Proteasome‐independent functions of lysine‐63 polyubiquitination in plants

Abstract

Contents Summary995I.Introduction995II.The plant Ub machinery996III.From Ub to Ub linkage types in plants997IV.Increasing analytical resolution for K63 polyUb in plants998V.How to build K63 polyUb chains?998VI.Cellular roles of K63 polyUb in plants999VII.Physiological roles of K63 polyUb in plants1004VIII.Future perspectives: towards the next level of the Ub code1006Acknowledgements1006References1007 Summary Ubiquitination is a post‐translational modification essential for the regulation of eukaryotic proteins, having an impact on protein fate, function, localization or activity. What originally appeared to be a simple system to regulate protein turnover by the 26S proteasome is now known to be the most intricate regulatory process cells have evolved. Ubiquitin can be arranged in countless chain assemblies, triggering various cellular outcomes. Polyubiquitin chains using lysine‐63 from ubiquitin represent the second most abundant type of ubiquitin modification. Recent studies have exposed their common function in proteasome‐independent functions in non‐plant model organisms. The existence of lysine‐63 polyubiquitination in plants is, however, only just emerging. In this review, we discuss the recent advances on the characterization of ubiquitin chains and the molecular mechanisms driving the formation of lysine‐63‐linked ubiquitin modifications. We provide an overview of the roles associated with lysine‐63 polyubiquitination in plant cells in the light of what is known in non‐plant models. Finally, we review the crucial roles of lysine‐63 polyubiquitin‐dependent processes in plant growth, development and responses to environmental conditions.

Site-specific K63 ubiquitinomics reveals post-initiation regulation of ribosomes under oxidative stress

“…Other targets functioned in autophagy, ion transport, carbohydrate metabolism, endocytosis, and nutritional response ( Figure S1C). These results were in agreement with reports that many proteins involved in trafficking, metabolism, and translation are regulated by K63 ubiquitin 15,16 .…”

ABA inhibits myristoylation and induces shuttling of the RGLG1 E3 ligase to promote nuclear degradation of PP2CA

“…In hypocotyl cells, we found that RGLG1‐GFP was localized both in the plasma membrane and in the small vesicles found close to or associated with the plasma membrane (Figure a). This is in agreement with the previously observed localization of RGLG1 in the plasma membrane and its role in K63‐linked polyubiquitination (Yin et al ., ; Romero‐Barrios and Vert, ). Upon treatment with 50 μ m ABA for 6 h, however, a pool of RGLG1‐GFP was localized in the cell nucleus.…”

“…Sequence alignment has revealed that RGLG1, RGLG2 and RGLG5 belong to a different branch than RGLG3/4 (Zhang et al, 2012). RGLG1 and RGLG2 show functional overlap in K63-linked polyubiquitination in plasma membrane, which is a proteasome-independent function of RGLG1 and RGLG2 (Yin et al, 2007;Romero-Barrios and Vert, 2018). Indeed the rglg1 rglg2 double mutant shows reduced levels of Ub-K63 chain-specific signals for PIN2, which affects the regulation of PIN2 turnover and the root-hair phenotype of irondeficient plants (Yin et al, 2007;Li and Schmidt, 2010;Leitner et al, 2012).…”

The crossroads of receptor‐mediated signaling and endocytosis in plants

“…In plants, both the FLS2 and BRI1 receptors are ubiquitinated and, subsequently, targeted for degradation (Lu et al ; Martins et al ; Zhou et al ). BRI1 is post‐translationally modified by addition of lysine‐63 polyubiquitin chains (Martins et al ), a key signal for internalization, endosomal sorting, and vacuolar targeting (Romero‐Barrios and Vert ). Indeed, the BRI1 endocytosis is clearly reduced by compromised ubiquitination (Martins et al ).…”