PLANTS IN NATURE ARE UBIQUITOUSLY COLONIZED BY BACTERIA AND THESE PLANT-MICROBE RELATIONSHIPS RANGE FROM PATHOGENIC TO COMMENSAL TO BENEFICIAL. ROOTS ARE A HOTSPOT OF MICROBIAL COLONIZATION, HOSTING UP TO 10^8 BACTERIAL CELLS PER GRAM OF HOST ROOT TISSUE. BACTERIA COLONIZE NOT ONLY THE ROOT SURFACE, BUT ALSO THE ROOT INTERIOR. CONVERSELY, PLANTS ENCODE AN INNATE IMMUNE SYSTEM THAT IS SEEMINGLY POISED TO ELIMINATE BACTERIA UPON PERCEPTION. RECEPTORS ON THE SURFACE OF PLANT CELLS RECOGNIZE CONSERVED BACTERIAL MOTIFS WHICH THEN INITIATEA DOWNSTREAM SIGNALLING CASCADE ULTIMATELY DETERRING INFECTION. THESE TWO PHENOMENON - THAT BACTERIA COLONIZE ROOT TISSUE AND THAT THE PLANT HAS AN ACTIVE IMMUNE SYSTEM THAT RECOGNIZES CONSERVED BACTERIAL MOTIFS - ARE AT ODDS. THIS PROPOSAL AIMS TO INVESTIGATE THE HYPOTHESIS THAT CERTAIN MEMBERS OF THE ROOT BACTERIAL MICROBIOTA CAN EVADE OR EVEN SUPPRESS THE INNATE IMMUNES SYSTEM OF THE HOST PLANT. THIS HYPOTHESIS WILL BE ADDRESSED IN THE MODEL PLANT ARABIDOPSIS THALIANA, WHERE RELATIVELY MORE IS KNOWN ABOUT THE INNATE IMMUNE SYSTEM, AS WELL AS 6 GRASS SPECIES THAT SERVE AS IMPORTANT FOOD AND BIOFUEL CROPS OR ARE IMPORTANT MODELS. THE BACTERIAL MICROBIOTA WILL BE CHARACTERIZED IN EACH HOST PLANT TO BETTER UNDERSTAND THE SIMILARITIES AND DIFFERENCES OF COLONIZATION PATTERNS OF SPECIFIC BACTERIA BETWEEN THE HOST PLANTS. INDIVIDUAL BACTERIAL STRAINS WILL BE COLLECTED FROM THE ROOTS OF THE HOST PLANTS GROWING IN SOIL AND THESE BACTERIAL ISOLATES WILL BE SCREENED TO DETECT WHETHER THEY ELICIT AN IMMUNE RESPONSE IN EACH HOST SPECIES. BETTER UNDERSTANDING HOW MICROBIOTA INTERACT WITH THE PLANT INNATE IMMUNE SYSTEM WILL ENABLE FUTURE EFFORTS TO ENGINEER ROOT-ASSOCIATED MICROBIOTA FOR STRONGER CROPS THAT ARE MORE RESISTANT TO PATHOGEN ATTACK AND ARE MORE RESILIENT AGAINST THE IMPACTS OF CLIMATE CHANGE.