BUILDING A FITNESS PROFILE FOR NEUROSPORA CRASSA
Linda Ma, Boya Song, Marcus Roper.
University of California, Los Angeles, Los Angeles, CA.
Filamentous fungi such as Neurospora crassa are capable of proliferating indefinitely. Their growth is limited only by space and resources. Armillaria solidipes, also known as the humongous fungus, is considered the world’s largest living organism, covering 2,385 acres of Oregon’s Malheur National Park. However, should the edge of this fungus be considered to be the same individual as its center? Each fungus contains millions of totipotent, genetically diverse, and potentially selfish nuclei. Interactions between nuclei are mapped by removing single nuclei from the colony and measuring their fitness against wild type. To build a fitness profile with N. crassa, we seek to determine whether competitive interactions exist between nuclei, and how these impact the overall fitness of the fungus. Further, we seek to learn the role that spore size and germination rate play in fitness and growth rate. We measure fitness changes with colony size by isolating single GFP-tagged spores from different parts of a 30 cm-long colony. By confronting individual GFP-tagged spores with wild-type DsRed-tagged spores we can measure fitness changes during growth. Spores isolated from the first few centimeters of the colony outcompete the wild-type, but spores from the end are outcompeted by wild-type. Our preliminary data suggest that initial proliferation favors the fastest growing nuclei, but that over time, and despite intense competition between nuclei, deleterious mutations are accumulated and start to reduce overall nuclear fitness within the mycelium. That fungal growth rate itself is not affected suggests that cellular mechanisms exist to prevent tragedies of the common between these competitive nuclei.