Mating-Type Structure, Evolution, and Function in Euascomycetes

The past several years have seen a rapid rise in the number of cloned and characterized mating-type loci from an ever-expanding group of filamentous Ascomycetes. However, the available mating-type gene database still lacks some representatives of functionally or taxonomically important groups. No complete mating-type sequences are available for the Euascomycetes that undergo mating-type switching, or for lichen-forming fungi. The analysis of the evolution of mating types is at the beginning, focusing first on the evolutionary relationship between self-compatible and self-incompatible species from the same genus. A comparative evolutionary history of the mating-type loci of organisms with more distant connections, such as those of Candida albicans, N. crassa, and Cryptococcus neoformans, will require much effort to be understood. Finally, investigations into the role of mating-type proteins during development of the fruiting body must be scaled up. The major challenge in the mating-type field is to identify the target genes of the mating-type transcription factors, and to determine the function of these target genes, as well as the function of the MAT1-1-2 and MAT1-1-4 proteins themselves. Until recently, this topic was limited due to intractable difficulties with genetical approaches, or tedious and uncertain molecular methods for finding target genes. Now, entire genomes are available for all model systems, and microarrays have been made or are under construction for most of them. Whole-genome methods will accelerate the discovery of target genes, provided that microarray strategies include careful selection of the mutants to be profiled, to avoid including candidate genes not related to mating-type function.