ECLIPSE mediates selective degradation of inner nuclear membrane protein in plants.

Abstract

The inner nuclear membrane (INM) hosts a unique set of membrane proteins essential for nuclear functions. Proteolytic removal of mislocalized or defective membrane proteins is of critical importance for maintaining the homeostasis and integrity of the INM. Previous studies revealed that INM protein degradation depends on a specialized ubiquitin-proteasome system termed INM-Associated Degradation (INMAD) in plants, requiring the CDC48 complex and the 26S proteasome for membrane protein retrotranslocation and destruction, respectively. However, adaptor proteins that link membrane substrates to the CDC48/proteasome degradation machinery remain missing in the pathway. Here, we report the discovery of ECLIPSE, a previously uncharacterized protein that may serve as such a molecular bridge in the degradation of the conserved INM protein SUN1. We demonstrate that ECLIPSE physically associates with CDC48 and exhibits strong transcriptional co-regulation with multiple established plant INMAD components. Mechanistically, ECLIPSE may act as an adaptor through its dual-domain architecture: its C-terminal PUB domain mediates direct interaction with CDC48, while its N-terminal Ubiquitin-Associated domain recognizes ubiquitinated INM substrates. Genetic and biochemical analyses further established that ECLIPSE is required for SUN1 protein degradation in Arabidopsis, supporting its role in the turnover of at least some inner nuclear membrane proteins in plants.