Abstract
Osmotic stress can be detrimental to plants whose survival relies heavily on proteomic plasticity. Protein ubiquitination is a central post-translational modification in abiotic mediated stresses (Stone 2018). Ubiquitin (Ub) is covalently linked to a lysine residue in the target protein through the sequential action of three enzyme classes: Ub-activating enzymes (E1s), Ub-conjugating enzymes (E2s), and Ub ligases (E3s) (Callis 2014). Mono and poly-ubiquitination are associated with diverse biological functions. Hence, poly-ubiquitination involving residue K48 from Ub (K48- Ub linkage) triggers the degradation of target proteins by the 26S proteasome (Komander & Rape 2012); then, a role for K63-Ub linkage in mediating endocytosis and trafficking of plant plasma membrane proteins has recently emerged (Romero-Barrios & Vert 2018). In this study, we used the K-Ɛ-GG antibodyenrichment method integrated with high-resolution mass spectrometry to compile a list of 719ubiquitinated lysine residues from 450 Arabidopsis root membrane proteins, 60 % of which are transmembrane proteins, thereby adding to the database of ubiquitinated membrane protein substrates in plants. Ubiquitinome analysis and quantification suggested a broad role of ubiquitination in the internalization and sorting of cargo proteins. To extend the role of ubiquitination, a network for the ubiquitinated proteins and their interactants was obtained, identifying two E2 Ub-conjugating enzymes, UBC32 and UBC34, putatively targeting membrane proteins under osmotic stress. Importantly, we showed that the suppression of UBC32 and UBC34 favor primary root growth inhibition under mannitol treatment, suggesting that UBC32- and UBC34-mediated ubiquitination contributes to primary root growth under osmotic stress (Berger et al. 2022).References-Berger et al. 2022. International Journal of Molecular Sciences, 23(4):1956.-Callis. 2014. The Arabidopsis Book, 12:e0174.-Komander and Rape. 2012, Annual Review of Biochemistry, 81:203-229.-Romero-Barrios and Vert. 2018. New Phytologist, 217(3):995-1011.-Stone. 2019. International Review of Cell and Molecular Biology, 343:65-110.