The inner nuclear membrane-associated degradation system in plants

The homeostasis of the inner nuclear membrane (INM) proteins plays a critical role in regulating the nuclear structure, genome integrity, and signal transduction. However, little is known about the turnover of INM proteins in higher eukaryotes. Here we demonstrated that the conserved INM protein SUN1 undergoes proteasome-dependent degradation in Arabidopsis. Using in vivo proximity labeling-coupled mass spectrometry, we showed that SUN1 associates with the CDC48 complex, which mediates membrane protein extraction and proteolysis. Moreover, we discovered a specific subclade of plant ubiquitin regulatory X (UBX) domain-containing proteins (PUXs), including PUX3, PUX4, and PXU5, that negatively regulate this process. The three PUX proteins associate with the nucleoskeleton to target the INM, where they physically interact with CDC48, likely directly regulating the activity or substrate specificity of CDC48. Our findings provide direct evidence for the existence of plant INM-associated degradation pathway and uncover a nucleoskeleton-associated regulatory mechanism for it.