Aspergillus nidulans has three high mobility group box (HMGB) proteins, HmbA, HmbB and HmbC that are chromatin-associated architectural proteins involved in DNA-related functions. By creating and studying deletion strains in both veA + and veA1 background, we have characterized the role of HmbA, HmbB and HmbC in sexual development. Expression of the mating-type MAT1-1 and MAT1-2 coding genes were found to be extremely down-regulated in all three mutants on day 4 of sexual development, which results in deficient ascospore production and/or ascospore viability in the mutants. In addition, we found that HmbA and HmbB play also a role in sensing of and response to environmental signals, while HmbC functionally interacts with VeA, a key regulator of the coordination of asexual and sexual development, as well as of secondary metabolism.

Aspergillus nidulans produces sterigmatocystin, a secondary metabolite mycotoxin, for the protection of its reproductive structures. Previous studies on grazing behavior of fungivore arthropods, regulation of sexual development, and secondary metabolite biosynthesis have revealed the association of sterigmatocystin biosynthesis with sexual reproduction, but the spatial distribution of sterigmatocystin producing hyphae within the colony has never been investigated. In this work, we aimed to locate the site of sterigmatocystin production within the colony by employing a yCFP reporter system. We demonstrated that the stcO promoter is active only in vegetative hyphae that surround groups of hülle cells and the activity decreases and eventually ceases as the distance between the hypha and the hülle cells increases. This phenomenon indicates that the vegetative mycelium might consist of morphologically uniform, but functionally different hyphae.

No abstract