** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** UNDERSTANDING HOW HOST ORGANISMS AND THEIR RESIDENT MICROBIAL COMMUNITIES INTERACT IS A CENTRAL CHALLENGE IN BIOLOGY, WITH BROAD IMPLICATIONS RANGING FROM AGRICULTURE TO HUMAN HEALTH. A PRIMARY QUESTION IS WHAT FACTORS AND MECHANISMS SHAPE THE COMPOSITION OF MICROBIAL COMMUNITIES. A RELATED ISSUE IS WHETHER AND HOW THE STRUCTURE OF MICROBIAL COMMUNITIES AFFECTS THE HOST. THIS PROJECT ADDRESSES THESE TWO QUESTIONS BY FOCUSING ON HOW DISTINCT ENVIRONMENTAL FACTORS, IN COMBINATION WITH HOST GENETIC VARIATION, SHAPE THE COMPOSITION AND FUNCTIONAL INFLUENCE OF MICROBIAL COMMUNITIES. THE WORK WILL TAKE ADVANTAGE OF AN ESTABLISHED, HIGHLY ACCESSIBLE PLANT-FUNGAL SYMBIOSIS IN POPULUS, IN WHICH LEAF ENDOPHYTES ARE KNOWN TO CONFER DISEASE PROTECTION. A COMPLEMENTARY EDUCATIONAL PROGRAM WILL ENRICH AND BROADEN THE RESEARCH THROUGH STUDENT-LED WORK INVESTIGATING SEASONAL VARIATION IN THE DRIVERS OF ENDOPHYTE COMMUNITY STRUCTURE IN COMMON GARDENS AND IN GREENHOUSE EXPERIMENTS. OVERALL, THIS CAREERPROJECT WILL DEEPEN OUR UNDERSTANDING OF HOW ENVIRONMENT AND GENOTYPE AFFECT ENDOPHYTE COMMUNITIES AND DISEASE PROTECTION IN PLANTS, WHILE PROMOTING DIVERSITY IN A STEM FIELD AND CONTRIBUTING TO CONSERVATION AND CROP PRODUCTION IN THE FACE OF CLIMATE CHANGE.