Conservation and Divergence in the Asexual Sporulation Gene Regulatory Network Across a Genus of Filamentous Fungi

Asexual sporulation is fundamental to the ecology and lifestyle of filamentous fungi and can facilitate both plant and human infection. InAspergillus, the production of asexual spores is primarily governed by the BrlA→AbaA→WetA regulatory cascade. The final step in this cascade is controlled by the WetA protein and not only governs the morphological differentiation of spores but also the production and deposition of diverse metabolites into spores. While WetA is conserved across the genusAspergillus, the structure and degree of conservation of thewetAgene regulatory network (GRN) remains largely unknown. We carried out comparative transcriptome analyses betweenwetAnull mutant and wild type asexual spores in three representative species spanning the diversity of the genusAspergillus:A. nidulans, A. flavus, andA. fumigatus. We discovered that WetA regulates asexual sporulation in all three species via a negative feedback loop that represses BrlA, the cascade’s first step. Furthermore, ChIP-seq experiments inA. nidulansasexual spores suggest that WetA is a DNA-binding protein that interacts with a novel regulatory motif. Several global regulators known to bridge spore production and the production of secondary metabolites show species-specific regulatory patterns in our data. These results suggest that the BrlA→AbaA→WetA cascade’s regulatory role in cellular and chemical asexual spore development is functionally conserved, but that thewetA-associated GRN has diverged duringAspergillusevolution.