Identification of the Mating-Type (MAT) Locus That Controls Sexual Reproduction of Blastomyces dermatitidis

Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC USA.
Eukaryotic Cell (Impact Factor: 3.18). 11/2012; 12(1). DOI: 10.1128/EC.00249-12
Source: PubMed


Blastomyces dermatitidis is a dimorphic fungal pathogen that primarily causes blastomycosis in the midwestern and northern United States and Canada.
While the genes controlling sexual development have been known for a long time, the genes controlling sexual reproduction
of B. dermatitidis (teleomorph, Ajellomyces dermatitidis) are unknown. We identified the mating-type (MAT) locus in the B. dermatitidis genome by comparative genomic approaches. The B. dermatitidis MAT locus resembles those of other dimorphic fungi, containing either an alpha-box (MAT1-1) or an HMG domain (MAT1-2) gene linked to the APN2, SLA2, and COX13 genes. However, in some strains of B. dermatitidis, the MAT locus harbors transposable elements (TEs) that make it unusually large compared to the MAT locus of other dimorphic fungi. Based on the MAT locus sequences of B. dermatitidis, we designed specific primers for PCR determination of the mating type. Two B. dermatitidis isolates of opposite mating types were cocultured on mating medium. Immature sexual structures were observed starting at
3 weeks of coculture, with coiled-hyphae-containing cleistothecia developing over the next 3 to 6 weeks. Genetic recombination
was detected in potential progeny by mating-type determination, PCR-restriction fragment length polymorphism (PCR-RFLP), and
random amplification of polymorphic DNA (RAPD) analyses, suggesting that a meiotic sexual cycle might have been completed.
The F1 progeny were sexually fertile when tested with strains of the opposite mating type. Our studies provide a model for
the evolution of the MAT locus in the dimorphic and closely related fungi and open the door to classic genetic analysis and studies on the possible
roles of mating and mating type in infection and virulence.

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    • "Identification of compatible mating partners using DNA markers results in a reliable and effective tool that can be implemented at any stage of a breeding programme. A range of molecular markers, including ISSR (Nazrul & Yin Bing, 2010), RAPD (Kavousi et al., 2008; Larraya et al., 2001), isozyme analysis (Khush et al., 1995), and RFLP (Li et al., 2012) have been employed to identify mushroom monokaryon isolates. "
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    ABSTRACT: The problems in precise discrimination of monokaryotic isolates of edible fungi hindered the breeders to enhance the improvement cycle of mushroom strains in an effective manner. In current study, 5′ end of intergenic spacer 2 (IGS2) region was amplified and used to assist categorizing the selected monokaryotic isolates of Pleurotus pulmonarius into two distinct groups (type A and B). Moreover, the dikaryotic isolates were able to produce double-banded PCR product and the monokaryons create only one unique amplicon. Candidate region approach was used in this study and enabled pedigree history to be recorded, and thus breeders are able to make informative decisions. Hence, this approach promotes time saving and breeding space to be allocated for strain improvement programmes. Meanwhile, this highly variable DNA marker can be used for the confirmation of successfully crossed strains. Eventually, this methodology can assist towards detecting efficient mating partners of P. pulmonarius in any breeding programmes including selective breeding, production of high yield hybrids and studies on structure mating types.
    Full-text · Article · Feb 2014 · Journal of Animal and Plant Sciences
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    • "Very little work has been done exploring genetic recombination in B. dermatitidis. Although B. dermatitidis can reproduce sexually, the mating-type locus was only recently identified [25], and it is unknown how frequently sexual reproduction occurs in nature. The rate of recombination between and among the 2 major genetic groups of B. dermatitidis could significantly impact the population genetic structure of this pathogen. "
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    ABSTRACT: Background Several studies have shown that Blastomyces dermatitidis, the etiologic agent of blastomycosis, is a genetically diverse pathogen. Blastomycosis is a significant health issue in humans and other mammals. Veterinary and human isolates matched with epidemiological case data from the same geographic area and time period were used to determine: (i) if differences in genetic diversity and structure exist between clinical veterinary and human isolates of B. dermatitidis and (ii) if comparable epidemiologic features differ among veterinary and human blastomycosis cases. Results Genetic typing of 301 clinical B. dermatitidis isolates produced 196 haplotypes (59 unique to veterinary isolates, 134 unique to human isolates, and 3 shared between canine and human isolates). Private allelic richness was higher in veterinary (median 2.27) compared to human isolates (median 1.14) (p = 0.005). Concordant with previous studies, two distinct genetic groups were identified among all isolates. Genetic group assignment was different between human and veterinary isolates (p < 0.001), with more veterinary isolates assigned to Group 2. The mean age of dogs diagnosed with blastomycosis was 6 years. Thirty cases were in male dogs (52%) and 24 were females (41%). The breed of dog was able to be retrieved in 38 of 58 cases with 19 (50%) being sporting breeds. Three of four felines infected with blastomycosis were domestic shorthair males between ages 6–12, and presented with disseminated disease. The other was a lynx with pulmonary disease. The equine isolate was from an 11-year-old male Halflinger with disseminated disease. Disseminated disease was reported more often in veterinary (62%) than human cases (19%) (p < 0.001). Conclusions Isolates from all hosts clustered largely into previously identified genetic groups, with 3 haplotypes being shared between human and canine isolates confirming that B. dermatitidis isolates capable of infecting both species occur in nature. Allelic diversity measures trended higher in veterinary samples, with a higher number of total alleles and private alleles. Veterinary isolates of B. dermatitidis contributed a substantial amount of diversity to the overall population genetic structure demonstrating the importance of including veterinary isolates in genetic studies of evolution and virulence in this organism.
    Full-text · Article · Apr 2013 · BMC Veterinary Research
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    ABSTRACT: Aspergillus lentulus was described in 2005 as a new species within the A. fumigatus sensu lato complex. It is an opportunistic human pathogen causing invasive aspergillosis with high mortality rates, and it has been isolated from clinical and environmental sources. The species is morphologically nearly identical to A. fumigatus sensu stricto, and this similarity has resulted in their frequent misidentification. Comparative studies show that A. lentulus has some distinguishing growth features and decreased in vitro susceptibility to several antifungal agents, including amphotericin B and caspofungin. Similar to the once-presumed-asexual A. fumigatus, it has only been known to reproduce mitotically. However, we now show that A. lentulus has a heterothallic sexual breeding system. A PCR-based mating-type diagnostic detected isolates of either the MAT1-1 or MAT1-2 genotype, and examination of 26 worldwide clinical and environmental isolates revealed similar ratios of the two mating types (38% versus 62%, respectively). MAT1-1 and MAT1-2 idiomorph regions were analyzed, revealing the presence of characteristic alpha and high-mobility-group (HMG) domain genes, together with other more unusual features such as a MAT1-2-4 gene. We then demonstrated that A. lentulus possesses a functional sexual cycle with mature cleistothecia, containing heat-resistant ascospores, being produced after 3 weeks of incubation. Recombination was confirmed using molecular markers. However, isolates of A. lentulus failed to cross with highly fertile strains of A. fumigatus, demonstrating reproductive isolation between these sibling species. The discovery of the A. lentulus sexual stage has significant implications for the management of drug resistance and control of invasive aspergillosis associated with this emerging fungal pathogen.
    Full-text · Article · May 2013 · Eukaryotic Cell
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