Proteasome-dependent proteolysis has a critical role in fine-tuning the feedback inhibition of cytokinin signaling.

The ubiquitin/26S proteasome-dependent proteolysis of response regulators is a critical element of many plant hormone signaling pathways. We have recently shown that cytokinin signaling requires the AXR1 component of the related to ubiquitin (RUB) protein modification pathway to promote the proteasome-dependent degradation of the cytokinin response inhibitor ARR5. Here, we show that ARR5 also accumulates in the 26S proteasome mutant rpn12a-1, and leads to a marked resistance to cytokinins. Collectively, these results suggest that proteasome-dependent proteolysis of feedback inhibitors such as ARR5 is essential for the maintenance of optimal responsivity and plasticity in cytokinin signaling.