Figure 6.

Rate motif deletions slow degradation of FL IAA28 and result in phenotypes similar to stabilized IAA28 when expressed in plants. A, Degradation profiles of IAA28 variants were measured in yeast expressing either TIR1 or AFB2 auxin receptors. Partial deletion of the IAA28 C-terminal rate motif (ΔLTAQL, white triangles) in the context of FL IAA28 substantially slowed degradation when compared with the wild-type protein (black circles). As expected, a mutation in the degron (V55G, white squares) completely abolished auxin-induced degradation. Raw mean fluorescence values from two independent experiments are shown. B, Half-lives with 95% confidence intervals for data in A. Half-lives for IAA28.FL-V55G were not applicable (NA) as no auxin-induced degradation was observed. C, Plants expressing IAA28.FL-ΔLTAQL or IAA28.FL-V55G from the IAA28 promoter showed a range of phenotypes, including disruptions in phyllotaxy (gray arrows) and reduced fertility, when compared with plants expressing wild-type (WT) IAA28. Phenotypes of plants expressing IAA28.FL-V55G were more severe than those of plants expressing IAA28.FL-ΔLTAQL, consistent with a stronger effect of the respective mutations on auxin-induced degradation.