Proposed nomenclature for mating type genes of filamentous ascomycetes

Mutations and Differential Transcription of Mating-Type and Pheromone Receptor Genes in Hirsutella sinensis and the Natural Cordyceps sinensis Insect-Fungi Complex

Sexual reproduction in ascomycetes is controlled by the mating-type (MAT) locus. (Pseudo)homothallic reproduction has been hypothesized on the basis of genetic data from Hirsutella sinensis (Genotype #1 of Ophiocordyceps sinensis). However, the differential occurrence and differential transcription of mating-type genes in the MAT1-1 and MAT1-2 idiomorphs were found in the genome and transcriptome assemblies of H. sinensis, and the introns of the MAT1-2-1 transcript were alternatively spliced with an unspliced intron I that contains stop codons. These findings reveal that O. sinensis reproduction is controlled at the genetic, transcriptional, and coupled transcriptional-translational levels. This study revealed that mutant mating proteins could potentially have various secondary structures. Differential occurrence and transcription of the a-/α-pheromone receptor genes were also found in H. sinensis. The data were inconsistent with self-fertilization under (pseudo)homothallism but suggest the self-sterility of H. sinensis and the requirement of mating partners to achieve O. sinensis sexual outcrossing under heterothallism or hybridization. Although consistent occurrence and transcription of the mating-type genes of both the MAT1-1 and MAT1-2 idiomorphs have been reported in natural and cultivated Cordyceps sinensis insect-fungi complexes, the mutant MAT1-1-1 and α-pheromone receptor transcripts in natural C. sinensis result in N-terminal or middle-truncated proteins with significantly altered overall hydrophobicity and secondary structures of the proteins, suggesting heterogeneous fungal source(s) of the proteins and hybridization reproduction because of the co-occurrence of multiple genomically independent genotypes of O. sinensis and >90 fungal species in natural C. sinensis.

Emerging Cases of Cat-Transmitted Sporotrichosis Driven by Sporothrix brasiliensis in Northeast Brazil

Cat-transmitted sporotrichosis is caused by the emerging fungal pathogen Sporothrix brasiliensis and constitutes a significant public health issue that affects people living in resource-poor urban centers in Brazil. The lack of knowledge about transmission dynamics makes it difficult to propose public health policies to contain the advance of sporotrichosis. We describe the recent emergence of 1,176 cases of sporotrichosis in cats (2016 to 2021) in the metropolitan region of Recife, Brazil, leading to significant zoonotic transmission and an overwhelming occurrence of S. brasiliensis as the etiological agent. Most cases were from cats in the cities of Olinda (408/1,176; 34.70%), Jaboatão dos Guararapes (332/1,176; 28.23%), and Recife (237/1,176; 20.15%). Molecular typing using amplified fragment length polymorphism (EcoRI-GA/MseI-AG) revealed low polymorphic information content (PIC = 0.2499) and heterozygosity (H = 0.2928), typical of an outbreak scenario. Dendrogram and multivariate cluster analysis revealed that isolates from Pernambuco are closely related to Rio de Janeiro isolates. We report a substantial occurrence of MAT1-2 idiomorphs in the metropolitan region of Recife (0:60 ratio; χ2 = 60.000, P < 0.0001). The limited population differentiation and genetic diversity of the isolates from Pernambuco suggest a recent introduction, possibly via a founder effect, from the parental population in Rio de Janeiro. Our findings emphasize the critical importance of molecular surveillance of S. brasiliensis for outbreak response. A comprehensive one-health strategy is mandatory to control the spread of cat-transmitted sporotrichosis driven by S. brasiliensis, encompassing sanitary barriers, quick diagnosis, and treatment.

Halophilomyces hongkongensis, a Novel Species and Genus in the Lulworthiaceae with Antibacterial Potential, Colonizing the Roots and Rhizomes of the Seagrass Halophila ovalis

Seagrass serves as a quintessential reservoir for obligate marine Lulworthiaceae fungi. Our current knowledge of the mycological diversity associated with seagrass in Hong Kong remains poor. We analyzed the diversity of fungi associated with the most widely distributed seagrass species in Hong Kong Halophila ovalis (Hydrocharitaceae), using a combination of culture-based methods and high-throughput amplicon sequencing. Halophilomyces hongkongensis, a novel fungal species in a newly proposed genus within the Lulworthiaceae family, was isolated from H. ovalis roots and rhizomes. The novel fungus showed distinct morphological characteristics, while both combined 18S-28S and internal transcribed spacer (ITS) phylogenetic trees based on maximum likelihood and Bayesian methods supported its discrimination from other existing Lulworthiaceae members. The ITS2 region in the Illumina sequencing results of multiple H. ovalis compartments, water, and adjacent non-seagrass sediments revealed continuous recruitment of H. hongkongensis by H. ovalis throughout the year despite dramatically fluctuating environmental conditions, with remarkably high proportions of this taxon found in root and rhizome internal tissues, possibly indicating a strong and specialized relationship established between the Lulworthiaceae fungal partner and its seagrass host. The inhibitory abilities exhibited by H. hongkongensis against Staphylococcus aureus SA29213 and ATCC 43300 (methicillin-resistant) may imply its capacity in producing (novel) antibacterial compounds. The discovery of H. hongkongensis as the first novel Lulworthiaceae taxon in Hong Kong, along with its distributional pattern in the seagrass meadow, provides valuable insights into the systematics and ecology of this strictly marine fungal family.

Recombination and repeat-induced point mutation landscapes reveal trade-offs between the sexual and asexual cycles of Magnaporthe oryzae

The fungal disease caused by Magnaporthe oryzae is one of the most devastating diseases that endanger many crops worldwide. Evidence shows that sexual reproduction can be advantageous for fungal diseases as hybridization facilitates host-jumping. However, the pervasive clonal lineages of M. oryzae observed in natural fields contradict this expectation. A better understanding of the roles of recombination and the fungi-specific repeat-induced point mutation (RIP) in shaping its evolutionary trajectory is essential to bridge this knowledge gap. Here we systematically investigate the RIP and recombination landscapes in M. oryzae using a whole genome sequencing data from 252 population samples and 92 cross progenies. Our data reveal that the RIP can robustly capture the population history of M. oryzae, and we provide accurate estimations of the recombination and RIP rates across different M. oryzae clades. Significantly, our results highlight a parent-of-origin bias in both recombination and RIP rates, tightly associating with their sexual potential and variations of effector proteins. This bias suggests a critical trade-off between generating novel allelic combinations in the sexual cycle to facilitate host-jumping and stimulating transposon-associated diversification of effectors in the asexual cycle to facilitate host coevolution. These findings provide unique insights into understanding the evolution of blast fungus.

Genotypic diversity, virulence, and molecular genetic tools in Histoplasma

SUMMARYHistoplasmosis is arguably the most common fungal respiratory infection worldwide, with hundreds of thousands of new infections occurring annually in the United States alone. The infection can progress in the lung or disseminate to visceral organs and can be difficult to treat with antifungal drugs. Histoplasma, the causative agent of the disease, is a pathogenic fungus that causes life-threatening lung infections and is globally distributed. The fungus has the ability to germinate from conidia into either hyphal (mold) or yeast form, depending on the environmental temperature. This transition also regulates virulence. Histoplasma and histoplasmosis have been classified as being of emergent importance, and in 2022, the World Health Organization included Histoplasma as 1 of the 19 most concerning human fungal pathogens. In this review, we synthesize the current understanding of the ecological niche, evolutionary history, and virulence strategies of Histoplasma. We also describe general patterns of the symptomatology and epidemiology of histoplasmosis. We underscore areas where research is sorely needed and highlight research avenues that have been productive.

Functional analysis of the mating type genes in Verticillium dahliae

BACKGROUND

Populations of the plant pathogenic fungus Verticillium dahliae display a complex and rich genetic diversity, yet the existence of sexual reproduction in the fungus remains contested. As pivotal genes, MAT genes play a crucial role in regulating cell differentiation, morphological development, and mating of compatible cells. However, the functions of the two mating type genes in V. dahliae, VdMAT1-1-1, and VdMAT1-2-1, remain poorly understood.

RESULTS

In this study, we confirmed that the MAT loci in V. dahliae are highly conserved, including both VdMAT1-1-1 and VdMAT1-2-1 which share high collinearity. The conserved core transcription factor encoded by the two MAT loci may facilitate the regulation of pheromone precursor and pheromone receptor genes by directly binding to their promoter regions. Additionally, peptide activity assays demonstrated that the signal peptide of the pheromone VdPpg1 possessed secretory activity, while VdPpg2, lacked a predicted signal peptide. Chemotactic growth assays revealed that V. dahliae senses and grows towards the pheromones FO-a and FO-α of Fusarium oxysporum, as well as towards VdPpg2 of V. dahliae, but not in response to VdPpg1. The findings herein also revealed that VdMAT1-1-1 and VdMAT1-2-1 regulate vegetative growth, carbon source utilization, and resistance to stressors in V. dahliae, while negatively regulating virulence.

CONCLUSIONS

These findings underscore the potential roles of VdMAT1-1-1 and VdMAT1-2-1 in sexual reproduction and confirm their involvement in various asexual processes of V. dahliae, offering novel insights into the functions of mating type genes in this species.

Structure of the Mating-Type Genes and Mating Systems of Verpa bohemica and Verpa conica (Ascomycota, Pezizomycotina)

Verpa spp. are potentially important economic fungi within Morchellaceae. However, fundamental research on their mating systems, the key aspects of their life cycle, remains scarce. Fungal sexual reproduction is chiefly governed by mating-type genes, where the configuration of these genes plays a pivotal role in facilitating the reproductive process. For this study, de novo assembly methodologies based on genomic data from Verpa spp. were employed to extract precise information on the mating-type genes, which were then precisely identified in silico and by amplifying their single-ascospore populations using MAT-specific primers. The results suggest that the MAT loci of the three tested strains of V. bohemica encompassed both the MAT1-1-1 and MAT1-2-1 genes, implying homothallism. On the other hand, amongst the three V. conica isolates, only the MAT1-1-1 or MAT1-2-1 genes were present in their MAT loci, suggesting that V. conica is heterothallic. Moreover, bioinformatic analysis reveals that the three tested V. bohemica strains and one V. conica No. 21110 strain include a MAT1-1-10 gene in their MAT loci, while the other two V. conica strains contained MAT1-1-11, exhibiting high amino acid identities with those from corresponding Morchella species. In addition, MEME analysis shows that a total of 17 conserved protein motifs are present among the MAT1-1-10 encoded protein, while the MAT1-1-11 protein contained 10. Finally, the mating type genes were successfully amplified in corresponding single-ascospore populations of V. bohemica and V. conica, further confirming their life-cycle type. This is the first report on the mating-type genes and mating systems of Verpa spp., and the presented results are expected to benefit further exploitation of these potentially important economic fungi.

Characterisation of the mating-type loci in species of Elsinoe causing scab diseases

The genus Elsinoe includes many aggressive plant pathogens that infect various economically important agricultural, horticultural and forestry plants. Significant diseases include citrus scab caused by E. fawcettii and E. australis, grapevine spot anthracnose by E. ampelina, and the emerging Eucalyptus scab and shoot malformation disease caused by the recently described E. necatrix. Despite their importance as plant pathogens, little is known regarding the biology of many Elsinoe spp. To gain insights into the reproductive biology of these fungi, we characterized the mating-type loci of seven species using whole genome sequence data. Results showed that the MAT1 locus organization and its flanking genes is relatively conserved in most cases. All seven species manifested a typical heterothallic mating system characterized by having either the MAT1-1 or MAT1-2 idiomorph present in an isolate. These idiomorphs were defined by the MAT1-1-1 or the MAT1-2-1 gene, respectively. A unique MAT1-1 idiomorph containing a truncated MAT1-2-1 gene, and a MAT1-1-1 gene, was identified in E. necatrix and E. fawcettii genomes. Additionally, two idiomorph-specific proteins were found in the MAT1-1 and MAT1-2 idiomorphs of E. australis. Universal mating-type markers confirmed heterothallism across 21 Elsinoe spp., are poised to advance future studies regarding the biology of these fungi.

Didymella fabae Punith.: mating type occurrence, distribution and phenotyping of the anamorph Ascochyta fabae Speg. in Tunisia

Faba bean ascochyta blight, caused by Ascochyta fabae Speg. (teleomorph: Didymella fabae Punith.), is one of the most devastating diseases of the crop. It can cause yield losses that reach 95% in conducive weather conditions. Surveys were carried out in five regions of Tunisia: Beja, Bizerte, Jendouba, Kef and Tunis-Cap Bon. A total of 513 fungal isolates were collected from 2011 to 2013. A molecular characterization was conducted to identify the mating type of each individual using a mating type specific PCR. Results revealed that the two mating types MAT1-2 and MAT1-1 coexisted in all surveyed regions. An imbalance in favor of MAT1-2 was observed particularly in Bizerte and Jendouba regions (sex ratio was 18:85 and 32:80, respectively). Moreover, morphological and pathogenic characterization of 122 isolates among the collection revealed a significant variability in conidia type (one celled or two celled conidia) frequency, in conidia mean size and in aggressiveness toward Badii faba bean cultivar (incubation period, IP; percentage necrotic leaf area, S; and area under disease progression curve, AUDPC). A principal component analysis (PCA) performed on morphologically studied parameters (frequency of conidia cell number and conidia mean size) identified three groups of isolates based on morphological traits: one celled (1C) and two celled (2C) conidia rates, one celled and two celled conidia length and width (1L, 1W, 2L and 2W, respectively). A second PCA using aggressiveness parameters (IP: Incubation period, S1, S4 and S9: percentage of necrotic leaf area respectively 5, 20 and 45 days after inoculation) identified three distinct pathogenic groups: poorly pathogenic AG1, moderately pathogenic AG2 and highly pathogenic AG3. Morphological and pathogenic groups and mating type data were used to conduct a multiple factorial correspondence analysis (MFCA) which revealed a correlation between the variables studied. Five groups were identified, each associated with a morphological and pathogenic trait and mating type. The most pathogenic group belonged to MAT1-2 suggesting that in locations where MAT1-2 is prevalent the epidemic risk is more important.

The Unique Homothallic Mating-Type Loci of the Fungal Tree Pathogens Chrysoporthe syzygiicola and Chrysoporthe zambiensis from Africa

Chrysoporthe syzygiicola and C. zambiensis are ascomycete tree pathogens first described from Zambia, causing stem canker on Syzygium guineense and Eucalyptus grandis, respectively. The taxonomic descriptions of these two species were based on their anamorphic states, as no sexual states are known. The main purpose of this work was to use whole genome sequences to identify and define the mating-type (MAT1) loci of these two species. The unique MAT1 loci for C. zambiensis and C. syzygiicola consist of the MAT1-1-1, MAT1-1-2, and MAT1-2-1 genes, but the MAT1-1-3 gene is absent. Genes canonically associated with opposite mating types were present at the single mating-type locus, suggesting that C. zambiensis and C. syzygiicola have homothallic mating systems.

Stepwise recombination suppression around the mating-type locus in an ascomycete fungus with self-fertile spores

Recombination is often suppressed at sex-determining loci in plants and animals, and at self-incompatibility or mating-type loci in plants and fungi. In fungal ascomycetes, recombination suppression around the mating-type locus is associated with pseudo-homothallism, i.e. the production of self-fertile dikaryotic sexual spores carrying the two opposite mating types. This has been well studied in two species complexes from different families of Sordariales: Podospora anserina and Neurospora tetrasperma. However, it is unclear whether this intriguing association holds in other species. We show here that Schizothecium tetrasporum, a fungus from a third family in the order Sordariales, also produces mostly self-fertile dikaryotic spores carrying the two opposite mating types. This was due to a high frequency of second meiotic division segregation at the mating-type locus, indicating the occurrence of a single and systematic crossing-over event between the mating-type locus and the centromere, as in P. anserina. The mating-type locus has the typical Sordariales organization, plus a MAT1-1-1 pseudogene in the MAT1-2 haplotype. High-quality genome assemblies of opposite mating types and segregation analyses revealed a suppression of recombination in a region of 1.47 Mb around the mating-type locus. We detected three evolutionary strata, indicating a stepwise extension of recombination suppression. The three strata displayed no rearrangement or transposable element accumulation but gene losses and gene disruptions were present, and precisely at the strata margins. Our findings indicate a convergent evolution of self-fertile dikaryotic sexual spores across multiple ascomycete fungi. The particular pattern of meiotic segregation at the mating-type locus was associated with recombination suppression around this locus, that had extended stepwise. This association between pseudo-homothallism and recombination suppression across lineages and the presence of gene disruption at the strata limits are consistent with a recently proposed mechanism of sheltering deleterious alleles to explain stepwise recombination suppression.

Diversity Analysis of the Rice False Smut Pathogen Ustilaginoidea virens in Southwest China

Rice false smut caused by Ustilaginoidea virens is a destructive disease in rice cropping areas of the world. The present study is focused on the morphology, pathogenicity, mating-type loci distribution, and genetic characterization of different isolates of U. virens. A total of 221 strains of U. virens were collected from 13 rice-growing regions in southwest China. The morphological features of these strains exhibited high diversity, and the pathogenicity of the smut fungus showed significant differentiation. There was no correlation between pathogenicity and sporulation. Mating-type locus (MAT) analysis revealed that all 221 isolates comprised heterothallic and homothallic forms, wherein 204 (92.31%) and 17 (7.69%) isolates belonged to heterothallic and homothallic mating types, respectively. Among 204 strains of heterothallic mating types, 62 (28.05%) contained MAT1-1-1 idiomorphs, and 142 isolates (64.25%) had the MAT1-2-1 idiomorph. Interestingly, strains isolated from the same fungus ball had different mating types. The genetic structure of the isolates was analyzed using simple sequence repeats (SSRs) and single-nucleotide polymorphisms (SNPs). All isolates were clustered into five genetic groups. The values of Nei's gene diversity (H) and Shannon's information index (I) indicated that all strains as a group had higher genetic diversity than strains from a single geographical population. The pairwise population fixation index (FST) values also indicated significant genetic differentiation among all compared geographical populations. The analysis of molecular variation (AMOVA) indicated greater genetic variation within individual populations and less genetic variation among populations. The results showed that most of the strains were not clustered according to their geographical origin, showing the rich genetic diversity and the complex and diverse genetic background of U. virens in southwest China. These results should help to better understand the biological and genetic diversity of U. virens in southwest China and provide a theoretical basis for building effective management strategies.

Truncation of MAT1-2-7 Deregulates Developmental Pathways Associated with Sexual Reproduction in Huntiella omanensis

The MAT1-1-1 and MAT1-2-1 genes are thought to be the master regulators of sexual development in most ascomycete fungi, and they are often essential for this process. In contrast, it has been suggested that the secondary mating-type genes act to calibrate the sexual cycle and can be dispensable. Recent functional characterization of genes such as Aspergillus fumigatus MAT1-2-4, Huntiella omanensis MAT1-2-7, and Botrytis cinerea MAT1-1-5 has, however, shown that these secondary genes may play more central roles in the sexual pathway and are essential for the production of mature fruiting structures. We used a comparative transcriptome sequencing (RNA-seq) experiment to show that the truncation of MAT1-2-7 in the wood inhabiting H. omanensis residing in the Ceratocystidaceae is associated with the differential expression of approximately 25% of all the genes present in the genome, including the transcriptional regulators ste12, wc-2, sub1, VeA, HMG8, and pro1. This suggests that MAT1-2-7 may act as a transcription factor and that ΔMAT1-2-7 mutant sterility is the result of layered deregulation of a variety of signaling and developmental pathways. This study is one of only a few that details the functional characterization of a secondary MAT gene in a nonmodel species. Given that this gene is present in other Ceratocystidaceae species and that there are diverse secondary MAT genes present throughout the Pezizomycotina, further investigation into this gene and others like it will provide a clearer understanding of sexual development in these eukaryotes. IMPORTANCE Secondary mating-type genes are being described almost as quickly as new fungal genomes are being sequenced. Understanding the functions of these genes has lagged behind their description, in part due to limited taxonomic distribution, lack of conserved functional domains, and difficulties with regard to genetic manipulation protocols. This study aimed to address this by investigating a novel mating-type gene, MAT1-2-7, for which two independent mutant strains were generated in a previous study. We characterized the molecular response to the truncation of this gene in a nonmodel, wood-infecting fungus and showed that it resulted in widespread differential expression throughout the transcriptome of this fungus. This suggests that secondary MAT genes may play a more important role than previously thought. This study also emphasizes the need for further research into the life cycles of nonmodel fungi, which often exhibit unique features that are very different from the systems understood from model species.

Organization and Unconventional Integration of the Mating-Type Loci in Morchella Species

True morels (Morchella spp.) are a group of delicious fungi in high demand worldwide, and some species of morels have been successfully cultivated in recent years. To better understand the sexual reproductive mechanisms of these fungi, we characterized the structure of the mating-type loci from ten morel species, and seven of them were obtained using long-range PCR amplification. Among the studied species, eight were heterothallic, two were homothallic, and four types of composition were observed in the MAT loci. In three of the five black morel species, the MAT1-1-1, MAT1-1-10, and MAT1-1-11 genes were in the MAT1-1 idiomorph, and only the MAT1-2-1 gene was in the MAT1-2 idiomorph, while an integration event occurred in the other two species and resulted in the importation of the MAT1-1-11 gene into the MAT1-2 idiomorph and survival as a truncated fragment in the MAT1-1 idiomorph. However, the MAT1-1-11 gene was not available in the four yellow morels and one blushing morel species. M. rufobrunnea, a representative species of the earliest diverging branch of true morels, along with another yellow morel Mes-15, were confirmed to be homothallic, and the MAT1-1-1, MAT1-1-10, and MAT1-2-1 genes were arranged in a tandem array. Therefore, we hypothesized that homothallism should be the ancestral reproductive state in Morchella. RT-PCR analyses revealed that four mating genes could be constitutively expressed, while the MAT1-1-10 gene underwent alternative splicing to produce different splice variants.

Calonectria in the age of genes and genomes: Towards understanding an important but relatively unknown group of pathogens

The genus Calonectria includes many aggressive plant pathogens causing diseases on various agricultural crops as well as forestry and ornamental tree species. Some species have been accidentally introduced into new environments via international trade of putatively asymptomatic plant germplasm or contaminated soil, resulting in significant economic losses. This review provides an overview of the taxonomy, population biology, and pathology of Calonectria species, specifically emerging from contemporary studies that have relied on DNA-based technologies. The growing importance of genomics in future research is highlighted. A life cycle is proposed for Calonectria species, aimed at improving our ability to manage diseases caused by these pathogens.

The population genetics of the causative agent of snake fungal disease indicate recent introductions to the USA

Snake fungal disease (SFD; ophidiomycosis), caused by the pathogen Ophidiomyces ophiodiicola (Oo), has been documented in wild snakes in North America and Eurasia, and is considered an emerging disease in the eastern United States of America. However, a lack of historical disease data has made it challenging to determine whether Oo is a recent arrival to the USA or whether SFD emergence is due to other factors. Here, we examined the genomes of 82 Oo strains to determine the pathogen’s history in the eastern USA. Oo strains from the USA formed a clade (Clade II) distinct from European strains (Clade I), and molecular dating indicated that these clades diverged too recently (approximately 2,000 years ago) for transcontinental dispersal of Oo to have occurred via natural snake movements across Beringia. A lack of nonrecombinant intermediates between clonal lineages in Clade II indicates that Oo has actually been introduced multiple times to North America from an unsampled source population, and molecular dating indicates that several of these introductions occurred within the last few hundred years. Molecular dating also indicated that the most common Clade II clonal lineages have expanded recently in the USA, with time of most recent common ancestor mean estimates ranging from 1985 to 2007 CE. The presence of Clade II in captive snakes worldwide demonstrates a potential mechanism of introduction and highlights that additional incursions are likely unless action is taken to reduce the risk of pathogen translocation and spillover into wild snake populations.

Snake fungal disease is an emerging disease in eastern North America, but the origins of the disease have been unclear. This study uses population genetic data to show that the fungus that causes the disease was introduced multiple times to North America over the last few hundred years.

The Diversity of Passalora fulva Isolates Collected from Tomato Plants in U.S. High Tunnels

High tunnels extend the growing season of high value crops, including tomatoes, but the environmental conditions within high tunnels favor the spread of the tomato leaf mold pathogen, Passalora fulva (syn. Cladosporium fulvum). Tomato leaf mold results in defoliation, and if severe, losses in yield. Despite substantial research, little is known regarding the genetic structure and diversity of populations of P. fulva associated with high tunnel tomato production in the United States. From 2016 to 2019, a total of 50 P. fulva isolates were collected from tomato leaf samples in high tunnels in the Northeast and Minnesota. Other Cladosporium species were also isolated from the leaf surfaces. Koch's postulates were conducted to confirm that P. fulva was the cause of the disease symptoms observed. Race determination experiments revealed that the isolates belonged to either race 0 (six isolates) or race 2 (44 isolates). Polymorphisms were identified within four previously characterized effector genes: Avr2, Avr4, Avr4e, and Avr9. The largest number of polymorphisms were observed for Avr2. Both mating type genes, MAT1-1-1 and MAT1-2-1, were present in the isolate collection. For further insights into the pathogen diversity, the 50 isolates were genotyped at 7,514 single-nucleotide polymorphism loci using genotyping-by-sequencing. Differentiation by region but not by year was observed. Within the collection of 50 isolates, there were 18 distinct genotypes. Information regarding P. fulva population diversity will enable better management recommendations for growers, as high tunnel production of tomatoes expands.

Mating-Type Genes Control Sexual Reproduction, Conidial Germination, and Virulence in Cochliobolus lunatus

Cochliobolus lunatus (anamorph: Curvularia lunata) is a major pathogenic fungus that causes the Curvularia leaf spot of maize. ClMAT1-1-1 and ClMAT1-2-1, the C. lunatus orthologs of C. heterostrophus ChMAT1-1-1 and ChMAT1-2-1, were investigated in the present study to uncover their functions in C. lunatus. Southern blot analysis showed that these mating-type MAT genes exist in the C. lunatus genome as a single copy. ClMAT1-1-1 and ClMAT1-2-1 were knocked out and complemented to generate ΔClmat1-1-1 and ΔClmat1-2-1 and ΔClmat1-1-1-C and ΔClmat1-2-1-C, respectively. The mutant strains had defective sexual development and failed to produce pseudothecia. There were no significant differences in growth rate or conidia production between the mutant and wild-type strains. However, the aerial mycelia and mycelial dry weight of ΔClmat1-1-1 and ΔClmat1-2-1 were lower than those of wild type, suggesting that MAT genes affect asexual development. ClMAT genes were involved in the responses to cell wall integrity and osmotic adaptation. ΔClmat1-2-1 had a lower conidial germination rate than the wild-type strain CX-3. The virulence of ΔClmat1-2-1 and ΔClmat1-1-1 was also reduced compared with the wild-type. Complementary strains could restore all the phenotypes.

Characterization of Vegetative Incompatibility in Morchella importuna and Location of the Related-Genes by Bulk Segregant Analysis

Vegetative incompatibility (VI) is a widespread phenomenon developed in Morchella importuna, a species of ascomycete fungus that is cultivated on a rapidly expanding scale in China. Understanding the genetic bases of this nonself-recognition phenomenon is beneficial for resolving some problems that are associated with the production of this highly prized edible fungus, such as crossbreeding, strain classification, and pathogen transmission. VI is genetically controlled by het genes, organized in two different systems, namely allelic and nonallelic. These het genes have been well characterized in Podospora anserina and Neurospora crassa. In this work, putative het-homologs were identified in the genome of M. importuna, but their low allelic polymorphism in different vegetative compatibility groups (VCGs) suggested that VI in this fungus might not be regulated by these het genes. The progeny derived from vegetative compatible parents became a VCG, while the single-ascospore strains from vegetative incompatible parents were divided into four VCGs, and the interaction between the inter-group strains led to the formation of two types of barrages, viz., thin dark line and raised aggregate of hyphae. The Bulk Segregant Analysis confirmed that the genes mimpvic32 and mimpvic33 were linked to VI reactions in M. importuna; nevertheless, the formation of barrages also occurred between the pairs carrying the same allele of these two genes. In sum, the VI control system in M. importuna was complicated, and there were more other allelic or non-allelic VI-related genes.

Multilocus sequence analysis and identification of mating-type idiomorphs distribution in Magnaporthe oryzae population of Karnataka state of India

AIMS

To investigate the genetic diversity, population structure, and mating-type distribution among the eco-distinct isolates of Magnaporthe oryzae from Karnataka, India.

METHODS AND RESULTS

A set of 38 isolates of M. oryzae associated with leaf blast disease of rice were collected from different rice ecosystems of Karnataka, India, and analyzed for their diversity at actin, β-tubulin, calmodulin, translation elongation factor 1-α (TEF-1-α), and internal transcribed spacer (ITS) genes/region. The isolates were grouped into two clusters based on the multilocus sequence diversity, the majority being in cluster-IA (n=37), and only one isolate formed cluster-IB. Population structure was analyzed using 123 SNP data to understand the genetic relationship. Based on K=2 and ancestry threshold of >70%, blast strains were classified into two subgroups (SG1 and SG2) whereas, based on K=4 and ancestry threshold of >70%, blast strains were classified into four subgroups (SG1, SG2, SG3, and SG4). We have identified 13 haplotype groups where haplotype-group-2 was predominant (n=20) in the population. The Tajima's and Fu's Fs neutrality tests exhibited many rare alleles. Further, the mating-type analysis was also performed using MAT1 gene-specific primers to find the potentiality of sexual reproduction in different ecosystems. The majority of the isolates (54.5%) had MAT1-2 idiomorph, whereas 45.5 per cent of the isolates possessed MAT1-1 idiomorph.

CONCLUSIONS

The present study found the genetically homogenous population of M. oryzae by multilocus sequence analysis. Both mating types, MAT1-1 and MAT1-2, were found within the M. oryzae population of Karnataka.

SIGNIFICANCE AND IMPACT OF STUDY

The study on the population structure and sexual mating behavior of M. oryzae is important in developing region-specific blast-resistant rice cultivars. This is the first report of MAT1 idiomorphs distribution in the M. oryzae population in any Southern state of India.

Genome-wide identification and expression profiling of thes MAPK, MAPKK, and MAPKKK gene families in Ophiocordyceps sinensis

Mitogen-activated protein kinase (MAPK) cascades have a universal cell signaling mechanism in eukaryotes. A typical MAPK signal transduction module comprises three kinds of sequentially phosphorylated protein kinases: MAPK, Mitogen-activated protein kinase kinase (MAPKK), and Mitogen-activated protein kinase kinase kinase (MAPKKK). However, little is known regarding the genes involved in MAPK cascades in Ophiocordyceps sinensis. Nine genes (three MAPK, three MAPKK, and three MAPKKK) were identified in this study. The MAPK, MAPKK, and MAPKKK genes were divided into three subfamilies, according to the phylogenetic analysis. TEY and TGY represented the activation domains of the MAPKs; the corresponding domains in MAPKKs were SDIWS and SDVWS, and those in the MAPKKs were GSVFYWMAPEV and GTPMYMSPEV. Transcription data analysis and quantitative real-time polymerase chain reaction showed that the MAPK cascade was related to the growth of the fruiting body. This is the first study to report a genome-wide identification of the MAPK, MAPKK, and MAPKK gene families in O. sinensis.

Genetic Networks That Govern Sexual Reproduction in the Pezizomycotina

Sexual development in filamentous fungi is a complex process that relies on the precise control of and interaction between a variety of genetic networks and pathways. The mating-type (MAT) genes are the master regulators of this process and typically act as transcription factors, which control the expression of genes involved at all stages of the sexual cycle. In many fungi, the sexual cycle typically begins when the mating pheromones of one mating type are recognized by a compatible partner, followed by physical interaction and fertilization. Subsequently, highly specialized sexual structures are formed, within which the sexual spores develop after rounds of meiosis and mitosis. These spores are then released and germinate, forming new individuals that initiate new cycles of growth. This review provides an overview of the known genetic networks and pathways that are involved in each major stage of the sexual cycle in filamentous ascomycete fungi.

MAT Loci Play Crucial Roles in Sexual Development but Are Dispensable for Asexual Reproduction and Pathogenicity in Rice Blast Fungus Magnaporthe oryzae

Magnaporthe oryzae, a fungal pathogen that causes rice blast, which is the most destructive disease of rice worldwide, has the potential to perform both asexual and sexual reproduction. MAT loci, consisting of MAT genes, were deemed to determine the mating types of M. oryzae strains. However, investigation was rarely performed on the development and molecular mechanisms of the sexual reproduction of the fungus. In the present work, we analyzed the roles of two MAT loci and five individual MAT genes in the sex determination, sexual development and pathogenicity of M. oryzae. Both of the MAT1-1 and MAT1-2 loci are required for sex determination and the development of sexual structures. MAT1-1-1, MAT1-1-3 and MAT1-2-1 genes are crucial for the formation of perithecium. MAT1-1-2 impacts the generation of asci and ascospores, while MAT1-2-2 is dispensable for sexual development. A GFP fusion experiment indicated that the protein of MAT1-1-3 is distributed in the nucleus. However, all of the MAT loci or MAT genes are dispensable for vegetative growth, asexual reproduction, pathogenicity and pathogenicity-related developments of the fungus, suggesting that sexual reproduction is regulated relatively independently in the development of the fungus. The data and methods of this work may be helpful to further understand the life cycle and the variation of the fungus.

A new duplex PCR assay for the rapid screening of mating-type idiomorphs of pathogenic Sporothrix species

Sporothrix schenckii and allied species are thermodimorphic fungi widely distributed in nature which causes human and animal sporotrichosis, the most common subcutaneous mycosis globally. Sporotrichosis is acquired after a traumatic inoculation of soil or plant material contaminated with Sporothrix propagules or through bites and scratches from diseased cats. In Ascomycota, the master regulators of sex are MAT genes that lie in a single mating-type locus, in Sporothrix these are determined by two nonhomologous alleles, MAT1-1 and MAT1-2. We assessed the whole-genome sequences of medically relevant Sporothrix to develop a single-tube duplex PCR assay to screen S. brasiliensis, S. schenckii, S. globosa, and S. luriei idiomorphs (MAT1-1 or MAT1-2) and understand the distribution and incidence of mating-type strains from natural populations. Using our duplex PCR assay, a 673 bp amplicon (α-box protein) was consistently amplified from all MAT1-1 isolates, while a 291 bp fragment was only amplified from the isolates harboring MAT1-2 (HMG box). Molecular evidence suggests heterothallism (self-sterility) as the unique mating strategy among the species evaluated. The mating-type identity of 93 isolates revealed a nearly equal distribution (1:1 ratio) of mating type alleles within species but deviating between different outbreak areas. Remarkably, for S. brasiliensis in Rio de Janeiro, we report an overwhelming occurrence of MAT1-2 (1:13 ratio; χ² = 10.286, P = 0.0013) opposing the high prevalence MAT1-1 in the Rio Grande do Sul (10:1 ratio; χ² = 7.364, P = 0.0067). Therefore, the population structure of Sporothrix species refers from paucity to regular cycles of sexual recombination in most of the studied regions. Our PCR-based mating-type diagnostic assay is proposed here as an important marker to track the geographical expansion during the long-lasting outbreak of cat-transmitted sporotrichosis driven by S. brasiliensis.

Unique patterns of mating pheromone presence and absence could result in the ambiguous sexual behaviors of Colletotrichum species

Colletotrichum species are known to engage in unique sexual behaviors that differ significantly from the mating strategies of other filamentous ascomycete species. For example, most ascomycete fungi require the expression of both the MAT1-1-1 and MAT1-2-1 genes to induce sexual reproduction. In contrast, all isolates of Colletotrichum harbor only the MAT1-2-1 gene and yet, are capable of recognizing suitable mating partners and producing sexual progeny. The molecular mechanisms contributing to mating types and behaviors in Colletotrichum are, however, unknown. A comparative genomics approach analyzing 35 genomes, representing 31 Colletotrichum species and two Verticillium species, was used to elucidate a putative molecular mechanism underlying the unique sexual behaviors observed in Colletotrichum species. The existence of only the MAT1-2 idiomorph was confirmed across all species included in this study. Comparisons of the loci harboring the two mating pheromones and their cognate receptors revealed interesting patterns of gene presence and absence. The results showed that these genes have been lost multiple, independent times over the evolutionary history of this genus. These losses indicate that the pheromone pathway no longer plays an active role in mating type determination, suggesting an undiscovered mechanism by which mating partner recognition is controlled in these species. This further suggests that there has been a redirection of the underlying genetic mechanisms that regulate sexual development in Colletotrichum species. This research thus provides a foundation from which further interrogation of this topic can take place.

Genome Sequence Data of MAT1-1 and MAT1-2 Idiomorphs from Verticillium dahliae

Though Verticillium dahliae is an asexually reproducing fungus, it is considered heterothallic owing to the presence of only one of the two mating-type idiomorphs (MAT1-1 or MAT1-2) in individual isolates. But sexual reproduction has never been observed either in nature or in the laboratory. All of the genomic information in the literature thus far has therefore come from studies on isolates carrying only the MAT1-2 idiomorph. Herein, we sequenced and compared high-quality reference genomes of MAT1-1 strain S011 and MAT1-2 strain S023 obtained from the same sunflower field. The two genomic sequences displayed high synteny, and encoded similar number genes, a similarity especially notable among pathogenicity-related genes. Homolog analysis between these two genomes revealed that 80% of encoded genes are highly conserved (95% identity and coverage), but only 20% of the single copy genes were identical. These novel genome resources will support the analysis of the structure and function of the two idiomorphs and provide valuable tools to elucidate the evolution and potential mechanisms of sexual reproduction in V. dahliae.

A 20-kb lineage-specific genomic region tames virulence in pathogenic amphidiploid Verticillium longisporum

Amphidiploid fungal Verticillium longisporum strains Vl43 and Vl32 colonize the plant host Brassica napus but differ in their ability to cause disease symptoms. These strains represent two V. longisporum lineages derived from different hybridization events of haploid parental Verticillium strains. Vl32 and Vl43 carry same-sex mating-type genes derived from both parental lineages. Vl32 and Vl43 similarly colonize and penetrate plant roots, but asymptomatic Vl32 proliferation in planta is lower than virulent Vl43. The highly conserved Vl43 and Vl32 genomes include less than 1% unique genes, and the karyotypes of 15 or 16 chromosomes display changed genetic synteny due to substantial genomic reshuffling. A 20 kb Vl43 lineage-specific (LS) region apparently originating from the Verticillium dahliae-related ancestor is specific for symptomatic Vl43 and encodes seven genes, including two putative transcription factors. Either partial or complete deletion of this LS region in Vl43 did not reduce virulence but led to induction of even more severe disease symptoms in rapeseed. This suggests that the LS insertion in the genome of symptomatic V. longisporum Vl43 mediates virulence-reducing functions, limits damage on the host plant, and therefore tames Vl43 from being even more virulent.

Mating Systems in True Morels (Morchella)

True morels (Morchella spp., Morchellaceae, Ascomycota) are widely regarded as a highly prized delicacy and are of great economic and scientific value. Recently, the rapid development of cultivation technology and expansion of areas for artificial morel cultivation have propelled morel research into a hot topic. Many studies have been conducted in various aspects of morel biology, but despite this, cultivation sites still frequently report failure to fruit or only low production of fruiting bodies. Key problems include the gap between cultivation practices and basic knowledge of morel biology. In this review, in an effort to highlight the mating systems, evolution, and life cycle of morels, we summarize the current state of knowledge of morel sexual reproduction, the structure and evolution of mating-type genes, the sexual process itself, and the influence of mating-type genes on the asexual stages and conidium production. Understanding of these processes is critical for improving technology for the cultivation of morels and for scaling up their commercial production. Morel species may well be good candidates as model species for improving sexual development research in ascomycetes in the future.

Comparative Transcriptome and Endophytic Bacterial Community Analysis of Morchella conica SH

The precious rare edible fungus Morchella conica is popular worldwide for its rich nutrition, savory flavor, and varieties of bioactive components. Due to its high commercial, nutritional, and medicinal value, it has always been a hot spot. However, the molecular mechanism and endophytic bacterial communities in M. conica were poorly understood. In this study, we sequenced, assembled, and analyzed the genome of M. conica SH. Transcriptome analysis reveals significant differences between the mycelia and fruiting body. As shown in this study, 1,329 and 2,796 genes were specifically expressed in the mycelia and fruiting body, respectively. The Gene Ontology (GO) enrichment showed that RNA polymerase II transcription activity-related genes were enriched in the mycelium-specific gene cluster, and nucleotide binding-related genes were enriched in the fruiting body-specific gene cluster. Further analysis of differentially expressed genes in different development stages resulted in finding two groups with distinct expression patterns. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment displays that glycan degradation and ABC transporters were enriched in the group 1 with low expressed level in the mycelia, while taurine and hypotaurine metabolismand tyrosine metabolism-related genes were significantly enriched in the group 2 with high expressed level in mycelia. Moreover, a dynamic shift of bacterial communities in the developing fruiting body was detected by 16S rRNA sequencing, and co-expression analysis suggested that bacterial communities might play an important role in regulating gene expression. Taken together, our study provided a better understanding of the molecular biology of M. conica SH and direction for future research on artificial cultivation.

The Plot Thickens: Haploid and Triploid-Like Thalli, Hybridization, and Biased Mating Type Ratios in Letharia

The study of the reproductive biology of lichen fungal symbionts has been traditionally challenging due to their complex lifestyles. Against the common belief of haploidy, a recent genomic study found a triploid-like signal in Letharia. Here, we infer the genome organization and reproduction in Letharia by analyzing genomic data from a pure culture and from thalli, and performing a PCR survey of the MAT locus in natural populations. We found that the read count variation in the four Letharia specimens, including the pure culture derived from a single sexual spore of L. lupina, is consistent with haploidy. By contrast, the L. lupina read counts from a thallus' metagenome are triploid-like. Characterization of the mating-type locus revealed a conserved heterothallic configuration across the genus, along with auxiliary genes that we identified. We found that the mating-type distributions are balanced in North America for L. vulpina and L. lupina, suggesting widespread sexual reproduction, but highly skewed in Europe for L. vulpina, consistent with predominant asexuality. Taken together, we propose that Letharia fungi are heterothallic and typically haploid, and provide evidence that triploid-like individuals are hybrids between L. lupina and an unknown Letharia lineage, reconciling classic systematic and genetic studies with recent genomic observations.

Genetic Diversity and Mating Type Distribution of Pseudocercospora fijiensis on Banana in Uganda and Tanzania

Black Sigatoka, caused by Pseudocercospora fijiensis, is a major foliar disease of banana and plantain worldwide. There are few available data regarding the genetic diversity and population structure of the pathogen in East Africa, which are needed to design effective and durable disease management strategies. We genotyped 319 single-spore isolates of P. fijiensis collected from seven regions in Uganda and Tanzania and five isolates from Nigeria using 16 simple sequence repeat markers and mating type-specific primers. Isolates from each country and region within the country were treated as populations and subpopulations, respectively. A total of 296 multilocus genotypes (MLGs) were recovered, representing a clonal fraction of 7%. Subpopulations had a moderate level of genetic diversity (H_exp = 0.12 to 0.31; mean, 0.29). Mating type distribution did not deviate from equilibrium (MAT1-1: MAT1-2, 1:1 ratio) in Uganda; however, in Tanzania the mating types were not in equilibrium (4:1 ratio). The index of association tests (I_A and r̄_d) showed that all populations were at linkage equilibrium (P > 0.05), thus supporting the hypothesis of random association of alleles. These findings are consistent with a pathogen that reproduces both clonally and sexually. Low and insignificant levels of population differentiation were detected, with 90% of the variation occurring among isolates within subpopulations. The high intrapopulation variation has implications in breeding for resistance to P. fijiensis because isolates differing in aggressiveness and virulence are likely to exist over small spatial scales. Diverse isolates will be required for resistance screening to ensure selection of banana cultivars with durable resistance to Sigatoka in East Africa.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Morpho-molecular and mating-type locus diversity of Ustilaginoidea virens: an incitant of false smut of rice from Southern parts of India

AIMS

To characterize the geo-distinct isolates of Ustilaginoidea virens for morpho-molecular and mating-type locus diversity.

METHODS AND RESULTS

Sixty-one isolates of U. virens collected from Southern India exhibited significant diversity in mycelial width (3·45-5·50 µm), colony colour (yellow, pale yellow, and white), and growth pattern (thick leather mat, raised-fluffy, flat-fluffy, and raised). Field-borne chlamydospores of each isolate were significantly smaller in size (3·34-5·26 µm² ) compared to those formed on culture media (18·6-100·89 µm² ). The phylogenetic study based on internal transcribed sequences revealed two clusters; however, most isolates (n = 54) were grouped in cluster-I, indicating common ancestral origin. We also identified 42 haplotypes; among them, Hap_3 has the highest number of isolates (n = 19). Mating-type locus (MAT1) analysis revealed all sixty-one isolates as heterothallic, wherein 37 and 24 isolates belonging to MAT1-1-1 and MAT1-2-1 heterothallic mating types, respectively. The microsynteny analysis of MAT1 loci of one of the Indian strain (Uv-Gvt) along with Uv-8b (China) strain revealed synteny conservation at MAT1 locus, which is flanked by conserved genes SLA2 and a hypothetical protein in the upstream and APN2, COX12 and APC5 in the downstream of the locus.

CONCLUSIONS

Morpho-molecular study revealed the significant diversity among geo-distinct isolates, and MAT1 loci analysis indicated the distribution of heterothallic mating types in south Indian paddy fields. And also, complete synteny conservation between Indian and Chinese strain was observed at the MAT1 locus.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report describing the sexuality of Indian strains of the U. virens, which would help better understand the genetic diversity of the U. virens prevailing in Southern India and aid in developing resistant rice cultivars against this pathogen population.

Mating Type Idiomorphs, Heterothallism, and High Genetic Diversity in Venturia carpophila, Cause of Peach Scab

Scab (caused by Venturia carpophila) is a major disease affecting peach in the eastern United States. The aims of the study were to characterize the mating-type loci in V. carpophila, determine whether they are in equilibrium, and assess the population genetic diversity and structure of the pathogen. The mating-type gene MAT1-1-1 was identified in isolate JP3-5 in an available genome sequence, and the MAT1-2-1 gene was PCR amplified from isolate PS1-1, thus indicating a heterothallic structure. Mating-type loci structures were consistent with those of other Venturia spp. (V. effusa and V. inaequalis): the mating-type gene is positioned between APN2 encoding a DNA lyase and a gene encoding a Pleckstrin homology domain. Primers designed to each of the mating-type genes and a reference gene TUB2 were used as a multiplex PCR to screen a population (n = 81) of V. carpophila from various locations in the eastern United States. Mating types in five of the nine populations studied were in equilibrium. Among the 81 isolates, there were 69 multilocus genotypes. A population genetic analysis of the populations with >10 individuals (four populations) showed them to be genetically diverse. Linkage disequilibrium was found in five of nine populations with ≥4 isolates. A discriminant analysis of principal components indicated three genetic clusters, although extensive admixture was observed. Mating-type identification in V. carpophila provides a basis for understanding reproductive methods of the pathogen and can be a basis for further studies of the genetics of the peach scab pathogen.

Unidirectional mating-type switching confers self-fertility to Thielaviopsis cerberus, the only homothallic species in the genus

Sexual reproduction is ubiquitous in nature, and nowhere is this more so than in the fungi. Heterothallic behaviour is observed when there is a strict requirement of contact between two individuals of opposite mating type for sexual reproduction to occur. In contrast, a homothallic species can complete the entire sexual cycle in isolation, although several genetic mechanisms underpin this self-fertility. These can be inferred by characterising the structure and gene-content of the mating-type locus, which contains genes that are involved in the regulation of sexual reproduction. In this study, the genetic basis of homothallism in Thielaviopsis cerberus was investigated, the only known self-fertile species within this genus. Using genome sequencing and conventional molecular techniques, two versions of the mating-type locus were identified in this species. This is typical of species that have a unidirectional mating-type switching reproductive strategy. The first version was a self-fertile locus that contained four known mating-type genes, while the second was a self-sterile version with a single mating-type gene. The conversion from a self-fertile to a self-sterile locus is likely mediated by a homologous recombination event at two direct repeats present in the self-fertile locus, resulting in the deletion of three mating-type genes and one of the repeats. Both locus versions were present in isolates that were self-fertile, while self-sterility was caused by the presence of only a switched locus. This study provides a clear example of the architectural fluidity in the mating-type loci that is common among even closely related fungal species.

Molecular-based assessment of diversity and population structure of Sporothrix spp. clinical isolates from Espírito Santo-Brazil

BACKGROUND

Sporotrichosis is a subcutaneous mycosis caused by Sporothrix species that affects humans and animals. Little information on the genetic diversity and population structure of the pathogen is available for Brazil, which is needed to design effective strategies to tackle the advance of sporotrichosis in endemic areas.

OBJECTIVES

We assessed the genetic diversity and mating-type distribution of Sporothrix isolates recovered from human and feline cases of sporotrichosis in Espírito Santo-Brazil to better understand the population structure, epidemiology and diversification of this pathogen, as well as to explore the possible routes of transmission involved in the ongoing outbreaks.

METHODS

In all, 75 Sporothrix isolates were identified with phenotypic characteristics. Then, fungal DNA extraction was performed, and the species-specific PCR technique was applied, using markers directed to the calmodulin gene. The mating-type idiomorph of species was identified by PCR using primers targeting the MAT1-1 and MAT1-2 loci.

RESULTS

Among the 75 Sporothrix isolates, 76% were confirmed as S brasiliensis and 24% as S schenckii sensu stricto. S brasiliensis was more prevalent in the metropolitan area and S schenckii s. str. in the mountainous region of the state. In both species, the presence of the two sexual idiomorphs was detected, suggesting that they are heterothallic species.

CONCLUSIONS

Our data suggest that sporotrichosis takes on an epidemic-urban character involving S brasiliensis. This species in Espírito Santo is likely to originate from Rio de Janeiro, as most isolates harbour the same MAT 1-2 locus. We confirm that S brasiliensis has significantly broadened its area of occurrence, an essential feature of emerging pathogens.

Molecular analysis of mating type loci from the mycophenolic acid producer Penicillium brevicompactum: Phylogeny and MAT protein characterization suggest a cryptic sexual life cycle

The mycophenolic acid producing ascomycete Penicillium brevicompactum is considered to be an anamorphic (asexual) species, for which a sexual cycle was never observed. However, since recent reports of otherwise asexually propagating filamentous fungi have demonstrated a sexual cycle controlled by mating type loci, we carried out a molecular analysis of mating type loci from P. brevicompactum. Using data from extensive DNA sequencing analysis, we determined the mating type loci from 22 strains derived from various type culture collections. We found 8 strains carrying a MAT1-1 locus encoding a 362 amino acid alpha domain transcription factor. The other 14 possessed a MAT1-2 locus encoding a 298 amino acid HMG domain transcription factor. cDNA analysis confirmed that both mating type loci are transcriptionally expressed. The karyotype of six selected strains, determined using contour-clamped homogeneous electric field (CHEF) electrophoresis, demonstrated distinct differences in size and numbers of chromosomes between the strains investigated. Interestingly, our phylogenetic survey of 72 strains from 11 different Penicillium species revealed that MAT genes serve as excellent molecular markers to determine phylogenetic relationships among species closely related to P. brevicompactum. Based on our sequencing results, we constructed transformation vectors for site-specific deletion of mating type loci from two selected strains of opposite mating type. Complementation strains were constructed containing both the mating type locus deletion cassette and a MAT-egfp fusion gene. These strains were used for comparative phenotypic analyses between strains containing or lacking the mating type gene. Whereas all MAT1-2 strains were indistinguishable, the MAT1-1 and MAT1-1-1 deletion strains differed distinctly. The MAT1-1-1 deletion strain produced more conidiospores on solid media, but smaller pellets in liquid media. This is probably the consequence of fewer conidial germ tubes than with the wild type mating type strain. Finally, we showed that the MAT-EGPF fusion protein is localized to the nuclei and detectable in protein samples by Western analysis. Together, our results suggest that the asexually propagating fungus P. brevicompactum might be a heterothallic species with a cryptic sexual life cycle.

Pathogenomics Characterization of an Emerging Fungal Pathogen, Fusarium oxysporum f. sp. lycopersici in Greenhouse Tomato Production Systems

In recent years, greenhouse-grown tomato (Solanum lycopersicum) plants showing vascular wilt and yellowing symptoms have been observed between 2015 and 2018 in North Carolina (NC) and considered as an emerging threat to profitability. In total, 38 putative isolates were collected from symptomatic tomatoes in 12 grower greenhouses and characterized to infer pathogenic and genomic diversity, and mating-type (MAT) idiomorphs distribution. Morphology and polymerase chain reaction (PCR) markers confirmed that all isolates were Fusarium oxysporum f. sp. lycopersici (FOL) and most of them were race 3. Virulence analysis on four different tomato cultivars revealed that virulence among isolates, resistance in tomato cultivars, and the interaction between the isolates and cultivars differed significantly (P < 0.001). Cultivar 'Happy Root' (I-1, I-2, and I-3 genes for resistance) was highly resistant to FOL isolates tested. We sequenced and examined for the presence of 15 pathogenicity genes from different classes (Fmk1, Fow1, Ftf1, Orx1, Pda1, PelA, PelD, Pep1, Pep2, eIF-3, Rho1, Scd1, Snf1, Ste12, and Sge1), and 14 Secreted In Xylem (SIX) genes to use as genetic markers to identify and differentiate pathogenic isolates of FOL. Sequence data analysis showed that five pathogenicity genes, Fmk1, PelA, Rho1, Sge1, and Ste12 were present in all isolates while Fow1, Ftf1, Orx1, Peda1, Pep1, eIF-3, Scd1, and Snf1 genes were dispersed among isolates. Two genes, Pep2 and PelD, were absent in all isolates. Of the 14 SIX genes assessed, SIX1, SIX3, SIX5, SIX6, SIX7, SIX8, SIX12, and SIX14 were identified in most isolates while the remaining SIX genes varied among isolates. All isolates harbored one of the two mating-type (MAT-1 or MAT-2) idiomorphs, but not both. The SIX4 gene was present only in race 1 isolates. Diversity assessments based on sequences of the effector SIX3- and the translation elongation factor 1-α encoding genes SIX3 and tef1-α, respectively were the most informative to differentiate pathogenic races of FOL and resulted in race 1, forming a monophyletic clade while race 3 comprised multiple clades. Furthermore, phylogeny-based on SIX3- and tef1-α gene sequences showed that the predominant race 3 from greenhouse production systems significantly overlapped with previously designated race 3 isolates from various regions of the globe.

Mating-type locus rearrangements and shifts in thallism states in Citrus-associated Phyllosticta species

Currently, eight Phyllosticta species are known to be associated with several Citrus hosts, incorporating diverse lifestyles: while some of them are endophytic (P. capitalensis and P. citribraziliensis), others are pathogenic (P. citriasiana, P. citricarpa, P. citrichinaensis and P. paracitricarpa). Sexual reproduction plays a key role in the interaction between these Phyllosticta species and their Citrus hosts, especially for the spread and persistence of the pathogenic species in the environment. Given this, differences in sexual reproduction strategies could be related to the differences in lifestyles. To evaluate this hypothesis, we characterized the mating-type loci of six Citrus-associated Phyllosticta species from whole genome assemblies. Mating-type genes in the Citrus-associated Phyllosticta species are highly variable in their sequence content, but the genomic locations and organization of the mating-type loci are conserved. Phyllosticta citriasiana, P. citribraziliensis, P. citricarpa and P. paracitricarpa are heterothallic, while P. capitalensis and P. citrichinaensis are homothallic. In addition, the P. citrichinaensis MAT1-2 idiomorph occurs in a separate location from the mating-type locus. Ancestral state reconstruction suggests that homothallism is the ancestral thallism state in Phyllosticta, with a shift to heterothallism in Phyllosticta species that are pathogenic to Citrus. Moreover, the homothallic strategies of P. capitalensis and P. citrichinaensis result from independent evolutionary events, as P. capitalensis locus likely represents the ancestral state, and P. citrichinaensis homothallism has risen through a reversion in a heterothallic ancestor and underwent remodelling events. As the pathogenic species P. citriasiana, P. citricarpa and P. paracitricarpa are heterothallic and incapable of selfing, disease management practices focused in preventing the occurrence of sexual reproduction could assist in the control of Citrus Black Spot and Citrus Tan Spot diseases. This study emphasizes the importance of studying Citrus-Phyllosticta interactions under evolutionary and genomic perspectives, as these approaches can provide valuable information about the association between Phyllosticta species and their hosts, and also serve as guidance for the improvement of disease management practices.

Two mating-type genes MAT1-1-1 and MAT1-1-2 with significant functions in conidiation, stress response, sexual development, and pathogenicity of rice false smut fungus Villosiclava virens

Rice false smut caused by Villosiclava virens is one of the destructive diseases on panicles of rice. Sexual development of V. virens, controlled by mating-type locus, plays an important role in the prevalence of rice false smut and genetic diversity of the pathogen. However, how the mating-type genes mediate sexual development of the V. virens remains largely unknown. In this study, we characterized the two mating-type genes, MAT1-1-1 and MAT1-1-2, in V. virens. MAT1-1-1 knockout mutant showed defects in hyphal growth, conidia morphogenesis, sexual development, and increase in the tolerance to salt and osmotic stress. Targeted deletion of MAT1-1-2 not only impaired the sclerotia formation and pathogenicity of V. virens, but also reduced the production of conidia. The MAT1-1-2 mutant showed increases in tolerance to salt and hydrogen peroxide stress, but decreases in tolerance to osmotic stress. Yeast two-hybrid assay showed that MAT1-1-1 interacted with MAT1-1-2, indicating that those proteins might form a complex to regulate sexual development. In addition, MAT1-1-1 localized in the nucleus, and MAT1-1-2 localized in the cytoplasm. Collectively, our results demonstrate that MAT1-1-1 and MAT1-1-2 play important roles in the conidiation, stress response, sexual development, and pathogenicity of V. virens, thus providing new insights into the function of mating-type gene.

Mating genes in Calonectria and evidence for a heterothallic ancestral state

The genus Calonectria includes many important plant pathogens with a wide global distribution. In order to better understand the reproductive biology of these fungi, we characterised the structure of the mating type locus and flanking genes using the genome sequences for seven Calonectria species. Primers to amplify the mating type genes in other species were also developed. PCR amplification of the mating type genes and multi-gene phylogenetic analyses were used to investigate the mating strategies and evolution of mating type in a collection of 70 Calonectria species residing in 10 Calonectria species complexes. Results showed that the organisation of the MAT locus and flanking genes is conserved. In heterothallic species, a novel MAT gene, MAT1-2-12 was identified in the MAT1-2 idiomorph; the MAT1-1 idiomorph, in most cases, contained the MAT1-1-3 gene. Neither MAT1-1-3 nor MAT1-2-12 was found in homothallic Calonectria (Ca.) hongkongensis, Ca. lateralis, Ca. pseudoturangicola and Ca. turangicola. Four different homothallic MAT locus gene arrangements were observed. Ancestral state reconstruction analysis provided evidence that the homothallic state was basal in Calonectria and this evolved from a heterothallic ancestor.

The novel Huntiella omanensis mating gene, MAT1-2-7, is essential for ascomatal maturation

Sexual reproduction is a highly conserved feature of the eukaryotes, yet sexual compatibility is determined by a wide variety of mechanisms. In ascomycete fungi, sexual development is controlled by genes at the mating type (MAT) locus that confer either MAT1-1 or MAT1-2 mating identity. Although the locus harbours, at minimum, a single gene, the individual MAT loci of certain species, including Huntiella omanensis, encode for two or more genes. The MAT1-2 idiomorph of H. omanensis is made up of MAT1-2-1, a primary MAT gene that is highly conserved in the Pezizomycotina and possesses a well-characterized DNA binding motif, the HMG-box domain. The idiomorph also harbours a novel secondary MAT gene, named MAT1-2-7, with no recognizable functional domains. In this study, we developed a transformation and CRISPR-Cas9-based genome editing protocol to characterize the MAT1-2-7 gene with respect to its function in mating. We have shown that MAT1-2-7 is essential for sexual reproduction and that isolates carrying the truncated MAT1-2-7 gene are incapable of ascomatal maturation and further sexual development. MAT1-2-7 was also shown to influence the vegetative radial growth rate of H. omanensis, illustrating the pleiotropic effects often associated with MAT genes.

Colletotrichum: species complexes, lifestyle, and peculiarities of some sources of genetic variability

The genus Colletotrichum comprises species with different lifestyles but is mainly known for phytopathogenic species that infect crops of agronomic relevance causing considerable losses. The fungi of the genus Colletotrichum are distributed in species complexes and within each complex some species have particularities regarding their lifestyle. The most commonly found and described lifestyles in Colletotrichum are endophytic and hemibiotrophic phytopathogenic. Several of these phytopathogenic species show wide genetic variability, which makes long-term maintenance of resistance in plants difficult. Different mechanisms may play an important role in the emergence of genetic variants but are not yet fully understood in this genus. These mechanisms include heterokaryosis, a parasexual cycle, sexual cycle, transposable element activity, and repeat-induced point mutations. This review provides an overview of the genus Colletotrichum, the species complexes described so far and the most common lifestyles in the genus, with a special emphasis on the mechanisms that may be responsible, at least in part, for the emergence of new genotypes under field conditions.

Integrative Activity of Mating Loci, Environmentally Responsive Genes, and Secondary Metabolism Pathways during Sexual Development of Chaetomium globosum

Fungal diversity has amazed evolutionary biologists for decades. One societally important aspect of this diversity manifests in traits that enable pathogenicity. The opportunistic pathogen Chaetomium globosum is well adapted to a high-humidity environment and produces numerous secondary metabolites that defend it from predation. Many of these chemicals can threaten human health. Understanding the phases of the C. globosum life cycle in which these products are made enables better control and even utilization of this fungus. Among its intriguing traits is that it both is self-fertile and lacks any means of propagule-based asexual reproduction. By profiling genome-wide gene expression across the process of sexual reproduction in C. globosum and comparing it to genome-wide gene expression in the model filamentous fungus N. crassa and other closely related fungi, we revealed associations among mating-type genes, sexual developmental genes, sexual incompatibility regulators, environmentally responsive genes, and secondary metabolic pathways.

The origins and maintenance of the rich fungal diversity have been longstanding issues in evolutionary biology. To investigate how differences in expression regulation contribute to divergences in development and ecology among closely related species, transcriptomes were compared between Chaetomium globosum, a homothallic pathogenic fungus thriving in highly humid ecologies, and Neurospora crassa, a heterothallic postfire saprotroph. Gene expression was quantified in perithecia at nine distinct morphological stages during nearly synchronous sexual development. Unlike N. crassa, expression of all mating loci in C. globosum was highly correlated. Key regulators of the initiation of sexual development in response to light stimuli—including orthologs of N. crassasub-1, sub-1-dependent gene NCU00309, and asl-1—showed regulatory dynamics matching between C. globosum and N. crassa. Among 24 secondary metabolism gene clusters in C. globosum, 11—including the cochliodones biosynthesis cluster—exhibited highly coordinated expression across perithecial development. C. globosum exhibited coordinately upregulated expression of histidine kinases in hyperosmotic response pathways—consistent with gene expression responses to high humidity we identified in fellow pathogen Fusarium graminearum. Bayesian networks indicated that gene interactions during sexual development have diverged in concert with the capacities both to reproduce asexually and to live a self-compatible versus self-incompatible life cycle, shifting the hierarchical roles of genes associated with conidiation and heterokaryon incompatibility in N. crassa and C. globosum. This divergence supports an evolutionary history of loss of conidiation due to unfavorable combinations of heterokaryon incompatibility in homothallic species.

Phyllosticta citricarpa and sister species of global importance to Citrus

Several Phyllosticta species are known as pathogens of Citrus spp., and are responsible for various disease symptoms including leaf and fruit spots. One of the most important species is P. citricarpa, which causes a foliar and fruit disease called citrus black spot. The Phyllosticta species occurring on citrus can most effectively be distinguished from P. citricarpa by means of multilocus DNA sequence data. Recent studies also demonstrated P. citricarpa to be heterothallic, and reported successful mating in the laboratory. Since the domestication of citrus, different clones of P. citricarpa have escaped Asia to other continents via trade routes, with obvious disease management consequences. This pathogen profile represents a comprehensive literature review of this pathogen and allied taxa associated with citrus, focusing on identification, distribution, genomics, epidemiology and disease management. This review also considers the knowledge emerging from seven genomes of Phyllosticta spp., demonstrating unknown aspects of these species, including their mating behaviour.

TAXONOMY

Phyllosticta citricarpa (McAlpine) Aa, 1973. Kingdom Fungi, Phylum Ascomycota, Class Dothideomycetes, Order Botryosphaeriales, Family Phyllostictaceae, Genus Phyllosticta, Species citricarpa.

HOST RANGE

Confirmed on more than 12 Citrus species, Phyllosticta citricarpa has only been found on plant species in the Rutaceae.

DISEASE SYMPTOMS

P. citricarpa causes diverse symptoms such as hard spot, virulent spot, false melanose and freckle spot on fruit, and necrotic lesions on leaves and twigs.

USEFUL WEBSITES

DOE Joint Genome Institute MycoCosm portals for the Phyllosticta capitalensis (https://genome.jgi.doe.gov/Phycap1), P. citriasiana (https://genome.jgi.doe.gov/Phycit1), P. citribraziliensis (https://genome.jgi.doe.gov/Phcit1), P. citrichinaensis (https://genome.jgi.doe.gov/Phcitr1), P. citricarpa (https://genome.jgi.doe.gov/Phycitr1, https://genome.jgi.doe.gov/Phycpc1), P. paracitricarpa (https://genome.jgi.doe.gov/Phy27169) genomes. All available Phyllosticta genomes on MycoCosm can be viewed at https://genome.jgi.doe.gov/Phyllosticta.

Genetic Diversity of Verticillium dahliae Isolates From Mint Detected with Genotyping by Sequencing

Verticillium wilt is the most important disease threatening the commercial production of mint grown for essential oil. An important long-term goal for mint breeders is the production of cultivars with resistance to Verticillium wilt. Before that can be accomplished, a better understanding of the genetic variation within and among populations of Verticillium dahliae is needed. We characterized the extent of phenotypic and genetic diversity present in contemporary and archival populations of V. dahliae from mint fields in Oregon and other production regions of the United States using genotyping by sequencing, PCR assays for mating type and pathogenic race, vegetative compatibility group (VCG) tests, and aggressiveness assays. We report that the population in the Pacific Northwest can be described as one common genetic group and four relatively rare genetic groups. Eighty-three percent of the isolates belonged to VCG2B, and all isolates possessed the MAT1-2 idiomorph and were characterized as pathogenic race 2. These results indicate low levels of genetic diversity and a negligible risk of sexual recombination in populations of this host-adapted pathogen population. Knowledge of the genetic structure of V. dahliae in the Pacific Northwest will inform breeders about the diversity of pathogenicity factors that may need to be considered in their breeding programs.

Population structure and genetic diversity of Setosphaeria turcica from corn in Heilongjiang province, China

AIM

The aims of this study were to identify races and mating types of Setosphaeria turcica causing northern corn leaf blight in Heilongjiang province of China and analyse the genetic diversity of S. turcica isolates using SSR markers.

METHODS AND RESULTS

Based on gene-for-gene interactions, 13 races of S. turcica (races 0, 1, 2, 3, 12, 13, 23, 123, N, 1N, 12N, 3N and 23N) were isolated from infected corn plants in Heilongjiang province. Races 0 and 1 were the predominant races, and race 23N was identified for the first time in the region. Using two pairs of specific primers, three mating types, 'a', 'Aa' and 'A', were identified, with 'a' being the predominant mating type. SSR markers were used to analyse genetic diversity of 60 S. turcica isolates. Five SSR primers were polymorphic, which resulted in 45 reproducible bands with 2-15 bands for each primer. Cluster analysis separated the isolates into five groups at a similarity coefficient of 0·84. Analysis of molecular variance showed that there was significant correlation between SSR groups and mating type of the isolates. No significant correlation was found between SSR groups and physiological races or geographical location of the isolates.

CONCLUSIONS

The work reported that races 0 and 1 were the predominant races, and race 23N was identified for the first time in Heilongjiang province with 'a' being the predominant mating type. There was significant correlation between SSR groups and mating type of S. turcica isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results provide information on population structure and genetic diversity of S. turcica causing Northern corn leaf blight, which will facilitate the development of effective disease management programs.