Auxin Response Regulators in Arabidopsis Embryogenesis

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The Arabidopsis genome encodes at least 20 IAA proteins involved in response to the plant hormone auxin. IAA proteins share four conserved domains, with domain II conferring protein instability. Domain III interacts with ARF transcription factors that regulate auxin-responsive target genes. It is unknown how specific effects are brought about by different IAA proteins. We have focused on the bodenlos (bdl) mutant which displays specific defects in early embryogenesis, due to an amino acid exchange in domain II of IAA12. By contrast, homologous mutations in six other IAA genes do not lead to defects in embryogenesis. The aim of this project is to analyse what determines the specificity of the bdl phenotype. We will express other IAA coding sequences with bdl-homologous (bdlh) mutations under the control of the BDL cis-regulatory sequences in transgenic Arabidopsis plants. If these transgenes can mimic the bdl phenotype developmental gene regulation would confer specificity of action. If, however, these transgenes can not mimic the bdl phenotype specificity of BDL action resides in its amino acid sequence. In the latter case, we will "swap" regions of BDL and other IAA proteins to identify the specificity determinat(s). BDL specificity domain(s) will be used to isolate specific interactors in the yeast two-hybrid system, followed by functional analyses.