Ubiquitin-independent proteasome system is required for degradation of Arabidopsis COPPER TRANSPORTER 2

• Published in: Plant science (Limerick) Vol. 304; p. 110825
• Main Authors: Li, Jinjin, Wang, Weiwei, Yuan, Jinhong, Xu, Jinyu, He, Lifei, Zhang, Xinying, Zhang, Haiyan
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.03.2021
• Subjects: Arabidopsis; Arabidopsis - metabolism; Arabidopsis - ultrastructure; Arabidopsis Proteins - metabolism; Arabidopsis thaliana; Cell Membrane - metabolism; Cell Membrane - ultrastructure; confocal microscopy; copper; Copper - metabolism; Copper Transport Proteins - metabolism; COPT2; degradation; endocytosis; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; H-transporting ATP synthase; lysine; Microscopy, Confocal; nutrient uptake; nutrients; plasma membrane; Polymerase Chain Reaction; Proteasome; proteasome endopeptidase complex; Proteasome Endopeptidase Complex - metabolism; proteinases; site-directed mutagenesis; SLC31 Proteins - metabolism; soil; transcription (genetics); transporters; Ubiquitin; Ubiquitin - metabolism; Ubiquitination; Vacuolar degradation; vacuoles; Vesicle trafficking; Ubiquitin; Vesicle trafficking; Vacuolar degradation; Arabidopsis; COPT2; Proteasome
• ISSN: 0168-9452; 1873-2259; 1873-2259
• DOI: 10.1016/j.plantsci.2021.110825

•COPT2 is localized at the plasma membrane and endoplasmic reticulum.•COPT2 protein is downregulated in response to excess copper.•Turnover of COPT2 is controlled by ubiquitin-independent proteasomal degradation.•C-terminal lysine residues of COPT2 is required for copper acquisition but not for COPT2 degradation. Plants have evolved sophisticated mechanisms to adjust to deficiency or excess of nutrients. Membrane transport proteins play a central role in nutrient uptake from soil. In Arabidopsis thaliana, the COPPER TRANSPORTOR (COPT) family encodes high-affinity copper transporters. COPT2 is transcriptionally regulated in response to changing levels of cellular copper. However, little is known about whether COPT2 activity is subject to multiple levels of regulation. Here, we showed that the plasma membrane-/endoplasmic reticulum-resident COPT2 protein is degraded in response to excess copper. Confocal microscopy analysis together with pharmacological treatment with a vesicle trafficking inhibitor or vacuolar ATPase inhibitor indicated that copper-mediated downregulation of COPT2 is unlikely to be controlled by endosomal recycling and vacuolar system. However, COPT2 protein is stabilized by proteasome inhibition. Through site-directed mutagenesis, we found that COPT2 cannot be ubiquitinated, and lysine residues at the C-terminus is dispensable for copper-induced degradation of COPT2 but required for copper acquisition. Altogether, our findings reveal that unlike many metal transporters in Arabidopsis, COPT2 is a substrate of ubiquitin-independent proteasomal degradation but not of vacuolar proteases. These findings highlight the mechanistic diversity and complexity of plasma membrane transporter degradation.