The Aspergillus nidulans transcription factor SclB governs the transition from vegetative to asexual development.

Asexual reproduction in filamentous fungi is a common, efficient, and fast differentiation process for producing large numbers of asexual spores (conidia), which can be distributed through the air to colonize new environments. The whole process is tightly controlled by specific regulatory proteins. Among the major regulators is the zinc cluster protein of SclB (sclerotia-like B), known to influence various aspects of asexual growth and secondary metabolism in Aspergillus nidulans as well as other filamentous fungi. Two different growth conditions of A. nidulans were compared to obtain a mechanistic overview of the role of SclB, mainly during the transition of the fungus from vegetative to asexual growth. Chromatin immunoprecipitation (IP) was coupled with next-generation sequencing (ChIP-seq) and combined with transcriptomic analyses (RNA-seq). SclB coordinates this developmental shift mainly by controlling the expression of genes encoding a few, however, prominent regulators of conidiation. These include the transcription factors BrlA, VelB, and SclB and the pheromone oxygenase PpoC. Association of SclB to promoter regions requires the newly identified putative SclB response element with a nine-base-pair DNA motif. Scl2 is the corresponding protein in the fungal plant pathogen Verticillium dahliae and partially complements the A. nidulans ΔsclB asexual deficiency. This supports a partial functional complementation of this regulator among different fungal species. In summary, SclB coordinates the transition from vegetative growth to asexual reproduction in A. nidulans through in vivo transcriptional control over genes coding for established players of conidia formation.IMPORTANCEFungi constantly adapt to environmental changes in their various habitats. Asexual spore formation allows for quickly leaving an unfriendly habitat through dispersal into the air. The asexual developmental program of fungi enables the production of a large number of spores in a short period of time and in an energetically efficient manner. The SclB transcription factor is a key regulator of asexual growth and secondary metabolism in numerous fungal species. The mechanism through which SclB orchestrates the transition of the filamentous fungus Aspergillus nidulans from vegetative to asexual growth was revealed. This regulator directly in vivo controls itself as well as the expression of master genes for the asexual program, such as brlA for transcriptional control or ppoC for pheromone production. This study enhances the molecular understanding of how fungal asexual differentiation is initiated and coordinated, which supports the development of better strategies to control fungal pathogens, improving human health, safety, and crop management.