MIP: Bacterial Endosymbionts of Phyllosphere Fungi:resolving the Endophyte/Saprophyte/Pathogen continuum on the Navajo Nation

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Fungal endophytes, fungi that live within plant tissues such as leaves without causing disease, occur in healthy plants from the Arctic to the tropics, and from agricultural fields to primary forests. Although long overlooked by biologists, endophytes are now being recognized for their tremendous diversity, their distribution across all lineages of land plants, and their ecological roles in mediating plant stress and antipathogen defense. Drawing from a collection of over 8000 previously unknown endophytes, this laboratory is showing that these harmless symbionts are part of a complex evolutionary continuum that features frequent and repeated evolutionary transitions (1) between pathogenic and endophytic lifestyles, and (2) from endophytic to saprotrophic lifestyles. These observations raise the question: what are the genetic, ecological, and evolutionary factors that permit such frequent and repeated switching among distinctive ecological modes in fungi? The proposed study will test the general hypothesis that newly discovered bacterial endosymbionts living within plant-associated fungi play a significant and previously overlooked role in driving the "switching" of their fungal hosts, and thus are key to understanding the ecological modes of the fungi they inhabit. This study will combine field surveys, phylogenetic analyses, and experiments to examine the incidence, diversity, host affinity, evolutionary relationships, and ecological importance of bacterial endosymbionts associated with fungal endophytes, saprotrophs, and pathogens in the Chuska Mountains, a biotically rich but understudied area in northeastern Arizona. Much of this work will be carried out on the Navajo Nation with on-reservation research training for Navajo undergraduates at Dine College. The intellectual merit of this work lies in determining which cryptic bacterial endosymbionts drive the phenotypes of diverse fungi, which in turn are important in both the ecology and evolution of the plants they inhabit. Broader impacts include (1) curriculum development at a Native American tribal college, (2) support for mentored research by up to 30 undergraduates, including 18 Navajo students and (3) support for two female Ph.D. students in fungal and bacterial ecology, evolution, and taxonomy.