Evolutionary Biology: Microsporidia Sex — A Missing Link to Fungi

SummaryThe evolutionary origins of the microsporidia, a group of intracellular eukaryotic pathogens, have been unclear. Genome analysis of a sex locus and other gene clusters has now revealed conserved synteny with zygomycete fungi, indicating that microsporidia are true fungi descended from a zygomycete ancestor

Differences in MAT gene distribution and expression between Rhynchosporium species on grasses

Leaf blotch is a globally important disease of barley crops and other grasses that is caused by at least five host-specialized species in the fungal genus Rhynchosporium. The pathogen R. commune (specialized to barley, brome-grass and Italian ryegrass) has long been considered to reproduce only by asexual means, but there has been accumulating evidence for recombination and gene flow from population genetic studies and the detection of complementary MAT1-1 and MAT1-2 isolates in a c. 1:1 ratio in the field. Here, it is demonstrated that 28 isolates of the closely related species R. agropyri (on couch-grass) and R. secalis (on rye and triticale), collected from Europe, were also either of MAT1-1 or MAT1-2 genotype and that the distribution of mating types did not deviate significantly from a 1:1 ratio. Evidence is then provided for MAT1-1-1 and MAT1-2-1 gene expression during mycelial growth for all three species. By contrast, 27 isolates of the more distantly related R. orthosporum (on cocksfoot) and R. lolii (on Italian and perennial ryegrasses) from Europe were exclusively of the MAT1-1 genotype, and expression of the MAT1-1-1 gene could not be detected during mycelial growth. These data suggest that cryptic sexual cycles are more likely to exist for R. commune, R. agropyri and R. secalis than for either R. orthosporum or R. lolii. A phylogenetic analysis of partial MAT1-1 idiomorph sequences resolved these five species into two distinct groups (R. commune, R. agropyri and R. secalis versus R. orthosporum and R. lolii) but provided only limited resolution within each group

Local-scale panmixia in the lichenized fungus Xanthoria parietina contrasts with substantial genetic structure in its Trebouxia photobionts

Microsatellite markers can provide valuable information about gene flow and population history. We developed and tested new microsatellites for the nitrophilic lichenized fungus Xanthoria parietina and studied its genetic diversity and structure within the urban area of Munich, Bavaria. We compared its local genetic pattern with that of its photobiont partner Trebouxia decolorans, for which existing microsatellites were applied. For comparison, a reference site with clean air was included in the sampling. We found support for three genetic clusters in the fungus X. parietina, which occurred intermingled in collecting sites. There was a high degree of admixture within fungal populations and individuals, and analysis of molecular variance revealed a lack of population structure in the mycobiont. The Trebouxia photobiont, in contrast, exhibited structured populations which grouped into two to five genetic clusters, and individuals showed less admixture than in the mycobiont. This indicates that the two lichen partners differ in their ability to move around in the landscape. The microsatellite markers we report are polymorphic and are suitable for population genetic studies

Differences in MAT gene distribution and expression between Rhynchosporium species on grasses

Leaf blotch is a globally important disease of barley crops and other grasses that is caused by at least five host-specialized species in the fungal genus Rhynchosporium. The pathogen R. commune (specialized to barley, brome-grass and Italian ryegrass) has long been considered to reproduce only by asexual means, but there has been accumulating evidence for recombination and gene flow from population genetic studies and the detection of complementary MAT1-1 and MAT1-2 isolates in a c. 1:1 ratio in the field. Here, it is demonstrated that 28 isolates of the closely related species R. agropyri (on couch-grass) and R. secalis (on rye and triticale), collected from Europe, were also either of MAT1-1 or MAT1-2 genotype and that the distribution of mating types did not deviate significantly from a 1:1 ratio. Evidence is then provided for MAT1-1-1 and MAT1-2-1 gene expression during mycelial growth for all three species. By contrast, 27 isolates of the more distantly related R. orthosporum (on cocksfoot) and R. lolii (on Italian and perennial ryegrasses) from Europe were exclusively of the MAT1-1 genotype, and expression of the MAT1-1-1 gene could not be detected during mycelial growth. These data suggest that cryptic sexual cycles are more likely to exist for R. commune, R. agropyri and R. secalis than for either R. orthosporum or R. lolii. A phylogenetic analysis of partial MAT1-1 idiomorph sequences resolved these five species into two distinct groups (R. commune, R. agropyri and R. secalis versus R. orthosporum and R. lolii) but provided only limited resolution within each group

Sexual reproduction of human fungal pathogens

We review here recent advances in our understanding of sexual reproduction in fungal pathogens that commonly infect humans, including Candida albicans, Cryptococcus neoformans/gattii, and Aspergillus fumigatus. Where appropriate or relevant, we introduce findings on other species associated with human infections. In particular, we focus on rapid advances involving genetic, genomic, and population genetic approaches that have reshaped our view of how fungal pathogens evolve. Rather than being asexual, mitotic, and largely clonal, as was thought to be prevalent as recently as a decade ago, we now appreciate that the vast majority of pathogenic fungi have retained extant sexual, or parasexual, cycles. In some examples, sexual and parasexual unions of pathogenic fungi involve closely related individuals, generating diversity in the population but with more restricted recombination than expected from fertile, sexual, outcrossing and recombining populations. In other cases, species and isolates participate in global outcrossing populations with the capacity for considerable levels of gene flow. These findings illustrate general principles of eukaryotic pathogen emergence with relevance for other fungi, parasitic eukaryotic pathogens, and both unicellular and multicellular eukaryotic organisms

Culturing and Mating of Aspergillus fumigatus

Aspergillus fumigatus is an opportunistic human fungal pathogen, capable of causing invasive aspergillosis in patients with compromised immune systems. The fungus was long considered a purely asexual organism. However, a sexual cycle was reported in 2009, with methods described to induce mating under laboratory conditions. The presence of a sexual cycle now offers a valuable tool for classical genetic analysis of the fungus, such as allowing determination of whether traits of interest are mono- or poly-genic in nature. For example, the sexual cycle is currently being exploited to determine the genetic basis of traits of medical importance such as resistance to azole antifungals and virulence, and to characterise the genes involved. The sexual cycle can also be used to assess the possibility of gene flow between isolates.This unit describes protocols for culturing of A. fumigatus and for inducing sexual reproduction between compatible MAT1-1 and MAT1-2 isolates of the species. The unit also provides working methods for harvesting sexual structures, isolating single-spore progeny and confirming whether sexual recombination has occurred

Local-scale panmixia in the lichenized fungus Xanthoria parietina contrasts with substantial genetic structure in its Trebouxia photobionts

Microsatellite markers can provide valuable information about gene flow and population history. We developed and tested new microsatellites for the nitrophilic lichenized fungus Xanthoria parietina and studied its genetic diversity and structure within the urban area of Munich, Bavaria. We compared its local genetic pattern with that of its photobiont partner Trebouxia decolorans, for which existing microsatellites were applied. For comparison, a reference site with clean air was included in the sampling. We found support for three genetic clusters in the fungus X. parietina, which occurred intermingled in collecting sites. There was a high degree of admixture within fungal populations and individuals, and analysis of molecular variance revealed a lack of population structure in the mycobiont. The Trebouxia photobiont, in contrast, exhibited structured populations which grouped into two to five genetic clusters, and individuals showed less admixture than in the mycobiont. This indicates that the two lichen partners differ in their ability to move around in the landscape. The microsatellite markers we report are polymorphic and are suitable for population genetic studies

Free-induction-decay magnetometer with enhanced optical pumping

Spin preparation prior to a free-induction-decay (FID) measurement can be adversely affected by transverse bias fields, particularly in the geophysical field range. A strategy that enhances the spin polarization accumulated before readout is demonstrated, by synchronizing optical pumping with a magnetic field pulse that supersedes any transverse fields by over two order of magnitude. The pulsed magnetic field is generated along the optical pumping axis using a compact electromagnetic coil pair encompassing a micro-electromechanical systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs) vapor to the optimal atomic density without spurious magnetic field contributions as they are rapidly demagnetized to approximately zero field during spin readout. The demagnetization process is analyzed electronically, and directly with a FID measurement, to confirm that the residual magnetic field is minimal during detection. The sensitivity performance of this technique is compared to existing optical pumping modalities across a wide magnetic field range. A noise floor sensitivity of $238\,\mathrm{fT/\surd{Hz}}$ was achieved in a field of approximately $\mathrm{50\,\mu{T}}$, in close agreement with the Cram\'{e}r-Rao lower bound (CRLB) predicted noise density of $258\,\mathrm{fT/\surd{Hz}}$.Comment: 10 pages, 7 figure