RECENTLY, WE HAVE IDENTIFIED A NOVEL AND EVOLUTIONARILY CONSERVED PATTERN OF MICROBIOME DEVELOPMENT IN THE ROOT ENDOSPHERES OF MANY AGRONOMICALLY IMPORTANT CEREAL CROPS. SPECIFICALLY, WE OBSERVE AN ENRICHMENT OF A SUBSET OF THE BACTERIAL ROOT ENDOSPHERE FOLLOWING A PLANT'S EXPOSURE TO PROLONGED PERIODS OF DROUGHT. THIS PHENOMENA APPEARS CONSERVED ACROSS BOTH A BROAD RANGE OF HOSTS AND BACTERIAL LINEAGES, WHICH SUGGESTS THAT IT IS AN ANCIENT AND EVOLUTIONARILY-SELECTED PHENOTYPE WITH POTENTIAL BENEFITS TO HOST FITNESS. THE GOAL OF THIS PROPOSAL IS TO INVESTIGATE THE MOLECULAR CAUSES OF THIS ENRICHMENT FROM THE MICROBIAL AND HOST PERSPECTIVES, AND THE PHENOTYPIC CONSEQUENCES OF THIS ENRICHMENT FOR THE HOST PLANT. OUR TEAM WILL USE A COMBINATION OF NEW GENOMIC TECHNOLOGIES AND MICROBIOME MANIPULATION STRATEGIES, IN BOTH LAB AND FIELD-BASED EXPERIMENTAL DESIGNS, USING SORGHUM BICOLOR, WHICH REPRESENTS AN EXCELLENT AGRONOMIC MODEL FOR DROUGHT RESEARCH AND AN IMPORTANT FEEDSTOCK AND BIOENERGY CROP. THIS INVESTIGATION WILL ADVANCE THE PRACTICALITY OF USING MICROBIAL-BASED STRATEGIES FOR IMPROVING CROP DROUGHT TOLERANCE BY DISCOVERING MICROBES WITH THE ABILITY TO CONFER DROUGHT TOLERANCE IN AN AGRONOMIC SETTING, AND BY IDENTIFYING SPECIFIC GENETIC AND BIOCHEMICAL PATHWAYS THAT CAN BE MANIPULATED TO IMPROVE RATES AND EXTENTS OF COLONIZATION BY BENEFICIAL MICROORGANISMS. THIS SET OF GOALS ALIGNS WELL WITH THREE PROGRAM AREA PRIORITIES, NAMELY 1) IMPROVING UNDERSTANDINGS OF MULTIPARTITE INTERACTIONS AMONG THE HOST, ENVIRONMENT AND THE MICROBIOME, 2) CHARACTERIZING THE SPECIFIC MOLECULAR MECHANISMS INVOLVED IN MICROBIOME ASSEMBLY UNDER STRESS, AND 3) FUNCTIONALLY CHARACTERIZING MICROBIOMES IN CONFERRING SPECIFIC HOST PHENOTYPES