THE GROWTH OF THE MAIZE ROOT HAS BEEN PREVIOUSLY SHOWN TO BE CONTROLLED BY HORMONES, SPECIFICALLY AUXIN AND BRASSINOSTEROIDS. HOWEVER, THERE IS A GAP IN UNDERSTANDING THE DOWNSTREAM INTERDEPENDENT REGULATORY MECHANISMS THAT THESE HORMONES UTILIZE TO SIGNAL AND CONTROL MAIZE ROOT GROWTH. PLANT HORMONES HAVE SHOWN TO HAVE TREMENDOUS EFFECTS ON PLANT DEVELOPMENT AND MODULATION OF THEIR BIOSYNTHESIS, TRANSPORT, SIGNALING, OR PERCEPTION HAVE PREVIOUSLY BEEN UTILIZED TO IMPROVE PLANT GROWTH AND IMPROVE YIELD. HOWEVER, INVESTIGATION INTO THEIR ROLE ON THE BELOW GROUND GROWTH, SPECIFICALLY ROOTS, HAS NOT BEEN WELL STUDIED. IDENTIFYING REGULATORS OF ROOT GROWTH WILL HAVE TREMENDOUS EFFECTS FOR FUTURE MAIZE YIELDS BECAUSE THE ROOT SYSTEM IS NECESSARY TO ACQUIRE WATER AND NUTRIENTS FROM THE SOIL. THE GOAL OF THIS PROPOSAL IS TO IDENTIFY THE MECHANISMS THAT TWO PLANT HORMONES UTILIZE TO CONTROL PRIMARY ROOT GROWTH BY USING A COMBINATION OF DEVELOPMENTAL GENETICS, GENOME WIDE ASSOCIATIONSTUDIES, AND MUTANT SCREENS. PREVIOUSLY IDENTIFIED MUTANTS THAT ARE DEFICIENT IN THE SYNTHESIS OF AUXIN OR BRASSINOSTEROIDS WILL IDENTIFY THE PRIMARY DEVELOPMENTAL MECHANISMS, CELL DIVISION AND/OR ELONGATION, THAT THESE HORMONES INFLUENCE TO CONTROL ROOT GROWTH. THE GENOME WIDE ASSOCIATION STUDY WILL TEST THE RESPONSE OF 282 DIVERSE MAIZE LINES TO TREATMENT WITH AUXIN OR BRASSINOSTEROIDS TO IDENTIFY DOWNSTREAM REGULATORS THAT DIRECTLY AFFECT ROOT GROWTH. LASTLY, A MUTANT SCREEN FOR INSENSITIVE MUTANTS TO AUXIN AND BRASSINOSTEROIDS WILL BE CONDUCTED. THIS WILL IDENTIFY SPECIFIC GENES THAT CONTROL AUXIN AND BRASSINOSTEROID RESPONSE TO CONTROL ROOT GROWTH. THE RESULTS FROM THIS WORK COULD BE TARGETS FOR FUTURE BREEDING PROGRAMS TO IMPROVE ROOT DEVELOPMENT, AN UNDER STUDIED ASPECT OF PLANT GROWTH.