CDC48 protein regulates the turnover of peroxisomal catalase in tobacco

In plant cells, protein homeostasis is tightly regulated to prevent imbalances between protein synthesis and degradation that can lead to proteotoxic stress. Protein turnover is largely maintained by the ubiquitin-proteasome system (UPS), with the AAA+ ATPase CDC48 facilitating the extraction and processing of ubiquitinated substrates. Previous studies identified redox-related proteins as plant CDC48 partners. Here, using tobacco cell lines overexpressing CDC48, we identified the peroxisomal catalase CAT1 as a substrate of CDC48-dependent turnover. CDC48 overexpression markedly reduced CAT1 abundance and activity, indicating post-translational regulation. CAT1 undergoes extensive polyubiquitination, and was rapidly degraded in a CDC48-dependent manner. Inhibition of deubiquitinating enzymes or CDC48 ATPase activity both led to the accumulation of ubiquitinated CAT1. Finally, CDC48 overexpression, which leads to reduced CAT1 levels, correlated with impaired peroxisomal function. These findings reveal a role for CDC48 in regulating peroxisomal protein turnover in tobacco.