The Ubiquitin-Specific Protease TNI/UBP14 Functions in Ubiquitin Recycling and Affects Auxin Response.

The ubiquitin-mediated proteasomal pathway regulates diverse cellular processes in plants by rapidly degrading target proteins, including the repressors of hormone signaling. Though ubiquitin proteases play a key role in this process by cleaving polyubiquitin chains to monomers, their function has not been studied in detail by mutational analysis. Here, we show that mutation in / (/) leads to reduced auxin response and widespread auxin-related phenotypic defects in Arabidopsis (). In a partial loss-of-function mutant that was originally isolated based on altered leaf shape, activity of the auxin-responsive reporters , , and was reduced. Genetic interaction studies suggest that is involved in auxin signaling and acts alongside , , and Map-based cloning identified as Inefficient splicing of the mutant transcript resulted in the formation of an inactive UBP14 protein, which led to accumulation of polyubiquitin chains and excess polyubiquitinated proteins in the mutant. In addition to the reduced auxin response, increased levels of DII:VENUS, IAA18:GUS, and HS::AXR3-NT:GUS were also observed in , perhaps due to inefficient polyubiquitin hydrolysis and proteasome-mediated degradation. Together, our study identifies a function for TNI/UBP14 in the auxin response through ubiquitin recycling.