auxin regulates various aspects of plant growth and development the auxin indole 3 acetic acid aux iaa genes encode short lived transcriptional repressors that are targeted by the transport inhibitor response1 auxin receptor f box proteins the aux iaa proteins regulate auxin mediated gene expression by interacting with members of the auxin response factor protein family aux iaa function is poorly understood herein we report the identification and characterization of insertion mutants in 12 of the 29 aux iaa family members the mutants show no visible developmental defects compared with the wild type double or triple mutants of closely related aux iaa genes such as iaa8 1 iaa9 1 or iaa5 1 iaa6 1 iaa19 1 also exhibit wild type phenotypes global gene expression analysis reveals that the molecular phenotypes of auxin treated and untreated light grown seedlings are unaffected in the iaa17 6 and iaa5 1 iaa6 1 iaa19 1 mutants by contrast similar analysis with the gain of function axr3 1 iaa17 1 mutant seedlings reveals dramatic changes in basal and auxin induced gene expression compared with the wild type expression of several type a arabidopsis response regulator genes and a number of genes involved in cell wall biosynthesis and degradation is repressed in axr3 1 iaa17 1 the data suggest extensive functional redundancy among aux iaa gene family members and that enhanced stability of the axr3 iaa17 protein severely alters the molecular phenotype resulting in developmental defects.