** AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PHYTOPHTHORA PALMIVORA IS A FUNGUS-LIKE EUKARYOTIC MICROORGANISM THAT CAUSES DEVASTATING DISEASES OF NUMEROUS AGRICULTURALLY AND ECOLOGICALLY IMPORTANT PLANTS, INCLUDING CACAO, A TROPICAL PERENNIAL TREE THAT PRODUCES THE MAJOR COMPONENT OF THE MULTIBILLION-DOLLAR CHOCOLATE INDUSTRY. THE ANNUAL GLOBAL LOSS ON CACAO DUE TO DISEASES CAUSED BY P. PALMIVORA IS AT LEAST ONE BILLION U.S. DOLLARS. AS A VERY AGGRESSIVE PATHOGEN, P. PALMIVORA IS OFTEN CAPABLE OF INFECTING ALMOST ALL PLANT PARTS OF A HOST, RENDERING ITS CONTROL EXTREMELY CHALLENGING. AS A RESULT, IT HAS BECOME AN INCREASING THREAT TO AGRICULTURAL PRODUCTION AND ECOSYSTEMS. DISEASES CAUSED BY P. PALMIVORA ARE MANAGED BY FREQUENT APPLICATION OF FUNGICIDES WITH LIMITED SUCCESS. IN ADDITION TO HAVING A BROAD HOST RANGE, P. PALMIVORA ISOLATES EXHIBIT HOST SPECIFICITY, MEANING THAT DIFFERENT ISOLATES INFECT A DIFFERENT SUBSET OF PLANT SPECIES. LACK OF UNDERSTANDING OF THE MECHANISMS OF ITS BROAD-RANGE AND HOST-SPECIFIC PATHOGENICITY HAS IMPEDED THE DEVELOPMENT OF NOVEL MECHANISM-BASED CONTROL STRATEGIES. SIMILAR TO OTHER PLANT PATHOGENS, DURING INFECTION P. PALMIVORA DELIVERS A DIVERSE ARRAY OF PROTEINS INSIDE THE PLANT CELLS TO MANIPULATE THE HOST CELLULAR PROCESSES TO FACILITATE INFECTION. ABUNDANT EXPERIMENTAL EVIDENCE SUGGESTS THAT THESE PATHOGEN-DELIVERED PROTEINS DETERMINE THE CAPABILITY OF THEPATHOGEN TO INFECT CERTAIN PLANT SPECIES.THE LONG-TERM GOAL OF THIS PROJECT IS TO DEVELOP NOVEL, EFFECTIVE AND ENVIRONMENTALLY FRIENDLY STRATEGIES TO CONTROL P. PALMIVORA BASED ON THE FUNDAMENTAL UNDERSTANDINGS OF ITS INFECTION MECHANISMS. TO THIS END, A PROTEIN DESIGNATED AS PPALRXLR1 WAS IDENTIFIED AS A KEY PATHOGENICITY FACTOR ESSENTIAL FOR P. PALMIVORA TO INFECT CACAO. VERY INTERESTINGLY, PPALRXLR1 WAS FOUND TO BE PRESENT IN P. PALMIVORA ISOLATES FROM SOME HOST PLANTS AND ABSENT IN OTHERS, SUGGESTING THAT IT PLAYS A ROLE IN HOST RANGE EVOLUTION. THIS PROJECT WILL: 1) DETERMINE THE MOLECULAR MECHANISM BY WHICH PPALRXLR1 CONFERS PATHOGENICITY BY IDENTIFYING ITS HOST TARGETS AND THE HOST PROCESSES IT MODULATES, 2) IDENTIFY THE ROLES OF PPALRXLR1 IN HOST RANGE DETERMINATION AND EVOLUTION BY ANALYZING ITS EVOLUTION RELATIVE TO THE SPECIES AND ASSOCIATION WITH HOST RANGE, AND 3) IDENTIFY ADDITIONAL PATHOGEN PROTEINS WITH KEY ROLES IN PATHOGENICITY OF P. PALMIVORA ON SPECIFIC OR A BROAD RANGE OF HOSTS USING THE NATURAL VARIATION OF P. PALMIVORA ISOLATES. THIS PROJECT IS EXPECTED TO GENERATE SIGNIFICANT FOUNDATIONAL KNOWLEDGE ESSENTIAL FOR DEVELOPING DESIRABLE DISEASE CONTROL MEASURES, THEREFORE SIGNIFICANTLY CONTRIBUTING TO FOOD SECURITY AND SUSTAINABILITY OF NATURAL ECOSYSTEMS. IN ADDITION, THE PROJECT WILL CONTRIBUTE TO STEM WORKFORCE SUSTAINABILITY BY PROVIDING TRAINING OPPORTUNITIES TO GRADUATE, UNDERGRADUATE AND HIGH SCHOOL STUDENTS, AND INTRODUCING PLANT PATHOLOGY AND GENE-EDITING TECHNOLOGY TO MIDDLE/HIGH-SCHOOL TEACHERS TO ATTRACT A NEW GENERATION INTO AGRICULTURE AND LIFE SCIENCES.