FLOWERS ARE IMPORTANT REPRODUCTIVE ORGANS OF PLANTS AND EXCELLENT HABITATS FOR MICROORGANISMS. IT IS ESTIMATED THAT THE MICROBIAL DENSITY ON FLOWERS IS AT LEAST 100 TIMES HIGHER THAN THAT ON LEAVES. YET DUE TO THE SHORT LIFE SPAN, THE MICROBIOME ON FLOWERS AS WELL AS THE FUNCTIONS IT CONFERS ARE RELATIVELY UNDERSTUDIED COMPARED TO OTHER PARTS OF THE PLANTS, SUCH AS ROOTS AND LEAVES. COMPARED TO THE MICROBIOME ON VEGETATIVE ORGANS, THE MICOBIOME ON FLOWERS IS ASSEMBLED IN A MUCH MORE STOCHASTIC MANNER DUE TO THE SUDDEN EXPOSURE OF THE NUTRIENT RICH FLOWER PARTS TO THE ENVIRONMENT DURING BLOOM. IN OUR INITIAL CHARACTERIZATION OF MICROBIOME ASSEMBLY ON APPLE FLOWERS, WE OBSERVED THAT DESPITE THE VARIATION IN EARLY STAGES, THE MICROBIOME ON FLOWERS EVENTUALY FALLS INTO ONE OF THE THREE SIGNATURE STATES AT LATER STAGES (~FOUR DAYS AFTER FLOWER OPENING): 1. PSEUDOMONADACEAE-DOMINATED, 2. ENTEROBACTERIACEAE-DOMINATED, AND 3. PSEUDOMONADACEA-ENTEROBACTERIACEAE MIXED. DESPITE THESE DIFFERENCES IN COMPOSITION, THE BIOLOGICAL CONCEQUENCES OF HAIVNG THE MICROBIOME IN ALTERNATIVE STATES ARE UNKONWN. AS INDIVIDUAL FLOWERS OF THE SAME GENETIC BACKGROUND DISPLAY PHENOTYPIC DIFFERENCES IN DISEASE SUCCEPTIBILITY, POLLINATOR ATTRACTIVENESS, AND FRUIT DEVELOPMENT, WE HYPOTHESIZE THAT SOME OF THE THESE HOST DIFFERENCES MAY BE LINKED TO THE STRUCTURE OF THE MICROBIOME. IN THIS PROJECT, WE WILL USE A COMBINED APPROACH OF METATRANSCRIPTOMICS, 16S RRNA GENE SEQUENCING, MICROBIOME MANIPULATION, AND PHENOTYPIC ASSAYS TO INVESTIGATE THE FUNCTIONS OF THE FLOWER MICROBIOME IN FRUIT DEVELOPMENT AND RESISTANCE TO PLANT DISEASE. FINDINGS FROM THIS STUDY WILL PROVIDE KNOWLEDGE BASIS FOR HARNESING BENEFICIAL MEMBERS OF THE MICROBIOME TOWARDS IMPROVING PLANT PRODUCTIVITY, SUSTAINING PLANT HEALTH, WHILE REDUCING IMPACTS TO THE ENVIRONMENT