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

Abstract

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 those major regulators is the zinc-finger domain 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 for the role of SclB, mainly during the transition of the fungus from vegetative to asexual growth. Chromatin immunoprecipitation 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 for few, however, prominent regulators of conidiation. They include the transcription factors BrlA, VelB and SclB and the pheromone oxygenase PpoC. Association of SclB to promoter regions requires the newly identified SclB response element (SRE) with a nine base-pair DNA motif. Scl2 is the corresponding protein in the fungal plant pathogen Verticillium dahliae and partially complements the {Delta}sclB A. nidulans asexual deficiency. This supports a conserved function of this regulator among different fungal species. In summary, SclB coordinates 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 to quickly leave an unfriendly habitat through dispersal into the air. The asexual developmental program of fungi ensures large number of spores, in a short period of time and in energetically efficient manner. 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 Aspergillus nidulans filamentous fungus from the vegetative to the asexual growth was revealed. This regulator directly controls in vivo itself as well as 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, 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.