Sexual and vegetative compatibility genes in the aspergilli

Abstract

Gene flow within populations can occur by sexual and/or parasexual means. Analyses of experimental and in silico work are presented relevant to possible gene flow within the aspergilli. First, the discovery of mating-type (MAT) genes within certain species of Aspergillus is described. The implications for self-fertility, sexuality in supposedly asexual species and possible uses as phylogenetic markers are discussed. Second, the results of data mining for heterokaryon incompatibility (het) and programmed cell death (PCD) related genes in the genomes of two heterokaryon incompatible isolates of the asexual species Aspergillus niger are reported. Het-genes regulate the formation of anastomoses and heterokaryons, may protect resources and prevent the spread of infectious genetic elements. Depending on the het locus involved, hetero-allelism is not tolerated and fusion of genetically different individuals leads to growth inhibition or cell death. The high natural level of heterokaryon incompatibility in A. niger blocks parasexual analysis of the het-genes involved, but in silico experiments in the sequenced genomes allow us to identify putative het-genes. Homologous sequences to known het- and PCD-genes were compared between different sexual and asexual species including different Aspergillus species, Sordariales and the yeast Saccharomyces cerevisiae. Both het- and PCD-genes were well conserved in A. niger. However some point mutations and other small differences between the het-genes in the two A. niger isolates examined may hint to functions in heterokaryon incompatibility reactions.

Polyphasic characterization of “Aspergillus nidulans var. roseus” ATCC 58397

“…roseus, are the consequence of gene exchanges during the parasexual hybridization of different closely related Aspergillus species. Detailed analysis of the observed interspecific heterokaryon formation can also help to elucidate the regulation of vegetative (in)compatibility in the aspergilli (Pál et al 2007). …”

Population structure and diversity of the pathogenic fungus Aspergillus fumigatus isolated from different sources and geographic origins

“…This structure could be by natural selection, as suggested by the observed recombinant reproductive structure and revealed by the I A estimated in each isolate group, where all I A values were found to be approximately zero (Table III). It was previously thought that the variability seen in A. fumigatus could be attributed to the possibility of parasexual genetic recombinations (Pál et al 2007). However, these are infrequent and are limited to isolates within the same vegetative compatibility group.…”

The use of vegetative compatibility tests for identification of biodiversity of phytopathogenic fungi

“…Finding an appropriate partner for mitotic recombination is a crucial aspect of the parasexual cycle, similar to the sexual mating process (Pál et al, 2007). When two haploid mycelia of different genotypes are fused, a mycelium with two nuclear types is formed; in this mycelium, two haploid strains coexist and divide mitotically within the common cytoplasm.…”

“…After fusion, cell death may be associated with suppressor (sup) genes, which can modify the signal. In the final step of the parasexual cycle of fungi, programmed cell death genes initiate processes leading to apoptosis (Pál et al, 2007).…”