Fungi are of great importance to humankind as pathogens, environmental recyclers, industrial producers, and agricultural aids. A large number of fungi produce spores as the main means of dissemination and survival. Spores are also the primary agent for infecting hosts for many pathogenic fungi. Moreover, in some fungi spore formation is intimately related with production of toxic secondary metabolites called mycotoxins that cause adverse health effects to humans, animals and plants. Despite its fundamental importance in both basic and applied aspects, the mechanism underlying spore formation in molds is largely unknown. This project investigates functions of two newly identified velvet genes that play a key role in regulating sporulation and production of mycotoxins in molds. These two velvet genes are hypothesized to control expression of other genes associated with spore and toxin formation via binding to DNA and acting as transcriptional regulators. This project employs recently developed genetic and molecular tools that facilitate the understanding of gene function in fungi. Expected results include better understanding the functions of these novel regulators, identification of groups of genes that are controlled by the two genes, and defining the genetic networks regulating spore formation and toxin production in molds. Understanding the mechanisms governing sporulation and secondary metabolism in molds will provide new insights into controlling both beneficial and detrimental activities of other industrially, medically, and agriculturally important fungi. In broader impacts, this project will provide opportunities to promote excellence in science education and rigorous training of graduate and undergraduate students in the disciplines of microbiology, genetics and genomics.
Fungi are of great importance to humankind as pathogens, environmental recyclers, industrial producers, and agricultural aids. A large number of fungi produce spores as the primary means of reproduction, cell survival, propagation and infectivity. Despite its fundamental importance for both basic and applied aspects of fungal biology, the mechanisms coupling these unique developmental processes were largely unknown. This project investigated functions of two newly identified fungi-specific regulators that play a key role in regulating sporulation and production of mycotoxins. With the NSF support, we found that in the model mold Aspergillus nidulans the main regulators of these processes are the so-called "velvet" proteins VeA, VelB, and VosA, which share a 150-amino acid region known as the velvet domain. Velvet proteins interact with each other, alone ("homodimers"), in various combinations ("heterodimers"), and also with other proteins. VosA plays a critical role in coupling sporogenesis with trehalose biogenesis, and exerts feed-back regulation of the key developmental activator brlA in Aspergillus nidulans. VosA predominantly interacts with another key velvet regulator VelB and they together activate trehalose biogenesis in conidia. However, in vegetative cells (hyphae), VelB mainly interacts with itself or VeA-LaeA, and the trimeric velvet complex coordinately regulates fungal development and secondary metabolism. These suggest that VosA and VelB may regulate common and distinct target genes during the lifecycle of the fungus. We have revealed that velvet proteins form a family of fungus-specific transcription factors that directly bind to target DNA, even though analysis of their amino acid sequence does not reveal any known DNA-binding domains or motifs. We determined the three-dimensional structure of the VosA-VosA homodimer and the VosA-VelB heterodimer and found that the structure of the velvet domain is very similar to the N-terminal immunoglobulin-like domain found in the mammalian transcription factor NFκB-p50, despite the very low sequence similarity. Our finding suggest that, like NFκB, various homo- or heterodimers of velvet proteins modulate gene expression to drive development and defensive pathways in fungi. In summary, the completion of this project has advanced the fundamental knowledge concerning fungal cellular and chemical development. The fungi-specific velvet regulators are conserved in many agriculturally and medically important fungi, yet their molecular function was largely unknown. Outcomes of this project has provided the mechanistic insights into the novel regulatory roles of the velvet proteins in fungal development, trehalose biogenesis and secondary metabolism. Moreover, the proposed studies further illuminated the global functions of VosA and VelB in controlling complex expression, cellular and metabolic responses in fungi. It is expected that the results of the proposed research would provide important clues for investigating the velvet regulators in key pathogenic fungi. This project has provided great opportunities to promote excellence in science education and research training. The haploid fungus A. nidulans served as an effective and accessible model system for teaching difficult genetic concepts to pre-college, undergraduate students and secondary teachers. At the same time, students have been exposed to the most up-to-date research results and techniques. Through this NSF supported project, one postdoc, two graduate students, and three undergraduate have been trained. In addition, outcomes of this project would have great positive impacts on human life. Fungal spores are found in every environment inhabited by humankind. For many pathogenic fungi, spores are the primary infection particle. The airborne fungal spores often contain allergens (and mycotoxins) to which certain people respond with strong hypersensitive reactions. As the velvet regulators’ functions in governing development and secondary metabolism are conserved in many fungi, the outcomes of our studies have provided new insights into controlling the propagation and infection of human, animal and plant pathogenic fungi.
