Poster: Regulation of gene expression

Abs # 772: Analysis of Aux/IAA Proteins Domain I Function in Arabidopsis

Presenter:	Tiwari, Shiv B, tiwaris@missouri.edu
Authors	Tiwari, Shiv B (A)   Hagen, Gretchen  (A)   Guilfoyle, Tom  (A)
Affiliations:	(A): University of Missouri

Aux/IAA proteins are a large family of transcriptional repressors. Most Aux/IAA genes are inducible by auxin, and the proteins are known to repress ARF (Auxin Response Factor) mediated transcriptional activation of auxin-regulated genes. Most Aux/IAA proteins contain four conserved domains, designated as domain I, II, II and IV. Domain II functions as a stability domain and is responsible for the degradation of these proteins in an auxin dependent manner. Domains III and IV have a role in the interaction of these proteins with ARFs. Recently, by using transient transfection assays and site directed mutagenesis, we have shown that domain I of Aux/IAA proteins plays an important role in repression. To evaluate the in planta function of domain I in Aux/IAA proteins, IAA7 and IAA17 genes containing mutations in domain I and/or domain II were over-expressed in Arabidopsis alone and also as a chimeric fusion with the VP16 activation domain. Our results show that plants expressing Aux/IAA proteins with mutations in both domains (I and II) had moderate to no phenotypes compared to plants expressing Aux/IAA proteins containing a mutation in the domain II alone. VP16 fusion to the Aux/IAA proteins containing mutations in the both domains (I and II) generated plants with phenotypes that resembled auxin over-producing mutants. However, VP16 fusion to the proteins that contained a single mutation in domain II alone had phenotypic effects similar to domain II alone. These results demonstrate that the domain I of Aux/IAA proteins functions as a repression domain, and it can dominate over an activation domain. Most phenotypes were common for the both IAA7 and IAA17 proteins, suggesting that these proteins have redundant functions as repressors.