Figure 4.

Aux/IAA rate motifs are functional in plant roots. The C-terminal rate motif predictably influenced IAA28 degradation dynamics in plants. A, When expressed in Arabidopsis roots, an IAA28.Nd fragment (orange) lacking the C-terminal rate motif degrades more slowly in the presence of exogenous auxin than IAA28 fragments with a full (dC, light-blue) or partial (dC*, bright-blue) C-terminal rate motif. Root tips of 7-d-old Arabidopsis seedlings expressing heat shock-induced VENUS-tagged IAA28 reporters or VENUS alone (yellow) were treated with 5 μm auxin and imaged periodically for 1 h to capture degradation profiles. B, Quantification of fluorescence microscopy data from two replicates. Between one and five individuals representing two to four independent insertions were analyzed for each genotype. Mean fluorescence intensity values ±sem are plotted. Data were fit by one-phase decay nonlinear regression, and 95% confidence bands for the fit are shown. Auxin-induced degradation half-lives were calculated through nonlinear regression, and means were plotted with 95% confidence intervals (inset).