Search

Citrus black spot (CBS), caused by Phyllosticta citricarpa (McAlpine) van der Aa, is a disease that affects Citrus spp. causing production losses, high costs associated with management, and constraints on the fresh market trade. The present investigation aimed to confirm the identity of the CBS pathogen as P. citricarpa and determine its mating-type distribution in Cuba. Phyllosticta isolates were collected from major Cuban citrus-producing provinces (Matanzas, Cienfuegos, Camagüey, and Santiago de Cuba). P. citricarpa and the endophyte P. capitalensis (Henn.) were identified by polyphasic taxonomy, integrating morpho-physiological characteristics with the phylogenetic analysis of ITS, actA, LSU and tef1 loci. Mating-type (MAT) analysis revealed that only the MAT1-2 idiomorph of P. citricarpa is present in Cuba, providing evidence of an atypical CBS disease cycle. These results contribute to a better understanding of the epidemiology of CBS in Cuba and the improvement of CBS management. [ABSTRACT FROM AUTHOR]

Setosphaeria turcica is a heterothallic fungus that is the causal agent of northern leaf blight (NLB), which is a devastating foliar disease of sorghum and maize. Despite of its adversary to crop production, little is known about the genetic diversity and population genetic structure of this pathogen from sorghum. In this study, we explored the utilization of single nucleotide polymorphism (SNP) molecular markers and three mating type-specific primers to analyze the genetic diversity, population genetic structure, and mating type distribution of 87 S. turcica isolates that had been collected in sorghum production areas from three provinces, including Henan, Shaanxi, and Shanxi in China. The populations are featured with moderate genetic diversity and relatively equal mating type distribution of MAT1-1 and MAT1-2. The genetic differentiation was significant (p < 0.05) among different populations except those from Henan and Shanxi provinces that showed particularly frequent gene flow between them. Neither the maxinum likelihood phylogenetic tree, nor principal coordinate analysis, nor genetic structure analysis was able to completely separate the three populations. The relatively low genetic distance and high genetic identification were also observed among the three populations. Nevertheless, the genetic variation within populations was the major source of variation as revealed by AMOVA analysis. The findings of this study have improved our current understanding about the genetic diversity, population genetic structure, and the distribution of mating type of S. turcica , which are useful for unraveling the epidemiology of NLB and developing effective disease management strategies. [ABSTRACT FROM AUTHOR]

Barley net blotch is one of the most widespread and destructive foliar diseases of barley crops worldwide. The causal fungal agent, Pyrenophora teres (anamorphic stage: Drechslera teres) occurs in two forms, P. teres f. maculata (Ptm) and P. teres f. teres (Ptt) exhibiting the spot and net type symptoms, respectively. In this study, sixty-one P. teres single conidia isolates were obtained from different cereal-growing areas in Algeria. Fungal isolates of net and spot forms were identified using appropriate form-specific SNP primers. The results indicated that 57.38% of the isolates were Ptm, while 42.62% were identified as Ptt. Mating-type assessments of P. teres isolates were conducted using MAT-specific single nucleotide polymorphism primers. Among the tested strains of Ptt, 19 were found as MAT1-2 and only 7 were determined as MAT 1–1; while 27 were identified as MAT 1–1, and 8 were found as MAT1-2 for the Ptm population. Inter-simple sequence repeat markers (ISSR) were used to examine genetic variation and relationships within the P. teres population. The similarity rates were found as 0.60 and 0.63 within Ptt and Ptm populations, respectively. Our results suggested that both populations are reproducing sexually. It appears that P. teres f. teres population is reproducing exclusively sexually and P. teres f. maculata population is reproducing mostly sexually, but asexual reproduction is also occurring. Obviously, ascospore production is a key epidemiological aspect, but in the case of P. teres f. maculata, conidia may also be playing a role. [ABSTRACT FROM AUTHOR]

Lentinula edodes is one of the most widely consumed edible mushrooms in Korea. Mating in L. edodes is regulated by a tetrapolar system, and two unlinked genetic loci, A and B, are known to be major determinants of the mating types, as reported in other heterothallic basidiomycetes. The A locus of L. edodes encodes a pair of homeodomain (HD) transcription factors. The highly variable N-termini of these HD transcription factors contribute to the diversity among the A mating types. In this study, we developed a cleaved amplified polymorphic sequence (CAPS) marker to discriminate 11 different A mating type alleles predominant among both cultivated and wild strains. Amplification of the variable region of the A locus followed by digestion with HaeIII and EcoRI restriction enzymes enabled successful discrimination among the 11 A mating type alleles. We also evaluated the applicability of this method in the identification of two A mating types of a dikaryotic strain.

Setosphaeria turcica is a heterothallic fungus that is the causal agent of northern leaf blight (NLB), which is a devastating foliar disease of sorghum and maize. Despite of its adversary to crop production, little is known about the genetic diversity and population genetic structure of this pathogen from sorghum. In this study, we explored the utilization of single nucleotide polymorphism (SNP) molecular markers and three mating type-specific primers to analyze the genetic diversity, population genetic structure, and mating type distribution of 87 S. turcica isolates that had been collected in sorghum production areas from three provinces, including Henan, Shaanxi, and Shanxi in China. The populations are featured with moderate genetic diversity and relatively equal mating type distribution of MAT1-1 and MAT1-2. The genetic differentiation was significant (p

The human fungal pathogen Candida albicans can reversibly switch between two cell types named "white" and "opaque," each of which is stable through many cell divisions. These two cell types differ in their ability to mate, their metabolic preferences and their interactions with the mammalian innate immune system. A highly interconnected network of eight transcriptional regulators has been shown to control switching between these two cell types. To identify additional regulators of the switch, we systematically and quantitatively measured white-opaque switching rates of 196 strains, each deleted for a specific transcriptional regulator. We identified 19 new regulators with at least a 10-fold effect on switching rates and an additional 14 new regulators with more subtle effects. To investigate how these regulators affect switching rates, we examined several criteria, including the binding of the eight known regulators of switching to the control region of each new regulatory gene, differential expression of the newly found genes between cell types, and the growth rate of each mutant strain. This study highlights the complexity of the transcriptional network that regulates the white-opaque switch and the extent to which switching is linked to a variety of metabolic processes, including respiration and carbon utilization. In addition to revealing specific insights, the information reported here provides a foundation to understand the highly complex coupling of white-opaque switching to cellular physiology.

Many microorganisms with specialized lifestyles have reduced genomes. This is best understood in beneficial bacterial symbioses, where partner fidelity facilitates loss of genes necessary for living independently. Specialized microbial pathogens may also exhibit gene loss relative to generalists. Here, we demonstrate that Escovopsis weberi, a fungal parasite of the crops of fungus-growing ants, has a reduced genome in terms of both size and gene content relative to closely related but less specialized fungi. Although primary metabolism genes have been retained, the E. weberi genome is depleted in carbohydrate active enzymes, which is consistent with reliance on a host with these functions. E. weberi has also lost genes considered necessary for sexual reproduction. Contrasting these losses, the genome encodes unique secondary metabolite biosynthesis clusters, some of which include genes that exhibit up-regulated expression during host attack. Thus, the specialized nature of the interaction between Escovopsis and ant agriculture is reflected in the parasite's genome.

UnlabelledThe human commensal and opportunistic pathogen Candida albicans can switch between two distinct, heritable cell types, named "white" and "opaque," which differ in morphology, mating abilities, and metabolic preferences and in their interactions with the host immune system. Previous studies revealed a highly interconnected group of transcriptional regulators that control switching between the two cell types. Here, we identify Ssn6, the C. albicans functional homolog of the Saccharomyces cerevisiae transcriptional corepressor Cyc8, as a new regulator of white-opaque switching. In A: or α mating type strains, deletion of SSN6 results in mass switching from the white to the opaque cell type. Transcriptional profiling of ssn6 deletion mutant strains reveals that Ssn6 represses part of the opaque cell transcriptional program in white cells and the majority of the white cell transcriptional program in opaque cells. Genome-wide chromatin immunoprecipitation experiments demonstrate that Ssn6 is tightly integrated into the opaque cell regulatory circuit and that the positions to which it is bound across the genome strongly overlap those bound by Wor1 and Wor2, previously identified regulators of white-opaque switching. This work reveals the next layer in the white-opaque transcriptional circuitry by integrating a transcriptional regulator that does not bind DNA directly but instead associates with specific combinations of DNA-bound transcriptional regulators.ImportanceThe most common fungal pathogen of humans, C. albicans, undergoes several distinct morphological transitions during interactions with its host. One such transition, between cell types named "white" and "opaque," is regulated in an epigenetic manner, in the sense that changes in gene expression are heritably maintained without any modification of the primary genomic DNA sequence. Prior studies revealed a highly interconnected network of sequence-specific DNA-binding proteins that control this switch. We report the identification of Ssn6, which defines an additional layer of transcriptional regulation that is critical for this heritable switch. Ssn6 is necessary to maintain the white cell type and to properly express the opaque cell transcriptional program. Ssn6 does not bind DNA directly but rather associates with specific combinations of DNA-bound transcriptional regulators to control the switch. This work is significant because it reveals a new level of regulation of an important epigenetic switch in the predominant fungal pathogen of humans.

Phytophthora cinnamomi is the pathogen most frequently associated with avocado root rot. In Zitácuaro, Michoacán, production has increased by 19.8%; however, there are no studies of root rot in this area. The objective of the study was to characterize the isolates obtained from avocado roots and assess the sensitivity to fungicides. Samples from 5 avocado orchards were collected, sampling 5 trees per orchard (a total of 25 samples). The samples isolated were characterized morphological and molecularly. Mating type was analyzed using reference isolates of P. cinnamomi A1 (isolate from camelia) and A2 (isolate from avocado). To confirm the pathogenicity, tests were performed on avocado fruits with the isolates. The sensitivity of 15 isolates to potassium phosphite and to metalaxyl-M at different concentrations was evaluated in vitro. In a subgroup of six isolates, it was evaluated whether there was a relationship between growth rate and potassium phosphite sensitivity. Fifteen isolates were obtained with coenocytic coraloid mycelium, chlamydospores, sporangia without papilla, ovoid to ellipsoid, with internal proliferation, heterothallic with mating type A2, with amphigynous antheridia and plerotic oospores, characteristics consistent with P. cinnamomi. The inoculated isolates were pathogenic on avocado fruits. The isolates were more sensitive to potassium phosphite than to metalaxyl-M, with mean EC50 values of 24.62 and 0.215 μg mL-1 of i.a., respectively. No relationship was observed between growth rate and potassium phosphite sensitivity. It is necessary to obtain a greater number of P. cinnamomi isolates for virulence studies. [ABSTRACT FROM AUTHOR]

Copyright of Acta Edulis Fungi is the property of Acta Edulis Fungi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Evolution has provided a vast diversity of yeasts that play fundamental roles in nature and society. This diversity is not limited to genotypically homogeneous species with natural interspecies hybrids and allodiploids that blur species boundaries frequently isolated. Thus, life cycle and the nature of breeding systems have profound effects on genome variation, shaping heterozygosity, genotype diversity and ploidy level. The apparent enrichment of hybrids in industry-related environments suggests that hybridization provides an adaptive route against stressors and creates interest in developing new hybrids for biotechnological uses. For example, in the Saccharomyces genus where regulatory circuits controlling cell identity, mating competence and meiosis commitment have been extensively studied, this body of knowledge is being used to combine interesting traits into synthetic F1 hybrids, to bypass F1 hybrid sterility and to dissect complex phenotypes by bulk segregant analysis. Although these aspects are less known in other industrially promising yeasts, advances in whole-genome sequencing and analysis are changing this and new insights are being gained, especially in the food-associated genera Zygosaccharomyces and Kluyveromyces. We discuss this new knowledge and highlight how deciphering cell identity circuits in these lineages will contribute significantly to identify the genetic determinants underpinning complex phenotypes and open new avenues for breeding programmes. [ABSTRACT FROM AUTHOR]

While the process of meiosis is highly conserved across eukaryotes, the sexual systems that govern life cycle phase transitions are surprisingly labile. Switches between sexual systems have profound evolutionary and ecological consequences, in particular for plants, but our understanding of the fundamental mechanisms and ultimate causes underlying these transitions is still surprisingly incomplete. We explore here the idea that brown and green algae may be interesting comparative models that can increase our understanding of relevant processes in plant reproductive biology, from evolution of gamete dimorphism, gametogenesis, sex determination and transitions in sex-determining systems. [ABSTRACT FROM AUTHOR]

Next-generation sequencing (NGS) has revolutionized research on fungi including Botryosphaeriaceae, a family of important plant and particularly tree pathogens. This review highlights the impact that NGS-generated genomes and transcriptomes have had on our understanding of the biology and evolution of these fungi. In less than a decade, 49 genomes representing 31 species in eight genera have been published for the Botryosphaeriaceae. These genomes have been used to show that species in this family are capable of sexual reproduction and that the evolution of their mating strategy is highly dynamic, due to multiple independent transitions from a heterothallic ancestral state to homothallism. Comparative genomics has further revealed an abundance of genes involved in infection and aggressiveness. These include plant cell wall-degrading enzymes and secondary metabolite biosynthetic genes as well as genes related to detoxification and cellular transport. Transcriptomics studies have shown that gene expression is tightly regulated and that there are often significant changes in gene expression occurring between early and late infection and as a response to environmental stress. Furthermore, the genomes of species in the Botryosphaeriaceae do not present genomic architecture compartmentalization based on gene and repeat density. Rather, gene organization patterns are influenced by gene co-expression patterns. NGS data have also made possible the development of molecular markers for some species and these can now also be used for species lacking genomic data. The growth of NGS platforms and their integration with other emerging technologies promises an even deeper understanding of the biology and evolution of the Botryosphaeriaceae and other plant pathogens. This will continue to promote and will also revolutionize the field of plant pathology. • The number of Botryosphaeriaceae genomes and transcriptomes has increased rapidly • This provided insights into the biology and evolution of Botryosphaeriaceae • This family has undergone multiple transitions from heterothallism to homothallism • Botryosphaeriaceae genomes are rich in hydrolytic enzymes, toxins and transporters • Transcription changes between infection stages and environmental conditions [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fruiting body development in Agaricomycetes represents the most complex and unclear process in the fungi. Mating type pathways (A and B) and transcription factors are important regulators in the sexual development of mushrooms. It is known that clampless1 (clp1) is an additional gene that participate under the homeodomain (HD) genes in the matA pathway and clp1 inactivation blocks clamps formation in Coprinopsis cinerea. In this study we identified and analyzed a homologous Fvclp1 gene in the edible mushroom Flammulina velutipes. The coding sequence of the Fvclp1 was 1011 bp without intron interruption, encoding a protein of 336 amino acids. To exhibit the role of Fvclp1 in clamp development and fruiting body formation, knockdown and overexpression mutants were prepared. No significant difference was observed in the monokaryotic hyphal morphology of overexpression and knockdown transformants. In the dikaryotic hyphae from the compatible crossings between the wild-type L22 strain and Fvclp1 knockdown or overexpression mutants, clamp connections developed. However, knockdown mutants could generate fewer fruiting bodies than the wild-type strain. On the contrary, reduced mycelial growth rate but improved fruiting ability was observed in the dikaryotic Fvclp1 overexpression mutants as compared to the wild-type strain. These results indicate that Fvclp1 is necessary and actively involved in fruiting body development in F. velutipes. Overall, these findings suggest that further studies on the function of Fvclp1 would advance our understanding of sexual reproduction and fruiting body development in edible mushrooms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Agrocybe cylindracea, an edible mushroom, is widely cultivated for its abundance of nutrients and flavor, and many of its metabolites are reported to have beneficial roles, such as medicinal effects on tumors and chronical illnesses. However, the lack of genomic information has hindered further molecular studies on this fungus. Here, we present a genome assembly of A. cylindracea together with comparative genomics and pathway analyses of Agaricales species. The draft, generated from both next-generation sequencing (NGS) and single-molecule real-time (SMRT) sequencing platforms to overcome high genetic heterozygosity, is composed of a 56.5 Mb sequence and 15,384 predicted genes. This mushroom possesses a complex reproductive system, including tetrapolar heterothallic and secondary homothallic mechanisms, and harbors several hydrolases and peptidases for gradual and effective degradation of various carbon sources. Our pathway analysis reveals complex processes involved in the biosynthesis of polysaccharides and other active substances, including B vitamins, unsaturated fatty acids, and N-acetylglucosamine. RNA-seq data show that A. cylindracea stipes tend to synthesize carbohydrate for carbon sequestration and energy storage, whereas pilei are more active in carbon utilization and unsaturated fatty acid biosynthesis. These results reflect diverse functions of the two anatomical structures of the fruiting body. Our comprehensive genomic and transcriptomic data, as well as preliminary comparative analyses, provide insights into the molecular details of the medicinal effects in terms of active compounds and nutrient components.

Abstract Mating-type genes are central to sexual reproduction in ascomycete fungi and result in the establishment of reproductive barriers. Together with hybridization, they both play important roles in the evolution of fungi. Recently, potential hybridization events and MAT genes were separately found in the Elata Clade of Morchella. Herein, we characterized the MAT1–1-1 and MAT1–2-1 genes of twenty-two species in the Esculenta Clade, another main group in the genus Morchella, and proved heterothallism to be the predominant mating strategy among the twenty-two species tested. Ascospores of these species were multi-nuclear and had many mitochondrial nucleoids. The number of ascospore nuclei might be positively related with the species distribution range. Phylogenetic analyses of MAT1–1-1, MAT1–2-1, intergenic spacer (IGS), and partial histone acetyltransferase ELP3 (F1) were performed and compared with the species phylogeny framework derived from the ribosomal internal transcribed spacer region (ITS) and translation elongation factor 1-alpha (EF1-a) to evaluate their species delimitation ability and investigate potential hybridization events. Conflicting topologies among these genes genealogies and the species phylogeny were revealed and hybridization events were detected between several species. Different evolutionary patterns were suggested for MAT genes between the Esculenta and the Elata Clades. Complex evolutionary trajectories of MAT1–1-1, MAT1–2-1, F1 and IGS in the Esculenta Clade were highlighted. These findings contribute to a better understanding of the importance of hybridization and gene transfer in Morchella and especially for the appearance of reproductive modes during its evolutionary process.

Fusarium circinatum is an introduced fungal pathogen extended to the northern regions of Spain that causes Pine Pitch Canker (PPC) disease. In this work, we analyzed the pathogen’s genetic diversity to study changes over time and space since the first outbreak occurred in Spain. Using six polymorphic SSR markers, 15 MLGs were identified in 66 isolates, and only three haplotypes were found with frequencies higher than one. In general, genotypic diversity was low and decreased shortly over time in the northwestern regions while maintained at País Vasco, where only one haplotype (MLG32) was detected 10 years. This population also included isolates of a single mating type (MAT-2) and VCGs identified in only two groups, while isolates from NW regions were of both mating types and VCGs represented in 11 groups. The existence of haplotype MLG32 maintained on time and widely distributed suggests its good adaptation to the environment and the host. Results showed that the pathogen in País Vasco remains clearly differentiated from other northwestern populations. This fact was supported with no evidence of migration among regions. Results are explained by the asexual reproduction, but also selfing at least to a lesser extent that leads to identification of two new haplotypes.

Our previous study found that isolates from morel stipes showed a large proportion of mating type deletion, which implied the nuclear evolution and spatial heterogeneity. In this paper, the specific mating type genes of Mat1-1-1 and Mat1-2-1 in Morchella importuna were analyzed using the relative quantitative method of qRT-PCR to study the uneven nuclear distribution in morel life cycle. The results demonstrated obvious unbalanced distribution of two karyotypes in tested commercially cultivated strains and stipe issue isolates from cultivated ascocarps. The ratio of two mating type genes in tissue isolates from different parts of the ascocarps (base soil, inside and surface of stipe, inside and outside of cap pit) was also different. The disequilibrium also existed in primordium, young ascocarp and mature ascocarp. Moreover, the imbalance in different positions of mature ascocarp (base of stipe, middle of stipe, junction of stipe and cap, middle of cap, and top of cap) gradually converged from bottom to top with the largest difference in base of stipe and almost equal distribution of two mating types in morel caps, which indicated that the deviation of two kinds of nuclei in sexual reproduction stage slowed down. More than half of the protoplast regenerated strains from the heterokaryotic M04 strain were homokaryotic, with the dominant Mat1-1-1 genotype accounted for 85.7%. Overall, the Mat1-1-1 genotype nucleus dominated in all samples from different stage of the life cycle. The imbalance of nuclear distribution during the life cycle of M. importuna may imply the evolutionary-driven nuclear-level selection. This is the first study of spatial and temporal disequilibrium of nuclear distribution in macro-ascomycetes. For scale cultivation, it is necessary to perform genotype integrity testing in potential cultivated strains to ensure the existence of both mating type genes.

Blackleg (Phoma) disease, caused by the ascomycete fungi Plenodomus biglobosus and P. lingam, threatens oilseed rape (OSR; Brassica napus) crops internationally. In many parts of the world, both species co-occur, but in China only P. biglobosus has so far been reported. Plenodomus biglobosus reproduces asexually (pycnidiospores), but also sexually (pseudothecia-yielding ascospores), via a heterothallic mating system requiring MAT1-1 and MAT1-2 genotypes. However, the roles of airborne ascospore inoculum in driving blackleg disease outbreaks in China are less well understood compared to elsewhere in the world. This is despite the very different agronomic cropping practices in parts of China, in which paddy rice and OSR are often grown in rotation; OSR stubble is often submerged under water for long periods potentially affecting pseudothecial development. Here, we indirectly investigate the potential role of sexual reproduction by developing new polymerase chain reaction (PCR) -based mating-type diagnostics for P. biglobosus and subsequently screening an international collection of 59 European and 157 Chinese isolates. Overall, in both Europe and China, P. biglobosus mating types did not deviate from a 1:1 ratio, such as is generally thought to occur under frequency-dependent selection in sexually reproducing pathogen populations. Both mating types were balanced in all the individual European countries tested (Austria, France, Poland, UK). Conversely, in China, mating types were only balanced in the eastern region; in the northern and southwestern regions there were skewed ratios, more typical of predominantly asexual reproduction, towards MAT1-1 and MAT1-2, respectively. The implications of these findings and future research directions for improved understanding of P. biglobosus epidemiology on OSR, particularly in China, are considered.

Knowledge of a pathogen's genetic variability and population structure is of great importance to effective disease management. In this study, 193 isolates of Phytophthora infestans collected from three Estonian islands were characterized over 3 years using simple sequence repeat (SSR) marker data complemented by information on their mating type and resistance to metalaxyl. In combination with SSR marker data from samples in the neighboring Pskov region of Northwest Russia, the impact of regional and landscape structure on the level of genetic exchange was also examined. Among the 111 P. infestans isolates from Estonian islands, 49 alleles were detected among 12 SSR loci, and 59 SSR multilocus genotypes were found, of which 64% were unique. The genetic variation was higher among years than that among islands, as revealed by the analysis of molecular variance. The frequency of metalaxyl-resistant isolates increased from 9% in 2012 to 30% in 2014, and metalaxyl resistance was most frequent among A1 isolates. The test for isolation by distance among the studied regions was not significant, and coupled with the absence of genetic differentiation, the result revealed gene flow and the absence of local adaptation. The data are consistent with a sexual population in which diversity is driven by an annual germination of soilborne oospores. The absence of shared genotypes over the years has important implications when it comes to the management of diseases. Such population diversity can make it difficult to predict the nature of the outbreak in the coming year as the genetic makeup is different for each year., Competing Interests: The author(s) declare no conflict of interest.

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.

Setosphaeria turcica is the causal agent of northern corn leaf blight (NCLB), which is a destructive foliar disease of corn around the world. To date, limited information is available on the genetic diversity, population structure, and mating type distribution of the pathogen in the mid-west of China. In this study, based on single nucleotide polymorphism (SNP) markers and mating type-specific primers, we characterized 117 S. turcica isolates collected from Henan, Hebei, Shanxi, and Shaanxi provinces in China. Based on the developed 33 SNP markers, all isolates can be categorized into two genetic groups. Each group consisted of isolates from all four provinces. The Nei’s gene diversity of four populations ranged from 0.328 to 0.419 with a mean of 0.391. The analysis of fixation index (Fst) and gene flow (Nm) suggested that low genetic differentiation and high gene flow existed among four geographic populations. The analysis of molecular variance (AMOVA) demonstrated that the principal molecular variance existed within populations (98%) rather than among populations (2%). The analysis of mating type loci revealed that two mating types (MAT1-1 and MAT1-2) were basically in equilibrium in all four populations. These findings advance our understanding of the genetic diversity, population structure and mating type distribution of S. turcica on corn in the mid-west of China and will aid in developing efficient strategies to control NCLB.

Aflatoxin contamination of corn is a major threat to the safe food and feed. The United States Federal Grain Inspection Service (FGIS) monitors commercial grain shipments for the presence of aflatoxin. A total of 146 Aspergillus flavus were isolated from 29 highly contaminated grain samples to characterize the visual phenotypes, aflatoxin-producing potential, and genotypes to explore the etiological cause of high aflatoxin contamination of US corn. Five of the isolates had reduced sensitivity (43–49% resistant) to the fungicide azoxystrobin, with the remainder all being over 50% resistant to azoxystrobin at the discriminating dose of 2.5 µg/mL. Only six isolates of the highly aflatoxigenic S morphotype were found, and 48 isolates were non-aflatoxigenic. Analysis of the mating type locus revealed 45% MAT 1-1 and 55% MAT 1-2. The A. flavus population originating from the highly aflatoxin contaminated grain samples was compared to a randomly selected subset of isolates originating from commercial corn samples with typical levels of aflatoxin contamination (average < 50 ppb). Use of simple sequence repeat (SSR) genotyping followed by principal component analysis (PCoA) revealed a similar pattern of genotypic distribution in the two populations, but greater diversity in the FGIS-derived population. The noticeable difference between the two populations was that genotypes identical to strain NRRL 21882, the active component of the aflatoxin biocontrol product Afla-Guard™, were ten times more common in the commercial corn population of A. flavus compared to the population from the high-aflatoxin corn samples. The other similarities between the two populations suggest that high aflatoxin concentrations in corn grain are generally the result of infection with common A. flavus genotypes.

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., (© 2024. The Author(s).)

Mango malformation disease caused by Fusarium spp. is one of the main limiting factors for mango production in Mexico. Fungal isolates obtained from symptomatic tissue from mango trees in Sinaloa, Mexico, were subjected to phylogenetic analysis of the TEF-1α gene, and evaluated for mating type, morphological markers and pathogenicity. Fifteen monosporic Fusarium isolates were identified as Fusarium neocosmosporiellum O'Donnell & Geiser. Phylogenetic analysis confirmed that the sequence obtained in this study corresponds to F. neocosmosporiellum. All 15 isolates were found to be pathogenic, but no differences were observed in aggressiveness among the isolates, which may be a result of low genetic variability within the fungal population. According to the morphological and molecular results, this study confirmed that the causal agent of mango malformation disease was F. neocosmosporiellum. This is the first report of mango malformation disease caused by this fungus in Mexico. This study provides a basis for the development and implementation of an integrated management system for this disease, confirms a new location of this fungus, and highlights that this pathogen is a potential threat to mango cultivation in Mexico. [ABSTRACT FROM AUTHOR]

The fungal pathogen Diaporthe citri is a major cause of diseases in citrus. One common disease is melanose, responsible for large economic losses to the citrus fruit industry. However, very little is known about the epidemiology and genetic structure of D. citri. In this study, we analyzed 339 isolates from leaves and fruits with melanose symptoms from five provinces in southern China at 14 polymorphic simple sequence repeat (SSR) loci and the mating type idiomorphs. The genetic variations were analyzed at three levels with separate samples: among provinces, among orchards within one county, and among trees within one orchard. The five provincial populations from Fujian, Zhejiang, Jiangxi, Hunan, and Guizhou were significantly differentiated, while limited differences were found among orchards from the same county or among trees from the same orchard. STRUCTURE analysis detected two genetic clusters in the total sample, with different provincial subpopulations showing different frequencies of isolates in these two clusters. Mantel analysis showed significant positive correlation between genetic and geographic distances, consistent with geographic separation as a significant barrier to gene flow in D. citri in China. High levels of genetic diversity were found within individual subpopulations at all three spatial scales of analyses. Interestingly, most subpopulations at all three spatial scales had the two mating types in similar frequencies and with alleles at the 14 SSR loci not significantly different from linkage equilibrium. Indeed, strains with different mating types and different multilocus genotypes were frequently isolated from the same leaves and fruits. The results indicate that sexual reproduction plays an important role in natural populations of D. citri in southern China and that its ascospores likely represent an important contributor to citrus disease. [ABSTRACT FROM AUTHOR]

Rhynchosporium commune, the cause of barley scald, is an important disease of barley in Canada. Multiple studies have indicated that cryptic sexual reproduction may occur between opposite mating types (MAT1-1 and MAT1-2). The occurrence of R. commune mating types in Canada has not been determined previously. Infected leaves from barley cultivars in seven commercial fields and three breeding nurseries in central Alberta were collected and subjected to multiplex PCR to assess the presence of scald mating types within the lesions. Mating types were determined in 410 scald lesions from 288 leaves. Over 10% of lesions contained both mating types, and 44% of leaves with more than one lesion analyzed were colonized by both mating types. The mating types significantly deviated from the 1:1 ratio that would have been expected with frequent sexual reproduction. MAT1-2 was more common in six of the ten locations and for the region as a whole. The presence of both mating types, often in close proximity to each other, suggests that the cryptic sexual stage could be present in Alberta if it does occur. The skewed mating type ratio does suggest, however, that asexual reproduction is predominant within the pathogen population. [ABSTRACT FROM AUTHOR]

Melanins are pigments used by fungi to withstand various stresses and to strengthen vegetative and reproductive structures. In Sordariales fungi, their biosynthesis starts with a condensation step catalyzed by an evolutionary-conserved polyketide synthase. Here we show that complete inactivation of this enzyme in the model ascomycete Podospora anserina through targeted deletion of the PaPks1 gene results in reduced female fertility, in contrast to a previously analyzed nonsense mutation in the same gene that retains full fertility. We also show the utility of PaPks1 mutants for detecting rare genetic events in P. anserina, such as parasexuality and possible fertilization and/or apomixis of nuclei devoid of mating-type gene. [ABSTRACT FROM AUTHOR]

Epidermophyton floccosum is one of the most common agents of human superficial fungal infections, compared with genus Trichophyton and Microsporum, it possesses uniqueness in ecology traits and rarely causing hair infections. E. floccosum is so far the only representative species of genera Epidermophyton, and it is known as anthropophilic dermatophytes. To further reveal the genome sequences and clues of virulence factors, thus in this study, we sequenced the genome of E. floccosum (CGMCC (F) E1d), and performed comparative genomic analysis with other dermatophytes. It is revealed that E. floccosum owns the largest genome size and similar GC content compared with other dermatophytes. A total of 7565 genes are predicted. By comparing with the closest species N. gypseum, our study reveals that number and structure of adhesion factors, secreted proteases and LysM domain might contribute to the pathogenic and ecological traits of E. floccosum. Mating genes is also detected in genome data. Furthermore, we performed AFLP analysis trying to discuss intraspecific differences of E. floccosum, but no significant relationship is found between genotype and geographical distribution. Upon above, our study provides a deeper understanding and strong foundation for future researches about E. floccosum. [ABSTRACT FROM AUTHOR]

The human fungal pathogen Candida albicans undergoes white-opaque phenotypic switching, which enhances its adaptation to host niches. Switching is controlled by a transcriptional regulatory network of interlocking feedback loops acting on the transcription of WOR1, the master regulator of white-opaque switching, but regulation of the network on the translational level is not yet explored. Here, we show that the long 5' untranslated region of WOR1 regulates the white-opaque phenotype. Deletion of the WOR1 5' UTR promotes white-to-opaque switching and stabilizes the opaque state. The WOR1 5' UTR reduces translational efficiency and the association of the transcript with polysomes. Reduced polysome association was observed for additional key regulators of cell fate and morphology with long 5' UTR as well. Overall, we find a novel regulatory step of white-opaque switching at the translational level. This translational regulation is implicated for many key regulators of cell fate and morphology in C. albicans.

Sex determination in animals and fungi is regulated by specific sex-determining genes. The Aspergillus nidulans mating type gene matA and the human SRY (Sex-Determining Region Y) encode proteins containing a single HMG (high-mobility group) domain. Analysis of the amino-acid sequence of MatA and SRY transcription factors revealed significant structural similarity. The human SRY protein is able to functionally replace MatA and drives the sexual cycle in the fungus A. nidulans. Functional studies indicate that SRY drives early fruiting body development, and hybrid MatA protein carrying the SRY HMG box is fully capable of driving both early and late stages of sexual development, including gametogenesis. Our data suggest that SRY and MatA are both structurally and functionally related and conserved in regulating sexual processes. The fundamental mechanisms driving evolution of the genetic pathways underlying sex determination, sex chromosomes and sexual reproduction in eukaryotes appear similar.

In heterostylous, self-incompatible Turnera species, a member of the YUCCA gene family, YUC6, resides at the S-locus and has been hypothesized to determine the male mating type. YUCCA gene family members synthesize the auxin, indole-3-acetic acid, via a two-step process involving the TAA gene family. Consequently, it has been speculated that differences in auxin concentration in developing anthers are the biochemical basis underlying the male mating type. Here, we provide empirical evidence that supports this hypothesis. Using a transgenic knockdown approach, we show that YUC6 acts pleiotropically to control both the male physiological mating type and pollen size, but not the filament length dimorphism associated with heterostyly in Turnera. Using qPCR to assess YUC6 expression in different transgenic lines, we demonstrate that the level of YUC6 knockdown correlates with the degree of change observed in the male mating type. Further assessment of YUC6 expression through anther development, in the knockdown lines, suggests that the male mating type is irreversibly determined during a specific developmental window prior to microsporogenesis, which is consistent with the genetically sporophytic nature of this self-incompatibility system. These results represent the first gene controlling male mating type to be characterized in any species with heterostyly.

Long-term site-specific studies describing changes in the phenotypic variability of Phytophthora infestans populations allow quantitative predictions of pathogen spread and possible outbreaks of epidemics, and provide key input for regional resistance breeding programs. Late blight samples were collected from potato (Solanum tuberosum) breeding fields in Estonia during a twelve-year study period between 2001 and 2014. In total, 207 isolates were assessed for mating type and 235 isolates for metalaxyl resistance and 251 isolates for virulence factors. The frequency of mating types strongly fluctuated across the years, whereas the later period of 2010–2014 was dominated by the A2 mating. Despite fluctuations, both mating types were recorded in the same fields in most years, indicating sustained sexual reproduction of P. infestans with oospore production. Metalaxyl-resistant and intermediately resistant strains dominated in the first years of study, but with the progression of the study, metalaxyl-sensitive isolates became dominant, reaching up to 88%. Racial diversity, characterized by normalized Shannon diversity index decreased in time, varying from 1.00 in 2003 to 0.43 in 2013. The frequency of several virulence factors changed in a time-dependent manner, with R2 increasing and R6, R8, and R9 decreasing in time. Potato cultivar resistance background did not influence the frequency of P. infestans mating type, response to metalaxyl, and racial diversity. However, the diversity index decreased in time among isolates collected from resistant and susceptible cultivars, and remained at a high level in moderately resistant cultivars. These data demonstrate major time-dependent changes in racial diversity, fungicide resistance, and virulence factors in P. infestans, consistent with alterations in the control strategies and popularity of potato cultivars with different resistance.

The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian’ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian’ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts.

Copyright of Mycosystema is the property of Mycosystema Editorial Board and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The genetic regulation of Colletotrichum (Glomerella) sexual reproduction does not strictly adhere to the Ascomycota paradigm and remains poorly understood. Morphologically different but sexually compatible strain types, termed plus and minus, have been recognized, but the biological and molecular distinctions between these strain types remain elusive. In this study, we characterized the sexual behaviors of a pair of plus and minus strains of C. fructicola with the aid of live-cell nucleus-localized fluorescent protein labeling, gene expression, and gene mutation analyses. We confirmed a genetically stable plus-to-minus switching phenomenon and demonstrated the presence of both cross-fertilized and self-fertilized perithecia within the mating line (perithecia cluster at the line of colony contact) between plus and minus strains. We demonstrated that pheromone signaling genes (a-factor-like and a-factor-like pheromones and their corresponding GPCR receptors) were differently expressed between vegetative hyphae of the two strains. Moreover, deletion of pmk1 (a FUS/KSS1 mitogen-activate protein kinase) in the minus strain severely limited mating line formation, whereas deletion of a GPCR (FGSG_05239 homolog) and two histone modification factors (hos2, snt2) in the minus strain did not affect mating line development but altered the ratio between cross-fertilization and selffertilization within the mating line. We propose a model in which mating line formation in C. fructicola involves enhanced protoperithecium differentiation and enhanced perithecium maturation of the minus strain mediated by both cross-fertilization and diffusive effectors. This study provides insights into mechanisms underlying the mysterious phenomenon of plus-minus-mediated sexual enhancement being unique to Colletotrichum fungi. [ABSTRACT FROM AUTHOR]

The Eucalyptus foliar pathogen Teratosphaeria destructans causes severe and widespread damage in South‐East Asian and South African plantations. In 2016, leaf blight symptoms resembling those caused by T. destructans were observed in a plantation of a Eucalyptus grandis × E. urophylla hybrid in Sabah, Malaysia. The aims of this study were to confirm the identity of the causal agent as T. destructans and to investigate the genetic structure of isolates associated with this newly detected disease outbreak. Using sequence data of three gene regions, the identity of the pathogen was confirmed as T. destructans. The mating type and microsatellite genotypes of 41 isolates from this Malaysian population were identified and compared with those from previously characterized populations in South‐East Asia and South Africa. The Malaysian population had the highest genotypic diversity of any T. destructans population thus far investigated. Both the mating types were found in the collection of isolates, and these were in approximately equal proportions. Although structures linked to a sexual state of the fungus have not been found, sexual reproduction is theoretically possible and could explain the high genetic diversity in the pathogen that must have been accidentally introduced into Malaysia. This is the first record of T. destructans in Sabah and, to the best of our knowledge, in also other parts of Borneo. [ABSTRACT FROM AUTHOR]

In the 1970s, clones of the two subspecies of Ophiostoma novo-ulmi, subsp. americana (SSAM) and subsp. novo-ulmi (SSNU) began to overlap in Europe, resulting in hybrid swarms. By 1983–1986, hybrids with high, SSAM-like growth and pathogenic fitness comprised ~75% of popula-tions at Limburg, Netherlands and Orvieto, Italy. We resampled these populations in 2008 to examine trends in hybrid fitness traits. Since preliminary sampling in 1979–1980, MAT-1 locus frequency had increased from ~0% to ~32% at Orvieto and 5% to ~43% at Limburg, and vegeta-tive incompatibility type frequency had changed from near clonal to extremely diverse at both sites. This represents an enormous increase in outcrossing and recombination potential, due in part to selective acquisition (under virus pressure) of MAT-1 and vic loci from the resident O. ulmi and in part to SSAM × SSNU hybridisation. Overt virus infection in the 2008 samples was low (~4%), diagnostic SSAM and SSNU cu and col1 loci were recombinant, and no isolates exhib-ited a parental SSAM or SSNU colony pattern. At both sites, mean growth rate and mean patho-genicity to 3–5 m clonal elm were high SSAM-like, indicating sustained directional selection for these characters, though at Orvieto growth rate was slower. The once frequent SSNU-specific up-mut colony dimorphism was largely eliminated at both sites. Perithecia formed by Limburg isolates were mainly an extreme, long-necked SSNU-like form, consistent with transgressive segregation resulting from mismatch of SSAM and SSNU developmental loci. Orvieto isolates produced more parental-like perithecia, suggesting the extreme phenotypes may have been se-lected against. The novel phenotypes in the swarms are remodelling O. novo-ulmi in Europe. Locally adapted genotypes may emerge. [ABSTRACT FROM AUTHOR]

Copyright of Arab Journal of Plant Protection is the property of Arab Society for Plant Protection and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian'ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian'ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts. [ABSTRACT FROM AUTHOR]

Phyllosticta citriasiana is the causal agent of citrus tan spot, an important pomelo disease in Asia. At present, there is little or no information on the epidemiology or population structure of P. citriasiana. By using simple sequence repeat markers, we analyzed 94 isolates from three pomelo production regions in southern and southeastern China. The analyses showed high genetic diversity in each of the three geographic populations. A STRUCTURE analysis revealed two genetic clusters among the 94 isolates; one geographic population was dominated by genotypes in one cluster, and the other two geographic populations were dominated by genotypes of the second cluster. P. citriasiana has a heterothallic mating system with two idiomorphs, MAT1-1 and MAT1-2. Analyses using mating type-specific primers revealed that both mating types were present in all three geographic populations, and in all three populations the mating type ratios were in equilibrium. Although the sexual stage of the fungus has not been discovered yet, analyses of allelic associations indicated evidence for sexual and asexual reproduction within and between populations. Despite the observed genetic differentiation between the three geographic populations, evidence for longdistance gene flow was found. [ABSTRACT FROM AUTHOR]

Modes of sexual reproduction in eukaryotic organisms are extremely diverse. The human fungal pathogen Candida albicans undergoes a phenotypic switch from the white to the opaque phase in order to become mating-competent. In this study, we report that functionally- and morphologically-differentiated white and opaque cells show a coordinated behavior during mating. Although white cells are mating-incompetent, they can produce sexual pheromones when treated with pheromones of the opposite mating type or by physically interacting with opaque cells of the opposite mating type. In a co-culture system, pheromones released by white cells induce opaque cells to form mating projections, and facilitate both opposite- and same-sex mating of opaque cells. Deletion of genes encoding the pheromone precursor proteins and inactivation of the pheromone response signaling pathway (Ste2-MAPK-Cph1) impair the promoting role of white cells (MTLa) in the sexual mating of opaque cells. White and opaque cells communicate via a paracrine pheromone signaling system, creating an environment conducive to sexual mating. This coordination between the two different cell types may be a trade-off strategy between sexual and asexual lifestyles in C. albicans.

In this commentary, Michelle Arbeitman et al., examine the topic of the Genetics of Sex as explored in this month's issues of GENETICS and G3: Genes|Genomes|Genetics. These inaugural articles are part of a joint Genetics of Sex collection (ongoing) in the GSA journals.

Despite its essential role in development, molecular mechanisms of membrane merger during cell-cell fusion in most eukaryotic organisms remain elusive. In the filamentous fungus Neurospora crassa, cell fusion occurs during asexual spore germination, where genetically identical germlings show chemotropic interactions and cell-cell fusion. Fusion of germlings and hyphae is required for the formation of the interconnected mycelial network characteristic of filamentous fungi. Previously, a multipass membrane protein, PRM1, was characterized and acts at the step of bilayer fusion in N. crassa. Here we describe the identification and characterization of lfd-1, encoding a single pass transmembrane protein, which is also involved in membrane merger. lfd-1 was identified by a targeted analysis of a transcriptional profile of a transcription factor mutant (Δpp-1) defective in germling fusion. The Δlfd-1 mutant shows a similar, but less severe, membrane merger defect as a ΔPrm1 mutant. By genetic analyses, we show that LFD1 and PRM1 act independently, but share a redundant function. The cell fusion frequency of both Δlfd-1 and ΔPrm1 mutants was sensitive to extracellular calcium concentration and was associated with an increase in cell lysis, which was suppressed by a calcium-dependent mechanism involving a homologue to synaptotagmin.

Non-genetic phenotypic variations play a critical role in the adaption to environmental changes in microbial organisms. Candida albicans, a major human fungal pathogen, can switch between several morphological phenotypes. This ability is critical for its commensal lifestyle and for its ability to cause infections. Here, we report the discovery of a novel morphological form in C. albicans, referred to as the "gray" phenotype, which forms a tristable phenotypic switching system with the previously reported white and opaque phenotypes. White, gray, and opaque cell types differ in a number of aspects including cellular and colony appearances, mating competency, secreted aspartyl proteinase (Sap) activities, and virulence. Of the three cell types, gray cells exhibit the highest Sap activity and the highest ability to cause cutaneous infections. The three phenotypes form a tristable phenotypic switching system, which is independent of the regulation of the mating type locus (MTL). Gray cells mate over 1,000 times more efficiently than do white cells, but less efficiently than do opaque cells. We further demonstrate that the master regulator of white-opaque switching, Wor1, is essential for opaque cell formation, but is not required for white-gray transitions. The Efg1 regulator is required for maintenance of the white phenotype, but is not required for gray-opaque transitions. Interestingly, the wor1/wor1 efg1/efg1 double mutant is locked in the gray phenotype, suggesting that Wor1 and Efg1 could function coordinately and play a central role in the regulation of gray cell formation. Global transcriptional analysis indicates that white, gray, and opaque cells exhibit distinct gene expression profiles, which partly explain their differences in causing infections, adaptation ability to diverse host niches, metabolic profiles, and stress responses. Therefore, the white-gray-opaque tristable phenotypic switching system in C. albicans may play a significant role in a wide range of biological aspects in this common commensal and pathogenic fungus.

The leaf spot form of the barley disease net blotch, caused by the fungus Pyrenophora teres f. maculata (PTM), is an increasingly important foliar disease of barley. Studies of population genetic structure and reproductive mode are necessary to make predictions of the evolutionary potential of the pathogen. Sources of resistance to PTM have been found in Iranian landraces, which may have the potential to improve plant breeding efforts. However, little is known about the population genetic structure of this fungus in Iran. In this study, we analysed the frequency of the mating type genes to assess the potential for sexual mating of PTM collected from four provinces—Khuzestan, Hamadan, Golestan, and East Azerbaijan—and we investigated the population genetic structure using seven simple sequence repeat markers. High genotype diversity, linkage equilibrium, and equal ratios of mating types frequencies in the PTM populations at Khuzestan and Hamadan support the occurrence of sexual reproduction in these populations, while in Golestan and East Azerbaijan populations, significant gametic disequilibrium and relatively low genotype diversity suggest a higher incidence of clonality or different demographic histories. Unequal mating type frequencies in Golestan confirm a predominance of asexual reproduction. Finally, we found significant evidence for strong population structure with most of the genetic variation represented within regional populations (89%). Overall, our study provides evidence for high genetic variation in Iranian PTM populations, which may be the basis for rapid adaptive evolution in this pathosystem. This highlights the need for integrated efforts to control the disease. [ABSTRACT FROM AUTHOR]

Samples of blighted potato leaves were collected from fields in six potato-growing districts of the Punjab Province of Pakistan in 2017–2018. A total of 149 isolates of Phytophthora infestans were obtained from six potato cultivars (Asterix, Barsenna, Burana, Caroda, Mazika, Sante). Of these isolates, 73% were A1 mating type, 23% were A2 mating type and 4% were self-fertile. Both mating types of P. infestans occurred in all six districts sampled, but in every case, the A1 mating type predominated. The foliar aggressiveness of 104 of these isolates (weakly pathogenic isolates were excluded) was tested on detached leaflets of potato cv. Caroda, and a composite aggressiveness index (CAI) calculated from lesion area (measured after 10 days), latent period and infection frequency was used to compare isolates. There was no difference in CAI between isolates obtained from different districts or cultivars. The A2 mating type isolates had significantly greater CAIs than A1 isolates but this does not imply a genetic linkage nor a general association between mating type and aggressiveness. It may be that the A2 isolates belonged to an aggressive clonal lineage such as 13_A2 that has been reported in other countries in the region. While it was not possible to test the isolates collected in 2017–2018, genotyping of samples collected in 2019–2020 showed the widespread occurrence of the EU_13_A2 clonal lineage in the same districts of Pakistan and supported this hypothesis. This is the first report of EU_13_A2 from Pakistan. The implications for potato late blight management in the Punjab are discussed. [ABSTRACT FROM AUTHOR]