ABSTRACTAspergillus flavusis an opportunistic fungal plant and human pathogen and a producer of mycotoxins, including aflatoxin B1(AFB1). As part of our ongoing studies to elucidate the biological functions of theA. flavusrtfAgene, we examined its role in the pathogenicity of both plant and animal model systems.rtfAencodes a putative RNA polymerase II (Pol II) transcription elongation factor previously characterized inSaccharomyces cerevisiae,Aspergillus nidulans, andAspergillus fumigatus, where it was shown to regulate several important cellular processes, including morphogenesis and secondary metabolism. In addition, an initial study inA. flavusindicated thatrtfAalso influences development and production of AFB1; however, its effect on virulence is unknown. The current study reveals that thertfAgene is indispensable for normal pathogenicity in plants when using peanut seed as an infection model, as well as in animals, as shown in theGalleria mellonellainfection model. Interestingly,rtfApositively regulates several processes known to be necessary for successful fungal invasion and colonization of host tissue, such as adhesion to surfaces, protease and lipase activity, cell wall composition and integrity, and tolerance to oxidative stress. In addition, metabolomic analysis revealed thatA. flavusrtfAaffects the production of several secondary metabolites, including AFB1, aflatrem, leporins, aspirochlorine, ditryptophenaline, and aflavinines, supporting a role ofrtfAas a global regulator of secondary metabolism. Heterologous complementation of anA. flavusrtfAdeletion strain withrtfAhomologs fromA. nidulansorS. cerevisiaefully rescued the wild-type phenotype, indicating that thesertfAhomologs are functionally conserved among these three species.IMPORTANCEIn this study, the epigenetic global regulatorrtfA, which encodes a putative RNA-Pol II transcription elongation factor-like protein, was characterized in the mycotoxigenic and opportunistic pathogenA. flavus. Specifically, its involvement inA. flavuspathogenesis in plant and animal models was studied. Here, we show thatrtfApositively regulatesA. flavusvirulence in both models. Furthermore,rtfA-dependent effects on factors necessary for successful invasion and colonization of host tissue byA. flavuswere also assessed. Our study indicates thatrtfAplays a role inA. flavusadherence to surfaces, hydrolytic activity, normal cell wall formation, and response to oxidative stress. This study also revealed a profound effect ofrtfAon the metabolome ofA. flavus, including the production of potent mycotoxins.
Calcium- and hormone-driven regulation of secondary metabolism and cell wall enzymes in grape berry cells
