Sexual development and cryptic sexuality in fungi: insights fromAspergillusspecies

Abstract

Major insights into sexual development and cryptic sexuality within filamentous fungi have been gained from investigations using Aspergillus species. Here, an overview is first given into sexual morphogenesis in the aspergilli, describing the different types of sexual structures formed and how their production is influenced by a variety of environmental and nutritional factors. It is argued that the formation of cleistothecia and accessory tissues, such as Hülle cells and sclerotia, should be viewed as two independent but co-ordinated developmental pathways. Next, a comprehensive survey of over 75 genes associated with sexual reproduction in the aspergilli is presented, including genes relating to mating and the development of cleistothecia, sclerotia and ascospores. Most of these genes have been identified from studies involving the homothallic Aspergillus nidulans, but an increasing number of studies have now in addition characterized 'sex-related' genes from the heterothallic species Aspergillus fumigatus and Aspergillus flavus. A schematic developmental genetic network is proposed showing the inter-relatedness between these genes. Finally, the discovery of sexual reproduction in certain Aspergillus species that were formerly considered to be strictly asexual is reviewed, and the importance of these findings for cryptic sexuality in the aspergilli as a whole is discussed.

Sexual reproduction and mating-type–mediated strain development in the penicillin-producing fungus Penicillium chrysogenum

“…Sex in P. chrysogenum could be induced on oatmeal agar as reported recently for other supposedly "asexual" Aspergillus and Penicillium species (18,20,36,37). However, it was necessary to supplement the agar with biotin to achieve complete sexual development, and similar supplementation might be required for other sexually recalcitrant species (17,18). Even with biotin supplementation, not all of the crosses tested generated cleistothecia with ascospores, suggesting that P. chrysogenum is composed of isolates on a continuum of sexual fertility, rather than being purely sexual or asexual, as suggested by the "slow decline" hypothesis (38).…”

“…Recent findings suggest that sexual reproduction can be triggered in supposedly asexual fungi (13)(14)(15)(16) if the correct growth conditions are identified (17,18). The principle aim of the current study was therefore to determine whether a functional sexual cycle could be induced in P. chrysogenum, using knowledge of MAT gene organization in the species to set up directed crosses between known MAT1-1 and MAT1-2 isolates, and if the sexual cycle could be used for strain development purposes.…”

Genome survey uncovers the secrets of sex and lifestyle in caterpillar fungus

“…phi-base.org/about.php) with a cut-off E value of 1×10 -5 . Fungal sex-related genes that have been functionally verified in the model ascomycetes Aspergillus nidulans and Neurospora crassa [20] were used for blastp search against the genomes of O. sinensis and other insect pathogens to retrieve the respective homologs. To identify the gene clusters and their proteins responsible for the biosynthesis of secondary metabolites, the whole genome dataset was subject to analyses with the programs antiSMASH [21] and SMURF [22].…”

Investigating Aspergillus nidulans secretome during colonisation of cork cell walls

“…It is well-known that ascospores, which are more resistant than conidia, are usually formed in adverse growth conditions [58]. Thus, most likely, sexual development was triggered in A. nidulans due to the increasing recalcitrance of cork along the twenty-one days of colonisation.…”