Abstract Invasive infections due to Aspergillus fumigatus are increasing and are still associated with unacceptably high mortality, even with new therapies. Our understanding of A. fumigatus infection biology is limited. Among 10,180 predicted genes in the A. fumigatus genome, over 95% are uncharacterized, and fewer than 100 genes have demonstrated roles in virulence. It is critical to identify genes that govern virulence and the pathways in which they act because they can point to high priority targets for therapeutic and diagnostic development. We have identified a transcriptional regulator in A. fumigatus, WrpA, that shares limited homology with Candida albicans Wor1 and Histoplasma capsulatum Ryp1. Our preliminary data indicate that WrpA governs the capacity of A. fumigatus to withstand macrophage killing, grow under hypoxic conditions, and invade and damage pulmonary cells in vitro. ΔwrpA deletion mutants have highly attenuated virulence in the mouse model of invasive aspergillosis. Using RNA-seq, we found that WrpA governs the expression of ~15% of genes in the A. fumigatus genome, including multiple transcription factor genes. Our premise is that the WrpA is a master regulator that governs host cell interactions and virulence. In support of this premise, our initial investigations of the WrpA regulon have already revealed novel pathogenicity-related functions of three WrpA-dependent transcription factors, SrbB, Fcr1, and Ndt80. Our goal is to characterize the WrpA regulon in A. fumigatus and to identify downstream effector genes whose products mediate pathogenicity by: 1) identifying the transcription factors that are directly regulated by WrpA and determining their roles in pathogenicity; 2) analyzing selected WrpA- dependent transcription factors and identifying their downstream target genes; and 3) determining the function of effector genes controlled by the WrpA regulon and investigating their roles in virulence. The results of the experiments described in this proposal will enable us to characterize a key transcriptional regulator that governs A. fumigatus pathogenicity and then use this information to identify downstream effector genes, the products of which mediate host cell interactions and virulence. The results of this work will not only provide foundational understanding of A. fumigatus virulence mechanisms, but also hold promise to identify new diagnostic, therapeutic, and vaccine targets.