RESEARCH HIGHLIGHTS

URLs FUNGAL BIOLOGY To mate or not to mate?

Fungal sex is a hot topic, owing to fumigatus has a mating-type locus in different strains isolated from the recent studies in the opportunistic that is typical of sexual ascomycete same patient. Mating types were not pathogens Candida albicans and fungi. This warranted further investi- geographically isolated, so a 1:1 ratio Cryptococcus neoformans. Now, gation, as improved genetic analyses strongly suggests either that mating Paoletti et al. reveal that alone would be a welcome boon for does occur or that these two mating fumigatus, an often fatal opportun- researchers keen to understand the types arose very recently and that istic human pathogen, might have a virulence of this pathogen. insufficient time has passed for drift sexual cycle too. Although finding seemingly away from this ratio. Genetic analyses in the aspergilli intact mating-type genes is exciting, Having identified the partner have been hindered because this it only indicates the potential for sex. strains, population genetic analyses group is asexual (imperfect). In a paper just published in Current were used to evaluate polymorphisms Inspection of the recently completed Biology, Paoletti et al. report experi- in intergenic regions. The presence sequences of Aspergillus mental evidence for sex. Sex is not of 9 conserved substitutions in both nidulans (a model for cell biology), possible without two partner strains, mating types is a strong indicator A. fumigatus and Aspergillus oryzae which in filamentous ascomycetes that recombination through sex has (important in the industrial produc- are named MAT1-1 and MAT1-2, probably occurred over time. Semi- tion of ) revealed that A. so finding two distinct mating- quantitative PCR showed that genes type alleles was the first important in the mating-type locus, which endeavour. The sequenced strain include the MAT mating-type genes has a MAT1-2 locus. Degenerate and those encoding a pheromone PCR was used to amplify a puta- and pheromone receptors, were tive MAT1-1 sequence (the α box) expressed in both mating types in from environmental isolates. One mycelia. This is clear evidence that interesting feature that arose when the mating-type genes are active, the sequence of this MAT1-1 locus a surprise in a nominally ‘asexual’ was completed was that it contained . However, sex still hasn’t been some MAT1-2 sequences, indicating observed in the lab. that the sexual partner strains might Hints of sex in fungi are not new be derived from a homothallic ances- but, increasingly, it seems that more tor that contained both loci. fungi are having sex. This might prove What about the environmen- important in generating the diversity tal abundance of the mating-type that is required to exploit environ- strains? Using multiplex PCR, the mental niches and to be successful karyotypes of 290 environmental and pathogens. clinical isolates were determined. Susan Jones All strains were either MAT1-1 or References and links MAT1-2 with a 1:1 ratio of MAT1-1 ORIGINAL RESEARCH PAPER Paoletti, M. et al. Evidence for sexuality in the opportunistic fungal to MAT1-2. Unlike C. neoformans pathogen . Curr. Biol. 15, isolates, there was no bias to one 1242–1248 (2005) mating type in clinical isolates. In fact, both mating types were present

NATURE REVIEWS | MICROBIOLOGY VOLUME 3 | SEPTEMBER 2005 | 1