Sexual Reproduction and Significance ofMATin the Aspergilli

Abstract

The genus Aspergillus comprises over 180 species that are united by the presence of the “aspergillum,” which consists of a specialized, enlargened conidiophore bearing phialides and characteristic radiating asexual conidia. Of particular relevance to this chapter is the repeated failure to detect the presence of trichogynes or differentiated ascogonia and antheridia in this homothallic species. It has been noted that overexpression of the MAT genes does not result in increased expression of either the pheromone precursor gene ppgA or the pheromone receptor genes preA(gprB) and preB(gprB). It has been suggested that MAT gene expression might be involved in recognition of compatible MAT1 and MAT2 nuclei in heterothallic species. Hulle cells are also formed by three species of “asexual” aspergilli and single mating types of E. heterothallicus, which fail to form fertile cleistothecia. Paoletti and coworkers used RT-PCR to monitor expression of pheromone precursor (ppgA), pheromone receptor (preA and preB), and mating-type (MAT-1 and MAT-2) genes from A. fumigatus during growth on media, under conditions known to induce sexual reproduction in E. nidulans. It is intriguing to note that transposase genes have been found upstream of MAT loci in certain Aspergillus species, which might help to explain the particular ability of the aspergilli to evolve different breeding systems. A long-term goal is now to manipulate the life cycles of medically, economically, and scientifically important species of Aspergillus for the benefit of all.