CANDIDATUS LIBERIBACTER ASIATICUS (CLAS), IS A MEMBER OF THE ALPHA-PROTEOBACTERIA GROUP THAT HAS INFECTED MOST OF THE CITRUS CULTIVARS WORLDWIDE CAUSING A DISEASE CALLED CITRUS GREENING. THE DEVASTATING EFFECTS OF THIS PHLOEM RESTRICTED UNCULTURABLE BACTERIUM ON ALL CITRUS VARIETIES HAS CAUSED A SEVERE CRISIS IN THE INDUSTRY, WITH NO SOLUTION VISIBLE IN THE NEAR FUTURE. AS SUCH, IT IS CRITICAL TO FURTHER ADVANCE OUR UNDERSTANDING OF CLAS FUNDAMENTAL BIOLOGY TO FACILITATE THE DISCOVERY OF NEW AND EFFECTIVE MEANS TO TREAT THIS RECALCITRANT DISEASE. THE LONG TERM GOAL OF THIS PROJECT IS TO DEFINE AND CHARACTERIZE THE BIOLOGICAL STRATEGIES USED BY CLAS TO EVADE DEFENSIVE MECHANISMS AND PERSIST IN THE CITRUS HOST. AS A STEP IN THAT DIRECTION, THE OBJECTIVE OF THIS PROPOSAL IS TO CHARACTERIZE MEMBERS OF THE LDTR REGULON INVOLVED IN PEPTIDOGLYCAN SYNTHESIS AND REMODELING. THE PRESENCE OF SMALL MOLECULES THAT DECREASE LDTR DNA BINDING IN THE CULTIVABLE LIBERIBACTER CRESCENS RESULTED IN MORPHOLOGICAL CHANGES IMPAIRING THE BACTERIA TOLERANCE TO STRESS. WE HYPOTHESIZE THAT THE TRANSCRIPTIONAL ACTIVATION OF PEPTIDOGLYCAN MODIFICATION GENES ALLOWS FOR THE PERSISTENCE OF THE PATHOGEN IN THE CITRUS HOST. THIS HYPOTHESIS WILL BE TESTED BY (I) ESTABLISHING THE CORRELATION BETWEEN THE EXPRESSION OF GENES REGULATED BY LDTR AND THE BACTERIA PERSISTENCE IN THE CITRUS HOST, AND BY (II) ELUCIDATING THE BIOLOGICAL CONSEQUENCES OF LDTR-MEDIATED REGULATION. WITH THE COMPLETION OF THESE OBJECTIVES, THE EFFECTS OF PEPTIDOGLYCAN REMODELING ENZYMES ON THE PERSISTENCE IN THE HOST, WILL BE THOROUGHLY EVALUATED. THE MECHANISMS TO BE STUDIED ARE RELEVANT IN HOST-MICROBIAL INTERACTION.