Singlet Oxygen-Induced Membrane Disruption and Serpin-Protease Balance in Vacuolar-Driven Cell Death

Singlet oxygen signalling and its potential roles in plant biotic interactions

Singlet oxygen (SO) is among the most potent reactive oxygen species, and readily oxidizes proteins, lipids and DNA. It can be generated at the plant surface by phototoxins in the epidermis, acting as a direct defense against pathogens and herbivores (including humans). SO can also accumulate within mitochondria, peroxisomes, cytosol and the nucleus through multiple enzymatic and nonenzymatic processes. However, the majority of research on intracellular SO generation in plants has focused on transfer of light energy to triplet oxygen by photopigments from the chloroplast. SO accumulates in response to diverse stresses that perturb chloroplast metabolism, and while its high reactivity limits diffusion distances, it participates in retrograde signalling through the EXECUTER1 sensor, generation of carotenoid metabolites and possibly other unknown pathways. SO thereby reprogrammes nuclear gene expression and modulates hormone signalling and programmed cell death. While SO signalling has long been known to regulate plant responses to high-light stress, recent literature also suggests a role in plant interactions with insects, bacteria and fungi. The goals of this review are to provide a brief overview of SO, summarize evidence for its involvement in biotic stress responses and discuss future directions for the study of SO in defense signalling.

TcSERPIN, an inhibitor that interacts with cocoa defense proteins and has biotechnological potential against human pathogens

In plants, serpins are a superfamily of serine and cysteine protease inhibitors involved in stress and defense mechanisms, with potential for controlling agricultural pests, making them important biotechnological tools. The objective of this study was to characterize a serpin from Theobroma cacao, called TcSERPIN, to identify its endogenous targets and determine its function and biotechnological potential. TcSERPIN has 390 amino acid residues and shows conservation of the main active site, RCL. Cis-elements related to light, stress, hormones, anaerobic induction, cell cycle regulation and defense have been identified in the gene's regulatory region. TcSERPIN transcripts are accumulated in different tissues of Theobroma cacao. Furthermore, in plants infected with Moniliophtora perniciosa and Phytophthora palmivora, the expression of TcSERPIN was positively regulated. The protein spectrum, rTcSERPIN, reveals a typical β-sheet pattern and is thermostable at pH 8, but loses its structure with temperature increases above 66°C at pH 7. At the molar ratios of 0.65 and 0.49, rTcSERPIN inhibited 55 and 28% of the activity of papain from Carica papaya and trypsin from Sus scrofa, respectively. The protease trap containing immobilized rTcSERPIN captured endogenous defense proteins from cocoa extracts that are related to metabolic pathways, stress and defense. The evaluation of the biotechnological potential against geohelminth larvae showed that rTcSERPIN and rTcCYS4 (Theobroma cacao cystatin 4) reduced the movement of larvae after 24 hours. The results of this work show that TcSERPIN has ideal biochemical characteristics for biotechnological applications, as well as potential for studies of resistance to phytopathogens of agricultural crops.

A hidden demethylation pathway removes mercury from rice plants and mitigates mercury flux to food chains

Dietary exposure to methylmercury (MeHg) causes irreversible damage to human cognition and is mitigated by photolysis and microbial demethylation of MeHg. Rice (Oryza sativa L.) has been identified as a major dietary source of MeHg. However, it remains unknown what drives the process within plants for MeHg to make its way from soils to rice and the subsequent human dietary exposure to Hg. Here we report a hidden pathway of MeHg demethylation independent of light and microorganisms in rice plants. This natural pathway is driven by reactive oxygen species generated in vivo, rapidly transforming MeHg to inorganic Hg and then eliminating Hg from plants as gaseous Hg°. MeHg concentrations in rice grains would increase by 2.4- to 4.7-fold without this pathway, which equates to intelligence quotient losses of 0.01-0.51 points per newborn in major rice-consuming countries, corresponding to annual economic losses of US$30.7-84.2 billion globally. This discovered pathway effectively removes Hg from human food webs, playing an important role in exposure mitigation and global Hg cycling.

Plant Serpins: Potential Inhibitors of Serine and Cysteine Proteases with Multiple Functions

Plant serpins are a superfamily of protein inhibitors that have been continuously studied in different species and have great biotechnological potential. However, despite ongoing studies with these inhibitors, the biological role of this family in the plant kingdom has not yet been fully clarified. In order to obtain new insights into the potential of plant serpins, this study presents the first systematic review of the topic, whose main objective was to scrutinize the published literature to increase knowledge about this superfamily. Using keywords and the eligibility criteria defined in the protocol, we selected studies from the Scopus, PubMed, and Web of Science databases. According to the eligible studies, serpins inhibit different serine and non-serine proteases from plants, animals, and pathogens, and their expression is affected by biotic and abiotic stresses. Moreover, serpins like AtSerpin1, OSP-LRS, MtSer6, AtSRP4, AtSRP5, and MtPiI4, act in resistance and are involved in stress-induced cell death in the plant. Also, the system biology analysis demonstrates that serpins are related to proteolysis control, cell regulation, pollen development, catabolism, and protein dephosphorylation. The information systematized here contributes to the design of new studies of plant serpins, especially those aimed at exploring their biotechnological potential.

Photoacclimation of photosystem II photochemistry induced by rose Bengal and methyl viologen in Nannochloropsis oceanica

The photosynthetic apparatus is a major reactive oxygen species (ROS) proliferator, especially in high-light environments. The role of ROS in photoinhibition and photoacclimation mechanisms has been extensively explored, primarily in model plant species. However, little work has been performed on the topic in non-Archaeplastida organisms, such as the model heterokont species Nannochloropsis oceanica. To investigate the photoacclimation and damaging impact of singlet oxygen and superoxide anions on the photosynthetic apparatus of N. oceanica, we subjected cells to two doses of methyl viologen and rose bengal. Significant findings: Rose bengal (a singlet-oxygen photosensitizer) induced changes to the photosynthetic apparatus and PSII photochemistry mirroring high-light-acclimated cells, suggesting that singlet-oxygen signaling plays a role in the high-light acclimation of PSII. We further suggest that this singlet-oxygen pathway is mediated outside the plastid, given that rose bengal caused no detectable damage to the photosynthetic apparatus. Methyl viologen (a superoxide-anion sensitizer) induced an enhanced non-photochemical quenching response, similar to what occurs in high-light-acclimated cells. We propose that superoxide anions produced inside the plastid help regulate the high-light acclimation of photoprotective pathways.

Plastid and cytoplasmic origins of 1O2-mediated transcriptomic responses

The reactive oxygen species singlet oxygen, ¹O₂, has an extremely short half-life, yet is intimately involved with stress signalling in the cell. We previously showed that the effects of ¹O₂ on the transcriptome are highly correlated with 80S ribosomal arrest due to oxidation of guanosine residues in mRNA. Here, we show that dysregulation of chlorophyll biosynthesis in the flu mutant or through feeding by δ-aminolevulinic acid can lead to accumulation of photoactive chlorophyll intermediates in the cytoplasm, which generates ¹O₂ upon exposure to light and causes the oxidation of RNA, eliciting ¹O₂-responsive genes. In contrast, transcriptomes derived from DCMU treatment, or the Ch1 mutant under moderate light conditions display commonalties with each other but do not induce ¹O₂ gene signatures. Comparing ¹O₂ related transcriptomes to an index transcriptome induced by cycloheximide inhibition enables distinction between ¹O₂ of cytosolic or of plastid origin. These comparisons provide biological insight to cases of mutants or environmental conditions that produce ¹O₂.

Enhanced proteostasis, lipid remodeling, and nitrogen remobilization define barley flag leaf senescence

Leaf senescence is a developmental process allowing nutrient remobilization to sink organs. We characterized flag leaf senescence at 7, 14, and 21 d past anthesis in two near-isogenic barley lines varying in the allelic state of the HvNAM1 transcription factor gene, which influences senescence timing. Metabolomics and microscopy indicated that, as senescence progressed, thylakoid lipids were transiently converted to neutral lipids accumulating in lipid droplets. Senescing leaves also exhibited an accumulation of sugars including glucose, while nitrogen compounds (nucleobases, nucleotides, and amino acids) decreased. RNA-Seq analysis suggested lipid catabolism via β-oxidation and the glyoxylate cycle, producing carbon skeletons and feeding respiration as a replacement of the diminished carbon supply from photosynthesis. Comparison of the two barley lines highlighted a more prominent up-regulation of heat stress transcription factor- and chaperone-encoding genes in the late-senescing line, suggesting a role for these genes in the control of leaf longevity. While numerous genes with putative roles in nitrogen remobilization were up-regulated in both lines, several peptidases, nucleases, and nitrogen transporters were more highly induced in the early-senescing line; this finding identifies processes and specific candidates which may affect nitrogen remobilization from senescing barley leaves, downstream of the HvNAM1 transcription factor.

β-Cyclocitral: Emerging Bioactive Compound in Plants

β-cyclocitral (βCC), a main apocarotenoid of β-carotene, increases plants’ resistance against stresses. It has recently appeared as a novel bioactive composite in a variety of organisms from plants to animals. In plants, βCC marked as stress signals that accrue under adverse ecological conditions. βCC regulates nuclear gene expression through several signaling pathways, leading to stress tolerance. In this review, an attempt has been made to summarize the recent findings of the potential role of βCC. We emphasize the βCC biosynthesis, signaling, and involvement in the regulation of abiotic stresses. From this review, it is clear that discussing compound has great potential against abiotic stress tolerance and be used as photosynthetic rate enhancer. In conclusion, this review establishes a significant reference base for future research.

CAN OF SPINACH, a novel long non-coding RNA, affects iron deficiency responses in Arabidopsis thaliana

Long non-coding RNAs (lncRNAs) are RNA molecules with functions independent of any protein-coding potential. A whole transcriptome (RNA-seq) study of Arabidopsis shoots under iron sufficient and deficient conditions was carried out to determine the genes that are iron-regulated in the shoots. We identified two previously unannotated transcripts on chromosome 1 that are significantly iron-regulated. We have called this iron-regulated lncRNA, CAN OF SPINACH (COS). cos mutants have altered iron levels in leaves and seeds. Despite the low iron levels in the leaves, cos mutants have higher chlorophyll levels than WT plants. Moreover, cos mutants have abnormal development during iron deficiency. Roots of cos mutants are longer than those of WT plants, when grown on iron deficient medium. In addition, cos mutant plants accumulate singlet oxygen during iron deficiency. The mechanism through which COS affects iron deficiency responses is unclear, but small regions of sequence similarity to several genes involved in iron deficiency responses occur in COS, and small RNAs from these regions have been detected. We hypothesize that COS is required for normal adaptation to iron deficiency conditions.

Proteome Phenotypes Discriminate the Growing Location and Malting Traits in Field-Grown Barley

Barley is one of the key cereal grains for malting and brewing industries. However, climate variability and unprecedented weather events can impact barley yield and end-product quality. The genetic background and environmental conditions are key factors in defining the barley proteome content and malting characteristics. Here, we measure the barley proteome and malting characteristics of three barley lines grown in Western Australia, differing in genetic background and growing location, by applying liquid chromatography-mass spectrometry (LC-MS). Using data-dependent acquisition LC-MS, 1571 proteins were detected with high confidence. Quantitative data acquired using sequential window acquisition of all theoretical (SWATH) MS on barley samples resulted in quantitation of 920 proteins. Multivariate analyses revealed that the barley lines' genetics and their growing locations are strongly correlated between proteins and desired traits such as the malt yield. Linking meteorological data with proteomic measurements revealed how high-temperature stress in northern regions affects seed temperature tolerance during malting, resulting in a higher malt yield. Our results show the impact of environmental conditions on the barley proteome and malt characteristics; these findings have the potential to expedite breeding programs and malt quality prediction.

Attenuation of cytosolic translation by RNA oxidation is involved in singlet oxygen-mediated transcriptomic responses

Singlet oxygen (¹ O₂ ) production is associated with stress signalling. Here, using Arabidopsis as a model system, we study the effects of the accumulation of 8-hydroxyguanosine (8-oxoG), a major product of ¹ O₂ -mediated RNA oxidation. We show that 8-oxoG can accumulate in vivo when ¹ O₂ is produced in the cytoplasm. Conditions for such production include the application of RB in the light, dark-to-light transitions in the flu mutant, or subjecting plants to combined dehydration/light exposure. Transcriptomes of these treatments displayed a significant overlap with transcripts stimulated by the cytosolic 80S ribosomal translation inhibitors, cycloheximide and homoharringtonine. We demonstrate that 8-oxoG accumulation correlates with a decrease in RNA translatability, resulting in the rapid decrease of the levels of labile gene repressor elements such as IAA1 and JAZ1 in a proteasome-dependent manner. Indeed, genes regulated by the labile repressors of the jasmonic acid signalling pathway were induced by cycloheximide, RB or dehydration/light treatment independently of the hormone. The results suggest that ¹ O₂ , by oxidizing RNA, attenuated cellular translatability and caused specific genes to be released from the repression of their cognate short half-life repressors. The findings here describe a novel means of gene regulation via the direct interaction of ¹ O₂ with RNA.

Photoprotection during iron deficiency is mediated by the bHLH transcription factors PYE and ILR3

Iron (Fe) is an essential micronutrient whose availability is limiting in many soils. During Fe deficiency, plants alter the expression of many genes to increase Fe uptake, distribution, and utilization. In a genetic screen for suppressors of Fe sensitivity in the E3 ligase mutant bts-3, we isolated an allele of the bHLH transcription factor (TF) ILR3, ilr3-4 We identified a striking leaf bleaching phenotype in ilr3 mutants that was suppressed by limiting light intensity, indicating that ILR3 is required for phototolerance during Fe deficiency. Among its paralogs that are thought to be partially redundant, only ILR3 was required for phototolerance as well as repression of genes under Fe deficiency. A mutation in the gene-encoding PYE, a known transcriptional repressor under Fe deficiency, also caused leaf bleaching. We identified singlet oxygen as the accumulating reactive oxygen species (ROS) in ilr3-4 and pye, suggesting photosensitivity is due to a PSII defect resulting in ROS production. During Fe deficiency, ilr3-4 and pye chloroplasts retain normal ultrastructure and, unlike wild type (WT), contain stacked grana similar to Fe-sufficient plants. Additionally, we found that the D1 subunit of PSII is destabilized in WT during Fe deficiency but not in ilr3-4 and pye, suggesting that PSII repair is accelerated during Fe deficiency in an ILR3- and PYE-dependent manner. Collectively, our results indicate that ILR3 and PYE confer photoprotection during Fe deficiency to prevent the accumulation of singlet oxygen, potentially by promoting reduction of grana stacking to limit excitation and facilitate repair of the photosynthetic machinery.

RNA Binding by Plant Serpins in vitro

Serpins constitute a large family of protease inhibitors with regulatory functions found in all living organisms. Most plant serpins have not been functionally characterized, with the exception of Arabidopsis thaliana AtSerpin1, an inhibitor of pro-apoptotic proteases, which is involved in the regulation of the programmed cell death induction, and Cucurbita maxima CmPS1, a phloem protein, which presumably inhibits insect digestive proteases and binds RNA. CmPS1 interacts most efficiently with highly structured RNA; in particular, it forms a specific complex with tRNA. Here, we demonstrated that AtSerpin1 also forms a complex with tRNA. Analysis of tRNA species bound by AtSerpin1 and CmPS1 in the presence of tRNA excess revealed that both proteins have no strict selectivity for individual tRNAs, suggesting specific interaction of AtSerpin1 and CmPS1 proteins with elements of the secondary/tertiary structure universal for all tRNAs. Analysis of CmPS1 binding of the microRNA precursor pre-miR390 and its mutants demonstrated that the pre-miR390 mutant with a perfect duplex in the hairpin stem lost the ability to form a discrete complex with CmPS1, whereas another variant of pre-miR390 with the native unpaired nucleotide residues in the stem retained this ability. These data indicate that specific interactions of plant serpins with structured RNA are based on the recognition of structurally unique spatial motifs formed with the participation of unpaired nucleotide residues in the RNA duplexes.

Lipoxygenase functions in 1O2 production during root responses to osmotic stress

Drought induces osmotic stress in roots, a condition simulated by the application of high-molecular-weight polyethylene glycol. Osmotic stress results in the reduction of Arabidopsis thaliana root growth and production of 1O2 from an unknown non-photosynthetic source. Reduced root growth can be alleviated by application of the 1O2 scavenger histidine (HIS). Here, we examined the possibility that 1O2 production involves Russell reactions occurring among the enzymatic products of lipoxygenases (LOXs), the fatty acid hydroperoxides. LOX activity was measured for purified soybean (Glycine max) LOX1 and in crude Arabidopsis root extracts using linoleic acid as substrate. Formation of the 13(S)-Hydroperoxy-9(Z),11(E)-octadecadienoic acid product was inhibited by salicylhdroxamic acid, which is a LOX inhibitor, but not by HIS, whereas 1O2 production was inhibited by both. D2O, which specifically extends the half-life of 1O2, augmented the LOX-dependent generation of 1O2, as expected from a Russell-type reaction. The addition of linoleic acid to roots stimulated 1O2 production and inhibited growth, suggesting that the availability of LOX substrate is a rate-limiting step. Indeed, water stress rapidly increased linoleic and linolenic acids by 2.5-fold in roots. Mutants with root-specific microRNA repression of LOXs showed downregulation of LOX protein and activity. The lines with downregulated LOX displayed significantly less 1O2 formation, improved root growth in osmotic stress, and an altered transcriptome response compared with wild type. The results show that LOXs can serve as an enzymatic source of "dark" 1O2 during osmotic stress and demonstrate a role for 1O2 in defining the physiological response.

A Comprehensive Phylogenetic Analysis of the Serpin Superfamily

Serine protease inhibitors (serpins) are found in all kingdoms of life and play essential roles in multiple physiological processes. Owing to the diversity of the superfamily, phylogenetic analysis is challenging and prokaryotic serpins have been speculated to have been acquired from Metazoa through horizontal gene transfer due to their unexpectedly high homology. Here, we have leveraged a structural alignment of diverse serpins to generate a comprehensive 6,000-sequence phylogeny that encompasses serpins from all kingdoms of life. We show that in addition to a central “hub” of highly conserved serpins, there has been extensive diversification of the superfamily into many novel functional clades. Our analysis indicates that the hub proteins are ancient and are similar because of convergent evolution, rather than the alternative hypothesis of horizontal gene transfer. This work clarifies longstanding questions in the evolution of serpins and provides new directions for research in the field of serpin biology.

ApSerpin-ZX from Agapanthus praecox, is a potential cryoprotective agent to plant cryopreservation

Cryopreservation-induced cell death is regarded as an important problem faced by cryobiologists. Oxidative stress and programmed cell death are detrimental to cell survival. Serine protease inhibitors (serpins) inhibit pro-cell-death proteases and play a pro-survival role in excessive cell death induced by abiotic stress. In this study, ApSerpin-ZX was isolated from Agapanthus praecox and characterized as a protective protein in plant cryopreservation. The mRNA level of ApSerpin-ZX was elevated under abiotic stress, such as salt, osmosis, oxidative, cold, and cryoinjury. The purified recombinant protein expressed in E. coli was added to the plant vitrification solution and used for A. praecox embryogenic callus cryopreservation. The concentration of 0.6-4.8 mg∙L^-1 of ApSerpin-ZX protein was beneficial to the survival of cryopreserved embryogenic callus of A. praecox. The most effective concentration was 1.2 mg∙L^-1, which elevated the survival by 37.15%. Subsequently, the cryopreservation procedure with 1.2 mg∙L^-1 of ApSerpin-ZX protein was regarded as the treated group, compared to standard procedure, to determine the physiological mechanism of ApSerpin-ZX protein on cryopreserved cell. The MDA and H₂O₂ contents were significantly decreased in the treated group, along with reduced OH· generation activity in the recovery stage. After the addition of ApSerpin-ZX, the POD and CAT activities keep increased, while SOD activity increased only after dehydration. Besides, the caspase-1-like and caspase-3-like activities were lower than the standard procedure. This study indicated that ApSerpin-ZX was a potential cryoprotective agent that alleviated oxidative stress and cell death induced by cryopreservation.

Engineering of fluorescent or photoactive Trojan probes for detection and eradication of β-Amyloids

Trojan horse technology institutes a potentially promising strategy to bring together a diagnostic or cell-based drug design and a delivery platform. It provides the opportunity to re-engineer a novel multimodal, neurovascular detection probe, or medicine to fuse with blood-brain barrier (BBB) molecular Trojan horse. In Alzheimer's disease (AD) this could allow the targeted delivery of detection or therapeutic probes across the BBB to the sites of plaques and tangles development to image or decrease amyloid load, enhance perivascular Aβ clearance, and improve cerebral blood flow, owing principally to the significantly improved cerebral permeation. A Trojan horse can also be equipped with photosensitizers, nanoparticles, quantum dots, or fluorescent molecules to function as multiple targeting theranostic compounds that could be activated following changes in disease-specific processes of the diseased tissue such as pH and protease activity, or exogenous stimuli such as, light. This concept review theorizes the use of receptor-mediated transport-based platforms to transform such novel ideas to engineer systemic and smart Trojan detection or therapeutic probes to advance the neurodegenerative field.

Genome Wide Identification and Comparative Analysis of the Serpin Gene Family in Brachypodium and Barley

Serpins (serine protease inhibitors) constitute one of the largest and most widely distributed superfamilies of protease inhibitors and have been identified in nearly all organisms. To gain significant insights, a comprehensive in silico analysis of the serpin gene family was carried out in the model plant for temperate grasses Brachypodium distachyon and barley Hordeum vulgare using bioinformatic tools at the genome level for the first time. We identified a total of 27 BdSRPs and 25 HvSRP genes in Brachypodium and barley, respectively, showing an unexpectedly high gene number in these model plants. Gene structure, conserved motifs and phylogenetic comparisons of serpin genes supported the role of duplication events in the expansion and evolution of serpin gene family. Further, purifying selection pressure was found to be a main driving force in the evolution of serpin genes. Genome synteny analysis indicated that BdSRP genes were present in syntenic regions of barley, rice, sorghum and maize, suggesting that they evolved before the divergence of these species from common ancestor. The distinct expression pattern in specific tissues further suggested a specialization of functions during development and in plant defense. These results suggest that the LR serpins (serpins with Leu-Arg residues at P2-P1') identified here can be utilized as candidates for exploitation in disease resistance, pest control and preventing stress-induced cell death. Additionally, serpins were identified that could lead to further research aimed at validating and functionally characterizing the role of potential serpin genes from other plants.

Population sequencing enhances understanding of tea plant evolution

Tea is an economically important plant characterized by a large genome, high heterozygosity, and high species diversity. In this study, we assemble a 3.26-Gb high-quality chromosome-scale genome for the 'Longjing 43' cultivar of Camellia sinensis var. sinensis. Genomic resequencing of 139 tea accessions from around the world is used to investigate the evolution and phylogenetic relationships of tea accessions. We find that hybridization has increased the heterozygosity and wide-ranging gene flow among tea populations with the spread of tea cultivation. Population genetic and transcriptomic analyses reveal that during domestication, selection for disease resistance and flavor in C. sinensis var. sinensis populations has been stronger than that in C. sinensis var. assamica populations. This study provides resources for marker-assisted breeding of tea and sets the foundation for further research on tea genetics and evolution.

Singlet Oxygen in Plants: Generation, Detection, and Signaling Roles

Singlet oxygen (1O2) refers to the lowest excited electronic state of molecular oxygen. It easily oxidizes biological molecules and, therefore, is cytotoxic. In plant cells, 1O2 is formed mostly in the light in thylakoid membranes by reaction centers of photosystem II. In high concentrations, 1O2 destroys membranes, proteins and DNA, inhibits protein synthesis in chloroplasts leading to photoinhibition of photosynthesis, and can result in cell death. However, 1O2 also acts as a signal relaying information from chloroplasts to the nucleus, regulating expression of nuclear genes. In spite of its extremely short lifetime, 1O2 can diffuse from the chloroplasts into the cytoplasm and the apoplast. As shown by recent studies, 1O2-activated signaling pathways depend not only on the levels but also on the sites of 1O2 production in chloroplasts, and can activate two types of responses, either acclimation to high light or programmed cell death. 1O2 can be produced in high amounts also in root cells during drought stress. This review summarizes recent advances in research on mechanisms and sites of 1O2 generation in plants, on 1O2-activated pathways of retrograde- and cellular signaling, and on the methods to study 1O2 production in plants.

The Apocarotenoid β-Cyclocitric Acid Elicits Drought Tolerance in Plants

β-Cyclocitral (β-CC) is a volatile compound deriving from 1O2 oxidation of β-carotene in plant leaves. β-CC elicits a retrograde signal, modulating 1O2-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that β-CC is converted into water-soluble β-cyclocitric acid (β-CCA) in leaves. This metabolite is a signal that enhances plant tolerance to drought by a mechanism different from known responses such as stomatal closure, osmotic potential adjustment, and jasmonate signaling. This action of β-CCA is a conserved mechanism, being observed in various plant species, and it does not fully overlap with the β-CC-dependent signaling, indicating that β-CCA induces only a branch of β-CC signaling. Overexpressing SCARECROW-LIKE14 (SCL14, a regulator of xenobiotic detoxification) increased drought tolerance and potentiated the protective effect of β-CCA, showing the involvement of the SCL14-dependent detoxification in the phenomenon. β-CCA is a bioactive apocarotenoid that could potentially be used to protect crop plants against drought.

H2O2 Induces Association of RCA with the Thylakoid Membrane to Enhance Resistance of Oryza meyeriana to Xanthomonas oryzae pv. oryzae

Oryza meyeriana is a wild species of rice with high resistance to Xanthomonas oryzae pv. oryzae (Xoo), but the detailed resistance mechanism is unclear. Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) activase (RCA) is an important enzyme that regulates photosynthesis by activating Rubisco. We have previously reported that Xoo infection induced the relocation of RCA from the chloroplast stroma to the thylakoid membrane in O. meyeriana, but the underlying regulating mechanism and physiological significance of this association remains unknown. In this study, "H₂O₂ burst" with rapid and large increase in the amount of H₂O₂ was found to be induced by Xoo invasion in the leaves of O. meyeriana. 3, 3-diaminobenzidine (DAB) and oxidative 2, 7-Dichlorodi-hydrofluorescein diacetate (H₂DCFDA) staining experiments both showed that H₂O₂ was generated in the chloroplast of O. meyeriana, and that this H₂O₂ generation as well as Xoo resistance of the wild rice were dramatically dependent on light. H₂O₂, methyl viologen with light, and the xanthine-xanthine oxidase system all induced RCA to associate with the thylakoid membrane in vitro, which showed that H₂O₂ could induce the relocation of RCA. In vitro experiments also showed that H₂O₂ induced changes in both the RCA and thylakoid membrane that were required for them to associate and that this association only occurred in O. meyeriana and not in the susceptible cultivated rice. These results suggest that the association of RCA with the thylakoid membrane helps to protect the thylakoid membrane against oxidative damage from H₂O₂. Therefore, in addition to its universal function of activating Rubisco, RCA appears to play a novel role in the resistance of O. meyeriana to Xoo.

Chemistry and biochemistry of cold physical plasma derived reactive species in liquids

Reactive oxygen and nitrogen species deposited by cold physical plasma are proposed as predominant effectors in the interaction between discharge and biomedical application. Most reactive species found in plasma sources are known in biology for inter- and intracellular communication (redox signaling) and mammalian cells are equipped to interpret the plasma derived redox signal. As such, considerable effort has been put into the investigation of potential clinical applications and the underlying mechanism, with a special emphasis on conditions orchestrated significantly via redox signaling. Among these, immune system control in wound healing and cancer control stands out with promising in vitro and in vivo effects. From the fundamental point of view, further insight in the interaction of the plasma-derived species with biological systems is desired to (a) optimize treatment conditions, (b) identify new fields of application, (c) to improve plasma source design, and (d) to identify the trajectories of reactive species. Knowledge on the biochemical reactivity of non-thermal plasmas is compiled and discussed. While there is considerable knowledge on proteins, lipids and carbohydrates have not received the attention deserved. Nucleic acids have been profoundly investigated yet focusing on molecule functionality rather than chemistry. The data collected underline the efforts taken to understand the fundamentals of plasma medicine but also indicate 'no man's lands' waiting to be discovered.

Extracellular silica nanocoat formed by layer-by-layer (LBL) self-assembly confers aluminum resistance in root border cells of pea (Pisum sativum)

BACKGROUND

Soil acidity (and associated Al toxicity) is a major factor limiting crop production worldwide and threatening global food security. Electrostatic layer-by-layer (LBL) self-assembly provides a convenient and versatile method to form an extracellular silica nanocoat, which possess the ability to protect cell from the damage of physical stress or toxic substances. In this work, we have tested a hypothesis that extracellular silica nanocoat formed by LBL self-assembly will protect root border cells (RBCs) and enhance their resistance to Al toxicity.

RESULTS

Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to compare the properties of RBCs surface coated with nanoshells with those that were exposed to Al without coating. The accumulation of Al, reactive oxygen species (ROS) levels, and the activity of mitochondria were detected by a laser-scanning confocal microscopy. We found that a crystal-like layer of silica nanoparticles on the surface of RBCs functions as an extracellular Al-proof coat by immobilizing Al in the apoplast and preventing its accumulation in the cytosol. The silica nanoshells on the RBCs had a positive impact on maintaining the integrity of the plasma and mitochondrial membranes, preventing ROS burst and ensuring higher mitochondria activity and cell viability under Al toxicity.

CONCLUSIONS

The study provides evidence that silica nanoshells confers RBCs Al resistance by restraining of Al in the silica-coat, suggesting that this method can be used an efficient tool to prevent multibillion-dollar losses caused by Al toxicity to agricultural crop production.

Plant serpin protease inhibitors: specificity and duality of function

The serpins are a family of structurally conserved protease inhibitors found in all animal and plant kingdoms. After interaction with their cognate substrate(s), their native energetically stressed state is relaxed by hydrolysis, resulting in a semi-stable covalent bond that disables the protease. The inherent flexible serpin structure supports additional non-inhibitory functions. This review will focus on several biological functions attributed to plant serpins, ranging from specific cell death protease inhibitors to a stabilizing role for β-amylase in seeds. Functional conservation of a particular serpin type, the LR serpins, is suggested by its compelling ubiquity throughout the plant kingdom. The multiple target specificity of plant serpins including the LR serpins enables them to perform dual functions that are not mutually exclusive both as a regulator of cell death and as a protective anti-pathogenic protein.

Cutting Out the Gaps Between Proteases and Programmed Cell Death

To date, many animal models for programmed cell death (PCD) have been extensively characterized and classified while such efforts in plant types of PCD still remain poorly understood. However, despite a wide range of functional differences between PCD types in animals and plants, it is certain that all of them are regulated through the recruitment of proteases. Most importantly, proteases are able to perform proteolysis that results in a gain or loss of protein function. This principle relies on the presence of proteolytic cascades where proteases are activated upon various upstream stimuli and which lead to repetitive cell death. While protease activation, proteolytic cascades and targeted substrates are described in detail mainly for nematode, human, and mice models of apoptosis, for plants, only fragmentary knowledge of protease involvement in PCD exists. However, recently, data on the regulation of general plant PCD and protease involvement have emerged which deepens our understanding of the molecular mechanisms responsible for PCD in plants. With this in mind, this article highlights major aspects of protease involvement in the execution of PCD in both animals and plants, addresses obstacles and advances in the field and proposes recommendations for further research of plant PCD.

Singlet Oxygen Plays an Essential Role in the Root's Response to Osmotic Stress

The high osmotic potentials in plants subjected to drought stress can be mimicked by the application of high molecular weight polyethylene glycol. Here, we quantified the effects of exposure to polyethylene glycol on the growth of the main and lateral roots of Arabidopsis (Arabidopsis thaliana) seedlings. The effects on root growth were highly correlated with the appearance of singlet oxygen, as visualized using the singlet oxygen-specific probe singlet oxygen sensor green. The production of singlet oxygen was followed by cell death, as indicated by the intracellular accumulation of propidium iodide due to the loss of membrane integrity. Cell death began in the epidermal region of the root tip and spread in a dynamic manner to meristematic sections. In parallel, gene expression changes specific to the presence of singlet oxygen were observed. The accumulation of other reactive oxygen species, namely hydrogen, peroxide, nitric oxide, and superoxide, did not correlate with cell death. In addition, both the singlet oxygen scavenger His and the lipoxygenase inhibitor salicylhydroxamic acid specifically inhibited singlet oxygen accumulation and cell death. These results suggest a light-independent, type-I source of singlet oxygen production. Serpin-protease interactions were used as a model to assess the possibility of vacuolar-type cell death. Osmotic stress induced the accumulation of complexes between the cytoplasmic serpin AtSERPIN1 and its cognate vacuolar proteases, indicating that vacuolar integrity was compromised. These findings imply that singlet oxygen plays an essential role in conveying the root response to osmotic stress.

Effects of Olive Oil supplementation on Sodium Arsenate-induced Hepatotoxicity in Mice

Background:

Sodium arsenate (As), a toxic substance with induced oxidative stress, lead to hepatotoxicity. Olive oil (OO) with antioxidant property has protective effect on toxicity. The aim of this study was to investigate protective effect of OO on sodium As-induced hepatotoxicity in mice.

Subjects and Methods:

In this experimental study, 32 adult male BALB/c mice were divided randomly into four groups: control group (received only normal saline, the same volume as other groups), OO (0.4 mL/day, gavage), sodium As (15 mg/kg, gavage), and OO + sodium As (received OO 1 h before sodium As). Drugs were given for 30 consecutive days. After the last receipt of the drugs, oxidative stress parameters [malondialdehyde (MDA), glutathione (GSH)] in tissue, liver function parameters [alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP)] in serum, ferric reducing ability of plasma (FRAP) in plasma, and histopathological assays were performed.

Results:

Sodium As induced hepatic injury as indicated by significant increase in AST, ALT, ALP, and LDH in serum and pathologic evidences. It also induces hepatic oxidative stress biomarkers as indicated by significant increase in levels of MDA and significant decrease in FRAP and GSH concentration. OO administration significantly improved oxidative stress parameters, histopathological changes, and enzymatic markers of liver injury.

Conclusions:

It was concluded that antioxidant activity of OO has hepatoprotective effect on As-induced hepatic injury.

Arabidopsis thaliana serpins AtSRP4 and AtSRP5 negatively regulate stress-induced cell death and effector-triggered immunity induced by bacterial effector AvrRpt2

Protease inhibitors and their cognate proteases regulate growth, development and defense. Serine protease inhibitors (serpins) constitute a large family of genes in most metazoans and plants. Drosophila NECROTIC (NEC) gene and its homologues in the mammalian system are well-characterized serpins, which play a role in regulating proteases that participate in cell death pathways. Although the Arabidopsis genome contains several serpin homologs, biological function is not known for most of them. Here we show that two Arabidopsis serpins, AtSRP4 and AtSRP5, are closest sequence homologue of Drosophila NEC protein, and are involved in stress-induced cell death and defense. Expression of both AtSRP4 and AtSRP5 genes induced upon ultra-violet (UV)-treatment and inoculation with avirulent pathogens. The knockout mutants and amiRNA lines of AtSRP4 and AtSRP5 exaggerated UV- and hypersensitive response (HR)-induced cell death. Over-expression of AtSRP4 reduced UV- and HR-induced cell death. Mutants of AtSRP4 and AtSRP5 suppressed whereas over-expression of AtSRP4 supported the growth of bacterial pathogen Pseudomonas syringae pv. tomato DC3000 carrying the AvrRpt2 effector, but not other avirulent or virulent pathogens. Results altogether identified AtSRP4 and AtSRP5 as negative regulators of stress-induced cell death and AvrRpt2-triggered immunity; however, the influence of AtSRP4 was more prominent than AtSRP5.

The relationship between vacuolation and initiation of PCD in rice (Oryza sativa) aleurone cells

Vacuole fusion is a necessary process for the establishment of a large central vacuole, which is the central location of various hydrolytic enzymes and other factors involved in death at the beginning of plant programmed cell death (PCD). In our report, the fusion of vacuoles has been presented in two ways: i) small vacuoles coalesce to form larger vacuoles through membrane fusion, and ii) larger vacuoles combine with small vacuoles when small vacuoles embed into larger vacuoles. Regardless of how fusion occurs, a large central vacuole is formed in rice (Oryza sativa) aleurone cells. Along with the development of vacuolation, the rupture of the large central vacuole leads to the loss of the intact plasma membrane and the degradation of the nucleus, resulting in cell death. Stabilizing or disrupting the structure of actin filaments (AFs) inhibits or promotes the fusion of vacuoles, which delays or induces PCD. In addition, the inhibitors of the vacuolar processing enzyme (VPE) and cathepsin B (CathB) block the occurrence of the large central vacuole and delay the progression of PCD in rice aleurone layers. Overall, our findings provide further evidence for the rupture of the large central vacuole triggering the PCD in aleruone layers.

Singlet oxygen detection in biological systems: Uses and limitations

The study of singlet oxygen in biological systems is challenging in many ways. Singlet oxygen is a relatively unstable ephemeral molecule, and its properties make it highly reactive with many biomolecules, making it difficult to quantify accurately. Several methods have been developed to study this elusive molecule, but most studies thus far have focused on those conditions that produce relatively large amounts of singlet oxygen. However, the need for more sensitive methods is required as one begins to explore the levels of singlet oxygen required in signaling and regulatory processes. Here we discuss the various methods used in the study of singlet oxygen, and outline their uses and limitations.