Project description:Boreal toads (Anaxyrus boreas boreas) of the Southern Rocky Mountain population are declining due to the introduction of the chytrid fungus Batrachochytrium dendrobatidis (Bd). Boreal toads in Colorado are generally susceptible to Bd infection, but some Bd-tolerant populations persist in parts of the Southern Rocky Mountain and broader Eastern boreal toad population. We conducted a Bd challenge with lab-reared sibling toads from Bd-susceptible Colorado and purportedly Bd-tolerant Utah populations and report on transcriptomic responses to Bd during late infection in skin and liver tissue. Fewer immune genes were expressed in response to Bd in Colorado toads, but with greater upregulation compared to Utah toads, indicating a dysregulated immune response. Signatures of Bd-tolerance in Utah toads included more moderate upregulation in immune gene expression and a significantly enriched suite of gene functions related to innate and adaptive immune responses. Our transcriptomic results support the notion that Utah toads are tolerant to Bd, rather than resistant, carrying Bd loads similar to Colorado yet having a unique transcriptomic profile and presenting minimal clinical signs of chytridiomycosis. We conclude that closely related populations have divergent transcriptomic responses to Bd with a dysregulated immune response in Bd-susceptible toads.
Project description:Strains of R. rickettsii, the agent of Rocky Mountain spotted fever, differ greatly in the severity of the disease caused. The genetic differences responsible for this disparity are only now being uncovered. An avirulent, laboratory adapted strain of R. rickettsii fails to proteolytically process several large surface protein antigens. We have identified a protease that cleaves the protein precursors to their mature form. The gene encoding this protease is mutated in the avirulent strain. Complementation of the active form of the gene identifies proteolytic processing of surface antigens as important to virulence.
