The phytohormone auxin controls numerous plant growth and developmental processes, including many traits of agronomic importance in crops. Thus, engineering endogenous auxin activity has tremendous potential for changing plant architecture by design. Yet this potential remains untapped due to pleiotropic effects associated with altering auxin levels. Auxin signals are locally translated to gene expression changes underlying growth and development by ARF transcription factors, whose DNA-binding mechanisms have recently been uncovered. In this project, I will engineer DNA-binding specificity in the Arabidopsis ARF5 protein to rewire endogenous auxin responses. Firstly, by systematically replacing DNA-contacting amino acids, I will generate ARF5 mutant proteins with novel or altered DNA-binding specificity. This resource will help reveal the elusive “code” underlying specific protein-DNA interactions and target gene selection. Secondly, by introducing mutant ARF5s into Arabidopsis, I will determine how intrinsic protein properties translate to DNA-binding properties in native chromatin, and additionally determine the developmental consequences of rewiring the endogenous auxin response. Thirdly, since variation in auxin response is expected to generate useful phenotypic variation in crops, I will identify induced mutations and standing variation in DNA-contacting residues in the tomato and Chrysanthemum ARF5 orthologue. Analyzing DNA-binding specificity of such mutant ARF5 proteins, as well as phenotypic analysis of the mutant plants, will provide an important proof of concept for inducing plant development adjustments through targeted modification of ARF-DNA interactions, heralding the foundation for plant shape by design.