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.