TOLs Function as Ubiquitin Receptors in the Early Steps of the ESCRT Pathway in Higher Plants

• Published in: Molecular plant 2020-05, Vol.13 (5), p.717-731
• Main Authors: Moulinier-Anzola, Jeanette, Schwihla, Maximilian, De-Araújo, Lucinda, Artner, Christina, Jörg, Lisa, Konstantinova, Nataliia, Luschnig, Christian, Korbei, Barbara
• Format: Article
• Language: English
• Subjects: Arabidopsis - metabolism; Arabidopsis Proteins - metabolism; Cell Membrane - metabolism; Endosomal Sorting Complexes Required for Transport - metabolism; ESCRT pathway; Lysine - metabolism; Membrane Proteins - metabolism; Mutation - genetics; plasma membrane protein degradation; Protein Binding; Protein Subunits - metabolism; Proteolysis; Receptors, Cell Surface - metabolism; Solubility; Subcellular Fractions - metabolism; Ubiquitin - metabolism; ubiquitin receptor; Ubiquitinated Proteins - metabolism; Ubiquitination
• ISSN: 1674-2052; 1752-9867
• DOI: 10.1016/j.molp.2020.02.012

Protein abundance and localization at the plasma membrane (PM) shapes plant development and mediates adaptation to changing environmental conditions. It is regulated by ubiquitination, a post-translational modification crucial for the proper sorting of endocytosed PM proteins to the vacuole for subsequent degradation. To understand the significance and the variety of roles played by this reversible modification, the function of ubiquitin receptors, which translate the ubiquitin signature into a cellular response, needs to be elucidated. In this study, we show that TOL (TOM1-like) proteins function in plants as multivalent ubiquitin receptors, governing ubiquitinated cargo delivery to the vacuole via the conserved Endosomal Sorting Complex Required for Transport (ESCRT) pathway. TOL2 and TOL6 interact with components of the ESCRT machinery and bind to K63-linked ubiquitin via two tandemly arranged conserved ubiquitin-binding domains. Mutation of these domains results not only in a loss of ubiquitin binding but also altered localization, abolishing TOL6 ubiquitin receptor activity. Function and localization of TOL6 is itself regulated by ubiquitination, whereby TOL6 ubiquitination potentially modulates degradation of PM-localized cargoes, assisting in the fine-tuning of the delicate interplay between protein recycling and downregulation. Taken together, our findings demonstrate the function and regulation of a ubiquitin receptor that mediates vacuolar degradation of PM proteins in higher plants. This study reveals that TOL2 and TOL6 proteins function as multivalent ubiquitin receptors, governing K63-linked ubiquitinated cargo delivery to the vacuole via the ESCRT pathway. The results suggest cytoplasmic TOL2 as well as plasma membrane-localized and early endosome-localized TOL6, thus potentially TOLs in general, as functional equivalents of the elusive ESCRT-0 complex in plants.