The metabolic flexibility of fungi has allowed them to adapt to diverse environments. One source of this flexibility is the cytochrome P450 monoxygenases used to detoxify xenobiotic compounds. Filamentous fungi possess a large family of cytochrome P450-encoding (CYP) genes that are absent in the model yeasts. A particularly large number of CYP genes present in plant-pathogenic fungi may reflect a diversification required to counteract plant defense compounds. Since detoxification-associated CYP genes are not usually expressed until the xenobiotic compound is present, regulatory mechanisms would also need to evolve in these fungi. What signaling pathways allow fungi to recognize and respond to specific xenobiotic compounds? In animals, detoxification-associated CYP genes are regulated by nuclear receptors, proteins that both bind the inducing xenobiotic compound and directly induce gene transcription. Fungi lack the nuclear receptor gene families so highly conserved among animals. In order to study the signaling used in fungi, this project focuses upon a well-characterized CYP gene (PDA1) in the plant pathogen Fusarium solani. The PDA1 product detoxifies a fungistatic isoflavonoid defense compound, pisatin, specifically produced by the host plant. A transcriptional regulator of PDA1 has been identified that mediates pisatin induction. The research will determine if this regulator acts either through a mechanism where it directly binds pisatin, or through a broader recognition of the physiological stress imposed by this defense compound. Testing for physical interactions between the transcriptional regulator and pisatin or with other cellular proteins will be used distinguish between these modes of action and indicate signaling pathways involved. The results will provide a model for how an organism develops or recruits regulatory circuits that function to chemically perceive other organisms in such co-evolving systems. Understanding the molecular mechanisms that control xenobiotic signaling in plant pathogenic fungi will have broader societal impact in the potential control of plant disease. The results may lead to novel strategies that interfere with the signaling that regulates resistance to natural defense compounds, and possibly to synthetic fungicides as well. The research also strengthens the ability of the P.I. to integrate research and teaching on a campus that provides education for minority students, and to incorporate undergraduates and high school students into research.
