English: Wild-type Arabidopsis thaliana (left) and the axr2-1 mutant (right). axr2-1 is a dominant gain-of-function mutation in an Aux/IAA gene that confers reduced auxin response. The mutant axr2-1 protein constitutively represses auxin response because it cannot be targeted for proteolysis by the SCFTIR1 ubiquitin ligase. The effect of the mutation on AXR2 stability is shown in a pulse-chase experiment (inset). Wild-type and axr2-1 seedlings were labeled with 35S-methionine and AXR2/axr2-1 protein was immunoprecipitated either immediately after the labeling period (t = 0) or following a 15-minute chase with unlabeled methionine (t = 15).