**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** PLANTS AND PATHOGENS ARE IN AN ONGOING CO-EVOLUTIONARY ARMS RACE. THE OUTCOME OF THIS STRUGGLE IS OF SOCIETAL IMPORTANCE BECAUSE PLANTS THAT CAN RESIST MICROBIAL INFECTION WILL IMPROVE FOOD SECURITY, BOTH DOMESTICALLY AND GLOBALLY. THUS, UNDERSTANDING HOW PATHOGENS INTERACT WITH HOST MACHINERY TO CAUSE DISEASE IS CRITICAL FOR IMPROVING PLANT BREEDING EFFORTS. MANY PLANT AND ANIMAL PATHOGENS HAVE EVOLVED TO SECRETE MOLECULES THAT RESEMBLE THOSE FOUND IN THEIR HOST THROUGH A PHENOMENON CALLED MOLECULAR MIMICRY. THERE ARE MANY EXAMPLES OF PLANT PATHOGENS THAT USE MOLECULAR MIMICRY TO ENHANCE VIRULENCE AND CAUSE DISEASE. FOR EXAMPLE, THE CAUSAL AGENT OF RICE BACTERIAL BLIGHTXANTHOMONAS ORYZAEPV.ORYZAE(XOO) USES A PLANT PEPTIDE HORMONE MIMIC, RAXX, TO FACILITATE INFECTION. MANY RICE VARIETIES ARE HIGHLY SUSCEPTIBLE TOXOOAND THIS DISEASE CAN ACCOUNT FOR UP TO 50% CROP YIELD LOSS. HOWEVER, SOME RICE VARIETIES CONTAIN THE IMMUNE RECEPTOR XA21 WHICH CAN RECOGNIZE THEXOO-SECRETED RAXX PEPTIDE TO ACTIVATE DEFENSE RESPONSES. INTERESTINGLY, THE RAXX PEPTIDE IS HIGHLY SIMILAR IN SEQUENCE TO THE PSY PLANT PEPTIDES, WHICH ARE PRESENT IN VIRTUALLY ALL CROP PLANTS AND ARE PREDICTED TO BE INVOLVED IN VARIOUS PHYSIOLOGICAL PROCESSES SUCH AS GROWTH AND DEFENSE. BASED ON THESE RESULTS, I HYPOTHESIZE THAT THEXOO-SECRETED RAXX PEPTIDE AND THE PSY PLANT PEPTIDE BIND TO THE SAME TARGET: THE PSY RECEPTOR.THROUGH THE SUPPORT OF THE USDA AFRI-NIFA POSTDOCTORAL FELLOWSHIP, I AM PROPOSING A COMBINED BIOCHEMICAL AND GENETICS APPROACH TO ELUCIDATE THE ROLE OF THE SMALL PEPTIDE RAXX IN TRIGGERING RICE IMMUNITY AND FACILITATING SUSCEPTIBILITY.THE OVERALL GOAL OF THIS RESEARCH PROJECT IS TO BETTER UNDERSTAND HOW PLANTS PERCEIVE PLANT (PSY) AND MICROBE (RAXX) DERIVED PEPTIDES, WITH THE END GOAL OF IMPROVING RICE DISEASE RESISTANCE. THE PROPOSED RESEARCH PROJECT AIMS TO ADDRESS TWO MAJOR KNOWLEDGE GAPS IN THEXOO-RICE PATHOSYSTEM IN RELATION TO RAXX RECOGNITION. THROUGH THIS RESEARCH FELLOWSHIP, I SEEK TO: (1) UNDERSTAND HOW RICE RECOGNIZES THEXOO-SECRETED RAXX PEPTIDE TO INITIATE DEFENSE RESPONSES AND (2) HOWXOOIS HIJACKING THE PSY PEPTIDE HORMONE SIGNALING PATHWAY TO CAUSE DISEASE. RESULTS FROM THIS WORK WILL ALLOW US TO IMPROVE BREEDING EFFORTS TO CREATE DISEASE RESISTANT CROPS BY PROVIDING NEW STRATEGIES TO ENGINEER PLANT RECEPTORS, EXPANDING DISEASE RESISTANCE OPTIONS AVAILABLE TO BREEDERS.