Transcriptional competition shapes proteotoxic ER stress resolution

Dynamics of ER stress-induced gene regulation in plants

Endoplasmic reticulum (ER) stress is a potentially lethal condition that is induced by the abnormal accumulation of unfolded or misfolded secretory proteins in the ER. In eukaryotes, ER stress is managed by the unfolded protein response (UPR) through a tightly regulated, yet highly dynamic, reprogramming of gene transcription. Although the core principles of the UPR are similar across eukaryotes, unique features of the plant UPR reflect the adaptability of plants to their ever-changing environments and the need to balance the demands of growth and development with the response to environmental stressors. The past decades have seen notable progress in understanding the mechanisms underlying ER stress sensing and signalling transduction pathways, implicating the UPR in the effects of physiological and induced ER stress on plant growth and crop yield. Facilitated by sequencing technologies and advances in genetic and genomic resources, recent efforts have driven the discovery of transcriptional regulators and elucidated the mechanisms that mediate the dynamic and precise gene regulation in response to ER stress at the systems level.

bZIP60 and Bax inhibitor 1 contribute IRE1-dependent and independent roles to potexvirus infection

IRE1, BI-1, and bZIP60 monitor compatible plant-potexvirus interactions though recognition of the viral TGB3 protein. This study was undertaken to elucidate the roles of three IRE1 isoforms, the bZIP60U and bZIP60S, and BI-1 roles in genetic reprogramming of cells during potexvirus infection. Experiments were performed using Arabidopsis thaliana knockout lines and Plantago asiatica mosaic virus infectious clone tagged with the green fluorescent protein gene (PlAMV-GFP). There were more PlAMV-GFP infection foci in ire1a/b, ire1c, bzip60, and bi-1 knockout than wild-type (WT) plants. Cell-to-cell movement and systemic RNA levels were greater bzip60 and bi-1 than in WT plants. Overall, these data indicate an increased susceptibility to virus infection. Transgenic overexpression of AtIRE1b or StbZIP60 in ire1a/b or bzip60 mutant background reduced virus infection foci, while StbZIP60 expression influences virus movement. Transgenic overexpression of StbZIP60 also confers endoplasmic reticulum (ER) stress resistance following tunicamycin treatment. We also show bZIP60U and TGB3 interact at the ER. This is the first demonstration of a potato bZIP transcription factor complementing genetic defects in Arabidopsis. Evidence indicates that the three IRE1 isoforms regulate the initial stages of virus replication and gene expression, while bZIP60 and BI-1 contribute separately to virus cell-to-cell and systemic movement.

Logistics of defense: The contribution of endomembranes to plant innate immunity

Phytopathogens cause plant diseases that threaten food security. Unlike mammals, plants lack an adaptive immune system and rely on their innate immune system to recognize and respond to pathogens. Plant response to a pathogen attack requires precise coordination of intracellular traffic and signaling. Spatial and/or temporal defects in coordinating signals and cargo can lead to detrimental effects on cell development. The role of intracellular traffic comes into a critical focus when the cell sustains biotic stress. In this review, we discuss the current understanding of the post-immune activation logistics of plant defense. Specifically, we focus on packaging and shipping of defense-related cargo, rerouting of intracellular traffic, the players enabling defense-related traffic, and pathogen-mediated subversion of these pathways. We highlight the roles of the cytoskeleton, cytoskeleton-organelle bridging proteins, and secretory vesicles in maintaining pathways of exocytic defense, acting as sentinels during pathogen attack, and the necessary elements for building the cell wall as a barrier to pathogens. We also identify points of convergence between mammalian and plant trafficking pathways during defense and highlight plant unique responses to illustrate evolutionary adaptations that plants have undergone to resist biotic stress.

Unraveling the unfolded protein response signature: implications for tumor immune microenvironment heterogeneity and clinical prognosis in stomach cancer

BACKGROUND

Stomach cancer is a leading cause of cancer-related deaths globally due to its high grade and poor response to treatment. Understanding the molecular network driving the rapid progression of stomach cancer is crucial for improving patient outcomes.

METHODS

This study aimed to investigate the role of unfolded protein response (UPR) related genes in stomach cancer and their potential as prognostic biomarkers. RNA expression data and clinical follow-up information were obtained from the TCGA and GEO databases. An unsupervised clustering algorithm was used to identify UPR genomic subtypes in stomach cancer. Functional enrichment analysis, immune landscape analysis, and chemotherapy benefit prediction were conducted for each subtype. A prognostic model based on UPR-related genes was developed and validated using LASSO-Cox regression, and a multivariate nomogram was created. Key gene expression analyses in pan-cancer and in vitro experiments were performed to further investigate the role of the identified genes in cancer progression.

RESULTS

A total of 375 stomach cancer patients were included in this study. Analysis of 113 UPR-related genes revealed their close functional correlation and significant enrichment in protein modification, transport, and RNA degradation pathways. Unsupervised clustering identified two molecular subtypes with significant differences in prognosis and gene expression profiles. Immune landscape analysis showed that UPR may influence the composition of the tumor immune microenvironment. Chemotherapy sensitivity analysis indicated that patients in the C2 molecular subtype were more responsive to chemotherapy compared to those in the C1 molecular subtype. A prognostic signature consisting of seven UPR-related genes was constructed and validated, and an independent prognostic nomogram was developed. The gene IGFBP1, which had the highest weight coefficient in the prognostic signature, was found to promote the malignant phenotype of stomach cancer cells, suggesting its potential as a therapeutic target.

CONCLUSIONS

The study developed a UPR-related gene classifier and risk signature for predicting survival in stomach cancer, identifying IGFBP1 as a key factor promoting the disease's malignancy and a potential therapeutic target. IGFBP1's role in enhancing cancer cell adaptation to endoplasmic reticulum stress suggests its importance in stomach cancer prognosis and treatment.

Post-translational modifications: emerging directors of cell-fate decisions during endoplasmic reticulum stress in Arabidopsis thaliana

Homeostasis of the endoplasmic reticulum (ER) is critical for growth, development, and stress responses. Perturbations causing an imbalance in ER proteostasis lead to a potentially lethal condition known as ER stress. In ER stress situations, cell-fate decisions either activate pro-life pathways that reestablish homeostasis or initiate pro-death pathways to prevent further damage to the organism. Understanding the mechanisms underpinning cell-fate decisions in ER stress is critical for crop development and has the potential to enable translation of conserved components to ER stress-related diseases in metazoans. Post-translational modifications (PTMs) of proteins are emerging as key players in cell-fate decisions in situations of imbalanced ER proteostasis. In this review, we address PTMs orchestrating cell-fate decisions in ER stress in plants and provide evidence-based perspectives for where future studies may focus to identify additional PTMs involved in ER stress management.

A transcriptomic dataset for investigating the Arabidopsis Unfolded Protein Response under chronic, proteotoxic endoplasmic reticulum stress

The Unfolded Protein Response (UPR) is a retrograde, ER-to-nucleus, signalling pathway which is conserved across kingdoms. In plants, it contributes to development, reproduction, immunity and tolerance to abiotic stress. This RNA sequencing (RNA-seq) dataset was produced from 14-day-old Arabidopsis thaliana seedlings challenged by tunicamycin (Tm), an antibiotic inhibiting Asn-linked glycosylation in the endoplasmic reticulum (ER), causing an ER stress and eventually activating the UPR. Wild-type (WT) and a double mutant deficient for two main actors of the UPR (INOSITOL-REQUIRING ENZYME 1A and INOSITOL-REQUIRING ENZYME 1B) were used as genetic backgrounds in our experimental setup, allowing to distinguish among differentially-expressed genes (DEGs) which ones are dependent on or independent on IRE1s. Also, shoots and roots were harvested separately to determine organ-specific transcriptomic responses to Tm. Library and sequencing were performed using DNBseq™ technology by the Beijing Genomics Institute. Reads were mapped and quantified against the Arabidopsis genome. Differentially-expressed genes were identified using Rflomics upon filtering and normalization by the Trimmed Mean of M-value (TMM) method. While the genotype effect was weak under mock conditions (with a total of 182 DEGs in shoots and 195 DEGs in roots), the tunicamycin effect on each genotype was characterized by several hundred of DEGs in both shoots and roots. Among these genes, 872 and 563 genes were statistically up- and down-regulated in the shoot tissues of the double mutant when compared to those of WT, respectively. In roots of Tm-challenged seedlings, 425 and 439 genes were significantly up- and down-regulated in mutants with respect to WT. We believe that our dataset could be reused for investigating any biological questions linked to ER homeostasis and its role in plant physiology.

Multi-omics Resources for Understanding Gene Regulation in Response to ER Stress in Plants

Proteotoxic stress of the endoplasmic reticulum (ER) is a potentially lethal condition that ensues when the biosynthetic capacity of the ER is overwhelmed. A sophisticated and largely conserved signaling, known as the unfolded protein response (UPR), is designed to monitor and alleviate ER stress. In plants, the emerging picture of gene regulation by the UPR now appears to be more complex than ever before, requiring multi-omics-enabled network-level approaches to be untangled. In the past decade, with an increasing access and decreasing costs of next-generation sequencing (NGS) and high-throughput protein-DNA interaction (PDI) screening technologies, multitudes of global molecular measurements, known as omics, have been generated and analyzed by the research community to investigate the complex gene regulation of plant UPR. In this chapter, we present a comprehensive catalog of omics resources at different molecular levels (transcriptomes, protein-DNA interactomes, and networks) along with the introduction of key concepts in experimental and computational tools in data generation and analyses. This chapter will serve as a starting point for both experimentalists and bioinformaticians to explore diverse omics datasets for their biological questions in the plant UPR, with likely applications also in other species for conserved mechanisms.

Mechanisms of Endoplasmic Reticulum Protein Homeostasis in Plants

Maintenance of proteome integrity is essential for cell function and survival in changing cellular and environmental conditions. The endoplasmic reticulum (ER) is the major site for the synthesis of secretory and membrane proteins. However, the accumulation of unfolded or misfolded proteins can perturb ER protein homeostasis, leading to ER stress and compromising cellular function. Eukaryotic organisms have evolved sophisticated and conserved protein quality control systems to ensure protein folding fidelity via the unfolded protein response (UPR) and to eliminate potentially harmful proteins via ER-associated degradation (ERAD) and ER-phagy. In this review, we summarize recent advances in our understanding of the mechanisms of ER protein homeostasis in plants and discuss the crosstalk between different quality control systems. Finally, we will address unanswered questions in this field.

An IRE1-proteasome system signalling cohort controls cell fate determination in unresolved proteotoxic stress of the plant endoplasmic reticulum

Excessive accumulation of misfolded proteins in the endoplasmic reticulum (ER) causes ER stress, which is an underlying cause of major crop losses and devastating human conditions. ER proteostasis surveillance is mediated by the conserved master regulator of the unfolded protein response (UPR), Inositol Requiring Enzyme 1 (IRE1), which determines cell fate by controlling pro-life and pro-death outcomes through as yet largely unknown mechanisms. Here we report that Arabidopsis IRE1 determines cell fate in ER stress by balancing the ubiquitin-proteasome system (UPS) and UPR through the plant-unique E3 ligase, PHOSPHATASE TYPE 2CA (PP2CA)-INTERACTING RING FINGER PROTEIN 1 (PIR1). Indeed, PIR1 loss leads to suppression of pro-death UPS and the lethal phenotype of an IRE1 loss-of-function mutant in unresolved ER stress in addition to activating pro-survival UPR. Specifically, in ER stress, PIR1 loss stabilizes ABI5, a basic leucine zipper (bZIP) transcription factor, that directly activates expression of the critical UPR regulator gene, bZIP60, triggering transcriptional cascades enhancing pro-survival UPR. Collectively, our results identify new cell fate effectors in plant ER stress by showing that IRE1's coordination of cell death and survival hinges on PIR1, a key pro-death component of the UPS, which controls ABI5, a pro-survival transcriptional activator of bZIP60.

ER Stress and the Unfolded Protein Response: Homeostatic Regulation Coordinate Plant Survival and Growth

The endoplasmic reticulum (ER), a eukaryotic organelle, is the major site of protein biosynthesis. The disturbance of ER function by biotic or abiotic stress triggers the accumulation of misfolded or unfolded proteins in the ER. The unfolded protein response (UPR) is the best-studied ER stress response. This transcriptional regulatory system senses ER stress, activates downstream genes that function to mitigate stress, and restores homeostasis. In addition to its conventional role in stress responses, recent reports indicate that the UPR is involved in plant growth and development. In this review, we summarize the current knowledge of ER stress sensing and the activation and downstream regulation of the UPR. We also describe how the UPR modulates both plant growth and stress tolerance by maintaining ER homeostasis. Lastly, we propose that the UPR is a major component of the machinery that balances the trade-off between plant growth and survival in a dynamic environment.

Unfolded protein response in balancing plant growth and stress tolerance

The ER (endoplasmic reticulum) is the largest membrane-bound multifunctional organelle in eukaryotic cells, serving particularly important in protein synthesis, modification, folding and transport. UPR (unfolded protein response) is one of the systematized strategies that eukaryotic cells employ for responding to ER stress, a condition represents the processing capability of ER is overwhelmed and stressed. UPR is usually triggered when the protein folding capacity of ER is overloaded, and indeed, mounting studies were focused on the stress responding side of UPR. In plants, beyond stress response, accumulating evidence suggests that UPR is essential for growth and development, and more importantly, the necessity of UPR in this regard requires its endogenous basal activation even without stress. Then plants must have to fine tune the activation level of UPR pathway for balancing growth and stress response. In this review, we summarized the recent progresses in plant UPR, centering on its role in controlling plant reproduction and root growth, and lay out some outstanding questions to be addressed in the future.