The effects of induced production of reactive oxygen species in organelles on endoplasmic reticulum stress and on the unfolded protein response in arabidopsis

Freezing treatment under light conditions leads to a dramatic enhancement of freezing tolerance in cold-acclimated Arabidopsis

Overwintering plants survive subzero temperatures by cold acclimation (CA), wherein they acquire freezing tolerance through short-term exposure to low temperatures above 0°C. The freezing tolerance of CA plants increases when they are subsequently exposed to mild subzero temperatures, a phenomenon known as second-phase cold hardening (2PH). Here, we explored the molecular mechanism and physiological conditions of 2PH. The results show that, compared with supercooling, a freezing treatment during 2PH after CA enhanced the freezing tolerance of Arabidopsis. This required CA as a pretreatment, and was designated as second-phase freezing acclimation (2PFA). Light increased the effect of 2PFA to enhance freezing tolerance after CA. C-repeat binding factor and cold-regulated genes were downregulated by light during the 2PFA treatment, a different transcription profile from that during CA. The freezing tolerance of 2PFA plants was decreased by the presence of the photosynthetic electron transfer inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea during the 2PFA treatment. Compared with wild-type plants, phototropin1,2 and phyb mutants showed lower freezing tolerance after 2PFA treatment. These results show that exposure to freezing after CA increases freezing tolerance as a secondary process, and that freezing under light conditions further increases freezing tolerance via pathways involving photoreceptors and photosynthetic electron transfer.

Salicylic acid- and ethylene-dependent effects of the ER stress-inducer tunicamycin on the photosynthetic light reactions in tomato plants

Plant hormones such as ethylene (ET) and salicylic acid (SA) have an elementary role in the regulation of ER stress and unfolded protein response (UPR) in plants via modulating defence responses or inducing oxidative stress. Chloroplasts can be sources and targets of reactive oxygen species (ROS) that affect photosynthetic efficiency, which has not been investigated under tunicamycin (Tm)-induced ER stress. In this study, the direct and indirect effects of Tm on chloroplastic ROS production were first investigated in leaves of wild-type tomato (Solanum lycopersicum L.) plants. Secondly changes in activities of photosystem II and I were analysed under Tm exposure and after application of the chemical chaperone 4-phenylbutyrate (PBA) in different genotypes, focusing on the regulatory role of SA and ET Tm treatments significantly but indirectly induced ROS production in tomato leaves and in parallel it decreased the effective quantum yield of PSII [Y(II)] and PSI [Y(I)], as well as the photochemical quenching coefficient (qP) and the quantum yield of non-photochemical energy dissipation in PSI due to acceptor-side limitation [Y(NA)]. At the same time, Tm increased non-photochemical quenching (NPQ) and cyclic electron flow (CEF) in tomato leaves after 24 h. However, the photosynthetic activity of the SA hydroxylase-overexpressing NahG tomato plants was more severely affected by Tm as compared to wild-type and ET-insensitive Never ripe (Nr) plants. These results suggest the protective role of SA in the regulation of photosynthetic activity contributing to UPR and the survival of plants under ER stress. Interestingly, the activation of photoprotective mechanisms by NPQ was independent of SA but dependent on active ET signalling under ER stress, whereas CEF was reduced by ET due to its higher ratio in Nr plants.

Investigating the effects of tauroursodeoxycholic acid (TUDCA) in mitigating endoplasmic reticulum stress and cellular responses in Pak choi

The accumulation of misfolded proteins in the endoplasmic reticulum (ER) within plant cells due to unfavourable conditions leads to ER stress. This activates interconnected pathways involving reactive oxygen species (ROS) and unfolded protein response (UPR), which play vital roles in regulating ER stress. The aim of this study is to investigate the underlying mechanisms of tunicamycin (TM) induced ER stress and explore the potential therapeutic applications of tauroursodeoxycholic acid (TUDCA) in mitigating cellular responses to ER stress in Pak choi (Brassica campestris subsp. chinensis). The study revealed that ER stress in Pak choi leads to detrimental effects on plant morphology, ROS levels, cellular membrane integrity, and the antioxidant defence system. However, treatment with TUDCA in TM-induced ER stressed Pak choi improved morphological indices, pigment contents, ROS accumulation, cellular membrane integrity, and antioxidant defence system restoration. Additionally, TUDCA also modulates the transcription levels of ER stress sensors genes, ER chaperone genes, and ER-associated degradation (ERAD) genes during ER stress in Pak choi. Furthermore, TUDCA has demonstrated its ability to alleviate ER stress, stabilize the UPR, reduce oxidative stress, prevent apoptosis, and positively influence plant growth and development. These results collectively comprehend TUDCA as a promising agent for mitigating ER stress-induced damage in Pak choi plants and provide valuable insights for further research and potential applications in crop protection and stress management.

The role of salicylic acid on glutathione metabolism under endoplasmic reticulum stress in tomato

The endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) are highly dependent on phytohormones such as salicylic acid (SA). In this study, the effect of SA supplementation and the lack of endogenous SA on glutathione metabolism were investigated under ER stress in wild-type (WT) and transgenic SA-deficient NahG tomato (Solanum lycopersicum L.) plants. The expression of the UPR marker gene SlBiP was dependent on SA levels and remained lower in NahG plants. Exogenous application of the chemical chaperone 4-phenylbutyrate (PBA) also reduced tunicamycin (Tm)-induced SlBiP transcript accumulation. At the same time, Tm-induced superoxide and hydrogen peroxide production were independent of SA, whereas the accumulation of reduced form of glutathione (GSH) and the oxidised glutathione (GSSG) was regulated by SA. Tm increased the activity of glutathione reductase (GR; EC 1.6.4.2) independently of SA, but the activities of dehydroascorbate reductase (DHAR; EC 1.8.5.1) and glutathione S-transferases (GSTs; EC 2.5.1.18) were increased by Tm in a SA-dependent manner. SlGR2, SlGGT and SlGSTT2 expression was activated in a SA-dependent way upon Tm. Although expression of SlGSH1, SlGSTF2, SlGSTU5 and SlGTT3 did not change upon Tm treatment in leaves, SlGR1 and SlDHAR2 transcription decreased. PBA significantly increased the expression of SlGR1, SlGR2, SlGSTT2, and SlGSTT3, which contributed to the amelioration of Tm-induced ER stress based on the changes in lipid peroxidation and cell viability. Malondialdehyde accumulation and electrolyte leakage were significantly higher in WT as compared to NahG tomato leaves under ER stress, further confirming the key role of SA in this process.

Unveiling a differential metabolite modulation of sorghum varieties under increasing tunicamycin-induced endoplasmic reticulum stress

Plants trigger endoplasmic reticulum (ER) pathways to survive stresses, but the assistance of ER in plant tolerance still needs to be explored. Thus, we selected sensitive and tolerant contrasting abiotic stress sorghum varieties to test if they present a degree of tolerance to ER stress. Accordingly, this work evaluated crescent concentrations of tunicamycin (TM µg mL-1): control (0), lower (0.5), mild (1.5), and higher (2.5) on the initial establishment of sorghum seedlings CSF18 and CSF20. ER stress promoted growth and metabolism reductions, mainly in CSF18, from mild to higher TM. The lowest TM increased SbBiP and SbPDI chaperones, as well as SbbZIP60, and SbbIRE1 gene expressions, but mild and higher TM decreased it. However, CSF20 exhibited higher levels of SbBiP and SbbIRE1 transcripts. It corroborated different metabolic profiles among all TM treatments in CSF18 shoots and similarities between profiles of mild and higher TM in CSF18 roots. Conversely, TM profiles of both shoots and roots of CSF20 overlapped, although it was not complete under low TM treatment. Furthermore, ER stress induced an increase of carbohydrates (dihydroxyacetone in shoots, and cellobiose, maltose, ribose, and sucrose in roots), and organic acids (pyruvic acid in shoots, and butyric and succinic acids in roots) in CSF20, which exhibited a higher degree of ER stress tolerance compared to CSF18 with the root being the most affected plant tissue. Thus, our study provides new insights that may help to understand sorghum tolerance and the ER disturbance as significant contributor for stress adaptation and tolerance engineering.

Transcription factor TERF1 promotes seed germination through HEXOKINASE 1 (HXK1)-mediated signaling pathway

Seed germination, a vital process for plant growth and development, is regulated by ethylene. Previously, we showed that Tomato Ethylene Responsive Factor 1 (TERF1), an ethylene-responsive factor (ERF) transcription factor, could significantly promote seed germination by increasing glucose content. As glucose can function as a signaling molecule to regulate plant growth and development through HEXOKINASE 1 (HXK1), we aim to illustrate how TERF1 promotes seed germination through the HXK1-mediated signaling pathway. We showed that seeds overexpressing TERF1 exhibited more resistance to N-acetylglucosamine (NAG), an inhibitor of the HXK1- mediated signaling pathway. We identified genes regulated by TERF1 through HXK1 based on transcriptome analysis. Gene expression and phenotype analysis demonstrated that TERF1 repressed the ABA signaling pathway through HXK1, which promoted germination through activating the plasma membrane (PM) H+-ATPase. TERF1 also alleviated the endoplasmic reticulum (ER) stress to accelerate germination by maintaining reactive oxygen species (ROS) homeostasis through HXK1. Our findings provide new insights into the mechanism regulated by ethylene through the glucose-HXK1 signaling pathway during seed germination.

The glutathione-dependent alarm triggers signalling responses involved in plant acclimation to cadmium

Cadmium (Cd) uptake from polluted soils inhibits plant growth and disturbs physiological processes, at least partly due to disturbances in the cellular redox environment. Although the sulfur-containing antioxidant glutathione is important in maintaining redox homeostasis, its role as an antioxidant can be overruled by its involvement in Cd chelation as a phytochelatin precursor. Following Cd exposure, plants rapidly invest in phytochelatin production, thereby disturbing the redox environment by transiently depleting glutathione concentrations. Consequently, a network of signalling responses is initiated, in which the phytohormone ethylene is an important player involved in the recovery of glutathione levels. Furthermore, these responses are intricately connected to organellar stress signalling and autophagy, and contribute to cell fate determination. In general, this may pave the way for acclimation (e.g. restoration of glutathione levels and organellar homeostasis) and plant tolerance in the case of mild stress conditions. This review addresses connections between these players and discusses the possible involvement of the gasotransmitter hydrogen sulfide in plant acclimation to Cd exposure.

Cadmium-induced oxidative stress responses and acclimation in plants require fine-tuning of redox biology at subcellular level

Cadmium (Cd) is one of the most toxic compounds released into our environment and is harmful to human health, urging the need to remediate Cd-polluted soils. To this end, it is important to increase our insight into the molecular mechanisms underlying Cd stress responses in plants, ultimately leading to acclimation, and to develop novel strategies for economic validation of these soils. Albeit its non-redox-active nature, Cd causes a cellular oxidative challenge, which is a crucial determinant in the onset of diverse signalling cascades required for long-term acclimation and survival of Cd-exposed plants. Although it is well known that Cd affects reactive oxygen species (ROS) production and scavenging, the contribution of individual organelles to Cd-induced oxidative stress responses is less well studied. Here, we provide an overview of the current information on Cd-induced organellar responses with special attention to redox biology. We propose that an integration of organellar ROS signals with other signalling pathways is essential to finetune plant acclimation to Cd stress.

Fine particulate matter induces heart defects via AHR/ROS-mediated endoplasmic reticulum stress

Accumulating body of evidence indicates that exposure to fine particulate matter (PM_2.5) is closely associated with congenital heart disease in the offspring, but the underlying molecular mechanisms remain to be elucidated. We previously reported that extractable organic matter (EOM) from PM_2.5 induces reactive oxygen species (ROS) overproduction by activating aromatic hydrocarbon receptor (AHR), leading to heart defects in zebrafish embryos. We hypothesized that endoplasmic reticulum (ER) stress might be elicited by the excessive ROS production and thereby contribute to the cardiac developmental toxicity of PM_2.5. In this study, we examined the effects of EOM on endoplasmic reticulum (ER) stress, apoptosis, and Wnt signal pathway in zebrafish embryos, and explored their roles in EOM-induced heart defects. Our results showed that 4-Phenylbutyric acid (4-PBA), a pharmaceutical inhibitor of ER stress, significantly attenuated the EOM-elevated heart malformation rates. Moreover, EOM upregulated the expression levels of ER stress marker genes including CHOP and PDI in the heart of zebrafish embryos, which were counteracted by genetic or pharmaceutical inhibition of AHR activity. The ROS scavenger N-Acetyl-l-cysteine (NAC) also abolished the EOM-induced ER stress. We further demonstrated that both 4-PBA and CHOP genetic knockdown rescued the PM_2.5-induced ROS overproduction, apoptosis and suppression of Wnt signaling. In conclusion, our results indicate that PM_2.5 induces AHR/ROS-mediated ER stress, which leads to apoptosis and Wnt signaling inhibition, ultimately resulting in heart defects.

Multiwalled Carbon Nanotubes Alter the PSII Photochemistry, Photosystem-Related Gene Expressions, and Chloroplastic Antioxidant System in Zea mays under Copper Toxicity

A critical approach against copper (Cu) toxicity is the use of carbon nanomaterials (CNMs). However, the effect of CNMs on Cu toxicity-exposed chloroplasts is not clear. The photosynthetic, genetic, and biochemical effects of multiwalled carbon nanotubes (50-100-250 mg L^-1 CNT) were investigated under Cu stress (50-100 μM CuSO₄) in Zea mays chloroplasts. F_v/F_m and F_v/F_o were suppressed under stress. Stress altered the antioxidant system and the expression of psaA, psaB, psbA, and psbD. The chloroplastic activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione S-transferase (GST), and glutathione peroxidase (GPX) increased under CNT + stress, and those of hydrogen peroxide (H₂O₂) and lipid peroxidation decreased. CNTs were promoted to the maintenance of the redox state by regulating enzyme/non-enzyme activity/contents involved in the AsA-GSH cycle. Furthermore, CNTs inverted the negative effects of Cu by upregulating the transcriptions of photosystem-related genes. However, the high CNT concentration had adverse effects on the antioxidant capacity. CNT has great potential to confer tolerance by reducing Cu-induced damage and protecting the biochemical reactions of photosynthesis.

THESEUS1 is involved in tunicamycin-induced root growth inhibition, ectopic lignin deposition, and cell wall damage-induced unfolded protein response

Endoplasmic reticulum (ER) stress activates unfolded protein responses (UPRs), such as promoting protein folding under the control of specific gene expression. Our previous study showed that ER stress induced by ER stress inducers such as tunicamycin (Tm), an inhibitor of N-linked glycan synthesis, causes ectopic lignin deposition in Arabidopsis roots, but the relationship between UPR and ectopic lignin deposition remains unclear. The receptor-like kinase THESEUS1 (THE1) has been shown to sense cell wall damage (CWD) induced in Arabidopsis by cellulose synthase inhibitors such as isoxaben (ISO) and to activate ectopic lignin deposition. In this study, we assessed the involvement of THE1 in ectopic lignin deposition caused by the ER stress inducer Tm. The loss-of-function mutation of THE1, the1-3, suppressed Tm-induced root growth inhibition and ectopic lignin deposition, revealing that THE1 is involved in root growth defects and ectopic lignin deposition caused by ER stress. Similarly, ISO treatment induced ectopic lignin deposition as well as the expression of the UPR marker genes binding protein 3 (BiP3) and ER-localized DnaJ 3b (ERdj3b). Conversely, in the the1-3 mutant, ISO-induced ectopic lignin deposition and the expression of BiP3 and ERdj3b were suppressed. These results showed that THE1 is involved in not only root growth inhibition and ectopic lignin deposition caused by ER stress but also CWD-induced UPR.

Endoplasmic Reticulum Stress and Reactive Oxygen Species in Plants

The endoplasmic reticulum (ER) is a key compartment responsible for protein processing and folding, and it also participates in many signal transduction and metabolic processes. Reactive oxygen species (ROS) are important signaling messengers involved in the redox equilibrium and stress response. A number of abiotic and biotic stresses can trigger the accumulation of unfolded or misfolded proteins and lead to ER stress. In recent years, a number of studies have reported that redox metabolism and ROS are closely related to ER stress. ER stress can benefit ROS generation and even cause oxidative burden in plants, finally leading to oxidative stress depending on the degree of ER stress. Moreover, ER stress activates nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-mediated ROS signaling, increases antioxidant defense mechanisms, and alters the glutathione (GSH) redox state. Meanwhile, the accumulation of ROS plays a special role in inducing the ER stress response. Given these factors, plants have evolved a series of complex regulatory mechanisms to interact with ROS in response to ER stress. In this review, we summarize the perceptions and responses of plant ER stress and oxidative protein folding in the ER. In addition, we analyze the production and signaling of ROS under ER stress in detail in order to provide a theoretical basis for reducing ER stress to improve the crop survival rate in agricultural applications.

The biphasic responses of nanomaterial fullerene on stomatal movement, water status, chlorophyll a fluorescence transient, radical scavenging system and aquaporin-related gene expression in Zea mays under cobalt stress

Nanomaterial fullerene (FLN) has different responses called the hormesis effect against stress conditions. The favorable/adverse impacts of hormesis on crop quality and productivity are under development in agrotechnology. In this study, the effect of FLN administration (100-250-500mg L^-1 for FLN1-2-3, respectively) on growth, water management, gas exchange, chlorophyll fluorescence kinetics and cobalt (Co)-induced oxidative stress in Zea mays was investigated. The negative alterations in relative growth rate (RGR), water status (relative water content, osmotic potential and proline content) and gas exchange/stomatal regulation were removed by FLNs. FLNs were shown to protect photosynthetic apparatus and preserve the photochemistry of photosystems (PSI-PSII) in photosynthesis, chlorophyll fluorescence transients and energy flux damaged under Co stress. The maize leaves exposed to Co stress exhibited a high accumulation of hydrogen peroxide (H₂O₂) due to insufficient scavenging activity, which was confirmed by reactive oxygen species (ROS)-specific fluorescence visualization in guard cells. FLN regulated the gene expression of ribulose-1,5-bisphosphate carboxylase large subunit (rbcL), nodulin 26-like intrinsic protein1-1 (NIP1-1) and tonoplast intrinsic protein2-1 (TIP2-1) under stress. After stress exposure, FLNs successfully eliminated H₂O₂ content produced by superoxide dismutase (SOD) activity of catalase (CAT) and peroxidase (POX). The ascorbate (AsA) regeneration was achieved in all FLN applications together with Co stress through the elevated monodehydroascorbate reductase (MDHAR, under all FLNs) and dehydroascorbate reductase (DHAR, only FLN1). However, dose-dependent FLNs (FLN1-2) provided the induced pool of glutathione (GSH) and GSH redox state. Hydroponically applied FLNs removed the restrictions on metabolism and biological process induced by lipid peroxidation (TBARS content) and excessive ROS production. Considering all data, the modulation of treatment practices in terms of FLN concentrations and forms of its application will provide a unique platform for improving agricultural productivity and stress resistance in crops. The current study provided the first findings on the chlorophyll a fluorescence transient and localization of ROS in guard cells of Zea mays exposed to FLN and Co stress.

Role of ethylene in ER stress and the unfolded protein response in tomato (Solanum lycopersicum L.) plants

The unfolded protein response (UPR) plays a significant role in the maintenance of cellular homeostasis under endoplasmic reticulum (ER) stress, which is highly dependent on the regulation of defense-related phytohormones. In this study, the role of ethylene (ET) in ER stress and UPR was investigated in the leaves of intact tomato (Solanum lycopersicum) plants. Exogenous application of the ET precursor 1-aminocyclopropane-1-carboxylic acid not only resulted in higher ET emission from leaves but also increased the expression of the UPR marker gene SlBiP and the transcript levels of the ER stress sensor SlIRE1, as well as the levels of SlbZIP60, after 24 h in tomato leaves. Using ET receptor Never ripe (Nr) mutants, a significant role of ET in tunicamycin (Tm)-induced ER stress sensing and signaling was confirmed based on the changes in the expression levels of SlIRE1b and SlBiP. Furthermore, the analysis of other defense-related phytohormones showed that the Tm-induced ET can affect positively the levels of and response to salicylic acid. Additionally, it was found that nitric oxide production and lipid peroxidation, as well as the electrolyte leakage induced by Tm, is regulated by ET, whereas the levels of H₂O₂ and proteolytic activity seemed to be independent of ET under ER stress in the leaves of tomato plants.

Rosmarinic acid and hesperidin regulate gas exchange, chlorophyll fluorescence, antioxidant system and the fatty acid biosynthesis-related gene expression in Arabidopsis thaliana under heat stress

The impacts of exogenous rosmarinic acid (RA, 100 μM) and/or hesperidin (HP, 100 μM) were evaluated in improving tolerance on the gas exchange, chlorophyll fluorescence and efficiencies, phenomenological fluxes of photosystems, antioxidant system and gene expression related to the lipid biosynthesis under heat stress. For this purpose, Arabidopsis thaliana was grown under RA and HP with heat stress (S, 38 °C) for 24 h(h). As shown in gas exchange parameters, heat stress caused mesophyll efficiency and non-stomatal restrictions. Both alone and combined forms of RA and HP to stress-treated A. thaliana alleviated the disturbance of carbon assimilation, transpiration rate and internal CO2 concentrations. Stress impaired the levels of energy flow reaching reaction centers of PSII and the photon capture ability of active reaction centers. RA and/or HP enhanced photosystems' structural/functional characteristics and photosynthetic performance. Histochemical staining and biochemical analyses revealed that heat stress caused the oxidation in A. thaliana. By activating several defensive mechanisms, RA and/or HP could reverse the harm caused by radical production. Both alone and combined forms of RA and HP removed superoxide anion radical (O2•-) accumulation, inducing superoxide dismutase (SOD). The common enzyme that scavenged hydrogen peroxide (H2O2) at all three applications (S + RA, S + HP and S + RA + HP) was POX. Also, only RA could utilize the ascorbate (AsA) regeneration in response to stress, suggesting increased ascorbate peroxidase (APX), monodehydroascorbate (MDHAR) and dehydroascorbate (DHAR) activities. However, the regeneration/redox state of AsA and glutathione (GSH) did not maintain under S + HP and S + RA + HP. While RA had no positive influence on the saturated fatty acids under stress, HP increased the total saturated fatty acids (primarily palmitic acid). Besides, the combined application of RA + HP effectively created the stress response by increasing the expression of genes involved in fatty acid synthesis. The synergetic interactions of RA and HP could explain the increased levels of saturated fatty acids in combining these compounds. The data obtained from the study will contribute to the responses of phenolic compounds in plants to heat stress.

The effects of fullerene on photosynthetic apparatus, chloroplast-encoded gene expression, and nitrogen assimilation in Zea mays under cobalt stress

Carbon nanostructures, such as the water-soluble fullerene (FLN) derivatives, are considered perspective agents for agriculture. FLN can be a novel nano-agent modulating plant response against stress conditions. However, the mechanism underlying the impacts of FLN on plants in agroecosystems remains unclear. Zea mays was exposed to exogenous C₆₀ -FLN applications (FLN1: 100; FLN2: 250; and FLN3: 500 mg L^-1 ) with/without cobalt stress (Co, 300 μM) for 3 days (d). In the maize chloroplasts, Co stress disrupted the photosynthetic efficiency and the expression of genes related to the photosystems (psaA and psbA). FLNs effectively improved the efficiency and photochemical reaction of photosystems. Co stress induced the accumulation of reactive oxygen species (ROS) as confirmed by ROS-specific fluorescence in guard cells. Co stress increased only chloroplastic superoxide dismutase (SOD) and peroxidase (POX). Stress triggered oxidative damages in maize chloroplasts, measured as an increase in TBARS content. In Co-stressed seedlings exposed to FLN1 and FLN2 exposures, the hydrogen peroxide (H₂ O₂ ) was scavenged through the nonenzymes/enzymes-related to the AsA-GSH cycle by preserving ascorbate (AsA) conversion, as well as GSH/GSSG and glutathione (GSH) redox state. Also, the alleviation effect of FLN3 against stress could be attributed to increased glutathione S-transferase (GST) activity and AsA regeneration. FLN applications reversed the inhibitory effects of Co stress on nitrogen assimilation. In maize chloroplasts, FLN increased the activities of nitrate reductase (NR), glutamate dehydrogenase (GDH), nitrite reductase (NiR), and glutamine synthetase (GS), which provided conversion of inorganic nitrogen (N) into organic N. The ammonium (NH₄ ⁺ ) toxicity was removed via GS and GDH but not glutamate synthase (GOGAT). The increased NAD-GDH (deaminating) and NADH-GDH (aminating) activities indicated that GDH was needed more for NH₄ ⁺ detoxification. Therefore, FLN exposure to Co-stressed maize plants might play a role in N metabolism regarding the partitioning of N assimilates. Exogenous FLN conceivably removed Co toxicity by improving the expressions of genes related to reaction center proteins of photosystems, increasing the level of enzymes related to the defense system, and improving the N assimilation in maize chloroplasts.

Nanomaterial sulfonated graphene oxide advances the tolerance against nitrate and ammonium toxicity by regulating chloroplastic redox balance, photochemistry of photosystems and antioxidant capacity in Triticum aestivum

The current study was designed to assess nanomaterial sulfonated graphene oxide (SGO) potential in improving tolerance of wheat chloroplasts against nitrate (NS) and ammonium (AS) toxicity. Triticum aestivum cv. Ekiz was grown under SGOs (50-250-500 mg L^-1) with/without 140 mM NS and 5 mM AS stress. SGOs were eliminated the adverse effects produced by stress on chlorophyll fluorescence, potential photochemical efficiency and physiological state of the photosynthetic apparatus. SGO reversed the negative effects on these parameters. Upon SGOs exposure, the induced expression levels of photosystems-related reaction center proteins were observed. SGOs reverted radical accumulation triggered by NS by enabling the increased superoxide dismutase (SOD) activity and ascorbate (AsA) regeneration. Under AS, the turnover of both AsA and glutathione (GSH) was maintained by 50-250 mg L^-1 SGO by increasing the enzymes and non-enzymes related to AsA-GSH cycle. 500 mg L^-1 SGO prevented the radical over-accumulation produced by AS via the regeneration of AsA and peroxidase (POX) activity rather than GSH regeneration. 50-250 mg L^-1 SGO protected from the NS+AS-induced disruptions through the defense pathways connected with AsA-GSH cycle represented the high rates of AsA/DHA and, GSH/GSSG and GSH redox state. Our findings specified that SGO to NS and AS-stressed wheat provides a new potential tool to advance the tolerance mechanism.

Synergistic Association With Root Endophytic Fungi Improves Morpho-Physiological and Biochemical Responses of Chenopodium quinoa to Salt Stress

Symbiotic associations with microbes can contribute to mitigating abiotic environmental stress in plants. In this study, we investigated individual and interactive effects of two root endophytic fungal species on physiological and biochemical mechanisms of the crop Chenopodium quinoa in response to salinity. Fungal endophytes (FE) Talaromyces minioluteus and Penicillium murcianum, isolated from quinoa plants that occur naturally in the Atacama Desert, were used for endophyte inoculation. A greenhouse experiment was developed using four plant groups: (1) plants inoculated with T. minioluteus (E1+), (2) plants inoculated with P. murcianum (E2+), (3) plants inoculated with both fungal species (E1E2+), and (4) non-inoculated plants (E-). Plants from each group were then assigned to either salt (300 mM) or control (no salt) treatments. Differences in morphological traits, photosynthesis, stomatal conductance, transpiration, superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase, (POD), phenylalanine ammonia-lyase (PAL), phenolic content, and lipid peroxidation between plant groups under each treatment were examined. We found that both endophyte species significantly improved morphological and physiological traits, including plant height, number of shoots, photosynthesis, stomatal conductance, and transpiration, in C. quinoa in response to salt, but optimal physiological responses were observed in E1E2+ plants. Under saline conditions, endophyte inoculation improved SOD, APX, and POD activity by over 50%, and phenolic content by approximately 30%, with optimal enzymatic responses again observed in E1E2+ plants. Lipid peroxidation was significantly lower in inoculated plants than in non-inoculated plants. Results demonstrate that both endophyte species enhanced the ability of C. quinoa to cope with salt stress by improving antioxidative enzyme and non-enzyme systems. In general, both FE species interacting in tandem yielded better morphological, physiological, and biochemical responses to salinity in quinoa than inoculation by a single species in isolation. Our study highlights the importance of stress-adapted FE as a biological agent for mitigating abiotic stress in crop plants.

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.

An update on redox signals in plant responses to biotic and abiotic stress crosstalk: insights from cadmium and fungal pathogen interactions

Complex signalling pathways are involved in plant protection against single and combined stresses. Plants are able to coordinate genome-wide transcriptional reprogramming and display a unique programme of transcriptional responses to a combination of stresses that differs from the response to single stresses. However, a significant overlap between pathways and some defence genes in the form of shared and general stress-responsive genes appears to be commonly involved in responses to multiple biotic and abiotic stresses. Reactive oxygen and nitrogen species, as well as redox signals, are key molecules involved at the crossroads of the perception of different stress factors and the regulation of both specific and general plant responses to biotic and abiotic stresses. In this review, we focus on crosstalk between plant responses to biotic and abiotic stresses, in addition to possible plant protection against pathogens caused by previous abiotic stress. Bioinformatic analyses of transcriptome data from cadmium- and fungal pathogen-treated plants focusing on redox gene ontology categories were carried out to gain a better understanding of common plant responses to abiotic and biotic stresses. The role of reactive oxygen and nitrogen species in the complex network involved in plant responses to changes in their environment is also discussed.

Cigarette smoke-induced toxicity consequences of intracellular iron dysregulation and ferroptosis

Despite numerous studies on the mechanisms of cigarette smoking toxicity over the past three decades, some aspects remain obscure. Recent developments have drawn attention to some hopeful indicators that allow us to advance our awareness of cigarette-induced cell death. Ferroptosis is considered a type of governed death of cells distinguished by the iron-dependent lipid hydroperoxide deposition to fatal concentrations. Ferroptosis has been linked with pathological settings such as neurodegenerative diseases, cancer, heart attack, hemorrhagic stroke, traumatic brain injury, ischemia-reperfusion injury, and renal dysfunction. This review tries to explain the causal role of ferroptosis cascade in cigarette smoke-mediated toxicity and cell death, highlighting associations on potential action mechanisms and proposing suggestions for its detoxifying and therapeutic interventions.

At the Crossroads of Survival and Death: The Reactive Oxygen Species-Ethylene-Sugar Triad and the Unfolded Protein Response

Upon stress, a trade-off between plant growth and defense responses defines the capacity for survival. Stress can result in accumulation of misfolded proteins in the endoplasmic reticulum (ER) and other organelles. To cope with these proteotoxic effects, plants rely on the unfolded protein response (UPR). The involvement of reactive oxygen species (ROS), ethylene (ETH), and sugars, as well as their crosstalk, in general stress responses is well established, yet their role in UPR deserves further scrutiny. Here, a synopsis of current evidence for ROS-ETH-sugar crosstalk in UPR is discussed. We propose that this triad acts as a major signaling hub at the crossroads of survival and death, integrating information from ER, chloroplasts, and mitochondria, thereby facilitating a coordinated stress response.

Transcriptional Regulatory Networks Associate with Early Stages of Potato Virus X Infection of Solanum tuberosum

Potato virus X (PVX) belongs to genus Potexvirus. This study characterizes the cellular transcriptome responses to PVX infection in Russet potato at 2 and 3 days post infection (dpi). Among the 1242 differentially expressed genes (DEGs), 268 genes were upregulated, and 37 genes were downregulated at 2 dpi while 677 genes were upregulated, and 265 genes were downregulated at 3 dpi. DEGs related to signal transduction, stress response, and redox processes. Key stress related transcription factors were identified. Twenty-five pathogen resistance gene analogs linked to effector triggered immunity or pathogen-associated molecular pattern (PAMP)-triggered immunity were identified. Comparative analysis with Arabidopsis unfolded protein response (UPR) induced DEGs revealed genes associated with UPR and plasmodesmata transport that are likely needed to establish infection. In conclusion, this study provides an insight on major transcriptional regulatory networked involved in early response to PVX infection and establishment.

Interaction of nobiletin with methotrexate ameliorates 7-OH methotrexate-induced nephrotoxicity through endoplasmic reticulum stress-dependent PERK/CHOP signaling pathway

Drug-induced nephrotoxicity is a frequent adverse event that contributes to acute kidney injury with tubular and/or glomerular lesions. Methotrexate (MTX) is a folate analog used against a myriad of malignancies and autoimmune diseases. Unfortunately, ambiguous renal toxicology limits its safe clinical usage. Based on our previous studies, 7-OH MTX as an overlooked oxidative metabolite of MTX was proposed to be the main culprit responsible for nephrotoxicity, while nobiletin, a naturally occurring polymethoxylated flavonoid screened from our prepared total phenolic extracts of Citrus aurantium L. (TPE-CA), was employed as a therapeutic agent for drug-drug interactions. According to the present study, nobiletin can ameliorate the renal accumulation of 7-OH MTX through the interaction with aldehyde oxidase. RNA-seq analysis revealed that 7-OH MTX was mainly related to protein processing in endoplasmic reticulum (ER) stress, with the PERK/CHOP pathway selected as the most significant for metabolic nephrotoxicity. Meanwhile, the cross-linked proteins and conducted signals were investigated by western blotting and further verified by GSK inhibition analyses. These results indicated that nobiletin protected renal function from MTX-induced nephrotoxicity by modulating metabolism and ameliorated the metabolic toxicity of 7-OH MTX on ER stress-induced PERK/CHOP conduction by maintaining Ca²⁺ homeostasis and reducing the production of reactive oxygen species.

Mi-RNA-888-5p Is Involved in S-Adenosylmethionine Antitumor Effects in Laryngeal Squamous Cancer Cells

Simple Summary

Laryngeal Squamous Cell Carcinoma (LSCC) is a leading cause of cancer-related death with a strong interest in identifying and developing new treatments. MicroRNAs (miRNAs) have emerged as one of the most important determinants of neoplastic transformation and progression. miRNA modulation causes significant antitumor effects both in vitro and in vivo and miRNA regulation by natural compounds, represents a promising approach in the field of cancer research. S-Adenosylmethionine (AdoMet), a natural compound and a nutritional supplement, is well known for its antiproliferative and pro-apoptotic effects in many kinds of human tumors. Here, we report that AdoMet induces ER-stress and autophagy paralleled by miR-888-5p downregulation and MYCBP and CDH1 increased expression in Laryngeal Squamous Cancer Cells (LSCC). This study contributes to understanding the mechanisms by which AdoMet exerts its effects in LSCC, suggesting the use of AdoMet as an attractive miRNA-mediated chemopreventive and therapeutic strategy against cancer.

Abstract

(1) Purpose: The methyl donor S-Adenosylmethionine (AdoMet) has been widely explored as a therapeutic compound, and its application-alone or in combination with other molecules-is emerging as a potential effective strategy for the treatment and chemoprevention of tumours. In this study, we investigated the antitumor activity of AdoMet in Laryngeal Squamous Cell Carcinoma (LSCC), exploring the underlying mechanisms. (2) Results: We demonstrated that AdoMet induced ROS generation and triggered autophagy with a consistent increase in LC3B-II autophagy-marker in JHU-SCC-011 and HNO210 LSCC cells. AdoMet induced ER-stress and activated UPR signaling through the upregulation of the spliced form of XBP1 and CHOP. To gain new insights into the molecular mechanisms underlying the antitumor activity of AdoMet, we evaluated the regulation of miRNA expression profile and we found a downregulation of miR-888-5p. We transfected LSCC cells with miR-888-5p inhibitor and exposed the cells to AdoMet for 48 and 72 h. The combination of AdoMet with miR-888-5p inhibitor synergistically induced both apoptosis and inhibited cell migration paralleled by the up-regulation of MYCBP and CDH1 genes and of their targets. (3) Conclusion: Overall, these data highlighted that epigenetic reprogramming of miRNAs by AdoMet play an important role in inhibiting apoptosis and migration in LSCC cell lines.

Naringenin induces tolerance to salt/osmotic stress through the regulation of nitrogen metabolism, cellular redox and ROS scavenging capacity in bean plants

The present study was conducted to uncover underlying possible effect mechanisms of flavonoid naringenin (Nar, 0.1-0.4 mM) in nitrogen assimilation, antioxidant response, redox status and the expression of NLP7 and DREB2A, on salt (100 mM NaCl) and osmotic-stressed (10% Polyethylene glycol, -0.54 MPa) Phaseolus vulgaris cv. Yunus 90). Nar ameliorated salt/osmotic stresses-induced growth inhibition and improved the accumulation of proline, glycine betaine and choline. In response to stress, Nar increased endogenous content of nitrate (NO₃^-) and nitrite (NO₂^-) by regulating of nitrate reductase and nitrite reductase. Stress-triggered NH₄⁺ was eliminated with Nar through increases in glutamine synthetase and glutamate synthase. After NaCl or NaCl + PEG exposure, Nar utilized the aminating activity of glutamate dehydrogenase in the conversion of NH₄⁺. The stress-inducible expression levels of DREB2A were increased further by Nar, which might have affected stress tolerance of bean. Nar induced effectively the relative expression of NLP7 in the presence of the combination or alone of stress. Also, the impaired redox state by stress was modulated by Nar and hydrogen peroxide (H₂O₂) and TBARS decreased. Nar regulated the different pathways for scavenging of H₂O₂ under NaCl and/or PEG treatments. When Nar + NaCl exposure, the damage was removed by superoxide dismutase (SOD), catalase (CAT), POX (only at 0.1 mM Nar + NaCl) and AsA-GSH cycle. Under osmotic stress plus Nar, the protection was manifested by activated CAT and, glutathione S-transferase and the regeneration of ascorbate. 0.1 mM Nar could protect bean plant against salt/osmotic stresses, likely by regulating nitrogen assimilation pathways, improving expression levels of genes associated with tolerance mechanisms and modulating the antioxidant capacity and AsA-GSH redox-based systems.

Tanned or Sunburned: How Excessive Light Triggers Plant Cell Death

Plants often encounter light intensities exceeding the capacity of photosynthesis (excessive light) mainly due to biotic and abiotic factors, which lower CO₂ fixation and reduce light energy sinks. Under excessive light, the photosynthetic electron transport chain generates damaging molecules, hence leading to photooxidative stress and eventually to cell death. In this review, we summarize the mechanisms linking the excessive absorption of light energy in chloroplasts to programmed cell death in plant leaves. We highlight the importance of reactive carbonyl species generated by lipid photooxidation, their detoxification, and the integrating role of the endoplasmic reticulum in the adoption of phototolerance or cell-death pathways. Finally, we invite the scientific community to standardize the conditions of excessive light treatments.

The involvement of gamma-aminobutyric acid shunt in the endoplasmic reticulum stress response of Arabidopsis thaliana

The endoplasmic reticulum (ER) is the main site of secretory protein production and folding and its homeostasis under environmental stress is vital for the maintenance of the protein secretory pathway. The loss of homeostasis and accumulation of unfolded proteins in the ER is referred to as ER stress. Although, γ-aminobutyric acid (GABA) is an important regulator of stress response in plants, its roles during ER stress remains unclear. This study investigated the involvement of GABA in the ER stress response of plants. For this, changes in GABA metabolism under ER stress was analysed in Arabidopsis thaliana, then to study the response of the ER-folding machinery, plants were treated with exogenous GABA under ER stress. The antibiotic tunicamycin, which inhibits N-glycosylation was used to specifically induce ER stress. This stress up-regulated the expression of five glutamate decarboxylase (GAD) genes except GAD2 and GABA content of A. thaliana plants increased with an increasing concentration of tunicamycin (0.1 μg ml^-1 and 0.25 μg ml^-1). Moreover, expressions of genes involved in the conversion of GABA to succinate was also induced, while genes involved in transport across plasma and mitochondrial membrane showed no response to ER stress. The exogenous treatment of plants with 1-and 5-mM GABA increased plant performance under ER stress but 0.1 mM proved ineffective. Plants treated with GABA under ER stress had decreased expression of ER stress marker genes such as BIP1, BIP3 or CNX, but the expression of genes related to ER stress perception or ER-associated protein degradation showed no changes with respect to GABA treatments.

Resveratrol decreases high glucose‑induced apoptosis in renal tubular cells via suppressing endoplasmic reticulum stress

Diabetic nephropathy (DN) is the second most common complication of diabetes mellitus after cardiovascular complications. Endoplasmic reticulum (ER) stress is known to be associated with DN. Resveratrol (RSV) exhibits anti-oxidative, anti-inflammatory and cytoprotective effects. Therefore, the aims of the present study were to investigate the role of RSV in the inhibition of high concentration glucose (HG)-induced apoptosis in renal tubular cells, as well as to examine the protective effects of RSV against diabetes-mediated renal damage via inhibition of ER stress in DN. RSV was orally administered to diabetic db/db mice once a day for 12 consecutive weeks. Compared with untreated db/db mice, treating db/db mice with RSV significantly decreased urine albumin excretion and the urine albumin to creatinine ratio, and attenuated renal histopathological injury. Furthermore, RSV treatment resulted in decreased expression levels of glucose-regulated protein of 78 kDa and C/EBP-homologous protein (two ER stress markers) and caspase12 in murine kidneys. RSV administration also inhibited the apoptosis of NRK-52E cells and activation of the ER stress signal transduction pathway induced by HG treatment in vitro. Collectively, the present results indicated that RSV protected renal tubular cells against HG-induced apoptosis in DN by suppressing ER stress.

PpAOX regulates ER stress tolerance in Physcomitrella patens

Severe environments disturb the folding or assembly of newly synthesized proteins, resulting in accumulation of misfolded or unfolded proteins in the endoplasmic reticulum (ER) as well as cytotoxic aggregation of abnormal proteins. Therefore, ER stress is evoked due to disturbed ER homeostasis. Alternative oxidase (AOX) plays an important role in coping with various abiotic stresses and plant growth. Our previous study has reported that PpAOX is involved in the regulation of salt tolerance in moss Physcomitrella patens (P. patens), but its biological functions in modulating ER stress remain unknown. Here we report that the gametophyte of P. patens displays severe growth inhibition and developmental deficiency under tunicamycin (Tm, an elicitor of ER stress)-induced ER stress conditions. PpAOX and selected ER stress response-like genes in P. patens were induced under Tm treatment. PpAOX knockout (PpAOX KO) plants exhibited decreased resistance to Tm-induced ER stress, whereas PpAOX-overexpressing lines (PpAOX OX) plants were more tolerant to Tm-induced ER stress. Data showed that PpAOX contributes to redox homeostasis under Tm treatment. In addition, we observed that PpAOX completely restores the Tm-sensitive phenotype of Arabidopsis AOX1a mutant (Ataox1a). Taken together, our work reveals a functional link between PpAOX and ER stress tolerance regulation in P. patens.

Effects of Jasmonic Acid in ER Stress and Unfolded Protein Response in Tomato Plants

Endoplasmic reticulum (ER) stress elicits a protective mechanism called unfolded protein response (UPR) to maintain cellular homeostasis, which can be regulated by defence hormones. In this study, the physiological role of jasmonic acid (JA) in ER stress and UPR signalling has been investigated in intact leaves of tomato plants. Exogenous JA treatments not only induced the transcript accumulation of UPR marker gene SlBiP but also elevated transcript levels of SlIRE1 and SlbZIP60. By the application of JA signalling mutant jai1 plants, the role of JA in ER stress sensing and signalling was further investigated. Treatment with tunicamycin (Tm), the inhibitor of N-glycosylation of secreted glycoproteins, increased the transcript levels of SlBiP. Interestingly, SlIRE1a and SlIRE1b were significantly lower in jai1. In contrast, the transcript accumulation of Bax Inhibitor-1 (SlBI1) and SlbZIP60 was higher in jai1. To evaluate how a chemical chaperone modulates Tm-induced ER stress, plants were treated with sodium 4-phenylbutyrate, which also decreased the Tm-induced increase in SlBiP, SlIRE1a, and SlBI1 transcripts. In addition, it was found that changes in hydrogen peroxide content, proteasomal activity, and lipid peroxidation induced by Tm is regulated by JA, while nitric oxide was not involved in ER stress and UPR signalling in leaves of tomato.

ERO1α inhibits cell apoptosis and regulates steroidogenesis in mouse granulosa cells

ER oxidoreduclin 1α (ERO1α), an oxidase that exists in the ER, participates in protein folding and secretion and inhibiting apoptosis, and regulates tumor progression, which is a novel factor of poor cancer prognosis. However, the other physiological functions of ERO1α remain undiscovered. Although our preliminary results of this study indicated that ERO1α revealed the robust expression in ovary, especially in granulosa cells, the role of ERO1α in follicular development is not well known. Therefore, the aims of the present study were to explore the role of ERO1α and the possible mechanisms in regulating cell apoptosis and steroidogenesis in ovarian granulosa cells. ERO1α was mainly localized in granulosa cells and oocytes in the adult ovary by immunohistochemistry. Western blot analysis showed that the expression of ERO1α was highest at oestrous stage during the estrous cycle. The effect of ERO1α on cell apoptosis and steroidogenesis was detected by transduction of ERO1α overexpression and knockdown lentiviruses into primary cultured granulosa cells. Flow cytometry analysis showed that ERO1α decreased granulosa cells apoptosis. Western bolt and RT-qPCR analysis found that ERO1α increased the ratio of BCL-2/BAX, and decreased BAD and Caspase-3 expression. ELISA analysis showed that ERO1α enhanced estrogen (E2) secretion. Western bolt and RT-qPCR analysis found that ERO1α increased StAR, CYP11A1, 3β-HSD, CYP17A1, and CYP19A1 expression, and decreased CYP1B1 expression. Furthermore, Western bolt analysis found that ERO1αincreased PDI and PRDX 4 expression, and activated the PI3K/AKT/mTOR signaling pathway through increasing the phosphorylation of AKT and P70 S6 kinase. In summary, these results suggested that ERO1α might play an anti-apoptotic role and regulate steroidogenesis in granulosa cells, at least partly, via activation of the PI3K/AKT/mTOR signaling pathway.

Arabidopsis SMALL DEFENSE-ASSOCIATED PROTEIN 1 Modulates Pathogen Defense and Tolerance to Oxidative Stress

Salicylic acid (SA) and reactive oxygen species (ROS) are known to be key modulators of plant defense. However, mechanisms of molecular signal perception and appropriate physiological responses to SA and ROS during biotic or abiotic stress are poorly understood. Here we report characterization of SMALL DEFENSE-ASSOCIATED PROTEIN 1 (SDA1), which modulates defense against bacterial pathogens and tolerance to oxidative stress. sda1 mutants are compromised in defense gene expression, SA accumulation, and defense against bacterial pathogens. External application of SA rescues compromised defense in sda1 mutants. sda1 mutants are also compromised in tolerance to ROS-generating chemicals. Overexpression of SDA1 leads to enhanced resistance against bacterial pathogens and tolerance to oxidative stress. These results suggest that SDA1 regulates plant immunity via the SA-mediated defense pathway and tolerance to oxidative stress. SDA1 encodes a novel small plant-specific protein containing a highly conserved seven amino acid (S/G)WA(D/E)QWD domain at the N-terminus that is critical for SDA1 function in pathogen defense and tolerance to oxidative stress. Taken together, our studies suggest that SDA1 plays a critical role in modulating both biotic and abiotic stresses in Arabidopsis (Arabidopsis thaliana) and appears to be a plant-specific stress responsive protein.

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.

Rare-earth element scandium improves stomatal regulation and enhances salt and drought stress tolerance by up-regulating antioxidant responses of Oryza sativa

Oryza sativa L. cv. Gönen grown in hydroponic culture was treated with scandium (Sc; 25 and 50 μM) alone or in combination with salt (100 mM NaCl) and/or drought (5% PEG-6000). Stress caused a decrease in growth (RGR), water content (RWC), osmotic potential (ΨΠ), chlorophyll fluorescence (Fv/Fm) and potential photochemical efficiency (Fv/Fo). Sc application prevented the decreases of these parameters. Sc also alleviated the changes on gas exchange parameters (carbon assimilation rate (A), stomatal conductance (gs), intercellular CO2 concentrations (Ci), transpiration rate (E) and stomatal limitation (Ls)). Stress caused no increase in superoxide dismutase (SOD) activity. After induvial applied NaCl or PEG, catalase (CAT) and ascorbate peroxidase (APX) showed an enhancement in activation and tried to scavenge of hydrogen peroxide (H2O2). On the other hand, in plants with the combination form of NaCl and PEG, only CAT activity was induced. Sc applications to NaCl-treated rice led to an increase of SOD, APX, glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) as well as peroxidase (POX). Sc under NaCl could be maintained both ascorbate (AsA) and glutathione (GSH) regeneration. Despite of induction of MDHAR and DHAR under Sc plus PEG, Sc did not maintain AsA redox state because of no induction in APX activity. However, GSH pool could be regenerated by induction in DHAR and GR in this group. Sc application (especially for 25 μM) in rice exposed to NaCl + PEG resulted an enhancement in APX and MDHAR and so Sc could be partially provided AsA regeneration. Since no increases in DHAR and GR were observed, GSH pool was reduced. Due to this activation of antioxidant enzymes, stress-induced H2O2 and TBARS content (lipid peroxidation) significantly decreased in rice with Sc applications. Sc in plants with stress also increased the transcript levels of OsCDPK7 and OsBG1 related to stomatal movement and signaling pathway. Consequently, Sc protected the rice plants by minimizing disturbances caused by NaCl or PEG exposure via the AsA-GSH redox-based systems.

Flavonoid Naringenin Alleviates Short-Term Osmotic and Salinity Stresses Through Regulating Photosynthetic Machinery and Chloroplastic Antioxidant Metabolism in Phaseolus vulgaris

The current study was conducted to demonstrate the possible roles of exogenously applied flavonoid naringenin (Nar) on the efficiency of PSII photochemistry and the responses of chloroplastic antioxidant of salt and osmotic-stressed Phaseolus vulgaris (cv. Yunus90). For this aim, plants were grown in a hydroponic culture and were treated with Nar (0.1 mM and 0.4 mM) alone or in a combination with salt (100 mM NaCl) and/or osmotic (10% Polyethylene glycol, -0.54 MPa). Both caused a reduction in water content (RWC), osmotic potential (Ψ_Π), chlorophyll fluorescence (F_v/F_m), and potential photochemical efficiency (F_v/F_o). Nar reversed the changes on these parameters. The phenomenological fluxes (TR_o/CS and ET_o/CS) altered by stress were induced by Nar and Nar led to a notable increase in the performance index (PI_ABS) and the capacity of light reaction [ΦP_o/(1-ΦP_o)]. Besides, Nar-applied plants exhibited higher specific fluxes values [ABS/RC, ET_o/RC, and ΨE_o/(1-ΨE_o)] and decreasing controlled dissipation of energy (DI_o/CS_o and DI_o/RC). The transcripts levels of psbA and psbD were lowered in stress-treated bean but upregulated in Nar-treated plants after stress exposure. Nar also alleviated the changes on gas exchange parameters [carbon assimilation rate (A), stomatal conductance (g_s), intercellular CO₂ concentrations (C_i), transpiration rate (E), and stomatal limitation (L_s)]. By regulating the antioxidant metabolism of the isolated chloroplasts, Nar was able to control the toxic levels of hydrogen peroxide (H₂O₂) and TBARS (lipid peroxidation) produced by stresses. Chloroplastic superoxide dismutase (SOD) activity reduced by stresses was increased by Nar. In response to NaCl, Nar increased the activities of ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), as well as peroxidase (POX). Nar protected the bean chloroplasts by minimizing disturbances caused by NaCl exposure via the ascorbate (AsA) and glutathione (GSH) redox-based systems. Under Nar plus PEG, Nar maintained the AsA regeneration by the induction of MDHAR and DHAR, but not GSH recycling by virtue of no induction in GR activity and the reduction in GSH/GSSG and GSH redox state. Based on these advances, Nar protected in bean chloroplasts by minimizing disturbances caused by NaCl or PEG exposure via the AsA or GSH redox-based systems and POX activity.

The Multifaceted Roles of Plant Hormone Salicylic Acid in Endoplasmic Reticulum Stress and Unfolded Protein Response

Different abiotic and biotic stresses lead to the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER), resulting in ER stress. In response to ER stress, cells activate various cytoprotective responses, enhancing chaperon synthesis, protein folding capacity, and degradation of misfolded proteins. These responses of plants are called the unfolded protein response (UPR). ER stress signaling and UPR can be regulated by salicylic acid (SA), but the mode of its action is not known in full detail. In this review, the current knowledge on the multifaceted role of SA in ER stress and UPR is summarized in model plants and crops to gain a better understanding of SA-regulated processes at the physiological, biochemical, and molecular levels.

Functional Diversification of ER Stress Responses in Arabidopsis

The endoplasmic reticulum (ER) is responsible for the synthesis of one-third of the cellular proteome and is constantly challenged by physiological and environmental situations that can perturb its homeostasis and lead to the accumulation of misfolded secretory proteins, a condition referred to as ER stress. In response, the ER evokes a set of intracellular signaling processes, collectively known as the unfolded protein response (UPR), which are designed to restore biosynthetic capacity of the ER. As single-cell organisms evolved into multicellular life, the UPR complexity has increased to suit their growth and development. In this review, we discuss recent advances in the understanding of the UPR, emphasizing conserved UPR elements between plants and metazoans and highlighting unique plant-specific features.

Basic-leucine zipper 17 and Hmg-CoA reductase degradation 3A are involved in salt acclimation memory in Arabidopsis

Salt acclimation, which is induced by previous salt exposure, increases the resistance of plants to future exposure to salt stress. However, little is known about the underlying mechanism, particularly how plants store the "memory" of salt exposure. In this study, we established a system to study salt acclimation in Arabidopsis thaliana. Following treatment with a low concentration of salt, seedlings were allowed to recover to allow transitory salt responses to subside while maintaining the sustainable effects of salt acclimation. We performed transcriptome profiling analysis of these seedlings to identify genes related to salt acclimation memory. Notably, the expression of Basic-leucine zipper 17 (bZIP17) and Hmg-CoA reductase degradation 3A (HRD3A), which are important in the unfolded protein response (UPR) and endoplasmic reticulum-associated degradation (ERAD), respectively, increased following treatment with a low concentration of salt and remained at stably high levels after the stimulus was removed, a treatment which improved plant tolerance to future high-salinity challenge. Our findings suggest that the upregulated expression of important genes involved in the UPR and ERAD represents a "memory" of the history of salt exposure and enables more potent responses to future exposure to salt stress, providing new insights into the mechanisms underlying salt acclimation in plants.

Effect of light on the transformation of BDE-47 by living and autoclaved cultures of Microcystis flos-aquae and Chlorella vulgaris

Polybrominated diphenyl ethers (PBDEs) are ubiquitous and toxic contaminants found in high concentrations in watercourses, and are not well removed by conventional wastewater treatment facilities. This study aimed to evaluate the removal and transformation of BDE-47, one of the environmentally predominant PBDE congener, by a green alga (Chlorella vulgaris) and a cyanobacterium (Microcystis flos-aquae) under different light conditions. Living and autoclaved cultures were exposed to BDE-47 at a concentration of 10 μg L^-1 for 7 days. Both species removed >90% of BDE-47 very shortly after spiking. Light intensity affected the transformation of BDE-47 in living cultures of both species, since 5 to 11 times more debromination products were measured at a light intensity of 100 μmol photons m^-2 s^-1 than at 20 μmol photons m^-2 s^-1. Living cultures of M. flos-aquae transformed BDE-47 at a rate of 0.22 day^-1 while no transformation was observed in the respective autoclaved cultures. On the contrary, both living and autoclaved cultures of C. vulgaris had similar BDE-47 transformation rates of 0.05-0.06 day^-1. Debromination of BDE-47 was a predominant transformation pathway in cultures of C. vulgaris, with two times higher BDE-28 concentrations measured than in M. flos-aquae, while hydroxylation was more dominant with the cyanobacterium. Most BDE-47 and its debromination product BDE-28 were found on the cell surface of both species. These results reveal that different transformation mechanisms were involved in C. vulgaris and M. flos-aquae cultures and confirm the importance of species selection for the removal of PBDEs from contaminated environments.

The Noncanonical Heat Shock Protein PvNod22 Is Essential for Infection Thread Progression During Rhizobial Endosymbiosis in Common Bean

In the establishment of plant-rhizobial symbiosis, the plant hosts express nodulin proteins during root nodule organogenesis. A limited number of nodulins have been characterized, and these perform essential functions in root nodule development and metabolism. Most nodulins are expressed in the nodule and at lower levels in other plant tissues. Previously, we isolated Nodulin 22 (PvNod22) from a common bean (Phaseolus vulgaris L.) cDNA library derived from Rhizobium-infected roots. PvNod22 is a noncanonical, endoplasmic reticulum (ER)-localized, small heat shock protein that confers protection against oxidative stress when overexpressed in Escherichia coli. Virus-induced gene silencing of PvNod22 resulted in necrotic lesions in the aerial organs of P. vulgaris plants cultivated under optimal conditions, activation of the ER-unfolded protein response (UPR), and, finally, plant death. Here, we examined the expression of PvNod22 in common bean plants during the establishment of rhizobial endosymbiosis and its relationship with two cellular processes associated with plant immunity, the UPR and autophagy. In the RNA interference lines, numerous infection threads stopped their progression before reaching the cortex cell layer of the root, and nodules contained fewer nitrogen-fixing bacteroids. Collectively, our results suggest that PvNod22 has a nonredundant function during legume-rhizobia symbiosis associated with infection thread elongation, likely by sustaining protein homeostasis in the ER.

Long-term treatment with finasteride induces apoptosis and pathological changes in female mice

Androgenetic alopecia is the most common type of alopecia, and it affects humans of both genders. Finasteride is a type II selective 5α-reductase inhibitor that is administered orally to treat androgenetic alopecia and benign prostatic hyperplasia in human males. However, its effect on the vital organs of females is unknown. This study was designed to investigate the effects of finasteride on the vital organs such as liver, kidney, and heart of female mice. To study the prospective effects of finasteride, female mice were orally administered two doses of finasteride (0.5 and 1.5 mg/kg) once daily for 35 days, and serum levels of various biochemical parameters and histopathology of various organs were examined. The results showed that serum levels of alkaline phosphatase were significantly increased by both high- and low-dose finasteride, whereas cholesterol was significantly increased by the high dose only. Creatine kinase was significantly increased by the high and low doses, whereas glucose was significantly decreased by both doses. Histopathological analysis and DNA damage assays showed that finasteride has adverse effects within both the short and the long periods in female mice. In addition, the proapoptotic genes Bax and caspase-3 were significantly increased by high dose finasteride, whereas the antiapoptotic gene Bcl-2 was significantly decreased by the low and high doses. In conclusion, finasteride is not currently approved for therapeutic use in females, and the findings in this study suggest caution in any future consideration of such use.

Piecing the Puzzle Together: The Central Role of Reactive Oxygen Species and Redox Hubs in Chloroplast Retrograde Signaling

SIGNIFICANCE

Reactive oxygen species (ROS) and redox regulation are established components of chloroplast-nucleus retrograde signaling. Recent Advances: In recent years, a complex array of putative retrograde signaling molecules and novel signaling pathways have emerged, including various metabolites, chloroplast translation, mobile transcription factors, calcium, and links to the unfolded protein response. This critical mass of information now permits us to fit individual pieces into a larger picture and outline a few important stimuli and pathways.

CRITICAL ISSUES

In this review, we summarize how ROS and redox hubs directly (e.g., via hydrogen peroxide [H₂O₂]) and indirectly (e.g., by triggering the production of signaling metabolites) regulate chloroplast retrograde signaling. Indeed, evidence is accumulating that most of the presumptive signaling metabolites so far identified are produced directly by ROS (such as β-cyclocitral) or indirectly by redox- or ROS-mediated regulation of key enzymes in metabolic pathways, ultimately leading to the accumulation of certain precursors (e.g., methylerythritol cyclodiphosphate and 3'-phosphoadenosine 5'-phosphate) with signal function. Of the ROS generated in the chloroplast, only H₂O₂ is likely to leave the organelle, and recent results suggest that efficient and specific transfer of information via H₂O₂ occurs through physical association of chloroplasts with the nucleus.

FUTURE DIRECTIONS

The impact of ROS and redox regulation on chloroplast-nucleus communication is even greater than previously thought, and it can be expected that further instances of control of retrograde signaling by ROS/redox regulation will be revealed in future, perhaps including the basis for the enigmatic GUN response and translation-dependent signals.

Arctigenin ameliorates renal impairment and inhibits endoplasmic reticulum stress in diabetic db/db mice

AIMS

Diabetic nephropathy (DN) is the most common complication of diabetes mellitus. Endoplasmic reticulum (ER) plays an important role in the development and progression of DN. Arctigenin (ATG), a lignan extract from Fructus Arctii, exhibits anti-inflammatory, anticarcinogenic, anti-oxidative stress and immunomodulatory properties. The present research aimed to investigate whether ATG could protect against diabetes-related renal injury and inhibit ER stress in db/db mice.

MAIN METHODS

Male db/db mice were randomly divided into two groups: DN group and ATG treatment group (DN + ATG). db/m mice were defined as the normal control group (NC). ATG was dissolved in 0.5% carboxymethyl cellulose sodium salt solution and administered orally at a dose of 80 mg/kg to mice in the DN + ATG group once daily for 8 consecutive weeks. HK2 cells were used to determine the effects of ATG on ER stress and cell apoptosis in vitro.

KEY FINDINGS

ATG administration significantly reduced blood glucose, urine albumin excretion, and urine albumin to creatinine ratio, and attenuated renal pathological injury when compared with untreated db/db mice. These changes were accompanied by decreased expression of both ER stress-related markers and caspase 12 level in the kidneys of db/db mice. In vitro, high glucose activated ER stress signal transduction pathway and induced cell apoptosis in HK2 cells, which were blocked by ATG.

SIGNIFICANCE

Our results suggest that ATG exerts renoprotective effects on diabetes-related renal injury in db/db mice and cytoprotective effects on high glucose induced cell apoptosis and inhibits ER stress.

Whole cigarette smoke condensates induce ferroptosis in human bronchial epithelial cells

Cigarette smoke is responsible for many fatal pulmonary diseases, however, the toxic mechanism is still unclear. In this study, we first confirmed that whole cigarette smoke condensates (WCSC) contain hydrophilic elements, lipophilic and gaseous components. Then, we treated BEAS-2B cells, a normal human bronchial epithelial cell line, at dosages of 0.25, 0.5, and 1% for 24 h and explored the toxic mechanism. Cell viability decreased in a dose-dependent manner, and fission and fusion of mitochondria, damage of endoplasmic reticulume (ER) structures, and formation of autophagosome-like vacuoles were found in cells treated with 1% WCSC. Mitochondrial and ER volumes, lysosomal fluorescence intensity, LDH release, and intracellular ROS levels notably decreased at the highest doses compared with the control, whereas intracellular calcium ion and NO levels were significantly elevated accompanying G2/M phase arrest. Expression of an iron-binding nuclear protein-related gene (pirin) was the most up-regulated in the WCSC-treated cells with enhanced expression of antioxidant-related genes, whereas expression of carbonic anhydrase IX gene, a marker of tumor hypoxia, was the most down-regulated. Additionally, levels of apoptosis (BAX, Apaf-1, and cleavage of caspase-3 and PARP), autophagy (p62 and LC3B-II), ER stress (PERK, IRE-1a, Bip, and CHOP), antioxidant (SOD-1 and SOD-2), and MAPkinase activation (p-ERK, p-p38, and p-JNK)-related proteins were clearly enhanced following exposure to WCSC, whereas expression of several mitochondrial dynamics-related proteins was reduced with dose. Interestingly, expression of ferritin protein (light chain) was dramatically enhanced near the ER along with that of p62 protein. More importantly, the hypoxia inducible factor-1 pathway and ferroptosis were proposed among the 20 terms in KEGG pathway analysis, and secretion of IL-6 and IL-8, which are involved in hypoxia-induced inflammation, were clearly elevated with dose. Taken together, we suggest that WCSC may induce ferroptosis in bronchial epithelial cells via ER stress and disturbed homeostasis in mitochondrial dynamics caused by induction of hypoxia conditions.

Communications Between the Endoplasmic Reticulum and Other Organelles During Abiotic Stress Response in Plants

To adapt to constantly changing environmental conditions, plants have evolved sophisticated tolerance mechanisms to integrate various stress signals and to coordinate plant growth and development. It is well known that inter-organellar communications play important roles in maintaining cellular homeostasis in response to environmental stresses. The endoplasmic reticulum (ER), extending throughout the cytoplasm of eukaryotic cells, is a central organelle involved in lipid metabolism, Ca²⁺ homeostasis, and synthesis and folding of secretory and transmembrane proteins crucial to perceive and transduce environmental signals. The ER communicates with the nucleus via the highly conserved unfolded protein response pathway to mitigate ER stress. Importantly, recent studies have revealed that the dynamic ER network physically interacts with other intracellular organelles and endomembrane compartments, such as the Golgi complex, mitochondria, chloroplast, peroxisome, vacuole, and the plasma membrane, through multiple membrane contact sites between closely apposed organelles. In this review, we will discuss the signaling and metabolite exchanges between the ER and other organelles during abiotic stress responses in plants as well as the ER-organelle membrane contact sites and their associated tethering complexes.

Protective effect of MOTILIPERM in varicocele-induced oxidative injury in rat testis by activating phosphorylated inositol requiring kinase 1α (p-IRE1α) and phosphorylated c-Jun N-terminal kinase (p-JNK) pathways

CONTEXT

MOTILIPERM was prepared as a mixture of extracts of three medicinal herbs [roots of Morinda officinalis How (Rubiaceae), outer scales of Allium cepa L. (Liliaceae) and seeds of Cuscuta chinensis Lamark (Convolvulaceae)].

OBJECTIVE

To investigate the role of reactive oxygen species (ROS)-based endoplasmic reticulum (ER) stress in a rat model of varicocele and the therapeutic efficacy of MOTILIPERM in this model.

MATERIALS AND METHODS

Sixty male rats were divided into five experimental groups: a normal control group (CTR + vehicle), a control group administered MOTILIPERM 200 mg/kg (CTR + M 200), a varicocele-induced control group (VC + vehicle) and two varicocele-induced groups administered MOTILIPERM 100 (VC + M 100) or 200 (VC + M 200) mg/kg for 4 weeks. Testis weights were recorded and serums were assayed for hormone concentrations. Tissues were subjected to semen analysis, histopathology, analyses of ER response protein expression levels and oxidative stress were assessed by measuring ROS, reactive nitrogen species (RNS), malondialdehyde (MDA) level and ratios of total glutathione (GSH)/oxidized GSH (GSSG).

RESULTS

MOTILIPERM treatment of varicocele-induced groups significantly increased left testis weight, testosterone level, sperm motility, count and spermatogenic cell density. ER-response protein expression levels were dose-dependently decreased in VC + M 200 group compared with VC + vehicle group. MOTILIPERM treatment also decreased MDA and ROS/RNS level but increased GSH/GSSG ratio.

DISCUSSION AND CONCLUSIONS

This study suggests that ROS-related ER stress may play a major role in varicocele-induced infertility and MOTILIPERM, a novel compound targeting ROS-based ER stress, may be therapeutically useful in treatment of varicocele, or as a supplement for the treatment of infertility.

NADPH oxidase activity is required for ER stress survival in plants

In all eukaryotes, the unfolded protein response (UPR) relieves endoplasmic reticulum (ER) stress, which is a potentially lethal condition caused by the accumulation of misfolded proteins in the ER. In mammalian and yeast cells, reactive oxygen species (ROS) generated during ER stress attenuate the UPR, negatively impacting cell survival. In plants, the relationship between the UPR and ROS is less clear. Although ROS develop during ER stress, the sources of ROS linked to ER stress responses and the physiological impact of ROS generation on the survival from proteotoxic stress are yet unknown. Here we show that in Arabidopsis thaliana the respiratory burst oxidase homologs, RBOHD and RBOHF, contribute to the production of ROS during ER stress. We also demonstrate that during ER stress RBOHD and RBOHF are necessary to properly mount the adaptive UPR and overcome temporary and chronic ER stress situations. These results ascribe a cytoprotective role to RBOH-generated ROS in the defense from proteotoxic stress in an essential organelle, and support a plant-specific feature of the UPR management among eukaryotes.

CaWRKY27 Negatively Regulates H2O2-Mediated Thermotolerance in Pepper (Capsicum annuum)

Heat stress, an important and damaging abiotic stress, regulates numerous WRKY transcription factors, but their roles in heat stress responses remain largely unexplored. Here, we show that pepper (Capsicum annuum) CaWRKY27 negatively regulates basal thermotolerance mediated by H2O2 signaling. CaWRKY27 expression increased during heat stress and persisted during recovery. CaWRKY27 overexpression impaired basal thermotolerance in tobacco (Nicotiana tabacum) and Arabidopsis thaliana, CaWRKY27-overexpressing plants had a lower survival rate under heat stress, accompanied by decreased expression of multiple thermotolerance-associated genes. Accordingly, silencing of CaWRKY27 increased basal thermotolerance in pepper plants. Exogenously applied H2O2 induced CaWRKY27 expression, and CaWRKY27 overexpression repressed the scavenging of H2O2 in Arabidopsis, indicating a positive feedback loop between H2O2 accumulation and CaWRKY27 expression. Consistent with this, CaWRKY27 expression was repressed under heat stress in the presence H2O2 scavengers and CaWRKY27 silencing decreased H2O2 accumulation in pepper leaves. These changes may result from changes in levels of reactive oxygen species (ROS)-scavenging enzymes, since the heat stress-challenged CaWRKY27-silenced pepper plants had significantly higher expression of multiple genes encoding ROS-scavenging enzymes, such as CaCAT1, CaAPX1, CaAPX2, CaCSD2, and CaSOD1. Therefore, CaWRKY27 acts as a downstream negative regulator of H2O2-mediated heat stress responses, preventing inappropriate responses during heat stress and recovery.

Camptothecin enhances c-Myc-mediated endoplasmic reticulum stress and leads to autophagy by activating Ca2+-mediated AMPK

Camptothecin (CPT) from Camptotheca acuminate was discovered for anticancer drugs, which targets topoisomease I. However, whether CPT regulates c-Myc expression has not been understood in endoplasmic reticulum (ER) stress and autophagy. In this study, we found that CPT enhanced c-Myc expression and that the transient knockdown of c-Myc abrogated reactive oxygen species (ROS) generation, which resulted in the accumulation of ER stress-regulating proteins, such as PERK, eIF2α, ATF4, and CHOP. Moreover, the transfection of eIF2α-targeted siRNA attenuated CPT-induced autophagy and decreased the levels of Beclin-1 and Atg7, which indicated that CPT upregulated ER stress-mediated autophagy. In addition, CPT phosphorylated AMPK in response to intracellular Ca²⁺ release. Ca²⁺ chelators, ethylene glycol tetraacetic acid and a CaMKII inhibitor, K252a, decreased CPT-induced Beclin-1 and Atg7, and downregulated AMPK phosphorylation, which suggested that CPT-induced Ca²⁺ release leads to the activation of autophagy through CaMKII-mediated AMPK phosphorylation. CPT also phosphorylated JNK and activated the DNA-binding activity of AP-1; furthermore, knockdown of JNK abolished the expression level of Beclin-1 and Atg7, which implied that the JNK-AP-1 pathway was a potent mediator of CPT-induced autophagy. Our findings indicated that CPT promoted c-Myc-mediated ER stress and ROS generation, which enhances autophagy via the Ca²⁺-AMPK and JNK-AP-1 pathways.