**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** BACTERIAL PANICLE BLIGHT IS A MAJOR RICE DISEASE WORLWIDE INCLUDING THE SOUTHEASTERN UNITED STATES, WHICH IS CAUSED BY THE BACTERIAL PATHOGENBURKHOLDERIA GLUMAE.THE QUORUM SENSING (QS) SYSTEM MEDIATED BY THE TOFI/TOFR QSHAS BEEN KNOWN TO BE AN ESSENTIAL REGULATORY ELEMENT OF B. GLUMAE FOR VIRULENCE. HOWEVER, OUR RECENT STUDIES WITH TWO DIFFERENT VIRULENT STRAINS AND ONE NATURALLY AVIRULENT STRAIN REVEALED THAT QSMR, ENCODING AN ICLR-FAMILY PROTEIN, IS A KEY REGULATORY FACTOR FOR THE VIRULENCE OF B. GLUMAE. THIS GENE GOVERNS BOTH TOFI/TOFR QS-DEPENDENT AND -INDEPENDENT REGULATORY PATHWAYS ACROSS MULTIPLE STRAINS OF B. GLUMAE. THUS, WE CONSIDER QSMR (RATHER THAN TOFI/TOFR QS) AS AN IDEAL TARGET TO MANAGE B. GLUMAE. THE MAIN GOAL OF THIS PROJECT IS TO UNDERSTAND HOW QSMR FUNCTIONS AS A KEY REGULATOR FOR THE PATHOGENIC BEHAVIORS OF B. GLUMAE. WE WILL STUDY QSMR WITH THE FOLLOWING OBJECTIVES: 1) CHARACTERIZE THE SIGNALING AND REGULATORY NETWORK CONNECTED WITH QSMR, 2) IDENTIFY METABOLIC CONDITIONS AND SIGNALS AFFECTING THE FUNCTION OF QSMR AND VIRULENCE, AND 3) INVESTIGATE THE DYNAMICS OF QSMR FUNCTION ASSOCIATED WITH BACTERIAL ADAPTATION TO CHANGING ENVIRONMENTS. ESPECIALLY, WE WILL TEST THE HYPOTHESIS THAT THE LOSS OF QSMR FUNCTION THROUGH SPONTANEOUS MUTATION IS ASSOCIATED WITH THE CONVERSION OF A PATHOGEN POPULATION FROM THE 'PATHOGENIC (OR INFECTIOUS) MODE' TO THE 'SAPROPHYTIC MODE' (OR VICE VERSA) DEPENDING ON ENVIRONMENTAL CONDITIONS. WE PROPOSE TO PERFORM COMPARATIVE DNA/RNA SEQUENCE ANALYSES TO TEST THIS HYPOTHESIS, AS WELL AS TO IDENTIFY DIRECT AND INDIRECT TARGETS OF THE QSMR REGULATORY FUNCTION. THE OUTCOMES OF THIS PROJECT WILL LEAD TO BETTER UNDERSTANDING OF THE REGULATORY MECHANISMS UNDERLYING SOCIAL BEHAVIORS OF PLANT PATHOGENIC BACTERIA FOR PATHOGENESIS AND ECOLOGICAL FITNESS, AS WELL AS EVOLUTION IN CHANGING ENVIRONMENTS. INFORMATION GAINED FROM THIS STUDY WILL PROVIDE GREAT INSIGHTS INTO THE DEVELOPMENT OF NOVEL DISEASE MANAGEMENT STRATEGIES FOR BACTERIAL PANICLE BLIGHT AND OTHER BACTERIAL DISEASES OF PLANTS AND ANIMALS.