Endoplasmic Reticulum Protein Quality Control and Its Relationship to Environmental Stress Responses in Plants

Abstract

The endoplasmic reticulum (ER) has a sophisticated quality control (QC) system to eliminate improperly folded proteins from the secretory pathway. Given that protein folding is such a fastidious process and subject to adverse environmental conditions, the ER QC system appears to have been usurped to serve as an environmental sensor and responder in plants. Under stressful conditions, the ER protein folding machinery reaches a limit as the demands for protein folding exceed the capacity of the system. Under these conditions, misfolded or unfolded proteins accumulate in the ER, triggering an unfolded protein response (UPR). UPR mitigates ER stress by upregulating the expression of genes encoding components of the protein folding machinery or the ER-associated degradation system. In Arabidopsis thaliana, ER stress is sensed and stress signals are transduced by membrane-bound transcription factors, which are activated and mobilized under environmental stress conditions. Under acute or chronic stress conditions, UPR can also lead to apoptosis or programmed cell death. Despite recent progress in our understanding of plant protein QC, discovering how different environmental conditions are perceived is one of the major challenges in understanding this system. Since the ER QC system is one among many stress response systems in plants, another major challenge is determining the extent to which the ER QC system contributes to various stress responses in plants.

The E3 Ligase TaSAP5 Alters Drought Stress Responses by Promoting the Degradation of DRIP Proteins

“…We are currently conducting yeast twohybrid assays to find possible substrates or protein partners of TaSAP5 and have identified SGT1 and HSC70 as potential interacting proteins. SGT1 was associated with components of the Skp1-Cullin-F-box protein complex in yeast and plants (Kitagawa et al, 1999;Liu et al, 2002), and HSC70 functions as a cochaperone that interacts with unfolded and denatured proteins, which are then subjected to degradation mediated by E3 ligases located in the endoplasmic reticulum (Lee et al, 2009b;Liu and Howell, 2010). Overall, TaSAP5 functioned with cooperative components by catalyzing the transfer of ubiquitin to substrate, but further research will be needed to identify the factors that enhance the protein interaction and polyubiquitin chain assembly in vivo.…”

Transcription factor interaction with COMPASS-like complex regulates histone H3K4 trimethylation for specific gene expression in plants

“…We present a general model on how histone H3K4 trimethylation is specifically formed during inducible gene expression by using the endoplasmic reticulum (ER) stress response system in Arabidopsis plants. demands according to different developmental programs and environmental conditions (24)(25)(26). For gene transcriptional control, two ER-membrane-associated transcription factors, ATF6 and XBP1, play important roles in UPR in animal cells (27).…”

N-Glycosylation of Effector Proteins by an α-1,3-Mannosyltransferase Is Required for the Rice Blast Fungus to Evade Host Innate Immunity

“…In mammals, for instance, N-linked glycosylation is involved in cell adhesion, molecular trafficking and clearance, receptor activation, signal transduction, and endocytosis and is important for human health and disease (Ohtsubo and Marth, 2006). In higher plants, enzymes involved in protein N-glycosylation and glycoproteins that are N-glycosylated have been widely identified and found to play vital roles in diverse aspects of development and physiology, including salt tolerance and plant immunity (Lerouge et al, 1998;Kang et al, 2008;Qin et al, 2008;Liebminger et al, 2009;Saijo et al, 2009;Häweker et al, 2010;Liu and Howell, 2010;Ruiz-May et al, 2012).…”