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Molecular markers reveal cryptic sex in the human pathogen Coccidioides immitis
A Burt1, D A Carter, G L Koenig
1Department of Plant Biology, University of California, Berkeley 94720, USA.
Abstract:
Coccidioides immitis, cause of a recent epidemic of "Valley fever" in California, is typical of many eukaryotic microbes in that mating and meiosis have yet to be reported, but it is not clear whether sex is truly absent or just cryptic. To find out, we have undertaken a population genetic study using PCR amplification, screening for single-strand conformation polymorphisms, and direct DNA sequencing to find molecular markers with nucleotide-level resolution. Both population genetic and phylogenetic analyses indicate that C. immitis is almost completely recombining. To our knowledge, this study is the first to find molecular evidence for recombination in a fungus for which no sexual stage has yet been described. These results motivate a directed search for mating and meiosis and illustrate the utility of single-strand conformation polymorphism and sequencing with arbitrary primer pairs in molecular population genetics.
Insights
Coccidioides immitis, the fungus causing Valley fever, shows strong evidence of genetic recombination, suggesting a hidden sexual cycle. This finding is crucial for understanding its population genetics and evolution.
Area of Science:
- Medical Mycology
- Population Genetics
- Molecular Biology
Background:
- Coccidioides immitis causes Valley fever, a significant public health concern in California.
- The absence of reported mating and meiosis in C. immitis raises questions about its reproductive strategies.
- Understanding the reproductive biology of C. immitis is essential for epidemiological and evolutionary studies.
Purpose of the Study:
- To investigate the presence of genetic recombination in Coccidioides immitis.
- To determine if sexual reproduction, though not overtly observed, occurs in this fungus.
- To identify molecular markers for population genetic analysis.
Main Methods:
- Population genetic study of C. immitis.
- Polymerase chain reaction (PCR) amplification.
- Screening for single-strand conformation polymorphisms (SSCP).
- Direct DNA sequencing for nucleotide-level resolution.
Main Results:
- Population genetic and phylogenetic analyses revealed that C. immitis is almost completely recombining.
- Molecular evidence for recombination was found in a fungus lacking a described sexual stage.
- Single-strand conformation polymorphism (SSCP) and arbitrary primer sequencing proved useful for molecular population genetics.
Conclusions:
- Coccidioides immitis exhibits significant genetic recombination, strongly suggesting the presence of a cryptic sexual cycle.
- This study provides the first molecular evidence for recombination in C. immitis.
- The findings encourage further research into the mating and meiotic processes of this important fungal pathogen.