Heterotrimeric G Proteins
Heterotrimeric (αβγ) G proteins control major signal transduction pathways in eukaryotes. Their importance is underscored by the fact that more than 30% of pharmaceutical drugs target G protein signaling pathways. My laboratory discovered heterotrimeric G proteins in filamentous fungi, using the model organism Neurospora crassa. My group has now characterized the myriad functions and physical interactions between three Gα, one Gβ and one Gγ proteins in Neurospora. Since our original discovery, Gα proteins have been implicated in pathogenesis in numerous plant and animal fungal pathogens. Therefore, our work is relevant to development of new infection control practices and identification of targets for chemical agents to combat fungal diseases in plants and animals.
Functional Genomics and Systems Biology of Fungi
Neurospora is the NIH model organism for the filamentous fungi, the group of organisms most closely related to animals and which includes important pathogens of animals and plants. I was heavily involved in the effort to sequence and annotate the Neurospora genome. My laboratory was a major player in the genome-wide targeted gene replacement project that successfully mutated nearly all of the nearly 10,000 genes. We have also completed large-scale analysis of mutants for Neurospora serine/threonine protein phosphatase and kinase genes, transcription factors and G protein coupled receptors. Notably, much of the functional analysis of these large gene families has been performed by undergraduate students in the capstone course for the Microbiology major, Experimental Microbiology (MCBL125).
Members of the Fusarium oxysporum species complex are root pathogens of numerous crops of economic importance to the United States. Certain subspecies are also opportunistic human pathogens. My group annotated signaling genes in the genome of F. oxysporum f.sp. lycopersici, a fungal pathogen of tomato and animals. Production of small RNAs that target and down-regulate specific genes has been associated with infection by microorganisms in other plants. We have used next generation sequencing to identify small RNAs from F. oxsporum and tomato that are associated with the disease state. Our results revealed two microRNAs that are differentially regulated in resistant (Motelle) and susceptible (Moneymaker) lines of tomato. We identified four mRNA targets of these microRNAs and showed that these targets are required for resistance to F. oxysporum and encode proteins with nucleotide-binding domains found on other plant resistance (R) proteins. The observation that none of the targets correspond to I-2, the only known R gene for F. oxysporum in tomato, supports roles for additional R genes in the immune response. We are continuing our studies in F. oxysporum, using small RNA and functional approaches.