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

New insights into mycotoxin risk management through fungal population genetics and genomics

Mycotoxin contamination of food and feed is a major global concern. Chronic or acute dietary exposure to contaminated food and feed can negatively affect both human and animal health. Contamination occurs through plant infection by toxigenic fungi, primarily Aspergillus and Fusarium spp., either before or after harvest. Despite the application of various management strategies, controlling these pathogens remains a major challenge primarily because of their ability to adapt to environmental changes and selection pressures. Understanding the genetic structure of plant pathogen populations is pivotal for gaining new insights into their biology and epidemiology, as well as for understanding the mechanisms behind their adaptability. Such deeper understanding is crucial for developing effective and preemptive management strategies tailored to the evolving nature of pathogenic populations. This review focuses on the population-level variations within the two most economically significant toxigenic fungal genera according to space, host, and pathogenicity. Outcomes in terms of migration patterns, gene flow within populations, mating abilities, and the potential for host jumps are examined. We also discuss effective yet often underutilized applications of population genetics and genomics to address practical challenges in the epidemiology and disease control of toxigenic fungi.

The complete mitochondrial genome of the rice blast fungus Pyricularia oryzae Cavara 1892 strain Guy11 and phylogenetic analysis

The complete mitochondrial genome of Pyricularia oryzae Cavara 1892 strain Guy11 is 34,865 bp in length (GenBank accession number OP095391), containing 29 tRNA genes, 2 rRNA genes, and 15 protein-coding genes (PCGs). The gene order and orientation are novel compared to other Sordariomycetes species with sequenced mitogenomes in the GenBank database. Phylogenetic analysis suggests that P. oryzae Guy11 and 19 other Sordariomycetes species form a monophyletic group. The complete mitochondrial sequence of P. oryzae Guy11 will be a valuable resource for species identification, population genetics, phylogenetics, and comparative genomics studies in Sordariomycetes and Magnaporthales.

Rapid and Sensitive Detection of Toxigenic Fusarium asiaticum Integrating Recombinase Polymerase Amplification, CRISPR/Cas12a, and Lateral Flow Techniques

Fusarium head blight (FHB) is a global cereal disease caused by a complex of Fusarium species. Both Fusarium graminearum and F. asiaticum are the causal agents of FHB in China. F. asiaticum is the predominant species in the Middle-Lower Reaches of the Yangtze River (MLRYR) and southwest China. Therefore, detecting F. asiaticum in a timely manner is crucial for controlling the disease and preventing mycotoxins from entering the food chain. Here, we combined rapid genomic DNA extraction, recombinase polymerase amplification, Cas12a cleavage, and lateral flow detection techniques to develop a method for the rapid detection of F. asiaticum. The reaction conditions were optimized to provide a rapid, sensitive, and cost-effective method for F. asiaticum detection. The optimized method demonstrated exceptional specificity in detecting F. asiaticum while not detecting any of the 14 other Fusarium strains and 3 non-Fusarium species. Additionally, it could detect F. asiaticum DNA at concentrations as low as 20 ag/μL, allowing for the diagnosis of F. asiaticum infection in maize and wheat kernels even after 3 days of inoculation. The developed assay will provide an efficient and robust detection platform to accelerate plant pathogen detection.

Multiple rearrangements and low inter- and intra-species mitogenome sequence variation in the Heterobasidion annosum s.l. species complex

Introduction

Mitochondria are essential organelles in the eukaryotic cells and responsible for the energy production but are also involved in many other functions including virulence of some fungal species. Although the evolution of fungal mitogenomes have been studied at some taxonomic levels there are still many things to be learned from studies of closely related species.

Methods

In this study, we have analyzed 60 mitogenomes in the five species of the Heterobasidion annosum sensu lato complex that all are necrotrophic pathogens on conifers.

Results and Discussion

Compared to other fungal genera the genomic and genetic variation between and within species in the complex was low except for multiple rearrangements. Several translocations of large blocks with core genes have occurred between the five species and rearrangements were frequent in intergenic areas. Mitogenome lengths ranged between 108 878 to 116 176 bp, mostly as a result of intron variation. There was a high degree of homology of introns, homing endonuclease genes, and intergenic ORFs among the five Heterobasidion species. Three intergenic ORFs with unknown function (uORF6, uORF8 and uORF9) were found in all five species and was located in conserved synteny blocks. A 13 bp long GC-containing self-complementary palindrome was discovered in many places in the five species that were optional in presence/absence. The within species variation is very low, among 48 H. parviporum mitogenomes, there was only one single intron exchange, and SNP frequency was 0.28% and indel frequency 0.043%. The overall low variation in the Heterobasidion annosum sensu lato complex suggests a slow evolution of the mitogenome.

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.

CRISPR-Cas12a-Based Diagnostics of Wheat Fungal Diseases

Fusarium head blight (FHB) of wheat, mainly caused by Fusarium graminearum (F. graminearum) infection, reduces crop yield and contaminates grain with mycotoxins. We report a clustered regularly interspaced short palindromic repeats (CRISPR)-Cas12a-based nucleic acid assay for an early and rapid diagnosis of wheat FHB. Guide RNA (gRNA) was screened for highly specific recognition of polymerase chain reaction (PCR) amplicon of the internal transcribed spacer (ITS) region and the transcription elongation factor 1α (EF1α) of F. graminearum. The trans-activation of Cas12a protein cleaves the single-stranded DNA probes with the terminal fluorophore and quencher groups, thus allowing us to report the presence of ITS and EF1α of F. graminearum. Owing to the dual recognition process through PCR primers and gRNA hybridization, the approach realized specific discrimination of F. graminearum from other pathogenic fungi. It also allowed us to detect as low as 1 fg/μL total DNA from F. graminearum, which is sufficient to diagnose a 4 day F. graminearum infection. CRISPR-Cas12a-based nucleic acid assay promises the molecular diagnosis of crop diseases and broadens the application of CRISPR tools.

Identification of causal agent of wilt of common sage (Salvia officinalis L.)

Introduction: Common sage is cultivated in Europe and North America. It has strong antiviral, antibacterial and antifungal properties. This plant can be infected by different pathogenic fungi species, such as Alternaria alternata, Fusarium spp. (F. culmorum, F. equiseti, F. oxysporum), Phomopsis sclarea and Botrytis cinerea. Those species are the most frequently isolated fungi from sage stem base.

Objective: The aim of this study was to identify the causal agent of common sage wilt disease.

Methods: Studies were carried out in 2018–2020. 23 fungal isolates were identified based on their morphology and with use of PCR technique. Length and width of 100 conidia growing on SNA medium were measured after 7 days. Koch’s postulates were checked and the development of one fungus isolate (no. 13) was compared on seven media: the CMA, MEA, OA, PCA, SNA, PDA and Czapek medium. Sequences of the second largest subunit of RNA polymerase II (RPB2) were used to identify the pathogen.

Results: The fungus formed 3 kinds of spores: thin-walled, hyaline, slightly folded at the base, mostly 4-cell macroconidia, oblong, hyaline one- or two-cell microconidia and oval thick-walled chlamydospores. The Koch’s postulates were fulfilled. The fungus formed the most abundant aerial mycelium on the Czapek medium, and the least on the CMA medium. On the SNA medium, the mycelium grew into the medium and the aerial mycelium was not formed. The obtained RPB2 nucleotide sequence was 100% similar to the Fusarium oxysporum sequence deposited in GenBank (NCBI).

Conclusions: The results of this research can be used in further studies on the biological diversity of this species.

Exploring Mitogenomes Diversity of Fusarium musae from Banana Fruits and Human Patients

Fusarium musae has recently been described as a cross-kingdom pathogen causing post-harvest disease in bananas and systemic and superficial infection in humans. The taxonomic identity of fungal cross-kingdom pathogens is essential for confirming the identification of the species on distant infected hosts. Understanding the level of variability within the species is essential to decipher the population homogeneity infecting human and plant hosts. In order to verify that F. musae strains isolated from fruits and patients are part of a common population and to estimate their overall diversity, we assembled, annotated and explored the diversity of the mitogenomes of 18 F. musae strains obtained from banana fruits and human patients. The mitogenomes showed a high level of similarity among strains with different hosts' origins, with sizes ranging from 56,493 to 59,256 bp. All contained 27 tRNA genes and 14 protein-coding genes, rps3 protein, and small and large ribosomal subunits (rns and rnl). Variations in the number of endonucleases were detected. A comparison of mitochondrial endonucleases distribution with a diverse set of Fusarium mitogenomes allowed us to specifically discriminate F. musae from its sister species F. verticillioides and the other Fusarium species. Despite the diversity in F. musae mitochondria, strains from bananas and strains from human patients group together, indirectly confirming F. musae as a cross-kingdom pathogen.

Molecular and Pathogenic Characterization of Fusarium Species Associated with Corm Rot Disease in Saffron from China

Saffron (Crocus sativus L.) is a commercial spice crop well-known throughout the world, valued for culinary, colorant, and pharmaceutical purposes. In China, Fusarium nirenbergiae was detected as causative agent of saffron corm rot, the most pervasive disease for the first time in 2020. In the present study, 261 Fusarium-like isolates were recovered from 120 rotted corms in four saffron producing fields at Zhejiang, Shanghai, and Yunnan provinces, China, in 2021. A combination of morpho-cultural features and multilocus sequence analysis (MLSA) of the concatenated rpb2 (DNA-directed RNA polymerase II largest subunit) and tef1 (translation elongation factor 1-α) partial sequences showed that the isolates from saffron belong to Fusarium nirenbergiae as well as F. commune, and F. annulatum with isolation frequencies of 58.2%, 26.8%, and 14.9%, respectively. Notably, F. commune was more prevalent than F. annulatum in the collected samples. Pathogenicity tests confirmed that both species were pathogenic on saffron corm. This is the first report of F. annulatum and F. commune causing corm rot of saffron, globally. Outcomes of the current research demonstrate that Fusarium spp. associated with saffron corm rot are more diverse than previously reported. Furthermore, some plants were infected by two or more Fusarium species. Our findings broaden knowledge about Fusarium spp. that inflict corm rot and assist the development of control measures.

Mitogenome-wide comparison and phylogeny reveal group I intron dynamics and intraspecific diversification within the phytopathogen Corynespora cassiicola

Corynespora cassiicola, the causal agent of an extensive range of plant diseases worldwide, is a momentous fungus with diverse lifestyles and rich in intraspecies variations. In the present study, a total of 56 mitochondrial genomes of C. cassiicola were assembled (except two available online) and analyzed, of which 16 mitogenomes were newly sequenced here. All these circular mitochondrial DNA (mtDNA) molecules, ranging from 39,223 bp to 45,786 bp in length, comprised the same set of 13 core protein-coding genes (PCGs), two rRNAs and 27 tRNAs arranged in identical order. Across the above conserved genes, nad3 had the largest genetic distance between different isolates and was possibly subjected to positive selection pressure. Comparative mitogenomic analysis indicated that seven group I (IB, IC1, and IC2) introns with a length range of 1013-1876 bp were differentially inserted in three core PCGs (cox1, nad1, and nad5), resulting in the varied mitogenome sizes among C. cassiicola isolates. In combination with dynamic distribution of the introns, a well-supported mitogenome-wide phylogeny of the 56 C. cassiicola isolates revealed eight phylogenetic groups, which only had weak correlations with host range and toxin class. Different groups of isolates exhibited obvious differences in length and GC content of some genes, while a degree of variance in codon usage and tRNA structure was also observed. This research served as the first report on mitogenomic comparisons within C. cassiicola, and could provide new insights into its intraspecific microevolution and genetic diversity.

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.

An Overview of Genomics, Phylogenomics and Proteomics Approaches in Ascomycota

Fungi are among the most successful eukaryotes on Earth: they have evolved strategies to survive in the most diverse environments and stressful conditions and have been selected and exploited for multiple aims by humans. The characteristic features intrinsic of Fungi have required evolutionary changes and adaptations at deep molecular levels. Omics approaches, nowadays including genomics, metagenomics, phylogenomics, transcriptomics, metabolomics, and proteomics have enormously advanced the way to understand fungal diversity at diverse taxonomic levels, under changeable conditions and in still under-investigated environments. These approaches can be applied both on environmental communities and on individual organisms, either in nature or in axenic culture and have led the traditional morphology-based fungal systematic to increasingly implement molecular-based approaches. The advent of next-generation sequencing technologies was key to boost advances in fungal genomics and proteomics research. Much effort has also been directed towards the development of methodologies for optimal genomic DNA and protein extraction and separation. To date, the amount of proteomics investigations in Ascomycetes exceeds those carried out in any other fungal group. This is primarily due to the preponderance of their involvement in plant and animal diseases and multiple industrial applications, and therefore the need to understand the biological basis of the infectious process to develop mechanisms for biologic control, as well as to detect key proteins with roles in stress survival. Here we chose to present an overview as much comprehensive as possible of the major advances, mainly of the past decade, in the fields of genomics (including phylogenomics) and proteomics of Ascomycota, focusing particularly on those reporting on opportunistic pathogenic, extremophilic, polyextremotolerant and lichenized fungi. We also present a review of the mostly used genome sequencing technologies and methods for DNA sequence and protein analyses applied so far for fungi.