Abstract
The endoplasmic reticulum (ER) is a highly dynamic organelle in eukaryotic cells and a major production site of proteins destined for vacuoles, the plasma membrane, or apoplast in plants. At the ER, these secreted proteins undergo multiple processing steps, which are supervised and conducted by the ER quality control system. Notably, processing of secreted proteins can considerably elevate under stress conditions and exceed ER folding capacities. The resulting accumulation of unfolded proteins is defined as ER stress. The efficiency of cells to re-establish proper ER function is crucial for stress adaptation. Besides delivering proteins directly antagonizing and resolving stress conditions, the ER monitors synthesis of immune receptors. This indicates the significance of the ER for the establishment and function of the plant immune system. Recent studies point out the fragility of the entire system and highlight the ER as initiator of programed cell death (PCD) in plants as was reported for vertebrates. This review summarizes current knowledge on the impact of the ER on immune and PCD signaling. Understanding the integration of stress signals by the ER bears a considerable potential to optimize development and to enhance stress resistance of plants.
Highlights
The endoplasmic reticulum (ER) is an organelle with important functions in eukaryotic cells
Responses to environmental stresses create an increased requirement for secreted proteins. If this demand exceeds the ER quality control (ER-QC) working capacity, unfolded proteins accumulate in the ER, which the cell senses as ER stress
Dynamic differential interactions with pro- and anti-apoptotic proteins modulated by the intensity and duration of ER stress signals might regulate separate functions of IRE1, and timely coordinated on- and offset of activating transcription factor 6 (ATF6), protein kinase RNAlike ER kinase (PERK), and IRE1 signaling may play a decisive role in determining cell fate
Summary
The endoplasmic reticulum (ER) is a highly dynamic organelle in eukaryotic cells and a major production site of proteins destined for vacuoles, the plasma membrane, or apoplast in plants. At the ER, these secreted proteins undergo multiple processing steps, which are supervised and conducted by the ER quality control system. Processing of secreted proteins can considerably elevate under stress conditions and exceed ER folding capacities. The efficiency of cells to re-establish proper ER function is crucial for stress adaptation. Besides delivering proteins directly antagonizing and resolving stress conditions, the ER monitors synthesis of immune receptors. This indicates the significance of the ER for the establishment and function of the plant immune system. This review summarizes current knowledge on the impact of the ER on immune and PCD signaling.
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