**AWARDS ISSUED PRIOR TO JANUARY 20, 2025, WERE FUNDED UNDER PREVIOUS ADMINISTRATIONS AND MAY NOT REFLECT THE PRIORITIES AND POLICIES OF THE CURRENT ADMINISTRATION.** HORIZONTAL GENE TRANSFER IS A MAJOR DRIVER OF THE EVOLUTION OF PLANT SYMBIOTIC BACTERIA. RHODOCOCCUS IS A GENUS OF GRAM-POSITIVE BACTERIA IN WHICH THE HORIZONTAL ACQUISITION OF VIRULENCE PLASMIDS CAN TRANSITION BENEFICIAL LINEAGES TO BEING PATHOGENIC. MEMBERS OF THE LATTER GROUP OF RHODOCOCCUS ARE A SIGNIFICANT BURDEN ON US AGRICULTURE. UNDERSTANDING THE MECHANISMS BY WHICH HORIZONTALLY ACQUIRED GENES ASSIMILATE INTO THE NETWORK OF THE RECIPIENT CELL AND CONFER VIRULENCE ARE CRITICAL TO INFORM ON MANAGEMENT STRATEGIES. TWO PLASMID LOCI HAVE BEEN IDENTIFIED AS NECESSARY FOR VIRULENCE. THE FASR LOCUS ENCODES A TRANSCRIPTION FACTOR. IT DOES NOT DIRECTLY REGULATE THE SECOND LOCUS NECESSARY FOR VIRULENCE, FAS, AND ITS REGULON REMAINS UNKNOWN. THE FAS LOCUS ENCODES PROTEINS IMPLICATED IN THE METABOLISM OF CYTOKININS. PRELIMINARY DATA REVEAL GENETIC INTERACTIONS BETWEEN FAS AND A CHROMOSOMAL GENE THAT MODIFIES TRNAS WITH CYTOKININS AND INFLUENCES PROTEIN TRANSLATION. IN THIS PROPOSAL, RESEARCH WILL TEST HYPOTHESES ON THE ROLE OF PLASMID-ENCODED GENES AND CYTOKININS IN COOPTING AND REPROGRAMMING CHROMOSOMAL GENES FOR VIRULENCE. THREE AIMS ARE PROPOSED TO DETERMINE THE NECESSITY AND SUFFICIENCY OF GENES IN PATHOGENESIS, UNDERSTAND HOW VIRULENCE GENES ARE REGULATED, AND TEST THE ROLE OF CYTOKININS IN REGULATING VIRULENCE OF BACTERIAL PATHOGENS.