DISSERTATION RESEARCH: Mechanisms of host preference in the ectomycorrhizal symbiosis

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Although mutually beneficial interactions are important in many natural systems, it remains unclear why some involve highly specialized partners, while others do not. This project investigates how different degrees of specificity have evolved and function in a particular type of symbiosis - a mutualistic relationship between a fungus and many temperate forest plants. This research will combine a fungus with multiple, distantly related host plants to investigate how the fungus alters its symbiotic behavior when interacting with different species of plants. This experiment will generate insight into symbiotic plant-microbe communication in this important mutualism, and will allow for comparison to similar systems in pathogens. Outreach to science enrichment programs for urban youth in San Francisco will also occur.This study will use RNA sequencing to determine the genetic basis of generalist host preference in the ectomycorrhizal fungus Thelephora terrestris. Six plant species from four families will be established in microcosms and inoculated with spores from Thelephora terrestris. At symbiotic maturity, microcosms will be labeled with carbon-13 and nitrogen-15 and plant, fungal, and symbiotic tissues will be harvested for isotope analysis and RNA sequencing. Transcriptional data will be combined with stable isotope enrichment measurements of plant and fungal resource allocation and compared across different plant-fungus combinations. Measuring gene expression in symbiotic tissues while simultaneously tracking resource allocation will reveal which genes are associated with improved symbiotic performance, providing a powerful link between gene transcription, physiological function, and the stability of mutualistic interactions.