Biological and molecular functions of two EAR motifs of Arabidopsis IAA7

Some Arabidopsis thaliana AUXIN/INDOLE ACETIC ACIDs (Aux/IAAs) were predicted to have two ETHYLENE RESPONSE FACTOR–associated Amphiphilic Repression (EAR) motifs which would be involved in repression of auxin responses by interacting with TOPLESS (TPL)/TPL-Related (TPR) corepressors. However, the function of the 2^nd EAR motif and any distinctive functions of two EAR motifs have remained to be characterized. Here, we analyzed the biological and molecular function of two EAR motifs of IAA7 by using the substitution mutant forms of the EAR motifs. The 2^nd EAR motif played a minor (compared with the 1st one) repressive role in auxin-related developmental processes such as root hair growth, primary root growth, cotyledon curling, and plant dwarfism, and also in auxinresponsive gene expression. The yeast two-hybrid assay revealed that while the 1st EAR motif played a dominant role in interacting with all TPL/TPR members, the 2^nd EAR was specifically required to interact with TPR1 and played a minor role in interaction with TPL. The protein pull-down analysis further supported the engagement of the 2^nd EAR motif in interaction with TPL and TPR1. These results indicate that two EAR motifs of IAA7 plays repressive roles in auxin responses by interacting with TPL/TPRs with specificity.