When supply does not meet demand-ER stress and plant programmed cell death

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.

Endoplasmic Reticulum Dysfunction: An Emerging Mechanism of Vitiligo Pathogenesis

The endoplasmic reticulum (ER) is the main site of protein synthesis, transport, and modification. Its abnormal status has now emerged as an established cause of many pathological processes, such as tumors and autoimmune diseases. Recent studies also demonstrated that the defective functions of ER may lead to pigmentary diseases. Vitiligo is a depigmenting ailment skin disorder whose pathogenesis is now found to be associated with ER. However, the detailed mechanism is still unclear. In this review, we try to link the association between ER with its inter- and intra-organellar interactions in vitiligo pathogenesis and focus on the function, mechanism, and clinical potential of ER with vitiligo. Expand ER is found in melanocytes of vitiligo and ER stress (ERS) might be a bridge between oxidative stress and innate and adaptive immunity. Meanwhile, the tight association between ER and mitochondria or melanosomes in organelles levels, as well as genes and cytokines, is the new paradigm in the pathogenesis of vitiligo. This undoubtedly adds a new aspect to the understanding of vitiligo, facilitating the design of targeted therapies for vitiligo.

Protein disulfide isomerase-9 interacts with the lumenal region of the transmembrane endoplasmic reticulum stress sensor kinase, IRE1, to modulate the unfolded protein response in Arabidopsis

Environmental stressors disrupt secretory protein folding and proteostasis in the endoplasmic reticulum (ER), leading to ER stress. The unfolded protein response (UPR) senses ER stress and restores proteostasis by increasing the expression of ER-resident protein folding chaperones, such as protein disulfide isomerases (PDIs). In plants, the transmembrane ER stress sensor kinase, IRE1, activates the UPR by unconventionally splicing the mRNA encoding the bZIP60 transcription factor, triggering UPR gene transcription. The induced PDIs catalyze disulfide-based polypeptide folding to restore the folding capacity in the ER; however, the substrates with which PDIs interact are largely unknown. Here, we demonstrate that the Arabidopsis PDI-M subfamily member, PDI9, modulates the UPR through interaction with IRE1. This PDI9-IRE1 interaction was largely dependent on Cys63 in the first dithiol redox active domain of PDI9, and Cys233 and Cys107 in the ER lumenal domain of IRE1A and IRE1B, respectively. In vitro and in vivo, PDI9 coimmunoprecipitated with IRE1A and IRE1B. Moreover, the PDI9:RFP and Green Fluorescence Protein (GFP):IRE1 fusions exhibited strong interactions as measured by fluorescence lifetime imaging microscopy-fluorescence resonance energy transfer (FLIM-FRET) when coexpressed in mesophyll protoplasts. The UPR-responsive PDI9 promoter:mCherry reporter and the UPR-dependent splicing of the bZIP60 intron from the mRNA of the 35S::bZIP60-intron:GFP reporter were both significantly induced in the pdi9 mutants, indicating a derepression and hyperactivation of UPR. The inductions of both reporters were substantially attenuated in the ire1a-ire1b mutant. We propose a model in which PDI9 modulates the UPR through two competing activities: secretory protein folding and via interaction with IRE1 to maintain proteostasis in plants.

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.

Diabetes-induced male infertility: potential mechanisms and treatment options

Male infertility is a physiological phenomenon in which a man is unable to impregnate a fertile woman during a 12-month period of continuous, unprotected sexual intercourse. A growing body of clinical and epidemiological evidence indicates that the increasing incidence of male reproductive problems, especially infertility, shows a very similar trend to the incidence of diabetes within the same age range. In addition, a large number of previous in vivo and in vitro experiments have also suggested that the complex pathophysiological changes caused by diabetes may induce male infertility in multiple aspects, including hypothalamic-pituitary-gonadal axis dysfunction, spermatogenesis and maturation disorders, testicular interstitial cell damage erectile dysfunction. Based on the above related mechanisms, a large number of studies have focused on the potential therapeutic association between diabetes progression and infertility in patients with diabetes and infertility, providing important clues for the treatment of this population. In this paper, we summarized the research results of the effects of diabetes on male reproductive function in recent 5 years, elaborated the potential pathophysiological mechanisms of male infertility induced by diabetes, and reviewed and prospected the therapeutic measures.

Kitaviruses: A Window to Atypical Plant Viruses Causing Nonsystemic Diseases

Kitaviridae is a family of plant-infecting viruses that have multiple positive-sense, single-stranded RNA genomic segments. Kitaviruses are assigned into the genera Cilevirus, Higrevirus, and Blunervirus, mainly on the basis of the diversity of their genomic organization. Cell-to-cell movement of most kitaviruses is provided by the 30K family of proteins or the binary movement block, considered an alternative movement module among plant viruses. Kitaviruses stand out for producing conspicuously unusual locally restricted infections and showing deficient or nonsystemic movement likely resulting from incompatible or suboptimal interactions with their hosts. Transmission of kitaviruses is mediated by mites of many species of the genus Brevipalpus and at least one species of eriophyids. Kitavirus genomes encode numerous orphan open reading frames but RNA-dependent RNA polymerase and the transmembrane helix-containing protein, generically called SP24, typify a close phylogenetic link with arthropod viruses. Kitaviruses infect a large range of host plants and cause diseases of economic concern in crops such as citrus, tomato, passion fruit, tea, and blueberry.

The boundary of life and death: changes in mitochondrial and cytosolic proteomes associated with programmed cell death of Arabidopsis thaliana suspension culture cells

Introduction

Despite the critical role of programmed cell death (PCD) in plant development and defense responses, its regulation is not fully understood. It has been proposed that mitochondria may be important in the control of the early stages of plant PCD, but the details of this regulation are currently unknown.

Methods

We used Arabidopsis thaliana cell suspension culture, a model system that enables induction and precise monitoring of PCD rates, as well as chemical manipulation of this process to generate a quantitative profile of the alterations in mitochondrial and cytosolic proteomes associated with early stages of plant PCD induced by heat stress. The cells were subjected to PCD-inducing heat levels (10 min, 54°C), with/without the calcium channel inhibitor and PCD blocker LaCl3. The stress treatment was followed by separation of cytosolic and mitochondrial fractions and mass spectrometry-based proteome analysis.

Results

Heat stress induced rapid and extensive changes in protein abundance in both fractions, with release of mitochondrial proteins into the cytosol upon PCD induction. In our system, LaCl3 appeared to act downstream of cell death initiation signal, as it did not affect the release of mitochondrial proteins, but instead partially inhibited changes occurring in the cytosolic fraction, including upregulation of proteins with hydrolytic activity.

Discussion

We characterized changes in protein abundance and localization associated with the early stages of heat stress-induced PCD. Collectively, the generated data provide new insights into the regulation of cell death and survival decisions in plant cells.

Effects of Phytotoxic Nonenolides, Stagonolide A and Herbarumin I, on Physiological and Biochemical Processes in Leaves and Roots of Sensitive Plants

Phytotoxic macrolides attract attention as prototypes of new herbicides. However, their mechanisms of action (MOA) on plants have not yet been elucidated. This study addresses the effects of two ten-membered lactones, stagonolide A (STA) and herbarumin I (HBI) produced by the fungus Stagonospora cirsii, on Cirsium arvense, Arabidopsis thaliana and Allium cepa. Bioassay of STA and HBI on punctured leaf discs of C. arvense and A. thaliana was conducted at a concentration of 2 mg/mL to evaluate phenotypic responses, the content of pigments, electrolyte leakage from leaf discs, the level of reactive oxygen species, Hill reaction rate, and the relative rise in chlorophyll a fluorescence. The toxin treatments resulted in necrotic and bleached leaf lesions in the dark and in the light, respectively. In the light, HBI treatment caused the drop of carotenoids content in leaves on both plants. The electrolyte leakage caused by HBI was light-dependent, in contrast with that caused by STA. Both compounds induced light-independent peroxide generation in leaf cells but did not affect photosynthesis 6 h after treatment. STA (10 µg/mL) caused strong disorders in root cells of A. thaliana leading to the complete dissipation of the mitochondrial membrane potential one hour post treatment, as well as DNA fragmentation and disappearance of acidic vesicles in the division zone after 8 h; the effects of HBI (50 µg/mL) were much milder. Furthermore, STA was found to inhibit mitosis but did not affect the cytoskeleton in cells of root tips of A. cepa and C. arvense, respectively. Finally, STA was supposed to inhibit the intracellular vesicular traffic from the endoplasmic reticulum to the Golgi apparatus, thus interfering with mitosis. HBI is likely to have another main MOA, probably inhibiting the biosynthesis of carotenoids.

Plastid methylerythritol phosphate pathway participates in the hypersensitive response-related cell death in Nicotiana benthamiana

Programmed cell death (PCD), a characteristic feature of hypersensitive response (HR) in plants, is an important cellular process often associated with the defense response against pathogens. Here, the involvement of LytB, a gene encoding 4-hydroxy-3-methylbut-2-enyl diphosphate reductase that participates in the final step of the plastid methylerythritol phosphate (MEP) pathway, in plant HR cell death was studied. In Nicotiana benthmiana plants, silencing of the NbLytB gene using virus-induced gene silencing (VIGS) caused plant growth retardation and albino leaves with severely malformed chloroplasts. In NbLytB-silenced plants, HR-related cell death mediated by the expression of either the human proapoptotic protein gene Bax or an R gene with its cognate Avr effector gene was inhibited, whereas that induced by the nonhost pathogen Pseudomonas syringae pv. syringae 61 was enhanced. To dissect the isoprenoid pathway and avoid the pleiotropic effects of VIGS, chemical inhibitors that specifically inhibit isoprenoid biosynthesis in plants were employed. Treatment of N. benthamiana plants with fosmidomycin, a specific inhibitor of the plastid MEP pathway, effectively inhibited HR-related PCD, whereas treatment with mevinolin (a cytoplasmic mevalonate pathway inhibitor) and fluridone (a carotenoid biosynthesis inhibitor) did not. Together, these results suggest that the MEP pathway as well as reactive oxygen species (ROS) generation in the chloroplast play an important role in HR-related PCD, which is not displaced by the cytosolic isoprenoid biosynthesis pathway.

Combined analysis of the transcriptome and proteome of Eucommia ulmoides Oliv. (Duzhong) in response to Fusarium oxysporum

Eucommia ulmoides Oliv. (Duzhong), a valued traditional herbal medicine in China, is rich in antibacterial proteins and is effective against a variety of plant pathogens. Fusarium oxysporum is a pathogenic fungus that infects plant roots, resulting in the death of the plant. In this study, transcriptomic and proteomic analyses were used to explore the molecular mechanism of E. ulmoides counteracts F. oxysporum infection. Transcriptomic analysis at 24, 48, 72, and 96 h after inoculation identified 17, 591, 1,205, and 625 differentially expressed genes (DEGs), while proteomics identified were 66, 138, 148, 234 differentially expressed proteins (DEPs). Meanwhile, GO and KEGG enrichment analyses of the DEGs and DEPs showed that they were mainly associated with endoplasmic reticulum (ER), fructose and mannose metabolism, protein processing in the ER, type II diabetes mellitus, the ribosome, antigen processing and presentation, and the phagosome. In addition, proteome and transcriptome association analysis and RT-qPCR showed that the response of E. ulmoides to F. oxysporum was likely related to the unfolded protein response (UPR) of the ER pathway. In conclusion, our study provided a theoretical basis for the control of F. oxysporum.

Genome-Wide Prediction and Analysis of Oryza Species NRP Genes in Rice Blast Resistance

Members of the N-rich proteins (NRPs) gene family play important roles in the plant endoplasmic reticulum stress in response, which can be triggered by plant pathogens’ infection. Previous studies of the NRP gene family have been limited to only a few plants, such as soybean and Arabidopsis thaliana. Thus, their evolutionary characteristics in the Oryza species and biological functions in rice defense against the pathogenic fungus Magnaporthe oryzae have remained unexplored. In the present study, we demonstrated that the NRP genes family may have originated in the early stages of plant evolution, and that they have been strongly conserved during the evolution of the Oryza species. Domain organization of NRPs was found to be highly conserved within but not between subgroups. OsNRP1, an NRP gene in the Oryza sativa japonica group, was specifically up-regulated during the early stages of rice-M. oryzae interactions-inhibited M. oryzae infection. Predicted protein-protein interaction networks and transcription-factor binding sites revealed a candidate interactor, bZIP50, which may be involved in OsNRP1-mediated rice resistance against M. oryzae infection. Taken together, our results established a basis for future studies of the NRP gene family and provided molecular insights into rice immune responses to M. oryzae.

Cell Death Signaling From Endoplasmic Reticulum Stress: Plant-Specific and Conserved Features

The endoplasmic reticulum (ER) stress response is triggered by any condition that disrupts protein folding and promotes the accumulation of unfolded proteins in the lumen of the organelle. In eukaryotic cells, the evolutionarily conserved unfolded protein response is activated to clear unfolded proteins and restore ER homeostasis. The recovery from ER stress is accomplished by decreasing protein translation and loading into the organelle, increasing the ER protein processing capacity and ER-associated protein degradation activity. However, if the ER stress persists and cannot be reversed, the chronically prolonged stress leads to cellular dysfunction that activates cell death signaling as an ultimate attempt to survive. Accumulating evidence implicates ER stress-induced cell death signaling pathways as significant contributors for stress adaptation in plants, making modulators of ER stress pathways potentially attractive targets for stress tolerance engineering. Here, we summarize recent advances in understanding plant-specific molecular mechanisms that elicit cell death signaling from ER stress. We also highlight the conserved features of ER stress-induced cell death signaling in plants shared by eukaryotic cells.

Effect of an Endoplasmic Reticulum Retention Signal Tagged to Human Anti-Rabies mAb SO57 on Its Expression in Arabidopsis and Plant Growth

Transgenic Arabidopsis thaliana expressing an anti-rabies monoclonal antibody (mAb), SO57, was obtained using Agrobacterium-mediated floral dip transformation. The endoplasmic reticulum (ER) retention signal Lys-Asp-Glu-Leu (KDEL) was tagged to the C-terminus of the anti-rabies mAb heavy chain to localize the mAb to the ER and enhance its accumulation. When the inaccurately folded proteins accumulated in the ER exceed its storage capacity, it results in stress that can affect plant development and growth. We generated T1 transformants and obtained homozygous T3 seeds from transgenic Arabidopsis to investigate the effect of KDEL on plant growth. The germination rate did not significantly differ between plants expressing mAb SO57 without KDEL (SO plant) and mAb SO57 with KDEL (SOK plant). The primary roots of SOK agar media grown plants were slightly shorter than those of SO plants. Transcriptomic analysis showed that expression of all 11 ER stress-related genes were not significantly changed in SOK plants relative to SO plants. SOK plants showed approximately three-fold higher mAb expression levels than those of SO plants. Consequently, the purified mAb amount per unit of SOK plant biomass was approximately three times higher than that of SO plants. A neutralization assay revealed that both plants exhibited efficient rapid fluorescent focus inhibition test values against the rabies virus relative to commercially available human rabies immunoglobulins. KDEL did not upregulate ER stress-related genes; therefore, the enhanced production of the mAb did not affect plant growth. Thus, KDEL fusion is recommended for enhancing mAb production in plant systems.

Constitutive Photomorphogenic 1 Enhances ER Stress Tolerance in Arabidopsis

Interaction between light signaling and stress response has been recently reported in plants. Here, we investigated the role of CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a key regulator of light signaling, in endoplasmic reticulum (ER) stress response in Arabidopsis. The cop1-4 mutant Arabidopsis plants were highly sensitive to ER stress induced by treatment with tunicarmycin (Tm). Interestingly, the abundance of nuclear-localized COP1 increased under ER stress conditions. Complementation of cop1-4 mutant plants with the wild-type or variant types of COP1 revealed that the nuclear localization and dimerization of COP1 are essential for its function in plant ER stress response. Moreover, the protein amount of ELONGATED HYPOCOTYL 5 (HY5), which inhibits bZIP28 to activate the unfolded protein response (UPR), decreased under ER stress conditions in a COP1-dependent manner. Accordingly, the binding of bZIP28 to the BIP3 promoter was reduced in cop1-4 plants and increased in hy5 plants compared with the wild type. Furthermore, introduction of the hy5 mutant locus into the cop1-4 mutant background rescued its ER stress-sensitive phenotype. Altogether, our results suggest that COP1, a negative regulator of light signaling, positively controls ER stress response by partially degrading HY5 in the nucleus.

Proteomic and Biochemical Analyses of the Mechanism of Tolerance in Mutant Soybean Responding to Flooding Stress

To investigate the mechanism of flooding tolerance of soybean, flooding-tolerant mutants derived from gamma-ray irradiated soybean were crossed with parent cultivar Enrei for removal of other factors besides the genes related to flooding tolerance in primary generated mutant soybean. Although the growth of the wild type was significantly suppressed by flooding compared with the non-flooding condition, that of the mutant lines was better than that of the wild type even if it was treated with flooding. A two-day-old mutant line was subjected to flooding for 2 days and proteins were analyzed using a gel-free/label-free proteomic technique. Oppositely changed proteins in abundance between the wild type and mutant line under flooding stress were associated in endoplasmic reticulum according to gene-ontology categorization. Immunoblot analysis confirmed that calnexin accumulation increased in both the wild type and mutant line; however, calreticulin accumulated in only the mutant line under flooding stress. Furthermore, although glycoproteins in the wild type decreased by flooding compared with the non-flooding condition, those in the mutant line increased even if it was under flooding stress. Alcohol dehydrogenase accumulated in the wild type and mutant line; however, this enzyme activity significantly increased and mildly increased in the wild type and mutant line, respectively, under flooding stress compared with the non-flooding condition. Cell death increased and decreased in the wild type and mutant line, respectively, by flooding stress. These results suggest that the regulation of cell death through the fermentation system and glycoprotein folding might be an important factor for the acquisition of flooding tolerance in mutant soybean.

Biocontrol Potential of Bacillus amyloliquefaciens against Botrytis pelargonii and Alternaria alternata on Capsicum annuum

The aim of this study was to assess the ability of Bacillus amyloliquefaciens, to augment plant growth and suppress gray mold and leaf spot in pepper plants. Morphological modifications in fungal pathogen hyphae that expanded toward the PGPR colonies were detected via scanning electron microscope. Furthermore, preliminary screening showed that PGPR could produce various hydrolytic enzymes in its media. Treatments with B. amyloliquefaciens suppressed Botrytis gray mold and Alternaria leaf spot diseases on pepper caused by Botrytis pelargonii and Alternaria alternata, respectively. The PGPR strain modulated plant physio-biochemical processes. The inoculation of pepper with PGPR decreased protein, amino acid, antioxidant, hydrogen peroxide, lipid peroxidation, and abscisic acid levels but increased salicylic acid and sugar levels compared to those of uninoculated plants, indicating a mitigation of the adverse effects of biotic stress. Moreover, gene expression studies confirmed physio-biochemical findings. PGPR inoculation led to increased expression of the CaXTH genes and decreased expression of CaAMP1, CaPR1, CaDEF1, CaWRKY2, CaBI-1, CaASRF1, CaSBP11, and CaBiP genes. Considering its beneficial effects, the inoculation of B. amyloliquefaciens can be proposed as an eco-friendly alternative to synthetic chemical fungicides.

BiP-overexpressing soybean plants display accelerated hypersensitivity response (HR) affecting the SA-dependent sphingolipid and flavonoid pathways

Biotic and abiotic environmental stresses have limited the increase in soybean productivity. Overexpression of the molecular chaperone BiP in transgenic plants has been associated with the response to osmotic stress and drought tolerance by maintaining cellular homeostasis and delaying hypersensitive cell death. Here, we evaluated the metabolic changes in response to the hypersensitivity response (HR) caused by the non-compatible bacteria Pseudomonas syringae pv. tomato in BiP-overexpressing plants. The HR-modified metabolic profiles in BiP-overexpressing plants were significantly distinct from the wild-type untransformed. The transgenic plants displayed a lower abundance of HR-responsive metabolites as amino acids, sugars, carboxylic acids and signal molecules, including p-aminobenzoic acid (PABA) and dihydrosphingosine (DHS), when compared to infected wild-type plants. In contrast, salicylic acid (SA) biosynthetic and signaling pathways were more stimulated in transgenic plants, and both pathogenesis-related genes (PRs) and transcriptional factors controlling the SA pathway were more induced in the BiP-overexpressing lines. Furthermore, the long-chain bases (LCBs) and ceramide biosynthetic pathways showed alterations in gene expression and metabolite abundance. Thus, as a protective pathway against pathogens, HR regulation by sphingolipids and SA may account at least in part by the enhanced resistance of transgenic plants. GmNAC32 transcriptional factor was more induced in the transgenic plants and it has also been reported to regulate flavonoid synthesis in response to SA. In fact, the BiP-overexpressing plants showed an increase in flavonoids, mainly prenylated isoflavones, as precursors for phytoalexins. Our results indicate that the BiP-mediated acceleration in the hypersensitive response may be a target for metabolic engineering of plant resistance against pathogens.

UPR signaling at the nexus of plant viral, bacterial, and fungal defenses

In recent years there have been significant advances in our understanding of the ER stress responses in plants that are associated with virus infection, as well as bacterial and fungal diseases. In plants, ER stress induced by virus infection includes several signaling pathways that include the unfolded protein response (UPR) to promote the expression of chaperone proteins for proper protein folding. Understanding how facets of ER stress signaling broadly engage in pathogen responses, as well as those that are specific to virus infection is important to distinguishing features essential for broad cellular defenses and processes that may be specifically linked to viral infectivity and disease.

BIP and the unfolded protein response are important for potyvirus and potexvirus infection

Plant potexvirus and potyvirus infection can trigger endoplasmic reticulum (ER) stress. ER stress signaling increases the expression of cytoprotective ER-chaperones, especially the BiP chaperones which contribute to pro-survival functions when plants are subjected to infection. The inositol requiring enzyme (IRE1) is one ER stress sensor that is activated to splice the bZIP60 mRNA which produces a truncated transcription factor that activates gene expression in the nucleus. The IRE1/bZIP60 pathway is associated with restricting potyvirus and potexvirus infection. Recent data also identified the IRE1-independent UPR pathways led by bZIP28 and bZIP17 contribute to potexvirus and potyvirus infection. These three bZIP pathways recognize cis-regulatory elements in the BiP promoters to enhance gene expression. BiP is part of a negative feedback loop that regulates the activities of the ER stress transducers IRE1, bZIP28, and bZIP17 to block their activation. We discuss a model in which bZIP60 and bZIP17 synergistically induce BiP and other genes restricting Plantago asiatica mosaic virus (PlAMV; a potexvirus) infection while bZIP60 and bZIP28 independently induce genes supporting PlAMV infection. Regarding Turnip mosiac virus (TuMV, a potyvirus) infection, bZIP60 and bZIP28 serve to repress local and systemic infection. Finally, tauroursodeoxycholic acid treatments were used to demonstrate that the protein folding capacity significantly influences PlAMV accumulation.

A novel PPARɣ ligand, PPZ023, overcomes radioresistance via ER stress and cell death in human non-small-cell lung cancer cells

Peroxisome proliferator-activated receptor gamma (PPARɣ) agonists exert powerful anticancer effects by suppressing tumor growth. In this study, we developed PPZ023 (1-(2-(ethylthio)benzyl)-4-(2-methoxyphenyl)piperazine), a novel PPAR ligand candidate, and investigated the underlying signaling pathways in both non-small-cell lung cancer (NSCLC) and radio-resistant NSCLC cells. To identify whether PPZ023 has anticancer effects in NSCLC and radioresistant NSCLC cells, we performed WST-1, LDH, Western blot, and caspase-3 and -9 activity assays. Furthermore, we isolated exosomes from PPZ023-treated NSCLC cells and studied cell death signaling. PPZ023 reduces cell viability and increases LDH cytotoxicity and caspase-3 activity in NSCLC cells. PPZ023 induces cell death by generating reactive oxygen species (ROS) and triggering mitochondrial cytochrome c release. PPZ023 treatment causes cell death via the PERK–eIF2α–CHOP axis in both NSCLC cell lysates and exosomes, and PERK and CHOP knockdown significantly blocks ER stress-mediated apoptosis by reducing cleaved caspase-3. Interestingly, diphenyleneiodonium (DPI, a Nox inhibitor) inhibits PPZ023-induced cell death via ER stress, and PPARɣ knockdown inhibits PPZ023-induced ROS, ER stress, and cell death. Moreover, PPZ023, in combination with radiation, causes synergic cell death via exosomal ER stress in radioresistant NSCLC cells, indicating that PPZ023/radiation overcomes radioresistance. Taken together, our results suggest that PPZ023 is a powerful anticancer reagent for overcoming radioresistance.

A novel small molecule drug candidate known as PPZ023 could be a powerful anti-cancer agent due to its ability to overcome the resistance of tumors to radiation therapy. Sung Hee Hong and colleagues at the Korea Institute of Radiological and Medical Sciences in Seoul, South Korea, investigated the effects of the molecule on lung cancer cells, including cells that that had acquired resistance to radiotherapy. PPZ023 induces the death of cancer cells by binding to a protein in a known signaling pathway, which generates damaging chemicals known as reactive oxygen species. The researchers identified additional molecular details of the anti-cancer activity. They found the radiotherapy resistance of cancer cells is reversed when PPZ023 promotes cell death via a pathway interfering with the folding of newly formed proteins in a cell structure called the endoplasmic reticulum.

Development of a Reverse Genetic System for Studying Rose Rosette Virus in Whole Plants

Rose rosette virus (RRV) is a negative-sense RNA virus with a seven-segmented genome that is enclosed by a double membrane. We constructed an unconventional minireplicon system encoding the antigenomic (ag)RNA1 (encoding the viral RNA-dependent RNA polymerase [RdRp]), agRNA3 (encoding the nucleocapsid protein [N]), and a modified agRNA5 containing the coding sequence for the iLOV protein in place of the P5 open reading frame (R5-iLOV). iLOV expression from the R5-iLOV template was amplified by activities of the RdRp and N proteins in Nicotiana benthamiana leaves. A mutation was introduced into the RdRp catalytic domain and iLOV expression was eliminated, indicating RNA1-encoded polymerase activity drives iLOV expression from the R5-iLOV template. Fluorescence from the replicon was highest at 3 days postinoculation (dpi) and declined at 7 and 13 dpi. Addition of the tomato bushy stunt virus (TBSV) P19 silencing-suppressor protein prolonged expression until 7 dpi. A full-length infectious clone system was constructed of seven binary plasmids encoding each of the seven genome segments. Agro-delivery of constructs encoding RRV RNAs 1 through 4 or RNAs 1 through 7 to N. benthamiana plants produced systemic infection. Finally, agro-delivery of the full-length RRV infectious clone including all segments produced systemic infection within 60 dpi. This advance opens new opportunities for studying RRV infection biology.

Loss of the Acetyltransferase NAA50 Induces Endoplasmic Reticulum Stress and Immune Responses and Suppresses Growth

Stress signaling in plants is carefully regulated to ensure proper development and reproductive fitness. Overactive defense signaling can result in dwarfism as well as developmental defects. In addition to requiring a substantial amount of energy, plant stress responses place a burden upon the cellular machinery, which can result in the accumulation of misfolded proteins and endoplasmic reticulum (ER) stress. Negative regulators of stress signaling, such as ENHANCED DISEASE RESISTANCE 1 (EDR1), ensure that stress responses are properly suspended when they are not needed, thereby conserving energy for growth and development. Here, we describe the role of an uncharacterized N-terminal acetyltransferase, NAA50, in the regulation of plant development and stress responses in Arabidopsis (Arabidopsis thaliana). Our results demonstrate that NAA50, an interactor of EDR1, plays an important role in regulating the tradeoff between plant growth and defense. Plants lacking NAA50 display severe developmental defects as well as induced stress responses. Reduction of NAA50 expression results in arrested stem and root growth as well as senescence. Furthermore, our results demonstrate that the loss of NAA50 results in constitutive ER stress signaling, indicating that NAA50 may be required for the suppression of ER stress. This work establishes NAA50 as essential for plant development and the suppression of stress responses, potentially through the regulation of ER stress.

Genome-wide identification and characterization of Solanum tuberosum BiP genes reveal the role of the promoter architecture in BiP gene diversity

The endoplasmic reticulum (ER) immunoglobulin binding proteins (BiPs) are molecular chaperones involved in normal protein maturation and refolding malformed proteins through the unfolded protein response (UPR). Plant BiPs belong to a multi-gene family contributing to development, immunity, and responses to environmental stresses. This study identified three BiP homologs in the Solanum tuberosum (potato) genome using phylogenetic, amino acid sequence, 3-D protein modeling, and gene structure analysis. These analyses revealed that StBiP1 and StBiP2 grouped with AtBiP2, whereas StBiP3 grouped with AtBiP3. While the protein sequences and folding structures are highly similar, these StBiPs are distinguishable by their expression patterns in different tissues and in response to environmental stressors such as treatment with heat, chemicals, or virus elicitors of UPR. Ab initio promoter analysis revealed that potato and Arabidopsis BiP1 and BiP2 promoters were highly enriched with cis-regulatory elements (CREs) linked to developmental processes, whereas BiP3 promoters were enriched with stress related CREs. The frequency and linear distribution of these CREs produced two phylogenetic branches that further resolve the groups identified through gene phylogeny and exon/intron phase analysis. These data reveal that the CRE architecture of BiP promoters potentially define their spatio-temporal expression patterns under developmental and stress related cues.

Exploring Mechanisms of Quantitative Resistance to Leptosphaeria maculans (Blackleg) in the Cotyledons of Canola (Brassica napus) Based on Transcriptomic and Microscopic Analyses

Using resistant cultivars is a common approach to managing blackleg of canola/rapeseed caused by Leptosphaeria maculans (Lm). Quantitative resistance (QR), as opposed to major-gene resistance, is of interest because it is generally more durable, due to its multi-genetic basis. However, the mechanisms and genes underlying QR are mostly unknown. In this study, potential QR modes of action in “74-44 BL” was explored. This Canadian canola cultivar showed moderate but consistent race-nonspecific resistance at the cotyledon and adult-plant stages. A susceptible cultivar, “Westar”, was used as a control. After inoculation, the lesions developed more slowly on the cotyledons of 74-44 BL than those of Westar. We used RNA sequencing (-RNA-seq) to identify genes and their functions, putatively related to this resistance, and found that genes involved in programmed cell death (PCD), reactive oxygen species (ROS), signal transduction or intracellular endomembrane transport were most differentially expressed. ROS production was assessed in relation to Lm hyphal growth and lesion size; it occurred beyond the tissue colonized by Lm in 74-44 BL and appeared to trigger rapid cell death, limiting cotyledon colonization by Lm. In contrast, Lm grew more rapidly in Westar, often catching up with the ring of ROS and surpassing lesion boundaries. It appears that QR in 74-44 BL cotyledons is associated with limited colonization by Lm possibly mediated via ROS. The RNA-seq data also showed a link between ROS, signal transduction, and endomembrane vesicle trafficking, as well as PCD in the resistance. These results provide a starting point for a better understanding of the mechanisms behind QR against Lm in canola.

Identification of a Novel NtLRR-RLK and Biological Pathways That Contribute to Tolerance of TMV in Nicotiana tabacum

Tobacco mosaic virus (TMV) infection can causes serious damage to tobacco crops. To explore the approach of preventing TMV infection of plants, two tobacco cultivars with different resistances to TMV were used to analyze transcription profiling before and after TMV infection. The involvement of biological pathways differed between the tolerant variety (Yuyan8) and the susceptible variety (NC89). In particular, the plant-virus interaction pathway was rapidly activated in Yuyan8, and specific resistance genes were enriched. Liquid chromatography tandem mass spectrometry analysis detected large quantities of antiviral substances in the tolerant Yuyan8. A novel Nicotiana tabacum leucine-rich repeat receptor kinase (NtLRR-RLK) gene was identified as being methylated and this was verified using bisulfite sequencing. Transient expression of TMV-green fluorescent protein in pRNAi-NtLRR-RLK transgenic plants confirmed that NtLRR-RLK was important for susceptibility to TMV. The specific protein interaction map generated from our study revealed that levels of BIP1, E3 ubiquitin ligase, and LRR-RLK were significantly elevated, and all were represented at node positions in the protein interaction map. The same expression tendency of these proteins was also found in pRNAi-NtLRR-RLK transgenic plants at 24 h after TMV inoculation. These data suggested that specific genes in the infection process can activate the immune signal cascade through different resistance genes, and the integration of signal pathways could produce resistance to the virus. These results contribute to the overall understanding of the molecular basis of plant resistance to TMV and in the long term could identify new strategies for prevention and control virus infection.

Structural and Functional Heat Stress Responses of Chloroplasts of Arabidopsis thaliana

Temperature elevations constitute a major threat to plant performance. In recent years, much was learned about the general molecular mode of heat stress reaction of plants. The current research focuses on the integration of the knowledge into more global networks, including the reactions of cellular compartments. For instance, chloroplast function is central for plant growth and survival, and the performance of chloroplasts is tightly linked to the general status of the cell and vice versa. We examined the changes in photosynthesis, chloroplast morphology and proteomic composition posed in Arabidopsis thaliana chloroplasts after a single or repetitive heat stress treatment over a period of two weeks. We observed that the acclimation is potent in the case of repetitive application of heat stress, while a single stress results in lasting alterations. Moreover, the physiological capacity and its adjustment are dependent on the efficiency of the protein translocation process as judged from the analysis of mutants of the two receptor units of the chloroplast translocon, TOC64, and TOC33. In response to repetitive heat stress, plants without TOC33 accumulate Hsp70 proteins and plants without TOC64 have a higher content of proteins involved in thylakoid structure determination when compared to wild-type plants.

Endoplasmic reticulum-mediated unfolded protein response is an integral part of singlet oxygen signalling in plants

Singlet oxygen (¹ O₂ ) is a by-product of photosynthesis that triggers a signalling pathway leading to stress acclimation or to cell death. By analyzing gene expressions in a ¹ O₂ -overproducing Arabidopsis mutant (ch1) under different light regimes, we show here that the ¹ O₂ signalling pathway involves the endoplasmic reticulum (ER)-mediated unfolded protein response (UPR). ch1 plants in low light exhibited a moderate activation of UPR genes, in particular bZIP60, and low concentrations of the UPR-inducer tunicamycin enhanced tolerance to photooxidative stress, together suggesting a role for UPR in plant acclimation to low ¹ O₂ levels. Exposure of ch1 to high light stress ultimately leading to cell death resulted in a marked upregulation of the two UPR branches (bZIP60/IRE1 and bZIP28/bZIP17). Accordingly, mutational suppression of bZIP60 and bZIP28 increased plant phototolerance, and a strong UPR activation by high tunicamycin concentrations promoted high light-induced cell death. Conversely, light acclimation of ch1 to ¹ O₂ stress put a limitation in the high light-induced expression of UPR genes, except for the gene encoding the BIP3 chaperone, which was selectively upregulated. BIP3 deletion enhanced Arabidopsis photosensitivity while plants treated with a chemical chaperone exhibited enhanced phototolerance. In conclusion, ¹ O₂ induces the ER-mediated UPR response that fulfils a dual role in high light stress: a moderate UPR, with selective induction of BIP3, is part of the acclimatory response to ¹ O₂ , and a strong activation of the whole UPR is associated with cell death.

Transcriptome analysis of responses in Brachypodium distachyon overexpressing the BdbZIP26 transcription factor

BACKGROUND

Biotic and abiotic stresses are the major cause of reduced growth, persistence, and yield in agriculture. Over the past decade, RNA-Sequencing and the use of transgenics with altered expression of stress related genes have been utilized to gain a better understanding of the molecular mechanisms leading to salt tolerance in a variety of species. Identification of transcription factors that, when overexpressed in plants, improve multiple stress tolerance may be valuable for crop improvement, but sometimes overexpression leads to deleterious effects during normal plant growth.

RESULTS

Brachypodium constitutively expressing the BdbZIP26:GFP gene showed reduced stature compared to wild type plants (WT). RNA-Seq analysis comparing WT and bZIP26 transgenic plants revealed 7772 differentially expressed genes (DEGs). Of these DEGs, 987 of the DEGs were differentially expressed in all three transgenic lines. Many of these DEGs are similar to those often observed in response to abiotic and biotic stress, including signaling proteins such as kinases/phosphatases, calcium/calmodulin related proteins, oxidases/reductases, hormone production and signaling, transcription factors, as well as disease responsive proteins. Interestingly, there were many DEGs associated with protein turnover including ubiquitin-related proteins, F-Box and U-box related proteins, membrane proteins, and ribosomal synthesis proteins. Transgenic and control plants were exposed to salinity stress. Many of the DEGs between the WT and transgenic lines under control conditions were also found to be differentially expressed in WT in response to salinity stress. This suggests that the over-expression of the transcription factor is placing the plant in a state of stress, which may contribute to the plants diminished stature.

CONCLUSION

The constitutive expression of BdbZIP26:GFP had an overall negative effect on plant growth and resulted in stunted plants compared to WT plants under control conditions, and a similar response to WT plants under salt stress conditions. The results of gene expression analysis suggest that the transgenic plants are in a constant state of stress, and that they are trying to allocate resources to survive.

Hsp70 plays a role in programmed cell death during the remodelling of leaves of the lace plant (Aponogeton madagascariensis)

Lace plant leaves utilize programmed cell death (PCD) to form perforations during development. The role of heat shock proteins (Hsps) in PCD during lace plant leaf development is currently unknown. Hsp70 amounts were measured throughout lace plant leaf development, and the results indicate that it is highest before and during PCD. Increased Hsp70 amounts correlate with raised anthocyanin content and caspase-like protease (CLP) activity. To investigate the effects of Hsp70 on leaf development, whole plants were treated with either of the known regulators of PCD [reactive oxygen species (ROS) or antioxidants] or an Hsp70 inhibitor, chlorophenylethynylsulfonamide (PES-Cl). ROS treatment significantly increased Hsp70 2-fold and CLP activity in early developing leaves, but no change in anthocyanin and the number of perforations formed was observed. Antioxidant treatment significantly decreased Hsp70, anthocyanin, and CLP activity in early leaves, resulting in the fewest perforations. PES-Cl (25 μM) treatment significantly increased Hsp70 4-fold in early leaves, while anthocyanin, superoxide, and CLP activity significantly declined, leading to fewer perforations. Results show that significantly increased (4-fold) or decreased Hsp70 amounts lead to lower anthocyanin and CLP activity, inhibiting PCD induction. Our data support the hypothesis that Hsp70 plays a role in regulating PCD at a threshold in lace plant leaf development. Hsp70 affects anthocyanin content and caspase-like protease activity, and helps regulate PCD during the remodelling of leaves of lace plant, Aponogeton madagascariensis.

Plant Immune System Activation Upon Citrus Leprosis Virus C Infection Is Mimicked by the Ectopic Expression of the P61 Viral Protein

Citrus leprosis virus C (CiLV-C, genus Cilevirus, family Kitaviridae) is an atypical virus that does not spread systemically in its plant hosts. Upon its inoculation by Brevipalpus mites, only localized lesions occur, and the infection remains limited to cells around mite feeding sites. Here, we aimed to gain insights into the putative causes of viral unfitness in plants by expanding the limited knowledge of the molecular mechanisms underlying plant/kitavirid interactions. Firstly, we quantified the CiLV-C viral RNAs during the infection in Arabidopsis thaliana plants using RT-qPCR and systematized it by defining three stages of distinguishing subgenomic and genomic RNA accumulation: i) 0-24 h after infestation, ii) 2-4 days after infestation (dai), and iii) 6-10 dai. Accordingly, the global plant response to CiLV-C infection was assessed by RNA-Seq at each period. Results indicated a progressive reprogramming of the plant transcriptome in parallel to the increasing viral loads. Gene ontology enrichment analysis revealed the induction of cell growth-related processes at the early stages of the infection and the triggering of the SA-mediated pathway, ROS burst and hypersensitive response (HR) at the presymptomatic stage. Conversely, infected plants downregulated JA/ET-mediated pathways and processes involved in the primary metabolism including photosynthesis. Marker genes of unfolded protein response were also induced, suggesting a contribution of the endoplasmic reticulum stress to the cell death caused by the viral infection. Finally, we transiently expressed CiLV-C proteins in Nicotiana benthamiana plants to undertake their roles in the elicited plant responses. Expression of the CiLV-C P61 protein consistently triggered ROS burst, upregulated SA- and HR-related genes, increased SA levels, reduced JA levels, and caused cell death. Mimicry of responses typically observed during CiLV-C-plant interaction indicates P61 as a putative viral effector causing the HR-like symptoms associated with the infection. Our data strengthen the hypothesis that symptoms of CiLV-C infection might be the outcome of a hypersensitive-like response during an incompatible interaction. Consequently, the locally restricted infection of CiLV-C, commonly observed across infections by kitavirids, supports the thesis that these viruses, likely arising from an ancestral arthropod-infecting virus, are unable to fully circumvent plant defenses.

Transcriptome and physiological analyses for revealing genes involved in wheat response to endoplasmic reticulum stress

BACKGROUND

Wheat production is largely restricted by adverse environmental stresses. Under many undesirable conditions, endoplasmic reticulum (ER) stress can be induced. However, the physiological and molecular responses of wheat to ER stress remain poorly understood. We used dithiothreitol (DTT) and tauroursodeoxycholic acid (TUDCA) to induce or suppress ER stress in wheat cells, respectively, with the aim to reveal the molecular background of ER stress responses using a combined approach of transcriptional profiling and morpho-physiological characterization.

METHODS

To understand the mechanism of wheat response to ER stress, three wheat cultivars were used in our pre-experiments. Among them, the cultivar with a moderate stress tolerance, Yunong211 was used in the following experiments. We used DTT (7.5 mM) to induce ER stress and TUDCA (25 μg·mL- 1) to suppress the stress. Under three treatment groups (Control, DTT and DTT + TUDCA), we firstly monitored the morphological, physiological and cytological changes of wheat seedlings. Then we collected leaf samples from each group for RNA extraction, library construction and RNA sequencing on an Illumina Hiseq platform. The sequencing data was then validated by qRT-PCR.

RESULTS

Morpho-physiological results showed DTT significantly reduced plant height and biomass, decreased contents of chlorophyll and water, increased electrolyte leakage rate and antioxidant enzymes activity, and accelerated the cell death ratio, whereas these changes were all remarkably alleviated after TUDCA co-treatment. Therefore, RNA sequencing was performed to determine the genes involved in regulating wheat response to stress. Transcriptomic analysis revealed that 8204 genes were differentially expressed in three treatment groups. Among these genes, 158 photosynthesis-related genes, 42 antioxidant enzyme genes, 318 plant hormone-related genes and 457 transcription factors (TFs) may play vital roles in regulating wheat response to ER stress. Based on the comprehensive analysis, we propose a hypothetical model to elucidate possible mechanisms of how plants adapt to environmental stresses.

CONCLUSIONS

We identified several important genes that may play vital roles in wheat responding to ER stress. This work should lay the foundations of future studies in plant response to environmental stresses.

Roots of the Resurrection Plant Tripogon loliiformis Survive Desiccation Without the Activation of Autophagy Pathways by Maintaining Energy Reserves

Being sessile, plants must regulate energy balance, potentially via source-sink relations, to compromise growth with survival in stressful conditions. Crops are sensitive, possibly because they allocate their energy resources toward growth and yield rather than stress tolerance. In contrast, resurrection plants tightly regulate sugar metabolism and use a series of physiological adaptations to suppress cell death in their vegetative tissue to regain full metabolic capacity from a desiccated state within 72 h of watering. Previously, we showed that shoots of the resurrection plant Tripogon loliiformis, initiate autophagy upon dehydration as one strategy to reinstate homeostasis and suppress cell death. Here, we describe the relationship between energy status, sugar metabolism, trehalose-mediated activation of autophagy pathways and investigate whether shoots and roots utilize similar desiccation tolerance strategies. We show that despite containing high levels of trehalose, dehydrated Tripogon roots do not display elevated activation of autophagy pathways. Using targeted and non-targeted metabolomics, transmission electron microscopy (TEM) and transcriptomics we show that T. loliiformis engages a strategy similar to the long-term drought responses of sensitive plants and continues to use the roots as a sink even during sustained stress. Dehydrating T. loliiformis roots contained more sucrose and trehalose-6-phosphate compared to shoots at an equivalent water content. The increased resources in the roots provides sufficient energy to cope with stress and thus autophagy is not required. These results were confirmed by the absence of autophagosomes in roots by TEM. Upregulation of sweet genes in both shoots and roots show transcriptional regulation of sucrose translocation from leaves to roots and within roots during dehydration. Differences in the cell's metabolic status caused starkly different cell death responses between shoots and roots. These findings show how shoots and roots utilize different stress response strategies and may provide candidate targets that can be used as tools for the improvement of stress tolerance in crops.

Cell death triggered by the P25 protein in Potato virus X-associated synergisms results from endoplasmic reticulum stress in Nicotiana benthamiana

The synergistic interaction of Potato virus X (PVX) with a number of potyviruses results in systemic necrosis in Nicotiana spp. Previous investigations have indicated that the viral suppressor of RNA silencing (VSR) protein P25 of PVX triggers systemic necrosis in PVX-associated synergisms in a threshold-dependent manner. However, little is still known about the cellular processes that lead to this necrosis, and whether the VSR activity of P25 is involved in its elicitation. Here, we show that transient expression of P25 in the presence of VSRs from different viruses, including the helper component-proteinase (HC-Pro) of potyviruses, induces endoplasmic reticulum (ER) stress and the unfolded protein response (UPR), which ultimately lead to ER collapse. However, the host RNA silencing pathway was dispensable for the elicitation of cell death by P25. Confocal microscopy studies in leaf patches co-expressing P25 and HC-Pro showed dramatic alterations in ER membrane structures, which correlated with the up-regulation of bZIP60 and several ER-resident chaperones, including the ER luminal binding protein (BiP). Overexpression of BiP alleviated the cell death induced by the potexviral P25 protein when expressed together with VSRs derived from different viruses. Conversely, silencing of the UPR master regulator, bZIP60, led to an increase in cell death elicited by the P25/HC-Pro combination as well as by PVX-associated synergism. In addition to its role as a negative regulator of P25-induced cell death, UPR partially restricted PVX infection. Thus, systemic necrosis caused by PVX-associated synergistic infections is probably the effect of an unmitigated ER stress following the overaccumulation of a viral protein, P25, with ER remodelling activity.

Genome-Wide Investigation of the Role of MicroRNAs in Desiccation Tolerance in the Resurrection Grass Tripogon loliiformis

Drought causes approximately two-thirds of crop and yield loss worldwide. To sustain future generations, there is a need to develop robust crops with enhanced water use efficiency. Resurrection plants are naturally resilient and tolerate up to 95% water loss with the ability to revive upon watering. Stress is genetically encoded and resilient species may garner tolerance by tightly regulating the expression of stress-related genes. MicroRNAs (miRNAs) post-transcriptionally regulate development and other stress response processes in eukaryotes. However, their role in resurrection plant desiccation tolerance is poorly understood. In this study, small RNA sequencing and miRNA expression profiling was conducted using Tripogon loliiformis plants subjected to extreme water deficit conditions. Differentially expressed miRNA profiles, target mRNAs, and their regulatory processes were elucidated. Gene ontology enrichment analysis revealed that development, stress response, and regulation of programmed cell death biological processes; Oxidoreductase and hydrolyase molecular activities; and SPL, MYB, and WRKY transcription factors were targeted by miRNAs during dehydration stress, indicating the indispensable regulatory role of miRNAs in desiccation tolerance. This study provides insights into the molecular mechanisms of desiccation tolerance in the resurrection plant T. loliiformis. This information will be useful in devising strategies for crop improvement on enhanced drought tolerance and water use efficiency.

Two Crinivirus-Conserved Small Proteins, P5 and P9, Are Indispensable for Efficient Lettuce infectious yellows virus Infectivity in Plants

Genomic analysis of Lettuce infectious yellows virus (LIYV) has revealed two short open reading frames (ORFs) on LIYV RNA2, that are predicted to encode a 5-kDa (P5) and a 9-kDa (P9) protein. The P5 ORF is part of the conserved quintuple gene block in the family Closteroviridae, while P9 orthologs are found in all Criniviruses. In this study, the expression of LIYV P5 and P9 proteins was confirmed; P5 is further characterized as an endoplasmic reticulum (ER)-localized integral transmembrane protein and P9 is a soluble protein. The knockout LIYV mutants presented reduced symptom severity and virus accumulation in Nicotiana benthamiana or lettuce plants, indicating their importance in efficient virus infection. The P5 mutant was successfully complemented by a dislocated P5 in the LIYV genome. The structural regions of P5 were tested and all were found to be required for the appropriate functions of P5. In addition, P5, as well as its ortholog P6, encoded by Citrus tristeza virus (CTV) and another ER-localized protein encoded by LIYV RNA1, were found to cause cell death when expressed in N. benthamiana plants from a TMV vector, and induce ER stress and the unfolded protein response (UPR).

GBS Mapping and Analysis of Genes Conserved between Gossypium tomentosum and Gossypium hirsutum Cotton Cultivars that Respond to Drought Stress at the Seedling Stage of the BC₂F₂ Generation

Cotton production is on the decline due to ever-changing environmental conditions. Drought and salinity stress contribute to over 30% of total loss in cotton production, the situation has worsened more due to the narrow genetic base of the cultivated upland cotton. The genetic diversity of upland cotton has been eroded over the years due to intense selection and inbreeding. To break the bottleneck, the wild cotton progenitors offer unique traits which can be introgressed into the cultivated cotton, thereby improving their performance. In this research, we developed a BC₂F₂ population between wild male parent, G. tomentosum as the donor, known for its high tolerance to drought and the elite female parent, G. hirsutum as the recurrent parent, which is high yielding but sensitive to drought stress. The population was genotyped through the genotyping by sequencing (GBS) method, in which 10,888 single-nucleotide polymorphism (SNP) s were generated and used to construct a genetic map. The map spanned 4191.3 cM, with average marker distance of 0.3849 cM. The map size of the two sub genomes had a narrow range, 2149 cM and 2042.3 cM for At and Dt_sub genomes respectively. A total of 66,434 genes were mined, with 32,032 (48.2%) and 34,402 (51.8%) genes being obtained within the At and Dt_sub genomes respectively. Pkinase (PF00069) was found to be the dominant domain, with 1069 genes. Analysis of the main sub family, serine threonine protein kinases through gene ontology (GO), cis element and miRNA targets analysis revealed that most of the genes were involved in various functions aimed at enhancing abiotic stress tolerance. Further analysis of the RNA sequence data and qRT-PCR validation revealed 16 putative genes, which were highly up regulated under drought stress condition, and were found to be targeted by ghr-miR169a and ghr-miR164, previously associated with NAC(NAM, ATAF1/2 and CUC2) and myeloblastosis (MYB), the top rank drought stress tolerance genes. These genes can be exploited further to aid in development of more drought tolerant cotton genotypes.

Two proteases with caspase-3-like activity, cathepsin B and proteasome, antagonistically control ER-stress-induced programmed cell death in Arabidopsis

Programmed cell death (PCD) induced by endoplasmic reticulum (ER) stress is implicated in various plant physiological processes, yet its mechanism is still elusive. An activation of caspase-3-like enzymatic activity was clearly demonstrated but the role of the two known plant proteases with caspase-3-like activity, cathepsin B and proteasome subunit PBA1, remains to be established. Both genetic downregulation and chemical inhibition were used to investigate the function of cathepsin B and PBA1 in ER-stress-induced PCD (ERSID). Transcript level and activity labelling of cathepsin B were used to assess activation. To study tonoplast rupture, a plant PCD feature, both confocal and electronic microscopies were used. Cathepsin B downregulation reduced reactive oxygen species (ROS) accumulation and ERSID without affecting the induction of the unfolded protein response (UPR), but downregulation of PBA1 increased UPR and ERSID. Tonoplast rupture was not altered in the cathepsin B mutant and cathepsin B activation was independent of vacuolar processing enzyme (VPE). VPE activity was independent of cathepsin B. ERSID is regulated positively by cathepsin B and negatively by PBA1, revealing a complex picture behind caspase-3-like activity in plants. Cathepsin B may execute its function after tonoplast rupture and works in parallel with VPE.

Expression of Arabidopsis class 1 phytoglobin (AtPgb1) delays death and degradation of the root apical meristem during severe PEG-induced water deficit

Maintenance of a functional root is fundamental to plant survival in response to some abiotic stresses, such as water deficit. In this study, we found that overexpression of Arabidopsis class 1 phytoglobin (AtPgb1) alleviated the growth retardation of polyethylene glycol (PEG)-induced water stress by reducing programmed cell death (PCD) associated with protein folding in the endoplasmic reticulum (ER). This was in contrast to PEG-stressed roots down-regulating AtPgb1 that exhibited extensive PCD and reduced expression of several attenuators of ER stress, including BAX Inhibitor-1 (BI-1). The death program experienced by the suppression of AtPgb1 in stressed roots was mediated by reactive oxygen species (ROS) and ethylene. Suppression of ROS synthesis or ethylene perception reduced PCD and partially restored root growth. The PEG-induced cessation of root growth was preceded by structural changes in the root apical meristem (RAM), including the loss of cell and tissue specification, possibly as a result of alterations in PIN1- and PIN4-mediated auxin accumulation at the root pole. These events were attenuated by the overexpression of AtPgb1 and aggravated when AtPgb1 was suppressed. Specifically, suppression of AtPgb1 compromised the functionality of the WOX5-expressing quiescent cells (QCs), leading to the early and premature differentiation of the adjacent columella stem cells and to a rapid reduction in meristem size. The expression and localization of other root domain markers, such as SCARECROW (SCR), which demarks the endodermis and QCs, and WEREWOLF (WER), which specifies the lateral root cap, were also most affected in PEG-treated roots with suppressed AtPgb1. Collectively, the results demonstrate that AtPgb1 exercises a protective role in roots exposed to lethal levels of PEG, and suggest a novel function of this gene in ensuring meristem functionality through the retention of cell fate specification.

Hop/Sti1 - A Two-Faced Cochaperone Involved in Pattern Recognition Receptor Maturation and Viral Infection

Perception of pathogens by host pattern recognition receptors (PRRs) or R proteins is a prerequisite to promote successful immune responses. The Hsp70/Hsp90 organizing protein Hop/Sti1, a multifunctional cochaperone, has been implicated in the maturation of a receptor-like kinase (RLK) necessary for chitin sensing. However, it remains unknown whether Hop/Sti1 is generally participating in PRR genesis. Using RNA-interference (RNAi), we silenced Hop/Sti1 expression in Nicotiana tabacum to gain further insight into the role of the cochaperone in plant defense responses. As expected, transgenic plants do not respond to chitin treatment anymore. In contrast to this, trafficking and functionality of the flagellin PRR FLS2 were unaltered, suggesting a selective involvement of Hop/Sti1 during PRR maturation. Furthermore, Hop/Sti1 was identified as a cellular determinant of Potato virus Y (PVY) symptom development in tobacco, since PVY was able to accumulate to near wild-type level without provoking the usual veinal necrosis phenotype. In addition, typical antiviral host defense responses were suppressed in the transgenic plants. These data suggest that perception of PVY is dependent on Hop/Sti1-mediated receptor maturation, while viral symptoms represent a failing attempt to restrict PVY spread. In addition, Hop/Sti1 colocalized with virus-induced membrane aggregates in wild-type plants. The retention of Hop/Sti1 in potential viral replication complexes suggests a role during viral translation/replication, explaining why RNAi-lines do not exhibit increased susceptibility to PVY. This study provides evidence for a dual role of Hop/Sti1 in PRR maturation and pathogen perception as well as in promoting viral proliferation.

HOP3, a member of the HOP family in Arabidopsis, interacts with BiP and plays a major role in the ER stress response

HSP70-HSP90 organizing protein (HOP) is a well-studied family of cytosolic cochaperones. However, the possible role of HOP during the endoplasmic reticulum (ER) stress response and the identity of its interactors within the ER were not previously addressed in any eukaryote. We have demonstrated that Arabidopsis HOP3, whose function was not studied before, interacts in vivo with cytosolic HSP90 and HSP70, and, unexpectedly, with binding immunoglobulin protein (BiP), a HSP70 ER-resident protein. Although BiP lacks the domain described in other eukaryotes for HOP-HSP70 binding, it interacts with HOP3 through a non-canonical association to its nucleotide binding domain. Consistent with this interaction with BiP, HOP3 is partially localized at the ER. Moreover, HOP3 is induced both at transcript and protein levels by unfolded protein response (UPR) inducer agents by a mechanism dependent on inositol-requiring enzyme 1 (IRE1). Importantly, hop3 loss-of-function mutants show a reduction in pollen germination and a hypersensitive phenotype in the presence of ER stress inducer agents, a phenotype that is reverted by the addition of the chemical chaperone tauroursodeoxycholic acid (TUDCA). All these data demonstrate, for the first time in any eukaryote, a main role of HOP as an important regulator of the ER stress response, a process intimately linked in plants to important specific developmental programs and to environmental stress sensing and response.

Osmotic Stress Induced Cell Death in Wheat Is Alleviated by Tauroursodeoxycholic Acid and Involves Endoplasmic Reticulum Stress-Related Gene Expression

Although, tauroursodeoxycholic acid (TUDCA) has been widely studied in mammalian cells because of its role in inhibiting apoptosis, its effects on plants remain almost unknown, especially in the case of crops such as wheat. In this study, we conducted a series of experiments to explore the effects and mechanisms of action of TUDCA on wheat growth and cell death induced by osmotic stress. Our results show that TUDCA: (1) ameliorates the impact of osmotic stress on wheat height, fresh weight, and water content; (2) alleviates the decrease in chlorophyll content as well as membrane damage caused by osmotic stress; (3) decreases the accumulation of reactive oxygen species (ROS) by increasing the activity of antioxidant enzymes under osmotic stress; and (4) to some extent alleviates osmotic stress-induced cell death probably by regulating endoplasmic reticulum (ER) stress-related gene expression, for example expression of the basic leucine zipper genes bZIP60B and bZIP60D, the binding proteins BiP1 and BiP2, the protein disulfide isomerase PDIL8-1, and the glucose-regulated protein GRP94. We also propose a model that illustrates how TUDCA alleviates osmotic stress-related wheat cell death, which provides an important theoretical basis for improving plant stress adaptation and elucidates the mechanisms of ER stress-related plant osmotic stress resistance.

The Life and Death of a Plant Cell

Like all eukaryotic organisms, plants possess an innate program for controlled cellular demise termed programmed cell death (PCD). Despite the functional conservation of PCD across broad evolutionary distances, an understanding of the molecular machinery underpinning this fundamental program in plants remains largely elusive. As in mammalian PCD, the regulation of plant PCD is critical to development, homeostasis, and proper responses to stress. Evidence is emerging that autophagy is key to the regulation of PCD in plants and that it can dictate the outcomes of PCD execution under various scenarios. Here, we provide a broad and comparative overview of PCD processes in plants, with an emphasis on stress-induced PCD. We also discuss the implications of the paradox that is functional conservation of apoptotic hallmarks in plants in the absence of core mammalian apoptosis regulators, what that means, and whether an equivalent form of death occurs in plants.

Arabidopsis B-cell lymphoma2 (Bcl-2)-associated athanogene 7 (BAG7)-mediated heat tolerance requires translocation, sumoylation and binding to WRKY29

To cope with stress and increased accumulation of misfolded proteins, plants and animals use a survival pathway known as the unfolded protein response (UPR) that signals between the endoplasmic reticulum (ER) and the nucleus to maintain cell homeostasis via proper folding of proteins. B-cell lymphoma2 (Bcl-2)-associated athanogene (BAG) proteins are an evolutionarily conserved family of co-chaperones that are linked to disease states in mammals and responses to environmental stimuli (biotic and abiotic) in plants. Molecular and physiological techniques were used to functionally characterize a newly identified branch of the UPR initiated by the ER-localized co-chaperone from Arabidopsis thaliana, AtBAG7. AtBAG7 has functional roles in both the ER and the nucleus. Upon heat stress, AtBAG7 is sumoylated, proteolytically processed and translocated from the ER to the nucleus, where interaction with the WRKY29 transcription factor occurs. Sumoylation and translocation are required for the AtBAG7-WRKY29 interaction and subsequent stress tolerance. In the ER, AtBAG7 interacts with the ER-localized transcription factor, AtbZIP28, and established UPR regulator, the AtBiP2 chaperone. The results indicate that AtBAG7 plays a central regulatory role in the heat-induced UPR pathway.

In silico study on Arabidopsis BAG gene expression in response to environmental stresses

BAG (Bcl-2 athanogene) family proteins are conserved in a wide range of eukaryotes, and they have been proposed to play a crucial role in plant programmed cell death (PCD). During the past decade, with the help of advanced bioinformatics tools, seven homologs of BAG genes have been identified in the Arabidopsis genome; these genes are involved in pathogen attack and abiotic stress conditions. In this study, gene expression of Arabidopsis BAG family members under environmental stresses was analyzed using the Botany Array Resource (BAR) expression browser tool and the in silico data were partially confirmed by qRT-PCR analysis for the selected stress- and hormone-treated conditions related to environmental stresses. Particularly, the induction of AtBAG6 gene in response to heat shock was confirmed by using GUS reporter lines. The loss of the AtBAG6 gene resulted into impairment in basal thermotolerance of plant and showed enhanced cell death in response to heat stress. To elucidate the regulatory mechanisms of BAG genes, we analyzed ∼1-kbp promoter regions for the presence of stress-responsive elements. Our transcription profiling finally revealed that the Arabidopsis BAG genes differentially respond to environmental stresses under the control of specifically organized upstream regulatory elements.

Baclofen Protects Primary Rat Retinal Ganglion Cells from Chemical Hypoxia-Induced Apoptosis Through the Akt and PERK Pathways

Retinal ganglion cells (RGCs) consume large quantities of energy to convert light information into a neuronal signal, which makes them highly susceptible to hypoxic injury. This study aimed to investigate the potential protection by baclofen, a GABA_B receptor agonist of RGCs against hypoxia-induced apoptosis. Cobalt chloride (CoCl₂) was applied to mimic hypoxia. Primary rat RGCs were subjected to CoCl₂ with or without baclofen treatment, and RNA interference techniques were used to knock down the GABA_B2 gene in the primary RGCs. The viability and apoptosis of RGCs were assessed using cell viability and terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assays, Hoechst staining, and flow cytometry. The expression of cleaved caspase-3, bcl-2, bax, Akt, phospho-Akt, protein kinase RNA (PKR)-like ER kinase (PERK), phospho-PERK, eIF2α, phospho-eIF2α, ATF-4 and CCAAT/enhancer-binding protein homologous protein (CHOP) were measured using western blotting. GABA_B2 mRNA expression was determined using quantitative real-time polymerase chain reaction (qRT-PCR) analysis. Our study revealed that CoCl₂ significantly induced RGC apoptosis and that baclofen reversed these effects. CoCl₂-induced reduction of Akt activity was also reversed by baclofen. Baclofen prevented the activation of the PERK pathway and the increase in CHOP expression induced by CoCl₂. Knockdown of GABA_B2 and the inactivation of the Akt pathway by inhibitors reduced the protective effect of baclofen on CoCl₂-treated RGCs. Taken together, these results demonstrate that baclofen protects RGCs from CoCl₂-induced apoptosis by increasing Akt activity and by suppressing the PERK pathway and CHOP activation.

The IRE1/bZIP60 Pathway and Bax Inhibitor 1 Suppress Systemic Accumulation of Potyviruses and Potexviruses in Arabidopsis and Nicotiana benthamiana Plants

The inositol requiring enzyme (IRE1) is an endoplasmic reticulum (ER) stress sensor. When activated, it splices the bZIP60 mRNA, producing a truncated transcription factor that upregulates genes involved in the unfolded protein response. Bax inhibitor 1 (BI-1) is another ER stress sensor that regulates cell death in response to environmental assaults. The potyvirus 6K2 and potexvirus TGB3 proteins are known to reside in the ER, serving, respectively, as anchors for the viral replicase and movement protein complex. This study used green fluorescent protein (GFP)-tagged Turnip mosaic virus (TuMV), Plantago asiatica mosaic virus (PlAMV), Potato virus Y (PVY), and Potato virus X (PVX) to determine that the IRE1/bZIP60 pathway and BI-1 machinery are induced early in virus infection in Arabidopsis thaliana, Nicotiana benthamiana, and Solanum tuberosum. Agrodelivery of only the potyvirus 6K2 or TGB3 genes into plant cells activated bZIP60 and BI-1 expression in Arabidopsis thaliana, N. benthamiana, and S. tuberosum. Homozygous ire1a-2, ire1b-4, and ire1a-2/ire1b-4 mutant Arabidopsis plants were inoculated with TuMV-GFP or PlAMV-GFP. PlAMV accumulates to a higher level in ire1a-2 or ire1a-2/ire1b-4 mutant plants than in ire1b-4 or wild-type plants. TuMV-GFP accumulates to a higher level in ire1a-2, ire1b-4, or ire1a-2/ire1b-4 compared with wild-type plants, suggesting that both isoforms contribute to TuMV-GFP infection. Gene silencing was used to knock down bZIP60 and BI-1 expression in N. benthamiana. PVX-GFP and PVY-GFP accumulation was significantly elevated in these silenced plants compared with control plants. This study demonstrates that two ER stress pathways, namely IRE1/bZIP60 and the BI-1 pathway, limit systemic accumulation of potyvirus and potexvirus infection. Silencing BI-1 expression also resulted in systemic necrosis. These data suggest that ER stress-activated pathways, led by IRE1 and BI-1, respond to invading potyvirus and potexviruses to restrict virus infection and enable physiological changes enabling plants to tolerate virus assault.

Allyl-isothiocyanate treatment induces a complex transcriptional reprogramming including heat stress, oxidative stress and plant defence responses in Arabidopsis thaliana

Background

Isothiocyanates (ITCs) are degradation products of the plant secondary metabolites glucosinolates (GSLs) and are known to affect human health as well as plant herbivores and pathogens. To investigate the processes engaged in plants upon exposure to isothiocyanate we performed a genome scale transcriptional profiling of Arabidopsis thaliana at different time points in response to an exogenous treatment with allyl-isothiocyanate.

Results

The treatment triggered a substantial response with the expression of 431 genes affected (P < 0.05 and log₂ ≥ 1 or ≤ -1) already after 30 min and that of 3915 genes affected after 9 h of exposure, most of the affected genes being upregulated. These are involved in a considerable number of different biological processes, some of which are described in detail: glucosinolate metabolism, sulphate uptake and assimilation, heat stress response, oxidative stress response, elicitor perception, plant defence and cell death mechanisms.

Conclusion

Exposure of Arabidopsis thaliana to vapours of allyl-isothiocyanate triggered a rapid and substantial transcriptional response affecting numerous biological processes. These include multiple stress stimuli such as heat stress response and oxidative stress response, cell death and sulphur secondary defence metabolism. Hence, effects of isothiocyanates on plants previously reported in the literature were found to be regulated at the gene expression level. This opens some avenues for further investigations to decipher the molecular mechanisms underlying the effects of isothiocyanates on plants.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3039-x) contains supplementary material, which is available to authorized users.

The Potyviral P3 Protein Targets Eukaryotic Elongation Factor 1A to Promote the Unfolded Protein Response and Viral Pathogenesis

The biochemical function of the potyviral P3 protein is not known, although it is known to regulate virus replication, movement, and pathogenesis. We show that P3, the putative virulence determinant of soybean mosaic virus (SMV), targets a component of the translation elongation complex in soybean. Eukaryotic elongation factor 1A (eEF1A), a well-known host factor in viral pathogenesis, is essential for SMV virulence and the associated unfolded protein response (UPR). Silencing GmEF1A inhibits accumulation of SMV and another ER-associated virus in soybean. Conversely, endoplasmic reticulum (ER) stress-inducing chemicals promote SMV accumulation in wild-type, but not GmEF1A-knockdown, plants. Knockdown of genes encoding the eEF1B isoform, which is important for eEF1A function in translation elongation, has similar effects on UPR and SMV resistance, suggesting a link to translation elongation. P3 and GmEF1A promote each other's nuclear localization, similar to the nuclear-cytoplasmic transport of eEF1A by the Human immunodeficiency virus 1 Nef protein. Our results suggest that P3 targets host elongation factors resulting in UPR, which in turn facilitates SMV replication and place eEF1A upstream of BiP in the ER stress response during pathogen infection.