisporus via mitogenome sequences of 361 global strains

Agaricus bisporus is the most widely cultivated edible mushroom in the world with a only around three hundred years known history of cultivation. Therefore, it represents an ideal organism not only to investigate the natural evolutionary history but also the understanding on the evolution going back to the early era of domestication. In this study, we generated the mitochondrial genome sequences of 352 A. bisporus strains and 9 strains from 4 closely related species around the world. The population mitogenomic study revealed all A. bisporus strains can be divided into seven clades, and all domesticated cultivars present only in two of those clades. The molecular dating analysis showed this species origin in Europe on 4.6 Ma and we proposed the main dispersal routes. The detailed mitogenome structure studies showed that the insertion of the plasmid-derived dpo gene caused a long fragment (MIR) inversion, and the distributions of the fragments of dpo gene were strictly in correspondence with these seven clades. Our studies also showed A. bisporus population contains 30 intron distribution patterns (IDPs), while all cultivars contain only two IDPs, which clearly exhibit intron loss compared to the others. Either the loss occurred before or after domestication, that could suggest that the change facilitates their adaptation to the cultivated environment.

Functional annotation and comparative analysis of four Botrytis cinerea mitogenomes reported from Punjab, Pakistan

Botrytis cinerea is one of the top phytopathogenic fungus which ubiquitously cause grey mold on a variety of horticultural plants. The mechanism of respiration in the fungus occurs within the mitochondria. Mitogenomes serve as a key molecular marker for the investigation of fungal evolutionary patterns. This study aimed at the complete assembly, characterization, and comparative relationship of four mitogenomes of Botrytis cinerea strains including Kst5C, Kst14A, Kst32B, Kst33A, respectively. High throughput sequencing of four mitogenomes allowed the full assembly and annotation of these sequences. The total genome length of these 4 isolates Kst5C Kst14A, Kst32B, Kst33A was 69,986 bp, 77,303 bp, 76,204 bp and 55, 226 bp respectively. The distribution of features represented 2 ribosomal RNA genes,14 respiration encoding proteins, 1 mitochondrial ribosomal protein-encoding gene, along with varying numbers of transfer RNA genes, protein-coding genes, mobile intronic regions and homing endonuclease genes including LAGLIDADG and GIY-YIG domains were found in all four mitogenomes. The comparative analyses performed also decipher significant results for four mitogenomes among fungal isolates included in the study. This is the first report on the detailed annotation of mitogenomes as a proof for investigation of variation patterns present with in the B. cinerea causing grey mold on strawberries in Pakistan. This study will also contribute to the rapid evolutionary analysis and population patterns present among Botrytis cinerea.

Mitochondrial genomes in the iconic reindeer lichens: Architecture, variation, and synteny across multiple evolutionary scales

Variation in mitochondrial genome composition across intraspecific, interspecific, and higher taxonomic scales has been little studied in lichen obligate symbioses. Cladonia is one of the most diverse and ecologically important lichen genera, with over 500 species representing an array of unique morphologies and chemical profiles. Here, we assess mitochondrial genome diversity and variation in this flagship genus, with focused sampling of two clades of the "true" reindeer lichens, Cladonia subgenus Cladina, and additional genomes from nine outgroup taxa. We describe composition and architecture at the gene and the genome scale, examining patterns in organellar genome size in larger taxonomic groups in Ascomycota. Mitochondrial genomes of Cladonia, Pilophorus, and Stereocaulon were consistently larger than those of Lepraria and contained more introns, suggesting a selective pressure in asexual morphology in Lepraria driving it toward genomic simplification. Collectively, lichen mitochondrial genomes were larger than most other fungal life strategies, reaffirming the notion that coevolutionary streamlining does not correlate to genome size reductions. Genomes from Cladonia ravenelii and Stereocaulon pileatum exhibited ATP9 duplication, bearing paralogs that may still be functional. Homing endonuclease genes (HEGs), though scarce in Lepraria, were diverse and abundant in Cladonia, exhibiting variable evolutionary histories that were sometimes independent of the mitochondrial evolutionary history. Intraspecific HEG diversity was also high, with C. rangiferina especially bearing a range of HEGs with one unique to the species. This study reveals a rich history of events that have transformed mitochondrial genomes of Cladonia and related genera, allowing future study alongside a wealth of assembled genomes.

Evolution and codon usage bias of mitochondrial and nuclear genomes in Aspergillus section Flavi

The fungal genus Aspergillus contains a diversity of species divided into taxonomic sections of closely related species. Section Flavi contains 33 species, many of industrial, agricultural, or medical relevance. Here, we analyze the mitochondrial genomes (mitogenomes) of 20 Flavi species-including 18 newly assembled mitogenomes-and compare their evolutionary history and codon usage bias patterns to their nuclear counterparts. Codon usage bias refers to variable frequencies of synonymous codons in coding DNA and is shaped by a balance of neutral processes and natural selection. All mitogenomes were circular DNA molecules with highly conserved gene content and order. As expected, genomic content, including GC content, and genome size differed greatly between mitochondrial and nuclear genomes. Phylogenetic analysis based on 14 concatenated mitochondrial genes predicted evolutionary relationships largely consistent with those predicted by a phylogeny constructed from 2,422 nuclear genes. Comparing similarities in interspecies patterns of codon usage bias between mitochondrial and nuclear genomes showed that species grouped differently by patterns of codon usage bias depending on whether analyses were performed using mitochondrial or nuclear relative synonymous usage values. We found that patterns of codon usage bias at gene level are more similar between mitogenomes of different species than the mitogenome and nuclear genome of the same species. Finally, we inferred that, although most genes-both nuclear and mitochondrial-deviated from the neutral expectation for codon usage, mitogenomes were not under translational selection while nuclear genomes were under moderate translational selection. These results contribute to the study of mitochondrial genome evolution in filamentous fungi.

Trichoderma - genomes and genomics as treasure troves for research towards biology, biotechnology and agriculture

The genus Trichoderma is among the best studied groups of filamentous fungi, largely because of its high relevance in applications from agriculture to enzyme biosynthesis to biofuel production. However, the physiological competences of these fungi, that led to these beneficial applications are intriguing also from a scientific and ecological point of view. This review therefore summarizes recent developments in studies of fungal genomes, updates on previously started genome annotation efforts and novel discoveries as well as efforts towards bioprospecting for enzymes and bioactive compounds such as cellulases, enzymes degrading xenobiotics and metabolites with potential pharmaceutical value. Thereby insights are provided into genomes, mitochondrial genomes and genomes of mycoviruses of Trichoderma strains relevant for enzyme production, biocontrol and mycoremediation. In several cases, production of bioactive compounds could be associated with responsible genes or clusters and bioremediation capabilities could be supported or predicted using genome information. Insights into evolution of the genus Trichoderma revealed large scale horizontal gene transfer, predominantly of CAZyme genes, but also secondary metabolite clusters. Investigation of sexual development showed that Trichoderma species are competent of repeat induced point mutation (RIP) and in some cases, segmental aneuploidy was observed. Some random mutants finally gave away their crucial mutations like T. reesei QM9978 and QM9136 and the fertility defect of QM6a was traced back to its gene defect. The Trichoderma core genome was narrowed down to 7000 genes and gene clustering was investigated in the genomes of multiple species. Finally, recent developments in application of CRISPR/Cas9 in Trichoderma, cloning and expression strategies for the workhorse T. reesei as well as the use genome mining tools for bioprospecting Trichoderma are highlighted. The intriguing new findings on evolution, genomics and physiology highlight emerging trends and illustrate worthwhile perspectives in diverse fields of research with Trichoderma.

The first two mitochondrial genomes for the genus Ramaria reveal mitochondrial genome evolution of Ramaria and phylogeny of Basidiomycota

In the present study, we assembled and analyzed the mitogenomes of two Ramaria species. The assembled mitogenomes of Ramaria cfr. rubripermanens and R. rubella were circularized, with sizes of 126,497 bp and 143,271 bp, respectively. Comparative mitogenome analysis showed that intron region contributed the most (contribution rate, 43.74%) to the size variations of Ramaria mitogenomes. The genetic contents, gene length, tRNAs, and codon usages of the two Ramaria mitogenomes varied greatly. In addition, the evolutionary rates of different core protein coding genes (PCGs) in Phallomycetidae mitogenomes varied. We detected large-scale gene rearrangements between Phallomycetidae mitogenomes, including gene displacement and tRNA doubling. A total of 4499 bp and 7746 bp aligned fragments were detected between the mitochondrial and nuclear genomes of R. cfr. rubripermanens and R. rubella, respectively, indicating possible gene transferring events. We further found frequent intron loss/gain and potential intron transfer events in Phallomycetidae mitogenomes during the evolution, and the mitogenomes of R. rubella contained a novel intron P44. Phylogenetic analyses using both Bayesian inference (BI) and Maximum Likelihood (ML) methods based on a combined mitochondrial gene dataset obtained an identical and well-supported phylogenetic tree for Basidiomycota, wherein R. cfr. rubripermanens and Turbinellus floccosus are sister species. This study served as the first report on mitogenomes from the genus Ramaria, which provides a basis for understanding the evolution, genetics, and taxonomy of this important fungal group.

Intraspecific comparison of mitochondrial genomes reveals the evolution in medicinal fungus Ganoderma lingzhi

Several mitogenomes of the genus Ganoderma have been assembled, but intraspecific comparisons of mitogenomes in Ganoderma lingzhi have not been reported. In this study, 19 G. lingzhi mitogenomes were assembled and analyzed combined with three mitogenomes of G. lingzhi from GenBank in term of the characteristics, evolution, and phylogeny. The results showed that the mitogenomes of the G. lingzhi strains are closed circular ranging from 49.23 kb to 68.37 kb. The genetic distance, selective pressure, and base variation indicate that the 14 common protein coding genes were highly conserved. The differences in introns, open reading frames, and repetitive sequences in the mitogenome were the main factors leaded to the variations in mitogenome. The introns were horizontally transferred in mitogenomes, and the differences between introns in the same insertion, which were primarily caused by the repetitive sequence, showed that the introns may be under degeneration. Besides, the frequent insertion and deletion of introns showed an evolutionary rate faster than protein coding genes. Phylogenetic analysis showed that the G. lingzhi strains gathered with high support, and those with the same intron distribution law had closer clustering relationships.

Cell Fusion May Be Involved in the Homothallic Mating of Pneumocystis Species

Pneumocystis species are obligate fungal biotrophs that colonize the lungs of mammals. They cause deadly pneumonia in immunocompromised hosts. The sexual phase seems obligate during their life cycle and essential for survival because it is believed to ensure proliferation and transmission between hosts. Here, we consider if the sexual phase is initiated by the fusion of two cells or by nucleus duplication in order to generate diploid cells that can undergo meiosis. The juxtaposition of the nucleus-associated organelles of pairs of cells with fused cytoplasmic membranes demonstrated that cell fusion can occur. Nevertheless, the frequency of cell fusion remains to be determined, and it cannot be excluded that both cell fusion and nucleus duplication are used to ensure the occurrence of the essential sexual phase. In vitro culturing of these fungi is a major milestone that could clarify the issue.

Comparative Mitogenomic Analysis Reveals Intraspecific, Interspecific Variations and Genetic Diversity of Medical Fungus Ganoderma

Ganoderma species are widely distributed in the world with high diversity. Some species are considered to be pathogenic fungi while others are used as traditional medicine in Asia. In this study, we sequenced and assembled four Ganoderma complete mitogenomes, including G. subamboinense s118, G. lucidum s37, G. lingzhi s62, and G. lingzhi s74. The sizes of the four mitogenomes ranged from 50,603 to 73,416 bp. All Ganoderma specimens had a full set of core protein-coding genes (PCGs), and the rps3 gene of Ganoderma species was detected to be under positive or relaxed selection. We found that the non-conserved PCGs, which encode RNA polymerases, DNA polymerases, homing endonucleases, and unknown functional proteins, are dynamic within and between Ganoderma species. Introns were thought to be the main contributing factor in Ganoderma mitogenome size variation (p < 0.01). Frequent intron loss/gain events were detected within and between Ganoderma species. The mitogenome of G. lucidum s26 gained intron P637 in the cox3 gene compared with the other two G. lucidum mitogenomes. In addition, some rare introns in Ganoderma were detected in distinct Basidiomycetes, indicating potential gene transfer events. Comparative mitogenomic analysis revealed that gene arrangements also varied within and between Ganoderma mitogenomes. Using maximum likelihood and Bayesian inference methods with a combined mitochondrial gene dataset, phylogenetic analyses generated identical, well-supported tree topologies for 71 Agaricomycetes species. This study reveals intraspecific and interspecific variations of the Ganoderma mitogenomes, which promotes the understanding of the origin, evolution, and genetic diversity of Ganoderma species.

Genetic Differentiation and Widespread Mitochondrial Heteroplasmy among Geographic Populations of the Gourmet Mushroom Thelephora ganbajun from Yunnan, China

The mitochondrial genomes are generally considered non-recombining and homoplasmic in nature. However, our previous study provided the first evidence of extensive and stable mitochondrial heteroplasmy in natural populations of the basidiomycete fungus Thelephora ganbajun from Yunnan province, China. The heteroplasmy was characterized by the presence of two types of introns residing at adjacent but different sites in the cytochrome oxidase subunits I (cox1) gene within an individual strain. However, the frequencies of these two introns among isolates from different geographical populations and the implications for the genetic structure in natural populations have not been investigated. In this study, we analyzed DNA sequence variation at the internal transcribed spacer (ITS) regions of the nuclear ribosomal RNA gene cluster among 489 specimens from 30 geographic locations from Yunnan and compared that variation with distribution patterns of the two signature introns in the cox1 gene that are indicative of heteroplasmy in this species. In our samples, evidence for gene flow, abundant genetic diversity, and genotypic uniqueness among geographic samples in Yunnan were revealed by ITS sequence variation. While there was insignificant positive correlation between geographic distance and genetic differentiation among the geographic samples based on ITS sequences, a moderate significant correlation was found between ITS sequence variation, geographical distance of sampling sites, and distribution patterns of the two heteroplasmic introns in the cox1 gene. Interestingly, there was a significantly negative correlation between the copy numbers of the two co-existing introns. We discussed the implications of our results for a better understanding of the spread of stable mitochondrial heteroplasmy, mito-nuclear interactions, and conservation of this important gourmet mushroom.

First two mitochondrial genomes for the order Filobasidiales reveal novel gene rearrangements and intron dynamics of Tremellomycetes

In the present study, two mitogenomes from the Filobasidium genus were assembled and compared with other Tremellomycetes mitogenomes. The mitogenomes of F. wieringae and F. globisporum both comprised circular DNA molecules, with sizes of 27,861 bp and 71,783 bp, respectively. Comparative mitogenomic analysis revealed that the genetic contents, tRNAs, and codon usages of the two Filobasidium species differed greatly. The sizes of the two Filobasidium mitogenomes varied greatly with the introns being the main factor contributing to mitogenome expansion in F. globisporum. Positive selection was observed in several protein-coding genes (PCGs) in the Agaricomycotina, Pucciniomycotina, and Ustilaginomycotina species, including cob, cox2, nad2, and rps3 genes. Frequent intron loss/gain events were detected to have occurred during the evolution of the Tremellomycetes mitogenomes, and the mitogenomes of 17 species from Agaricomycotina, Pucciniomycotina, and Ustilaginomycotina have undergone large-scale gene rearrangements. Phylogenetic analyses based on Bayesian inference and the maximum likelihood methods using a combined mitochondrial gene set generated identical and well-supported phylogenetic trees, wherein Filobasidium species had close relationships with Trichosporonales species. This study, which is the first report on mitogenomes from the order Filobasidiales, provides a basis for understanding the genomics, evolution, and taxonomy of this important fungal group.

Antifungal mechanism of 1-nonanol against Aspergillus flavus growth revealed by metabolomic analyses

Chemical control of fungal spoilage of postharvest cereal grains is an important strategy for the management of grain storage. Here, the potential antifungal activity of 1-nonanol, a main component of cereal volatiles, against Aspergillus flavus was studied. The growth of A. flavus was completely inhibited by 0.11 and 0.20 μL/mL 1-nonanol at vapor and liquid contact phases, respectively. Metabolomic analysis identified 135 metabolites whose expression was significantly different between 1-nonanol-treated and untreated A. flavus. These metabolites were involved in the tricarboxylic acid cycle, amino acid biosynthesis, protein degradation and absorption, aminoacyl-tRNA biosynthesis, mineral absorption, and in interactions with ABC transporters. Biochemical validation confirmed the disruptive effect of 1-nonanol on A. flavus growth, as indicated by the leakage of intracellular electrolytes, decreased succinate dehydrogenase, mitochondrial dehydrogenase, and ATPase activity, and the accumulation of reactive oxygen species. We speculated that 1-nonanol could disrupt cell membrane integrity and mitochondrial function and might induce apoptosis of A. flavus mycelia. Simulated grain storage experiments showed that 1-nonanol vapor, at a concentration of 264 μL/L, completely inhibited A. flavus growth in wheat, corn, and paddy grain with an 18% moisture content. This study provides new insights into the antifungal mechanism of 1-nonanol against A. flavus, indicating that it has a promising potential as a bio-preservative to prevent fungal spoilage of postharvest grains. KEY POINTS: • 1-Nonanol showed higher antifungal activity against A. flavus. • The antifungal mechanisms of 1-nonanol against A. flavus were revealed. • 1-Nonanol could damage cell membrane integrity and mitochondrial function.

Uncovering Diagnostic Value of Mitogenome for Identification of Cryptic Species Fusarium graminearum Sensu Stricto

Fungal complexes are often composed of morphologically nearly indistinguishable species with high genetic similarity. However, despite their close relationship, they can exhibit distinct phenotypic differences in pathogenicity and production of mycotoxins. Many plant pathogenic and toxigenic fungi have been shown to consist of such cryptic species. Identification of cryptic species in economically important pathogens has added value in epidemiologic studies and provides opportunities for better control. Analysis of mitochondrial genomes or mitogenomics opens up dimensions for improved diagnostics of fungi, especially when efficient recovery of DNA is problematic. In comparison to nuclear DNA, mitochondrial DNA (mtDNA) can be amplified with improved efficacy due to its multi-copy nature. However, to date, only a few studies have demonstrated the usefulness of mtDNA for identification of cryptic species within fungal complexes. In this study, we explored the value of mtDNA for identification of one of the most important cereal pathogens Fusarium graminearum sensu stricto (F.g.). We found that homing endonucleases (HEGs), which are widely distributed in mitogenomes of fungi, display small indel polymorphism, proven to be potentially species specific. The resulting small differences in their lengths may facilitate further differentiation of F.g. from the other cryptic species belonging to F. graminearum species complex. We also explored the value of SNP analysis of the mitogenome for typing F.g. The success in identifying F.g. strains was estimated at 96%, making this tool an attractive complement to other techniques for identification of F.g.

Spontaneous changes in somatic compatibility in Fusarium circinatum

Filamentous fungi grow by the elaboration of hyphae, which may fuse to form a network as a colony develops. Fusion of hyphae can occur between genetically different individuals, provided they share a common allele at loci affecting somatic compatibility. Diversity in somatic compatibility phenotypes reduces the frequency of hyphal fusion in a population, thereby slowing the spread of deleterious genetic elements such as viruses and plasmids, which require direct cytoplasmic contact for transmission. Diverse somatic compatibility phenotypes can be generated by recombining alleles through sexual reproduction, but this mechanism may not fully account for the diversity found in nature. For example, multiple compatibility phenotypes of Fusarium circinatum were shown to be associated with the same clonal lineage, which implies they were derived by a mutation rather than recombination through sexual reproduction. Experimental tests of this hypothesis confirmed that spontaneous changes in somatic compatibility can occur at a frequency between 5 and 8 per million spores. Genomic analysis of F. circinatum strains with altered somatic compatibility revealed no consistent evidence of recombination and supported the hypothesis that a spontaneous mutation generated the observed phenotypic change. Genes known to be involved in somatic compatibility had no mutations, suggesting that mutation occurred in a gene with an as yet unexplored function in somatic compatibility.

Interspecific hybridization as a driver of fungal evolution and adaptation

Cross-species gene transfer is often associated with bacteria, which have evolved several mechanisms that facilitate horizontal DNA exchange. However, the increased availability of whole-genome sequences has revealed that fungal species also exchange DNA, leading to intertwined lineages, blurred species boundaries or even novel species. In contrast to prokaryotes, fungal DNA exchange originates from interspecific hybridization, where two genomes are merged into a single, often highly unstable, polyploid genome that evolves rapidly into stabler derivatives. The resulting hybrids can display novel combinations of genetic and phenotypic variation that enhance fitness and allow colonization of new niches. Interspecific hybridization led to the emergence of important pathogens of humans and plants (for example, various Candida and 'powdery mildew' species, respectively) and industrially important yeasts, such as Saccharomyces hybrids that are important in the production of cold-fermented lagers or cold-cellared Belgian ales. In this Review, we discuss the genetic processes and evolutionary implications of fungal interspecific hybridization and highlight some of the best-studied examples. In addition, we explain how hybrids can be used to study molecular mechanisms underlying evolution, adaptation and speciation, and serve as a route towards development of new variants for industrial applications.

Mitochondrial genomes of the human pathogens Coccidioides immitis and Coccidioides posadasii

Fungal mitochondrial genomes encode genes involved in crucial cellular processes, such as oxidative phosphorylation and mitochondrial translation, and the molecule has been used as a molecular marker for population genetics studies. Coccidioides immitis and C. posadasii are endemic fungal pathogens that cause coccidioidomycosis in arid regions across both American continents. To date, approximately 150 Coccidioides isolates have been sequenced to infer patterns of variation in nuclear genomes. However, less attention has been given to the mitochondrial genomes of Coccidioides. In this report, we describe the assembly and annotation of mitochondrial reference genomes for two representative strains of C. posadasii and C. immitis, as well as assess population variation among 77 selected genomes. The sizes of the circular-mapping molecules are 68.2 Kb in C. immitis and 75.1 Kb in C. posadasii. We identify 14 mitochondrial protein-coding genes common to most fungal mitochondria, which are largely syntenic across different populations and species of Coccidioides. Both Coccidioides species are characterized by a large number of group I and II introns, harboring twice the number of elements as compared to closely related Onygenales. The introns contain complete or truncated ORFs with high similarity to homing endonucleases of the LAGLIDADG and GIY-YIG families. Phylogenetic comparisons of mitochondrial and nuclear genomes show extensive phylogenetic discordance suggesting that the evolution of the two types of genetic material is not identical. This work represents the first assessment of mitochondrial genomes among isolates of both species of Coccidioides, and provides a foundation for future functional work.

Evidence for Persistent Heteroplasmy and Ancient Recombination in the Mitochondrial Genomes of the Edible Yellow Chanterelles From Southwestern China and Europe

Mitochondrial genes and genomes have patterns of inheritance that are distinctly different from those of nuclear genes and genomes. In nature, the mitochondrial genomes in eukaryotes are generally considered non-recombining and homoplasmic. If heteroplasmy and recombination exist, they are typically very limited in both space and time. Here we show that mitochondrial heteroplasmy and recombination may not be limited to a specific population nor exit only transiently in the basidiomycete Cantharellus cibarius and related species. These edible yellow chanterelles are an ecologically very important group of fungi and among the most prominent wild edible mushrooms in the Northern Hemisphere. At present, very little is known about the genetics and population biology of these fungia cross large geographical distances. Our study here analyzed a total of 363 specimens of edible yellow chanterelles from 24 geographic locations in Yunnan in southwestern China and six geographic locations in five countries in Europe. For each mushroom sample, we obtained the DNA sequences at two genes, one in the nuclear genome and one in the mitochondrial genome. Our analyses of the nuclear gene, translation elongation factor 1-alpha (tef-1) and the DNA barcode of C. cibarius and related species, suggested these samples belong to four known species and five potential new species. Interestingly, analyses of the mitochondrial ATP synthase subunit 6 (atp6) gene fragment revealed evidence of heteroplasmy in two geographic samples in Yunnan and recombination within the two new putative species in Yunnan. Specifically, all four possible haplotypes at two polymorphic nucleotide sites within the mitochondrial atp6 gene were found distributed across several geographic locations in Yunnan. Furthermore, these four haplotypes were broadly distributed across multiple phylogenetic clades constructed based on nuclear tef-1 sequences. Our results suggest that heteroplasmy and mitochondrial recombination might have happened repeatedly during the evolution of the yellow chanterelles. Together, our results suggest that the edible yellow chanterelles represent an excellent system from which to study the evolution of mitochondrial-nuclear genome relationships.

Evolutionary Insights Into Two Widespread Ectomycorrhizal Fungi (Pisolithus) From Comparative Analysis of Mitochondrial Genomes

The genus Pisolithus is a group of global ectomycorrhizal fungi. The characterizations of Pisolithus mitochondrial genomes have still been unknown. In the present study, the complete mitogenomes of two Pisolithus species, Pisolithus microcarpus, and Pisolithus tinctorius, were assembled and compared with other Boletales mitogenomes. Both Pisolithus mitogenomes comprised circular DNA molecules with sizes of 43,990 and 44,054 bp, respectively. Comparative mitogenomic analysis showed that the rps3 gene differentiated greatly between Boletales species, and this gene may be subjected to strong pressure of positive selection between some Boletales species. Several plasmid-derived genes and genes with unknown functions were detected in the two Pisolithus mitogenomes, which needs further analysis. The two Pisolithus species show a high degree of collinearity, which may represent the gene arrangement of the ancestors of ectomycorrhizal Boletales species. Frequent intron loss/gain events were detected in Boletales and basidiomycetes, and intron P717 was only detected in P. tinctorius out of the eight Boletales mitogenomes tested. We reconstructed phylogeny of 79 basidiomycetes based on combined mitochondrial gene dataset, and obtained well-supported phylogenetic topologies. This study served as the first report on the mitogenomes of the family Pisolithaceae, which will promote the understanding of the evolution of Pisolithus species.

Pan-Mitogenomics Approach Discovers Diversity and Dynamism in the Prominent Brown Rot Fungal Pathogens

Monilinia fructicola and Monilinia laxa species are the most destructive and economically devastating fungal plant pathogens causing brown rot disease on stone and pome fruits worldwide. Mitochondrial genomes (mitogenomes) play critical roles influencing the mechanisms and directions of the evolution of fungal pathogens. The pan-mitogenomics approach predicts core and accessory regions of the mitochondrial genomes and explains the gain or loss of variation within and between species. The present study is a fungal pan-mitogenome of M. fructicola (N = 8) and M. laxa (N = 8) species. The completely sequenced and annotated mitogenomes showed high variability in size within and between the species. The mitogenomes of M. laxa were larger, ranging from 178,351 to 179,780bp, than the mitogenomes of M. fructicola, ranging from 158,607 to 167,838bp. However, size variation within the species showed that M. fructicola isolates were more variable in the size range than M. laxa isolates. All the mitogenomes included conserved mitochondrial genes, as well as variable regions including different mobile introns encoding homing endonucleases or maturase, non-coding introns, and repetitive elements. The linear model analysis supported the hypothesis that the mitogenome size expansion is due to presence of variable (accessory) regions. Gene synteny was mostly conserved among all samples, with the exception for order of the rps3 in the mitogenome of one isolate. The mitogenomes presented AT richness; however, A/T and G/C skew varied among the mitochondrial genes. The purifying selection was detected in almost all the protein-coding genes (PCGs) between the species. However, cytochrome b was the only gene showing a positive selection signal among the total samples. Combined datasets of amino acid sequences of 14 core mitochondrial PCGs and rps3 obtained from this study together with published mitochondrial genome sequences from some other species from Heliotales were used to infer a maximum likelihood (ML) phylogenetic tree. ML tree indicated that both Monilinia species highly diverged from each other as well as some other fungal species from the same order. Mitogenomes harbor much information about the evolution of fungal plant pathogens, which could be useful to predict pathogenic life strategies.

The Mitochondrial Genome of a Plant Fungal Pathogen Pseudocercospora fijiensis (Mycosphaerellaceae), Comparative Analysis and Diversification Times of the Sigatoka Disease Complex Using Fossil Calibrated Phylogenies

Mycosphaerellaceae is a highly diverse fungal family containing a variety of pathogens affecting many economically important crops. Mitochondria play a crucial role in fungal metabolism and in the study of fungal evolution. This study aims to: (i) describe the mitochondrial genome of Pseudocercospora fijiensis, and (ii) compare it with closely related species (Sphaerulina musiva, S. populicola, P. musae and P. eumusae) available online, paying particular attention to the Sigatoka disease’s complex causal agents. The mitochondrial genome of P. fijiensis is a circular molecule of 74,089 bp containing typical genes coding for the 14 proteins related to oxidative phosphorylation, 2 rRNA genes and a set of 38 tRNAs. P. fijiensis mitogenome has two truncated cox1 copies, and bicistronic transcription of nad2-nad3 and atp6-atp8 confirmed experimentally. Comparative analysis revealed high variability in size and gene order among selected Mycosphaerellaceae mitogenomes likely to be due to rearrangements caused by mobile intron invasion. Using fossil calibrated Bayesian phylogenies, we found later diversification times for Mycosphaerellaceae (66.6 MYA) and the Sigatoka disease complex causal agents, compared to previous strict molecular clock studies. An early divergent Pseudocercospora fijiensis split from the sister species P. musae + P. eumusae 13.31 MYA while their sister group, the sister species P. eumusae and P. musae, split from their shared common ancestor in the late Miocene 8.22 MYA. This newly dated phylogeny suggests that species belonging to the Sigatoka disease complex originated after wild relatives of domesticated bananas (section Eumusae; 27.9 MYA). During this time frame, mitochondrial genomes expanded significantly, possibly due to invasions of introns into different electron transport chain genes.

Recombination suppression and evolutionary strata around mating-type loci in fungi: documenting patterns and understanding evolutionary and mechanistic causes

Genomic regions determining sexual compatibility often display recombination suppression, as occurs in sex chromosomes, plant self-incompatibility loci and fungal mating-type loci. Regions lacking recombination can extend beyond the genes determining sexes or mating types, by several successive steps of recombination suppression. Here we review the evidence for recombination suppression around mating-type loci in fungi, sometimes encompassing vast regions of the mating-type chromosomes. The suppression of recombination at mating-type loci in fungi has long been recognized and maintains the multiallelic combinations required for correct compatibility determination. We review more recent evidence for expansions of recombination suppression beyond mating-type genes in fungi ('evolutionary strata'), which have been little studied and may be more pervasive than commonly thought. We discuss testable hypotheses for the ultimate (evolutionary) and proximate (mechanistic) causes for such expansions of recombination suppression, including (1) antagonistic selection, (2) association of additional functions to mating-type, such as uniparental mitochondria inheritance, (3) accumulation in the margin of nonrecombining regions of various factors, including deleterious mutations or transposable elements resulting from relaxed selection, or neutral rearrangements resulting from genetic drift. The study of recombination suppression in fungi could thus contribute to our understanding of recombination suppression expansion across a broader range of organisms.

Comparative Mitogenomic Analysis Reveals Dynamics of Intron Within and Between Tricholoma Species and Phylogeny of Basidiomycota

The genus of Tricholoma is a group of important ectomycorrhizal fungi. The overlapping of morphological characteristics often leads to the confusion of Tricholoma species classification. In this study, the mitogenomes of five Tricholoma species were sequenced based on the next-generation sequencing technology, including T. matsutake SCYJ1, T. bakamatsutake, T. terreum, T. flavovirens, and T. saponaceum. These five mitogenomes were all composed of circular DNA molecules, with sizes ranging from 49,480 to 103,090 bp. Intergenic sequences were considered to be the main factor contributing to size variations of Tricholoma mitogenomes. Comparative mitogenomic analysis showed that the introns of the Agaricales mitogenome experienced frequent loss/gain events. In addition, potential gene transfer was detected between the mitochondrial and nuclear genomes of the five species of Tricholoma. Evolutionary analysis showed that the rps3 gene of the Tricholoma species was under positive selection or relaxed selection in the evolutionary process. In addition, large-scale gene rearrangements were detected between some Tricholoma species. Phylogenetic analysis using the Bayesian inference and maximum likelihood methods based on a combined mitochondrial gene set yielded identical and well-supported tree topologies. This study promoted the understanding of the genetics, evolution, and phylogeny of the Tricholoma genus and related species.

Comparison of MultiLocus Sequence Typing (MLST) and Microsatellite Length Polymorphism (MLP) for Pneumocystis jirovecii genotyping

Pneumocystis jirovecii is an atypical fungus responsible for severe respiratory infections, often reported as local outbreaks in immunocompromised patients. Epidemiology of this infection, and transmission risk emphasises the need for developing genotyping techniques. Currently, two methods have emerged: Multilocus Sequence typing (MLST) and microsatellite length polymorphism (MLP). Here we compare an MLST strategy, including 2 nuclear loci and 2 mitochondrial loci, with an MLP strategy including 6 nuclear markers using 37 clinical PCR-positive respiratory samples from two French hospitals. Pneumocystis jirovecii MLST and MLP provided 30 and 35 different genotypes respectively. A higher number of mixed infections was detected using MLP (48.6% vs. 13.5% respectively; p = 0.002). Only one MLP marker (STR279) was statistically associated with the geographical origin of samples. Haplotype network inferred using the available genotypes yielded expanded network for MLP, characterized by more mutational steps as compared to MLST, suggesting that the MLP approach is more resolutive to separate genotypes. The correlation between genetic distances calculated based on MLST and MLP was modest with a R² value = 0.32 (p < 0.001). Finally, both genotyping methods fulfilled important criteria: (i) a discriminatory power from 97.5% to 99.5% and (ii) being quick and convenient genotyping tools. While MLP appeared highly resolutive regarding genotypes mixture within samples, using one genotyping method rather than the other may also depend on the context (i.e., MLST for investigation of suspected clonal outbreaks versus MLP for population structure study) as well as local facilities.

The insertion of a mitochondrial selfish element into the nuclear genome and its consequences

Homing endonucleases (HE) are enzymes capable of cutting DNA at highly specific target sequences, the repair of the generated double-strand break resulting in the insertion of the HE-encoding gene ("homing" mechanism). HEs are present in all three domains of life and viruses; in eukaryotes, they are mostly found in the genomes of mitochondria and chloroplasts, as well as nuclear ribosomal RNAs. We here report the case of a HE that accidentally integrated into a telomeric region of the nuclear genome of the fungal maize pathogen Ustilago maydis. We show that the gene has a mitochondrial origin, but its original copy is absent from the U. maydis mitochondrial genome, suggesting a subsequent loss or a horizontal transfer from a different species. The telomeric HE underwent mutations in its active site and lost its original start codon. A potential other start codon was retained downstream, but we did not detect any significant transcription of the newly created open reading frame, suggesting that the inserted gene is not functional. Besides, the insertion site is located in a putative RecQ helicase gene, truncating the C-terminal domain of the protein. The truncated helicase is expressed during infection of the host, together with other homologous telomeric helicases. This unusual mutational event altered two genes: The integrated HE gene subsequently lost its homing activity, while its insertion created a truncated version of an existing gene, possibly altering its function. As the insertion is absent in other field isolates, suggesting that it is recent, the U. maydis 521 reference strain offers a snapshot of this singular mutational event.

Fungal Mitogenomes: Relevant Features to Planning Plant Disease Management

Mitochondrial genomes (mt-genomes) are characterized by a distinct codon usage and their autonomous replication. Mt-genomes encode highly conserved genes (mt-genes), like proteins involved in electron transport and oxidative phosphorylation but they also carry highly variable regions that are in part responsible for their high plasticity. The degree of conservation of their genes is such that they allow the establishment of phylogenetic relationships even across distantly related species. Here, we describe the mechanisms that generate changes along mt-genomes, which play key roles at enlarging the ability of fungi to adapt to changing environments. Within mt-genomes of fungal pathogens, there are dispensable as well as indispensable genes for survival, virulence and/or pathogenicity. We also describe the different complexes or mechanisms targeted by fungicides, thus addressing a relevant issue regarding disease management. Despite the controversial origin and evolution of fungal mt-genomes, the intrinsic mechanisms and molecular biology involved in their evolution will help to understand, at the molecular level, the strategies for fungal disease management.

Diversity of Mobile Genetic Elements in the Mitogenomes of Closely Related Fusarium culmorum and F. graminearum sensu stricto Strains and Its Implication for Diagnostic Purposes

Much of the mitogenome variation observed in fungal lineages seems driven by mobile genetic elements (MGEs), which have invaded their genomes throughout evolution. The variation in the distribution and nucleotide diversity of these elements appears to be the main distinction between different fungal taxa, making them promising candidates for diagnostic purposes. Fungi of the genus Fusarium display a high variation in MGE content, from MGE-poor (Fusarium oxysporum and Fusarium fujikuroi species complex) to MGE-rich mitogenomes found in the important cereal pathogens F. culmorum and F. graminearum sensu stricto. In this study, we investigated the MGE variation in these latter two species by mitogenome analysis of geographically diverse strains. In addition, a smaller set of F. cerealis and F. pseudograminearum strains was included for comparison. Forty-seven introns harboring from 0 to 3 endonucleases (HEGs) were identified in the standard set of mitochondrial protein-coding genes. Most of them belonged to the group I intron family and harbored either LAGLIDADG or GIY-YIG HEGs. Among a total of 53 HEGs, 27 were shared by all fungal strains. Most of the optional HEGs were irregularly distributed among fungal strains/species indicating ancestral mosaicism in MGEs. However, among optional MGEs, one exhibited species-specific conservation in F. culmorum. While in F. graminearum s.s. MGE patterns in cox3 and in the intergenic spacer between cox2 and nad4L may facilitate the identification of this species. Thus, our results demonstrate distinctive traits of mitogenomes for diagnostic purposes of Fusaria.

Population Genomic Analysis Reveals a Highly Conserved Mitochondrial Genome in Fusarium asiaticum

Fusarium asiaticum is one of the pivotal members of the Fusarium graminearum species complex (FGSC) causing Fusarium head blight (FHB) on wheat, barley and rice in large parts of Asia. Besides resulting in yield losses, FHB also causes the accumulation of mycotoxins such as nivalenol (NIV) and deoxynivalenol (DON). The aim of this study was to conduct population studies on F. asiaticum from Southern China through mitochondrial genome analyses. All strains were isolated from wheat or rice from several geographic areas in seven provinces in Southern China. Based on geographic location and host, 210 isolates were selected for next generation sequencing, and their mitogenomes were assembled by GRAbB and annotated to explore the mitochondrial genome variability of F. asiaticum. The F. asiaticum mitogenome proves extremely conserved and variation is mainly caused by absence/presence of introns harboring homing endonuclease genes. These variations could be utilized to develop molecular markers for track and trace of migrations within and between populations. This study illustrates how mitochondrial introns can be used as markers for population genetic analysis. SNP analysis demonstrate the occurrence of mitochondrial recombination in F. asiaticum as was previously found for F. oxysporum and implied for F. graminearum. Furthermore, varying degrees of genetic diversity and recombination showed a high association with different geographic regions as well as with cropping systems. The mitogenome of F. graminearum showed a much higher SNP diversity while the interspecies intron variation showed no evidence of gene flow between the two closely related and sexual compatible species.

Exploring the Relationship Among Divergence Time and Coding and Non-coding Elements in the Shaping of Fungal Mitochondrial Genomes

The order Hypocreales (Ascomycota) is composed of ubiquitous and ecologically diverse fungi such as saprobes, biotrophs, and pathogens. Despite their phylogenetic relationship, these species exhibit high variability in biomolecules production, lifestyle, and fitness. The mitochondria play an important role in the fungal biology, providing energy to the cells and regulating diverse processes, such as immune response. In spite of its importance, the mechanisms that shape fungal mitogenomes are still poorly understood. Herein, we investigated the variability and evolution of mitogenomes and its relationship with the divergence time using the order Hypocreales as a study model. We sequenced and annotated for the first time Trichoderma harzianum mitochondrial genome (mtDNA), which was compared to other 34 mtDNAs species that were publicly available. Comparative analysis revealed a substantial structural and size variation on non-coding mtDNA regions, despite the conservation of copy number, length, and structure of protein-coding elements. Interestingly, we observed a highly significant correlation between mitogenome length, and the number and size of non-coding sequences in mitochondrial genome. Among the non-coding elements, group I and II introns and homing endonucleases genes (HEGs) were the main contributors to discrepancies in mitogenomes structure and length. Several intronic sequences displayed sequence similarity among species, and some of them are conserved even at gene position, and were present in the majority of mitogenomes, indicating its origin in a common ancestor. On the other hand, we also identified species-specific introns that advocate for the origin by different mechanisms. Investigation of mitochondrial gene transfer to the nuclear genome revealed that nuclear copies of the nad5 are the most frequent while atp8, atp9, and cox3 could not be identified in any of the nuclear genomes analyzed. Moreover, we also estimated the divergence time of each species and investigated its relationship with coding and non-coding elements as well as with the length of mitogenomes. Altogether, our results demonstrated that introns and HEGs are key elements on mitogenome shaping and its presence on fast-evolving mtDNAs could be mostly explained by its divergence time, although the intron sharing profile suggests the involvement of other mechanisms on the mitochondrial genome evolution, such as horizontal transference.

Complete Mitochondrial Genome of the Fungal Biocontrol Agent Trichoderma atroviride: Genomic Features, Comparative Analysis and Insight Into the Mitochondrial Evolution in Trichoderma

The improvement of biopesticides for use in the agriculture industry requires an understanding of the biological- and ecological principles underlying their behavior in natural environments. The nuclear genomes of members of the genus Trichoderma, which are representative fungal biocontrol agents, have been actively studied in relation to the unique characteristics of these species as effective producers of CAZymes/secondary metabolites and biopesticides, but their mitochondrial genomes have received much less attention. In this study, the mitochondrial genome of Trichoderma atroviride (Hypocreales, Sordariomycetes), which targets wood-decaying fungal pathogens and has the ability to degrade chemical fungicides, was assembled de novo. A 32,758 bp circular DNA molecule was revealed with specific features, such as a few more protein CDS and trn genes, two homing endonucleases (LAGLIDADG-/GIY-YIG-type), and even a putative overlapping tRNA gene, on a closer phylogenetic relationship with T. gamsii among hypocrealean fungi. Particularly, introns were observed with several footprints likely to be evolutionarily associated with the intron dynamics of the Trichoderma mitochondrial genomes. This study is the first to report the complete de novo mitochondrial genome of T. atroviride, while comparative analyses of Trichoderma mitochondrial genomes were also conducted from the perspective of mitochondrial evolution for the first time.

Comparative Analyses of Mitochondrial Genomes Provide Evolutionary Insights Into Nematode-Trapping Fungi

Predatory fungi in Orbiliaceae (Ascomycota) have evolved a diversity of trapping devices that enable them to trap and kill nematodes, other small animals, and protozoans. These trapping devices include adhesive hyphae, adhesive knobs, adhesive networks, constricting rings, and non-constricting rings. Their diversity and practical importance have attracted significant attention from biologists, making them excellent model organisms for studying adaptative evolution and as biological control agents against parasitic nematodes. The putative origins and evolutionary relationships among these carnivorous fungi have been investigated using nuclear protein-encoding genes, but their patterns of mitogenome relationships and divergences remain unknown. Here we analyze and compare the mitogenomes of 12 fungal strains belonging to eight species, including six species representing all four types of nematode trapping devices and two from related but non-predatory fungi. All 12 analyzed mitogenomes were of circular DNA molecules, with lengths ranging from 146,101 bp to 280,699 bp. Gene synteny analysis revealed several gene rearrangements and intron transfers among the mitogenomes. In addition, the number of protein coding genes (PCGs), GC content, AT skew, and GC skew varied among these mitogenomes. The increased number and total size of introns were the main contributors to the length differences among the mitogenomes. Phylogenetic analyses of the protein-coding genes indicated that mitochondrial and nuclear genomes evolved at different rates, and signals of positive selection were found in several genes involved in energy metabolism. Our study provides novel insights into the evolution of nematode-trapping fungi and shall facilitate further investigations of this ecologically and agriculturally important group of fungi.

Promising Perspectives for Detection, Identification, and Quantification of Plant Pathogenic Fungi and Oomycetes through Targeting Mitochondrial DNA

Fungi and oomycetes encompass many pathogens affecting crops worldwide. Their effective control requires screening pathogens across the local and international trade networks along with the monitoring of pathogen inocula in the field. Fundamentals to all of these concerns are their efficient detection, identification, and quantification. The use of molecular markers showed the best promise in the field of plant pathogen diagnostics. However, despite the unquestionable benefits of DNA-based methods, two significant limitations are associated with their use. The first limitation concerns the insufficient level of sensitivity due to the very low and uneven distribution of pathogens in plant material. The second limitation pertains to the inability of widely used diagnostic assays to detect cryptic species. Targeting mtDNA appears to provide a solution to these challenges. Its high copy number in microbial cells makes mtDNA an attractive target for developing highly sensitive assays. In addition, previous studies on different pathogen taxa indicated that mitogenome sequence variation could improve cryptic species delimitation accuracy. This review sheds light on the potential application of mtDNA for pathogen diagnostics. This paper covers a brief description of qPCR and DNA barcoding as two major strategies enabling the diagnostics of plant pathogenic fungi and oomycetes. Both strategies are discussed along with the potential use of mtDNA, including their strengths and weaknesses.

Evidence of Extensive Intraspecific Noncoding Reshuffling in a 169-kb Mitochondrial Genome of a Basidiomycetous Fungus

Comparative genomics of fungal mitochondrial genomes (mitogenomes) have revealed a remarkable pattern of rearrangement between and within major phyla owing to horizontal gene transfer and recombination. The role of recombination was exemplified at a finer evolutionary time scale in basidiomycetes group of fungi as they display a diversity of mitochondrial DNA inheritance patterns. Here, we assembled mitogenomes of six species from the Hymenochaetales order of basidiomycetes and examined 59 mitogenomes from 2 genetic lineages of Phellinus noxius. Gene order is largely collinear, while intergene regions are major determinants of mitogenome size variation. Substantial sequence divergence was found in shared introns consistent with high horizontal gene transfer frequency observed in yeasts, but we also identified a rare case where an intron was retained in five species since speciation. In contrast to the hyperdiversity observed in nuclear genomes of Phellinus noxius, mitogenomes’ intraspecific polymorphisms at protein-coding sequences are extremely low. Phylogeny network based on introns revealed turnover as well as exchange of introns between two lineages. Strikingly, some strains harbor a mosaic origin of introns from both lineages. Analysis of intergenic sequence indicated substantial differences between and within lineages, and an expansion may be ongoing as a result of exchange between distal intergenes. These findings suggest that the evolution in mitochondrial DNAs is usually lineage specific but chimeric mitotypes are frequently observed, thus capturing the possible evolutionary processes shaping mitogenomes in a basidiomycete. The large mitogenome sizes reported in various basidiomycetes appear to be a result of interspecific reshuffling of intergenes.

Evolving mtDNA populations within cells

Mitochondrial DNA (mtDNA) encodes vital respiratory machinery. Populations of mtDNA molecules exist in most eukaryotic cells, subject to replication, degradation, mutation, and other population processes. These processes affect the genetic makeup of cellular mtDNA populations, changing cell-to-cell distributions, means, and variances of mutant mtDNA load over time. As mtDNA mutant load has nonlinear effects on cell functionality, and cell functionality has nonlinear effects on tissue performance, these statistics of cellular mtDNA populations play vital roles in health, disease, and inheritance. This mini review will describe some of the better-known ways in which these populations change over time in different organisms, highlighting the importance of quantitatively understanding both mutant load mean and variance. Due to length constraints, we cannot attempt to be comprehensive but hope to provide useful links to some of the many excellent studies on these topics.

Mitochondrial genome and diverse inheritance patterns in Pleurotus pulmonarius

Pleurotus pulmonarius, a member of the Pleurotaceae family in Basidiomycota, is an edible, economically important mushroom in most Asian countries. In this study, the complete mitochondrial genomes (mtDNA) of three P. pulmonarius strains - two monokaryotic commercial (J1-13 and ZA3) and one wild (X1-15) - were sequenced and analyzed. In ZA3 and X1-15, the mtDNA molecule was found to be a single circle of 68,305 bp and 73,435 bp, respectively. Both strains contain 14 core protein-coding genes and two ribosomal RNA (rRNA) subunit genes. The ZA3 strain has 22 transfer RNA (tRNA) genes and nine introns: eight in cytochrome c oxidase subunit 1 (coxl), and one in the rRNA large subunit (rnl). Monokaryotic J1-13 and ZA3 mtDNAs were found to be similar in their structure. However, the wild strain X1-15 contains 25 tRNA genes and only seven introns in coxl. Open reading frames (ORFs) of ZA3/J1-13 and X1-15 encode LAGLIDADG, ribosomal protein S3, and DNA polymerase II. In addition, mtDNA inheritance in J1-13, ZA3, and X1-15 was also studied. Results showed that the mtDNA inheritance pattern was uniparental and closely related to dikaryotic hyphal location with respect to the parent. Results also show that mtDNA inheritance is influenced by both the parental nuclear genome and mitogenome in the zone of contact between two compatible parents. In summary, this analysis provides valuable information and a basis for further studies to improve our understanding of the inheritance of fungal mtDNA.

TALE homeobox heterodimer GSM1/GSP1 is a molecular switch that prevents unwarranted genetic recombination in Chlamydomonas

Eukaryotic sexual life cycles alternate between haploid and diploid stages, the transitions between which are delineated by cell fusion and meiotic division. Transcription factors in the TALE-class homeobox family, GSM1 and GSP1, predominantly control gene expression for the haploid-to-diploid transition during sexual reproduction in the unicellular green alga, Chlamydomonas reinhardtii. To understand the roles that GSM1 and GSP1 play in zygote development, we used gsm1 and gsp1 mutants and examined fused gametes that normally undergo the multiple organellar fusions required for the genetic unity of the zygotes. In gsm1 and gsp1 zygotes, no fusion was observed for the nucleus and chloroplast. Surprisingly, mitochondria and endoplasmic reticulum, which undergo dynamic autologous fusion/fission, did not undergo heterologous fusions in gsm1 or gsp1 zygotes. Furthermore, the mutants failed to resorb their flagella, an event that normally renders the zygotes immotile. When gsm1 and gsp1 zygotes resumed the mitotic cycle, their two nuclei fused prior to mitosis, but neither chloroplastic nor mitochondrial fusion took place, suggesting that these fusions are specifically turned on by GSM1/GSP1. Taken together, this study shows that organellar restructuring during zygotic diploidization does not occur by default but is triggered by a combinatorial switch, the GSM1/GSP1 dyad. This switch may represent an ancient mechanism that evolved to restrict genetic recombination during sexual development.