The mitochondrial glutathione peroxidase GPX3 is essential for H2O2 homeostasis and root and shoot development in rice

Differential expression of tRNA-derived small RNAs in Juvenile and adult sheep skin: implications for developmental and immune regulation

BACKGROUND

tRNA fragments (tRFs) are small non-coding RNAs generated from cleaved tRNA molecules, playing key roles in gene regulation and cellular processes. Produced by ribonucleases like angiogenin and Dicer, tRFs vary in length and function in gene silencing and stress responses. They interact with Argonaute proteins and affect mRNA levels, and are emerging as potential diagnostic and therapeutic targets for diseases such as cancer and neurodegenerative disorders. Given that the skin is the largest organ in mammals, it serves as an ideal model for studying development and various diseases. Therefore, this study investigates tRF expression in sheep skin tissues to understand their regulatory roles during growth and development.

RESULTS

This study analyzed skin tissue from five 1-month-old lambs and five 24-month-old adult Tan sheep using small RNA sequencing and proteomics. Raw sequencing data were filtered and aligned to identify various tsRNAs, while proteomic data were assessed for differential expression. Principal Component Analysis (PCA) revealed distinct separation between juvenile and adult samples based on tsRNA expression patterns, indicating intra-group similarity and inter-group differences. Differentially expressed tsRNAs were identified, with 19 highly expressed tsRNAs at 1 month of age. Proteomic screening identified 932 highly expressed and 835 lowly expressed proteins in the 1-month-old group, with functional enrichment highlighting immunity and inflammation pathways. Predictive analysis of tsRNA target genes intersected with 20 differentially expressed proteins involved in mitochondrial metabolism and stress response.

CONCLUSION

This study reveals that tsRNAs significantly influence developmental and immune processes in sheep, with distinct expression patterns between juveniles and adults. Future research should validate these findings and further elucidate the functional mechanisms of tsRNA regulation.

Foliar-selenium enhances plant growth and arsenic accumulation in As-hyperaccumulator Pteris vittata: Critical roles of GSH-GSSG cycle and arsenite antiporters PvACR3

It is known that selenium (Se) enhances plant growth and arsenic (As) accumulation in As-hyperaccumulator Pteris vittata, but the associated mechanisms are unclear. In this study, P. vittata was exposed to 50 μM arsenate (AsV) under hydroponics plus 25 or 50 μM foliar selenate. After 3-weeks of growth, the plant biomass, As and Se contents, As speciation, malondialdehyde (MDA) and glutathione (GSH and GSSG) levels, and important genes related to As-metabolism in P. vittata were determined. Foliar-Se increased plant biomass by 17 - 30 %, possibly due to 9.1 - 19 % reduction in MDA content compared to the As control. Further, foliar-Se enhanced the As contents by 1.9-3.5 folds and increased arsenite (AsIII) contents by 64 - 136 % in the fronds. The increased AsV reduction to AsIII was attributed to 60 - 131 % increase in glutathione peroxidase activity, which mediates GSH oxidation to GSSG (8.8 -29 % increase) in the fronds. Further, foliar-Se increased the expression of AsIII antiporters PvACR3;1-3;3 by 1.6 - 2.1 folds but had no impact on phosphate transporters PvPht1 or arsenate reductases PvHAC1/2. Our results indicate that foliar-Se effectively enhances plant growth and arsenic accumulation by promoting the GSH-GSSG cycle and upregulating gene expression of AsIII antiporters, which are responsible for AsIII translocation from the roots to fronds and AsIII sequestration into the fronds. The data indicate that foliar-Se can effectively improve phytoremediation efficiency of P. vittata in As-contaminated soils.

Characterization of GPX Gene Family in Pepper (Capsicum annuum L.) under Abiotic Stress and ABA Treatment

Plant glutathione peroxidases (GPXs) are important enzymes for removing reactive oxygen species in plant cells and are closely related to the stress resistance of plants. This study identified the GPX gene family members of pepper (Capsicum annuum L.), "CM333", at the whole-genome level to clarify their expression patterns and enzyme activity changes under abiotic stress and ABA treatment. The results showed that eight CaGPX genes were unevenly distributed across four chromosomes and one scaffold of the pepper genome, and their protein sequences had Cys residues typical of the plant GPX domains. The analysis of collinearity, phylogenetic tree, gene structure, and conserved motifs indicated that the CaGPX gene sequence is conserved, structurally similar, and more closely related to the sequence structure of Arabidopsis. Meanwhile, many cis elements involved in stress, hormones, development, and light response were found in the promoter region of the CaGPX gene. In addition, CaGPX1/4 and CaGPX6 were basically expressed in all tissues, and their expression levels were significantly upregulated under abiotic stress and ABA treatment. Subcellular localization showed that CaGPX1 and CaGPX4 are localized in chloroplasts. Additionally, the variations in glutathione peroxidase activity (GSH-Px) mostly agreed with the variations in gene expression. In summary, the CaGPXs gene may play an important role in the development of peppers and their response to abiotic stress and hormones.

Overexpression of Rhodiola crenulata glutathione peroxidase 5 increases cold tolerance and enhances the pharmaceutical value of the hairy roots

Rhodiola crenulata, a plant of great medicinal value found in cold high-altitude regions, has been excessively exploited due to the difficulty in cultivation. Understanding Rhodiola crenulata's adaptation mechanisms to cold environment can provide a theoretical basis for artificial breeding. Glutathione peroxidases (GPXs), critical enzymes found in plants, play essential roles in antioxidant defense through the ascorbate-glutathione cycle. However, it is unknown whether GPX5 contributes to Rhodiola crenulata's cold tolerance. In this study, we investigated the role of GPX5 in Rhodiola crenulata's cold tolerance mechanisms. By overexpressing Rhodiola crenulata GPX5 (RcGPX5) in yeast and Arabidopsis thaliana, we observed down-regulation of Arabidopsis thaliana GPX5 (AtGPX5) and increased cold tolerance in both organisms. Furthermore, the levels of antioxidants and enzyme activities in the ascorbate-glutathione cycle were elevated, and cold-responsive genes such as AtCBFs and AtCORs were induced. Additionally, RcGPX5 overexpressing lines showed insensitivity to exogenous abscisic acid (ABA), suggesting a negative regulation of the ABA pathway by RcGPX5. RcGPX5 also promoted the expression of several thioredoxin genes in Arabidopsis and interacted with two endogenous genes of Rhodiola crenulata, RcTrx2-3 and RcTrxo1, located in mitochondria and chloroplasts. These findings suggest a significantly different model in Rhodiola crenulata compared to Arabidopsis thaliana, highlighting a complex network involving the function of RcGPX5. Moreover, overexpressing RcGPX5 in Rhodiola crenulata hairy roots positively influenced the salidroside synthesis pathway, enhancing its pharmaceutical value for doxorubicin-induced cardiotoxicity. These results suggested that RcGPX5 might be a key component for Rhodiola crenulata to adapt to cold stress and overexpressing RcGPX5 could enhance the pharmaceutical value of the hairy roots.

Genetic diversity of durum wheat (Triticum turgidum ssp. durum) to mitigate abiotic stress: Drought, heat, and their combination

Drought and heat are the main abiotic constraints affecting durum wheat production. This study aimed to screen for tolerance to drought, heat, and combined stresses in durum wheat, at the juvenile stage under controlled conditions. Five durum wheat genotypes, including four landraces and one improved genotype, were used to test their tolerance to abiotic stress. After 15 days of growing, treatments were applied as three drought levels (100, 50, and 25% field capacity (FC)), three heat stress levels (24, 30, and 35°C), and three combined treatments (100% FC at 24°C, 50% FC at 30°C and 25% FC at 35°C). The screening was performed using a set of morpho-physiological, and biochemical traits. The results showed that the tested stresses significantly affect all measured parameters. The dry matter content (DM) decreased by 37.1% under heat stress (35°C), by 37.3% under severe drought stress (25% FC), and by 53.2% under severe combined stress (25% FC at 35°C). Correlation analyses of drought and heat stress confirmed that aerial part length, dry matter content, hydrogen peroxide content, catalase, and Glutathione peroxidase activities could be efficient screening criteria for both stresses. The principal component analysis (PCA) showed that only the landrace Aouija tolerated the three studied stresses, while Biskri and Hedhba genotypes were tolerant to drought and heat stresses and showed the same sensitivity under combined stress. Nevertheless, improved genotype Karim and the landrace Hmira were the most affected genotypes by drought, against a minimum growth for the Hmira genotype under heat stress. The results showed that combined drought and heat stresses had a more pronounced impact than simple effects. In addition, the tolerance of durum wheat to drought and heat stresses involves several adjustments of morpho-physiological and biochemical responses, which are proportional to the stress intensity.

The selenium-independent phospholipid hydroperoxide glutathione peroxidase from Theobroma cacao (TcPHGPX) protects plant cells against damages and cell death

Proteins from the glutathione peroxidase (GPX) family, such as GPX4 or PHGPX in animals, are extensively studied for their antioxidant functions and apoptosis inhibition. GPXs can be selenium-independent or selenium-dependent, with selenium acting as a potential cofactor for GPX activity. However, the relationship of plant GPXs to these functions remains unclear. Recent research indicated an upregulation of Theobroma cacao phospholipid hydroperoxide glutathione peroxidase gene (TcPHGPX) expression during early witches' broom disease stages, suggesting the use of antioxidant mechanisms as a plant defense strategy to reduce disease progression. Witches' broom disease, caused by the hemibiotrophic fungus Moniliophthora perniciosa, induces cell death through elicitors like MpNEP2 in advanced infection stages. In this context, in silico and in vitro analyses of TcPHGPX's physicochemical and functional characteristics may elucidate its antioxidant potential and effects against cell death, enhancing understanding of plant GPXs and informing strategies to control witches' broom disease. Results indicated TcPHGPX interaction with selenium compounds, mainly sodium selenite, but without improving the protein function. Protein-protein interaction network suggested cacao GPXs association with glutathione and thioredoxin metabolism, engaging in pathways like signaling, peroxide detection for ABA pathway components, and anthocyanin transport. Tests on tobacco cells revealed that TcPHGPX reduced cell death, associated with decreased membrane damage and H2O2 production induced by MpNEP2. This study is the first functional analysis of TcPHGPX, contributing to knowledge about plant GPXs and supporting studies for witches' broom disease control.

TaGPX1-D overexpression provides salinity and osmotic stress tolerance in Arabidopsis

Glutathione peroxidases (GPXs) are known to play an essential role in guarding cells against oxidative stress by catalyzing the reduction of hydrogen peroxide and organic hydroperoxides. The current study aims functional characterization of the TaGPX1-D gene of bread wheat (Triticum aestivum) for salinity and osmotic stress tolerance. To achieve this, we initially performed the spot assays of TaGPX1-D expressing yeast cells. The growth of recombinant TaGPX1-D expressing yeast cells was notably higher than the control cells under stress conditions. Later, we generated transgenic Arabidopsis plants expressing the TaGPX1-D gene and investigated their tolerance to various stress conditions. The transgenic plants exhibited improved tolerance to both salinity and osmotic stresses compared to the wild-type plants. The higher germination rates, increased antioxidant enzymes activities, improved chlorophyll, carotenoid, proline and relative water contents, and reduced hydrogen peroxide and MDA levels in the transgenic lines supported the stress tolerance mechanism. Overall, this study demonstrated the role of TaGPX1-D in abiotic stress tolerance, and it can be used for improving the tolerance of crops to environmental stressors, such as salinity and osmotic stress in future research.

Identification and validation of key biomarkers and potential therapeutic targets for primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a prevalent cause of blindness worldwide, resulting in degeneration of retinal ganglion cells and permanent damage to the optic nerve. However, the underlying pathogenetic mechanisms of POAG are currently indistinct, and there has been no effective nonsurgical treatment regimen. The objective of this study is to identify novel biomarkers and potential therapeutic targets for POAG. The mRNA expression microarray datasets GSE27276 and GSE138125, as well as the single-cell high-throughput RNA sequencing (scRNA-seq) dataset GSE148371 were utilized to screen POAG-related differentially expressed genes (DEGs). Functional enrichment analyses, protein-protein interaction (PPI) analysis, and weighted gene co-expression network analysis (WGCNA) of the DEGs were performed. Subsequently, the hub genes were validated at a single-cell level, where trabecular cells were annotated, and the mRNA expression levels of target genes in different cell clusters were analyzed. Immunofluorescence and quantitative real-time PCR (qPCR) were performed for further validation. DEGs analysis identified 43 downregulated and 32 upregulated genes in POAG, which were mainly enriched in immune-related pathways, oxidative stress, and endoplasmic reticulum (ER) stress. PPI networks showed that FN1 and DUSP1 were the central hub nodes, while GPX3 and VAV3 were screened out as hub genes through WGCNA and subsequently validated by qPCR. Finally, FN1, GPX3, and VAV3 were determined to be pivotal core genes via single-cell validation. The relevant biomarkers involved in the pathogenesis of POAG, may serve as potential therapeutic targets. Further studies are necessary to unveil the mechanisms underlying the expression variations of these genes in POAG.

Involvement of plant signaling network and cell metabolic homeostasis in nitrogen deficiency-induced early leaf senescence

Nitrogen (N) is a basic building block that plays an essential role in the maintenance of normal plant growth and its metabolic functions through complex regulatory networks. Such the N metabolic network comprises a series of transcription factors (TFs), with the coordinated actions of phytohormone and sugar signaling to sustain cell homeostasis. The fluctuating N concentration in plant tissues alters the sensitivity of several signaling pathways to stressful environments and regulates the senescent-associated changes in cellular structure and metabolic process. Here, we review recent advances in the interaction between N assimilation and carbon metabolism in response to N deficiency and its regulation to the nutrient remobilization from source to sink during leaf senescence. The regulatory networks of N and sugar signaling for N deficiency-induced leaf senescence is further discussed to explain the effects of N deficiency on chloroplast disassembly, reactive oxygen species (ROS) burst, asparagine metabolism, sugar transport, autophagy process, Ca2+ signaling, circadian clock response, brassinazole-resistant 1 (BZRI), and other stress cell signaling. A comprehensive understanding for the metabolic mechanism and regulatory network underlying N deficiency-induced leaf senescence may provide a theoretical guide to optimize the source-sink relationship during grain filling for the achievement of high yield by a selection of crop cultivars with the properly prolonged lifespan of functional leaves and/or by appropriate agronomic managements.

Comprehensive identification of glutathione peroxidase (GPX) gene family in response to abiotic stress in pepper (Capsicum annuum L.)

Plant glutathione peroxidase (GPX) plays an important role in the maintenance of cell homeostasis and in the antioxidant response in plants. In this study, the peroxidase (GPX) gene family was identified in the whole genome of pepper using bioinformatic method. As a result, a total of 5 CaGPX genes were identified, which were unevenly distributed on 3 of the 12 chromosomes of pepper genome. Based on phylogenetic analysis, 89 GPX genes in 17 species from lower plants to higher plants can be divided into 4 groups GroupⅠ, Group Ⅱ, Group Ⅲ, Group Ⅳ). The MEME Suite analysis of GPX proteins shows that all these proteins contain four highly conserved motifs, as well as other conserved sequences and amino acid residues. Gene structure analysis revealed the conservative exon-intron organization pattern of these genes. In the promoter region of CaGPX genes, many cis elements of plant hormone and abiotic stress response were identified in each of CaGPX proteins. In addition, expression patterns of CaGPX genes in different tissues, developmental stages and responses to abiotic stress were also performed. The results of qRT-PCR showed that the transcripts of CaGPX genes varied greatly under abiotic stress at different time points. There results suggest that the GPX gene family of pepper may play a role in plant development andstress response. In conclusion, our research provides new insights into the evolution of pepper GPX gene family, and understanding for functional of these genes in response to abiotic stresses.

Genome-Wide Analysis and Expression Profiling of the Glutathione Peroxidase-like Enzyme Gene Family in Solanum tuberosum

Glutathione peroxidase-like enzyme is an important enzymatic antioxidant in plants. It is involved in scavenging reactive oxygen species, which can effectively prevent oxidative damage and improve resistance. GPXL has been studied in many plants but has not been reported in potatoes, the world's fourth-largest food crop. This study identified eight StGPXL genes in potatoes for the first time through genome-wide bioinformatics analysis and further studied the expression patterns of these genes using qRT-PCR. The results showed that the expression of StGPXL1 was significantly upregulated under high-temperature stress, indicating its involvement in potato defense against high-temperature stress, while the expression levels of StGPXL4 and StGPXL5 were significantly downregulated. The expression of StGPXL1, StGPXL2, StGPXL3, and StGPXL6 was significantly upregulated under drought stress, indicating their involvement in potato defense against drought stress. After MeJA hormone treatment, the expression level of StGPXL6 was significantly upregulated, indicating its involvement in the chemical defense mechanism of potatoes. The expression of all StGPXL genes is inhibited under biotic stress, which indicates that GPXL is a multifunctional gene family, which may endow plants with resistance to various stresses. This study will help deepen the understanding of the function of the potato GPXL gene family, provide comprehensive information for the further analysis of the molecular function of the potato GPXL gene family as well as a theoretical basis for potato molecular breeding.

Proteomic and physiological responses of contrasting two different heat-resistant orchardgrass genotypes to heat stress

As an important forage crop worldwide, the growth and productivity of orchardgrass are greatly impacted by high temperatures. However, little information is known about how orchardgrass proteomic changes under heat conditions. Therefore, the present study investigated the proteomics and physiological changes in 667 [AKZ-NRGR667 (heat-tolerant)] and 7602 [PI237602 (heat-sensitive)] under heat stress (40/35 °C). In addition, the responses of translational regulating of heat stress in orchardgrass were analyzed through proteomic changes using the tandem mass tags (TMT) technique. Together, 410 differentially expressed proteins (DEPs) were identified from two orchardgrass genotypes under heat at 24 h. Proteomics analyses indicated that proteins related to substance metabolism, photosynthesis, and heat shock proteins (HSPs) were differentially expressed under heat stress and control conditions. Moreover, a large proportion of HSPs were expressed in the heat-tolerant genotype as compared to the heat-sensitive genotype. In conclusion, genotype 667 has higher adaptability and repairing capability due to stronger heat tolerance capacity that can make it more suited to sustaining its survival and growth than genotype 7602. These findings can provide the basis for genetic improvements in orchardgrass and other crops facing high-temperature stress or heat environment that may lead to heat resistance or tolerance.

Glutathione Contribution in Interactions between Turnip mosaic virus and Arabidopsis thaliana Mutants Lacking Respiratory Burst Oxidase Homologs D and F

Respiratory burst oxidase homologs (Rbohs) play crucial and diverse roles in plant tissue-mediated production of reactive oxygen species during the development, growth, and response of plants to abiotic and biotic stress. Many studies have demonstrated the contribution of RbohD and RbohF in stress signaling in pathogen response differentially modulating the immune response, but the potential role of the Rbohs-mediated response in plant-virus interactions remains unknown. The present study analyzed, for the first time, the metabolism of glutathione in rbohD-, rbohF-, and rbohD/F-transposon-knockout mutants in response to Turnip mosaic virus (TuMV) infection. rbohD-TuMV and Col-0-TuMV interactions were characterized by susceptible reaction to TuMV, associated with significant activity of GPXLs (glutathione peroxidase-like enzymes) and induction of lipid peroxidation in comparison to mock-inoculated plants, with reduced total cellular and apoplastic glutathione content observed at 7-14 dpi and dynamic induction of apoplast GSSG (oxidized glutathione) at 1-14 dpi. Systemic virus infection resulted in the induction of AtGSTU1 and AtGSTU24, which was highly correlated with significant downregulation of GSTs (glutathione transferases) and cellular and apoplastic GGT (γ-glutamyl transferase) with GR (glutathione reductase) activities. On the contrary, resistant rbohF-TuMV reactions, and especially enhanced rbohD/F-TuMV reactions, were characterized by a highly dynamic increase in total cellular and apoplastic glutathione content, with induction of relative expression of AtGGT1, AtGSTU13, and AtGSTU19 genes. Moreover, virus limitation was highly correlated with the upregulation of GSTs, as well as cellular and apoplastic GGT with GR activities. These findings clearly indicate that glutathione can act as a key signaling factor in not only susceptible rbohD reaction but also the resistance reaction presented by rbohF and rbohD/F mutants during TuMV interaction. Furthermore, by actively reducing the pool of glutathione in the apoplast, GGT and GR enzymes acted as a cell first line in the Arabidopsis-TuMV pathosystem response, protecting the cell from oxidative stress in resistant interactions. These dynamically changed signal transductions involved symplast and apoplast in mediated response to TuMV.

The Role of Nanoparticles in Response of Plants to Abiotic Stress at Physiological, Biochemical, and Molecular Levels

In recent years, the global agricultural system has been unfavorably impacted by adverse environmental changes. These changes in the climate, in turn, have altered the abiotic conditions of plants, affecting plant growth, physiology and production. Abiotic stress in plants is one of the main obstacles to global agricultural production and food security. Therefore, there is a need for the development of novel approaches to overcome these problems and achieve sustainability. Nanotechnology has emerged as one such novel approach to improve crop production, through the utilization of nanoscale products, such as nanofertilizer, nanofungicides, nanoherbicides and nanopesticides. Their ability to cross cellular barriers makes nanoparticles suitable for their application in agriculture. Since they are easily soluble, smaller, and effective for uptake by plants, nanoparticles are widely used as a modern agricultural tool. The implementation of nanoparticles has been found to be effective in improving the qualitative and quantitative aspects of crop production under various biotic and abiotic stress conditions. This review discusses various abiotic stresses to which plants are susceptible and highlights the importance of the application of nanoparticles in combating abiotic stress, in addition to the major physiological, biochemical and molecular-induced changes that can help plants tolerate stress conditions. It also addresses the potential environmental and health impacts as a result of the extensive use of nanoparticles.

Susceptibility of Rice Crop to Salt Threat: Proteomic, Metabolomic, and Physiological Inspections

Rice is a staple food crop worldwide; however, salinity stress is estimated to reduce its global production by 50%. Knowledge about initial molecular signaling and proteins associated with sensing salinity among crop plants is limited. We characterized early salt effects on the proteome and metabolome of rice tissues. Omics results were validated by western blotting and multiple reaction monitoring assays and integrated with physiological changes. We identified 8160 proteins and 2045 metabolites in rice tissues. Numerous signaling pathways were induced rapidly or partially by salinity. Combined data showed the most susceptible proteins or metabolites in each pathway that likely affected the sensitivity of rice to salinity, such as PLA1, BON3 (involved in sensing stress), SnRK2, pro-resilin, GDT1, G-proteins, calmodulin activators (Ca²⁺ and abscisic acid signaling), MAPK3/5, MAPKK1/3 (MAPK pathway), SOS1, ABC F/D, PIP2-7, and K⁺ transporter-23 (transporters), OPR1, JAR1, COL1, ABA2, and MAPKK3 (phytohormones). Additionally, our results expanded the stress-sensing function of receptor-like kinases, phosphatidylinositols, and Na⁺ sensing proteins (IPUT1). Combined analyses revealed the most sensitive components of signaling pathways causing salt-susceptibility in rice and suggested potential targets for crop improvement.

Genome-wide, evolutionary, and functional analyses of ascorbate peroxidase (APX) family in Poaceae species

Ascorbate peroxidases (APXs) are heme peroxidases involved in the control of hydrogen peroxide levels and signal transduction pathways related to development and stress responses. Here, a total of 238 APX, 30 APX-related (APX-R), and 34 APX-like (APX-L) genes were identified from 24 species from the Poaceae family. Phylogenetic analysis of APX indicated five distinct clades, equivalent to cytosolic (cAPX), peroxisomal (pAPX), mitochondrial (mitAPX), stromal (sAPX), and thylakoidal (tAPX) isoforms. Duplication events contributed to the expansion of this family and the divergence times. Different from other APX isoforms, the emergence of Poaceae mitAPXs occurred independently after eudicot and monocot divergence. Our results showed that the constitutive silencing of mitAPX genes is not viable in rice plants, suggesting that these isoforms are essential for rice regeneration or development. We also obtained rice plants silenced individually to sAPX isoforms, demonstrating that, different to plants double silenced to both sAPX and tAPX or single silenced to tAPX previously obtained, these plants do not show changes in the total APX activity and hydrogen peroxide content in the shoot. Among rice plants silenced to different isoforms, plants silenced to cAPX showed a higher decrease in total APX activity and an increase in hydrogen peroxide levels. These results suggest that the cAPXs are the main isoforms responsible for regulating hydrogen peroxide levels in the cell, whereas in the chloroplast, this role is provided mainly by the tAPX isoform. In addition to broadening our understanding of the core components of the antioxidant defense in Poaceae species, the present study also provides a platform for their functional characterization.

Arsenic inhibits citric acid accumulation via downregulating vacuolar proton pump gene expression in citrus fruits

Citric acid content is a critical quality determinant in citrus (Citrus spp.) fruits. Although arsenic (As) can effectively reduce citric acid content to improve citrus fruit quality, it can have adverse environmental effects. The discovery of nontoxic substitutes is hampered by the incomplete elucidation of the underlying mechanisms of As action in citrus fruits. Metabolic, transcriptomic, and physiological analyses were employed to investigate As action on citric acid accumulation to discover the mechanisms of As action in citrus. The enzyme activity related to citrate biosynthesis was not inhibited and the content of the involved metabolites was not reduced in As-treated fruits. However, the proton pump genes CitPH5 and CitPH1 control the vacuolar citric acid accumulation and transcription factor genes CitTT8 and CitMYB5, which regulate CitPH5 and CitPH1, were downregulated. The oxidative stress-response genes were upregulated in As-treated fruits. The reactive oxygen species (ROS) treatment also downregulated CitTT8 and CitMYB5 in juice cells. The mitochondrial ROS production rate increased in As-treated fruits. As^III was more potent in stimulating isolated mitochondria to overproduce ROS compared to As^V. Our results indicate that the As inhibition of citric acid accumulation may be primarily due to the transcriptional downregulation of CitPH5, CitPH1, CitTT8, and CitMYB5. As-induced oxidative stress signaling may operate upstream to downregulate these acid regulator genes. Mitochondrial thiol proteins may be the principal targets of As action in citrus fruits.

Plant Glutathione Peroxidases: Non-Heme Peroxidases with Large Functional Flexibility as a Core Component of ROS-Processing Mechanisms and Signalling

Glutathione peroxidases (GPXs) are non-heme peroxidases catalyzing the reduction of H₂O₂ or organic hydroperoxides to water or corresponding alcohols using glutathione (GSH) or thioredoxin (TRX) as a reducing agent. In contrast to animal GPXs, the plant enzymes are non-seleno monomeric proteins that generally utilize TRX more effectively than GSH but can be a putative link between the two main redox systems. Because of the substantial differences compared to non-plant GPXs, use of the GPX-like (GPXL) name was suggested for Arabidopsis enzymes. GPX(L)s not only can protect cells from stress-induced oxidative damages but are crucial components of plant development and growth. Due to fine-tuning the H₂O₂ metabolism and redox homeostasis, they are involved in the whole life cycle even under normal growth conditions. Significantly new mechanisms were discovered related to their transcriptional, post-transcriptional and post-translational modifications by describing gene regulatory networks, interacting microRNA families, or identifying Lys decrotonylation in enzyme activation. Their involvement in epigenetic mechanisms was evidenced. Detailed genetic, evolutionary, and bio-chemical characterization, and comparison of the main functions of GPXs, demonstrated their species-specific roles. The multisided involvement of GPX(L)s in the regulation of the entire plant life ensure that their significance will be more widely recognized and applied in the future.

Physiological and proteomic dissection of the rice roots in response to iron deficiency and excess

Iron (Fe) disorder is a pivotal factor that limits rice yields in many parts of the world. Extensive research has been devoted to studying how rice molecularly copes with the stresses of Fe deficiency or excess. However, a comprehensive dissection of the whole Fe-responsive atlas at the protein level is still lacking. Here, different concentrations of Fe (0, 40, 350, and 500 μM) were supplied to rice to demonstrate its response differences to Fe deficiency and excess via physiological and proteomic analysis. Results showed that compared with the normal condition, the seedling growth and contents of Fe and manganese were significantly disturbed under either Fe stress. Proteomic analysis revealed that differentially accumulated proteins under Fe deficiency and Fe excess were commonly enriched in localization, carbon metabolism, biosynthesis of amino acids, and antioxidant system. Notably, proteins with abundance retuned by Fe starvation were individually associated with phenylpropanoid biosynthesis, cysteine and methionine metabolism, while ribosome- and endocytosis-related proteins were specifically enriched in treatment of Fe overdose of 500 μM. Moreover, several novel proteins which may play potential roles in rice Fe homeostasis were predicted. These findings expand the understanding of rice Fe nutrition mechanisms, and provide efficient guidance for genetic breeding work. SIGNIFICANCE: Both iron (Fe) deficiency and excess significantly inhibited the growth of rice seedlings. Fe deficiency and excess disturbed processes of localization and cellular oxidant detoxification, metabolisms of carbohydrates and amino acids in different ways. The Fe-deficiency and Fe-excess-responsive proteins identified by the proteome were somewhat different from the reported transcriptional profiles, providing complementary information to the transcriptomic data.

Crosstalk between the Arabidopsis Glutathione Peroxidase-Like 5 Isoenzyme (AtGPXL5) and Ethylene

Glutathione peroxidases (GPXs) are important antioxidant enzymes in animals. Plants contain GPX-like (GPXL) enzymes, which-in contrast to GPXs-contain cysteine in their active site instead of selenocysteine. Although several studies proved their importance in development and stress responses, their interaction with ethylene (ET) signalling is not known. Our aim was to investigate the involvement of AtGPXL5 in ET biosynthesis and/or signalling using Atgpxl5 mutant and AtGPXL5 cDNA-overexpressing (OX-AtGPXL5) lines. Four-day-old dark-grown Atgpxl5 seedlings had shorter hypocotyls and primary roots, while OX-AtGPXL5 seedlings exhibited a similar phenotype as wild type under normal conditions. Six-week-old OX-AtGPXL5 plants contained less H₂O₂ and malondialdehyde, but higher polyamine and similar ascorbate- and glutathione contents and redox potential (E_GSH) than the Col-0. One-day treatment with the ET-precursor 1-aminocyclopropane-1-carboxylic acid (ACC) induced the activity of glutathione- and thioredoxin peroxidases and some other ROS-processing enzymes. In the Atgpxl5 mutants, the E_GSH became more oxidised; parallelly, it produced more ethylene after the ACC treatment than other genotypes. Although the enhanced ET evolution measured in the Atgpxl5 mutant can be the result of the increased ROS level, the altered expression pattern of ET-related genes both in the Atgpxl5 and OX-AtGPXL5 plants suggests the interplay between AtGPXL5 and ethylene signalling.

Evolutionary and functional characterisation of glutathione peroxidases showed splicing mediated stress responses in Maize

Maize (Zea mays L) is an important cereal with extensive adaptability and multifaceted usages. However, various abiotic and biotic stresses limit the productivity of maize across the globe. Exposure of plant to stresses disturb the balance between reactive oxygen species (ROS) production and scavenging, which subsequently increases cellular damage and death of plants. Tolerant genotypes have evolved higher output of scavenging antioxidative defence compounds (ADCs) during stresses as one of the protective mechanisms. The glutathione peroxidases (GPXs) are the broad class of ADCs family. The plant GPXs catalyse the reduction of hydrogen peroxide (H₂O₂), lipid hydroperoxides and organic hydroperoxides to the corresponding alcohol, and facilitate the regulation of stress tolerance mechanisms. The present investigation was framed to study the maize GPXs using evolutionary and functional analyses. Seven GPX genes with thirteen splice-variants and sixty-three types of cis-acting elements were identified through whole-genome scanning in maize. Evolutionary analysis of GPXs in monocots and dicots revealed mixed and lineage-specific grouping patterns in phylogeny. The expression of ZmGPX splice variants was studied in drought and waterlogging tolerant (L1621701) and sensitive (PML10) genotypes in root and shoot tissues. Further, the differential expression of splice variants of ZmGPX1, ZmGPX3, ZmGPX6 and ZmGPX7 and regulatory network analysis suggested the splicing and regulatory elements mediated stress responses. The present investigation suggests targeting the splicing machinery of GPXs as an approach to enhance the stress tolerance in maize.

SfGPX regulates low-temperature tolerance by affecting velocity and intensity of Ca2+ transfer and photosynthetic characteristics in interfered Spiraea fritschiana and overexpressed Spiraea japonica 'Gold Mound'

Genes play regulatory roles in plants' response to low-temperature stress. Our understanding of the mechanism of plants' response to low-temperature stress can be expanded by studying the functions of these genes. SfGPX was cloned from Spiraea fritschiana (S. fritschiana) with the highest low-temperature tolerance, to explore the molecular mechanisms of SfGPX in response to low-temperature stress and the physiological mechanisms involved in the regulation of SfGPX to adapt to low temperature, in two species of Spiraea. SfGPX, which was localized in the cytoplasm, was induced by low temperature. The low-temperature tolerance of Spiraea fritschiana was decreased via the interference of SfGPX, and the low-temperature tolerance of Spiraea japonica 'Gold Mound' (S. japonica 'Gold Mound') was elevated via the overexpression of SfGPX. Under low-temperature stress, the photosynthetic capacity of two species of Spiraea was affected by SfGPX; it was higher in the cold-tolerant plants and lower in the cold-intolerant plants. Under low-temperature stress, the transfer intensity of Ca²⁺ was affected by SfGPX. The transfer intensity of cold-tolerant plants with lower influx level of Ca²⁺ kinetics was weaker than that of cold-intolerant plants. Under low-temperature stress, the transfer velocity of Ca²⁺ was affected by SfGPX, and there were slower effluxes of Ca²⁺ from Ca²⁺ reservoir in cold-tolerant plants than in cold-intolerant plants. The above results indicate that the response of Spiraea to low temperature is regulated by SfGPX through affecting photosynthetic capacity as well as intensity and velocity of Ca²⁺ transfer in response to low temperature in Spiraea.

Rice GLUTATHIONE PEROXIDASE1-mediated oxidation of bZIP68 positively regulates ABA-independent osmotic stress signaling

Osmotic stress caused by drought and high salinity is a significant environmental threat that limits plant growth and agricultural yield. Redox regulation plays an important role in plant stress responses, but the mechanisms by which plants perceive and transduce redox signals are still underexplored. Here, we report a critical function for the thiol peroxidase GPX1 in osmotic stress response in rice, where it serves as a redox sensor and transducer. GPX1 is quickly oxidized upon exposure to osmotic stress and forms an intramolecular disulfide bond, which is required for the activation of bZIP68, a VRE-like basic leucine zipper (bZIP) transcription factor involved in the ABA-independent osmotic stress response pathway. The disulfide exchange between GPX1 and bZIP68 induces homo-tetramerization of bZIP68 and thus positively regulates osmotic stress response by regulating osmotic-responsive gene expression. Furthermore, we discovered that the nuclear translocation of GPX1 is regulated by its acetylation under osmotic stress. Taken together, our findings not only uncover the redox regulation of the GPX1-bZIP68 module during osmotic stress but also highlight the coordination of protein acetylation and redox signaling in plant osmotic stress responses.

Influence of arsenate imposition on modulation of antioxidative defense network and its implication on thiol metabolism in some contrasting rice (Oryza sativa L.) cultivars

Globally, many people have been suffering from arsenic poisoning. Arsenate (AsV) exposure to twelve rice cultivars caused growth retardation, triggered production of As-chelatin biopeptides and altered activities of antioxidants along with increase in ascorbate (AsA)-glutathione (GSH) contents as a protective measure. The effects were more conspicuous in cvs. Swarnadhan, Tulaipanji, Pusa basmati, Badshabhog, Tulsibhog and IR-20 to attenuate oxidative-overload mediated adversities. Contrastingly, in cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64, effects were less conspicuous in terms of alterations in the said variables due to reduced generation of oxidative stress. Under As(V) imposition, the protective role of phytochelatins (PCs) were recorded where peaks height and levels of PCs (PC2, PC3 and PC4) were elevated significantly in the test seedlings with an endeavour to detoxify cells by sequestering arsenic-phytochelatin (As-PC) complex into vacuole that resulted in reprogramming of antioxidants network. Additionally, scatter plot correlation matrices, color-coded heat map analysis and regression slopes demonstrated varied adaptive responses of test cultivars, where cvs. Bhutmuri, Kumargore, Binni, Vijaya, TN-1 and IR-64 found tolerant against As(V) toxicity. Results were further justified by hierarchical clustering. These findings could help to grow identified tolerant rice cultivars in As-prone soil with sustainable growth and productivity after proper agricultural execution.

How to Cope with the Challenges of Environmental Stresses in the Era of Global Climate Change: An Update on ROS Stave off in Plants

With the advent of human civilization and anthropogenic activities in the shade of urbanization and global climate change, plants are exposed to a complex set of abiotic stresses. These stresses affect plants’ growth, development, and yield and cause enormous crop losses worldwide. In this alarming scenario of global climate conditions, plants respond to such stresses through a highly balanced and finely tuned interaction between signaling molecules. The abiotic stresses initiate the quick release of reactive oxygen species (ROS) as toxic by-products of altered aerobic metabolism during different stress conditions at the cellular level. ROS includes both free oxygen radicals {superoxide (O₂^•−) and hydroxyl (OH⁻)} as well as non-radicals [hydrogen peroxide (H₂O₂) and singlet oxygen (¹O₂)]. ROS can be generated and scavenged in different cell organelles and cytoplasm depending on the type of stimulus. At high concentrations, ROS cause lipid peroxidation, DNA damage, protein oxidation, and necrosis, but at low to moderate concentrations, they play a crucial role as secondary messengers in intracellular signaling cascades. Because of their concentration-dependent dual role, a huge number of molecules tightly control the level of ROS in cells. The plants have evolved antioxidants and scavenging machinery equipped with different enzymes to maintain the equilibrium between the production and detoxification of ROS generated during stress. In this present article, we have focused on current insights on generation and scavenging of ROS during abiotic stresses. Moreover, the article will act as a knowledge base for new and pivotal studies on ROS generation and scavenging.

Synthesis of Abscisic Acid in Neopyropia yezoensis and Its Regulation of Antioxidase Genes Expressions Under Hypersaline Stress

Abscisic acid (ABA) is regarded as crucial for plant adaptation to water-limited conditions and it functions evolutionarily conserved. Thus, insights into the synthesis of ABA and its regulation on downstream stress-responsive genes in Neopyropia yezoensis, a typical Archaeplastida distributed in intertidal zone, will improve the knowledge about how ABA signaling evolved in plants. Here, the variations in ABA contents, antioxidant enzyme activities and expression of the target genes were determined under the presence of exogenous ABA and two specific inhibitors of the ABA precursor synthesis. ABA content was down-regulated under the treatments of each or the combination of the two inhibitors. Antioxidant enzyme activities like SOD, CAT and APX were decreased slightly with inhibitors, but up-regulated when the addition of exogenous ABA. The quantitative assays using real-time PCR (qRT-PCR) results were consistent with the enzyme activities. All the results suggested that ABA can also alleviate oxidative stress in N. yezoensis as it in terrestrial plant. Combined with the transcriptome assay, it was hypothesized that ABA is synthesized in N. yezoensis via a pathway that is similar to the carotenoid pathway in higher plants, and both the MVA and that the MEP pathways for isoprenyl pyrophosphate (IPP) synthesis likely exist simultaneously. The ABA signaling pathway in N. yezoensis was also analyzed from an evolutionary standpoint and it was illustrated that the emergence of the ABA signaling pathway in this alga is an ancestral one. In addition, the presence of the ABRE motif in the promoter region of antioxidase genes suggested that the antioxidase system is regulated by the ABA signaling pathway.

Laboratory phenomics predicts field performance and identifies superior indica haplotypes for early seedling vigour in dry direct-seeded rice

Seedling vigour is an important agronomic trait and is gaining attention in Asian rice (Oryza sativa) as cultivation practices shift from transplanting to forms of direct seeding. To understand the genetic control of rice seedling vigour in dry direct seeded (aerobic) conditions we measured multiple seedling traits in 684 accessions from the 3000 Rice Genomes (3K-RG) population in both the laboratory and field at three planting depths. Our data show that phenotyping of mesocotyl length in laboratory conditions is a good predictor of field performance. By performing a genome wide association study, we found that the main QTL for mesocotyl length, percentage seedling emergence and shoot biomass are co-located on the short arm of chromosome 7. We show that haplotypes in the indica subgroup from this region can be used to predict the seedling vigour of 3K-RG accessions. The selected accessions may serve as potential donors in genomics-assisted breeding programs.

Identification of Glutathione Peroxidase Gene Family in Ricinus communis and Functional Characterization of RcGPX4 in Cold Tolerance

Glutathione peroxidases (GPXs) protect cells against damage caused by reactive oxygen species (ROS) and play key roles in regulating many biological processes. Here, five GPXs were identified in the Ricinus communis genome. Phylogenetic analysis displayed that the GPXs were categorized into five groups. Conserved domain and gene structure analyses showed that the GPXs from different plant species harbored four highly similar motifs and conserved exon-intron arrangement patterns, indicating that their structure and function may have been conserved during evolution. Several abiotic stresses and hormone-responsive cis-acting elements existed in the promoters of the RcGPXs. The expression profiles indicated that the RcGPXs varied substantially, and some RcGPXs were coordinately regulated under abiotic stresses. Overexpression of RcGPX4 in Arabidopsis enhanced cold tolerance at seed germination but reduced freezing tolerance at seedlings. The expression of abscisic acid (ABA) signaling genes (AtABI4 and AtABI5), ABA catabolism genes (AtCYP707A1 and AtCYP707A2), gibberellin acid (GA) catabolism gene (AtGA2ox7), and cytokinin (CTK)-inducible gene (AtARR6) was regulated in the seeds of transgenic lines under cold stress. Overexpression of RcGPX4 can disturb the hydrogen peroxide (H2O2) homeostasis through the modulation of some antioxidant enzymes and compounds involved in the GSH-ascorbate cycle in transgenic plants. Additionally, RcGPX4 depended on the MAPK3-ICE1-C-repeat-binding factor (CBF)-COR signal transduction pathway and ABA-dependent pathway to negatively regulate the freezing tolerance of transgenic plants. This study provides valuable information for understanding the potential function of RcGPXs in regulating the abiotic stress responses of castor beans.

Regulatory functions of ROS dynamics via glutathione metabolism and glutathione peroxidase activity in developing rice zygote

Reactive oxygen species (ROS) play essential roles in plant development and environmental stress responses. In this study, ROS dynamics, the glutathione redox status, the expression and subcellular localization of glutathione peroxidases (GPXs), and the effects of inhibitors of ROS-mediated metabolism were investigated along with fertilization and early zygotic embryogenesis in rice (Oryza sativa). Zygotes and early embryos exhibited developmental arrest upon inhibition of ROS production. Egg cells accumulated high ROS levels, and, after fertilization, intracellular ROS levels progressively declined in zygotes in which de novo expression of GPX1 and 3 was observed through upregulation of the genes. In addition to inhibition of GPX activity, depletion of glutathione impeded early embryonic development and led to failure of the zygote to appropriately decrease H2 O2 levels. Moreover, through monitoring of the glutathione redox status, the developing zygotes exhibited a progressive glutathione oxidation, which became extremely delayed under inhibited GPX activity. Our results provide insights into the importance of ROS dynamics, GPX antioxidant activity, and glutathione redox metabolism during zygotic/embryonic development.

TaASR1-D confers abiotic stress resistance by affecting ROS accumulation and ABA signalling in transgenic wheat

Cultivating new crop cultivars with multiple abiotic stress tolerances is important for crop production. The abscisic acid-stress-ripening (ASR) protein has been shown to confer abiotic stress tolerance in plants. However, the mechanisms of ASR function under stress condition remain largely unclear. In this study, we characterized all ASR family members in common wheat and constitutively overexpressed TaASR1-D in a commercial hexaploid wheat cultivar Zhengmai 9023. The transgenic wheat plants exhibited increased tolerance to multiple abiotic stresses and increased grain yields under salt stress condition. Overexpression of TaASR1-D conferred enhanced antioxidant capacity and ABA sensitivity in transgenic wheat plants. Further, RNA in situ hybridization results showed that TaASR1-D had higher expression levels in the vascular tissues of leaves and the parenchyma cells around the vascular tissues of roots and stems. Yeast one-hybrid and electrophoretic mobility shift assays revealed that TaASR1-D could directly bind the specific cis-elements in the promoters of TaNCED1 and TaGPx1-D. In conclusion, our findings suggest that TaASR1-D can be used to breed new wheat cultivars with increased multiple abiotic stress tolerances, and TaASR1-D enhances abiotic stress tolerances by reinforcing antioxidant capacity and ABA signalling.

Mitochondrial redox systems as central hubs in plant metabolism and signaling

Plant mitochondria are indispensable for plant metabolism and are tightly integrated into cellular homeostasis. This review provides an update on the latest research concerning the organization and operation of plant mitochondrial redox systems, and how they affect cellular metabolism and signaling, plant development, and stress responses. New insights into the organization and operation of mitochondrial energy systems such as the tricarboxylic acid cycle and mitochondrial electron transport chain (mtETC) are discussed. The mtETC produces reactive oxygen and nitrogen species, which can act as signals or lead to cellular damage, and are thus efficiently removed by mitochondrial antioxidant systems, including Mn-superoxide dismutase, ascorbate-glutathione cycle, and thioredoxin-dependent peroxidases. Plant mitochondria are tightly connected with photosynthesis, photorespiration, and cytosolic metabolism, thereby providing redox-balancing. Mitochondrial proteins are targets of extensive post-translational modifications, but their functional significance and how they are added or removed remains unclear. To operate in sync with the whole cell, mitochondria can communicate their functional status via mitochondrial retrograde signaling to change nuclear gene expression, and several recent breakthroughs here are discussed. At a whole organism level, plant mitochondria thus play crucial roles from the first minutes after seed imbibition, supporting meristem activity, growth, and fertility, until senescence of darkened and aged tissue. Finally, plant mitochondria are tightly integrated with cellular and organismal responses to environmental challenges such as drought, salinity, heat, and submergence, but also threats posed by pathogens. Both the major recent advances and outstanding questions are reviewed, which may help future research efforts on plant mitochondria.

Exogenous Application of Zinc to Mitigate the Salt Stress in Vigna radiata (L.) Wilczek-Evaluation of Physiological and Biochemical Processes

Salt stress adversely affects the growth and productivity of crops. However, reports suggest that the application of various micronutrients could help the plant to cope with this stress. Hence, the objective of the study was to examine the effect of exogenous application of Zinc (Zn) on salt tolerance in Vigna radiata (L.) Wilczek (mungbean). Mungbean is considered to be an economically important crop and possess a strategic position in Southeast Asian countries for sustainable crop production. It is rich in quality proteins, minerals and vitamins. Three weeks old grown seedlings were subjected to NaCl (150 mM and 200 mM) alone or with Zn (250 µM). After 21 days of treatment, plants were harvested for investigating morphological, physiological and biochemical changes. We found that the Zn application mitigates the negative effect upon plant growth to a variable extent. This may be attributed to the increased shoot and root length, improved chlorophyll and carotenoid contents, enhanced total soluble sugar (TSS), total soluble protein (TSP) and proline accumulation, decreased H2O2 content and increased enzymatic antioxidant activities. Zn's application improved the performance of the enzymes such as phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) of the secondary metabolism, which resulted in the improvement of total phenol and flavonoids. The antioxidant activities such as 1,1diphenyl 2-picryl hydrazine (DPPH) and ferrous reducing antioxidant power assay (FRAP) of the plants also showed improved results in their salt only treatments. Furthermore, hydrogen peroxide (H2O2) and superoxide radical (SOD) scavenging activity were also improved upon the application of 250 µM zinc. Thus, Zn application in low doses offers promising potential for recovering plants suffering from salinity stress. In conclusion, we assume that zinc application improved salt tolerance in mungbean through the improvement of various physiological and photochemical processes which could prove to be useful in nutrient mediated management for crop improvement.

Novel QTL Associated with Shoot Branching Identified in Doubled Haploid Rice (Oryza sativa L.) under Low Nitrogen Cultivation

Shoot branching is considered as an important trait for the architecture of plants and contributes to their growth and productivity. In cereal crops, such as rice, shoot branching is controlled by many factors, including phytohormones signaling networks, operating either in synergy or antagonizing each other. In rice, shoot branching indicates the ability to produce more tillers that are essential for achieving high productivity and yield potential. In the present study, we evaluated the growth and development, and yield components of a doubled haploid population derived from a cross between 93-11 (P1, indica) and Milyang352 (P2, japonica), grown under normal nitrogen and low nitrogen cultivation open field conditions. The results of the phenotypic evaluation indicated that parental lines 93-11 (P1, a high tillering indica cultivar) and Milyang352 (P2, a low tillering japonica cultivar) showed distinctive phenotypic responses, also reflected in their derived population. In addition, the linkage mapping and quantitative trait locus (QTL) analysis detected three QTLs associated with tiller number on chromosome 2 (qTNN2-1, 130 cM, logarithm of the odds (LOD) 4.14, PVE 14.5%; and qTNL2-1, 134 cM, LOD: 6.05, PVE: 20.5%) and chromosome 4 (qTN4-1, 134 cM, LOD 3.92, PVE 14.5%), with qTNL2-1 having the highest phenotypic variation explained, and the only QTL associated with tiller number under low nitrogen cultivation conditions, using Kompetitive Allele-Specific PCR (KASP) and Fluidigm markers. The additive effect (1.81) of qTNL2-1 indicates that the allele from 93-11 (P1) contributed to the observed phenotypic variation for tiller number under low nitrogen cultivation. The breakthrough is that the majority of the candidate genes harbored by the QTLs qTNL2-1 and qTNN4-1 (here associated with the control of shoot branching under low and normal nitrogen cultivation, respectively), were also proposed to be involved in plant stress signaling or response mechanisms, with regard to their annotations and previous reports. Therefore, put together, these results would suggest that a possible crosstalk exists between the control of plant growth and development and the stress response in rice.

Identification of Ipomoea batatas anti-cancer peptide (IbACP)-responsive genes in sweet potato leaves

IbACP, Ipomoea batatas anti-cancer peptide, a sixteen-amino-acid peptide isolated from sweet potato leaves, is capable of mediating a rapid alkalinization of growth media in plant suspension cells. However, the biological roles of IbACP as a defense peptide have not been studied. The objective of this study was to investigate the effect of IbACP on the accumulation of reactive oxygen species (ROS) and the expression of the defense-related genes. IbACP treatment of sweet potato leaves resulted in marked accumulation of both superoxide ion (O₂^-) and hydrogen peroxide (H₂O₂). The activity of peroxidase (POD) was significantly enhanced by IbACP treatment, suggesting that high levels of POD antioxidant activity may be used to scavenge the excess H₂O₂ in sweet potato plants. The IbACP-related genes were identified by suppression subtractive hybridization (SSH), and were then classified and assigned to the following categories: defense, development, metabolism, signaling, gene expression, and abiotic stress. H₂O₂ acts as a second messenger for gene activation in some of the IbACP-triggered gene expressions. These results demonstrated that IbACP is part of an integrated strategy for genetic regulation in sweet potato. Our work highlights the function of IbACP and its potential use for enhancing stress tolerance in sweet potato, in an effort to improve our understanding of defense-response mechanisms.

Recent Developments in Enzymatic Antioxidant Defence Mechanism in Plants with Special Reference to Abiotic Stress

The stationary life of plants has led to the evolution of a complex gridded antioxidant defence system constituting numerous enzymatic components, playing a crucial role in overcoming various stress conditions. Mainly, these plant enzymes are superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR), glutathione S-transferases (GST), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase (DHAR), which work as part of the antioxidant defence system. These enzymes together form a complex set of mechanisms to minimise, buffer, and scavenge the reactive oxygen species (ROS) efficiently. The present review is aimed at articulating the current understanding of each of these enzymatic components, with special attention on the role of each enzyme in response to the various environmental, especially abiotic stresses, their molecular characterisation, and reaction mechanisms. The role of the enzymatic defence system for plant health and development, their significance, and cross-talk mechanisms are discussed in detail. Additionally, the application of antioxidant enzymes in developing stress-tolerant transgenic plants are also discussed.

Root responses of contrasting rice genotypes to low temperature stress

Rice (Oryza sativa L.) ssp. indica is the most cultivated species in the South of Brazil. However, these plants face low temperature stress from September to November, which is the period of early sowing, affecting plant development during the initial stages of growth, and reducing rice productivity. This study aimed to characterize the root response to low temperature stress during the early vegetative stage of two rice genotypes contrasting in their cold tolerance (CT, cold-tolerant; and CS, cold-sensitive). Root dry weight and length, as well as the number of root hairs, were higher in CT than CS when exposed to cold treatment. Histochemical analyses indicated that roots of CS genotype present higher levels of lipid peroxidation and H₂O₂ accumulation, along with lower levels of plasma membrane integrity than CT under low temperature stress. RNAseq analyses revealed that the contrasting genotypes present completely different molecular responses to cold stress. The number of over-represented functional categories was lower in CT than CS under cold condition, suggesting that CS genotype is more impacted by low temperature stress than CT. Several genes might contribute to rice cold tolerance, including the ones related with cell wall remodeling, cytoskeleton and growth, signaling, antioxidant system, lipid metabolism, and stress response. On the other hand, high expression of the genes SRC2 (defense), root architecture associated 1 (growth), ACC oxidase, ethylene-responsive transcription factor, and cytokinin-O-glucosyltransferase 2 (hormone-related) seems to be related with cold sensibility. Since these two genotypes have a similar genetic background (sister lines), the differentially expressed genes found here can be considered candidate genes for cold tolerance and could be used in future biotechnological approaches aiming to increase rice tolerance to low temperature.

The mitochondrial isoform glutathione peroxidase 3 (OsGPX3) is involved in ABA responses in rice plants

Different environmental conditions can lead plants to a condition termed oxidative stress, which is characterized by a disruption in the equilibrium between the production of reactive oxygen species (ROS) and antioxidant defenses. Glutathione peroxidase (GPX), an enzyme that acts as a peroxide scavenger in different organisms, has been identified as an important component in the signaling pathway during the developmental process and in stress responses in plants and yeast. Here, we demonstrate that the mitochondrial isoform of rice (Oryza sativa L. ssp. Japonica cv. Nipponbare) OsGPX3 is induced after treatment with the phytohormone abscisic acid (ABA) and is involved in its responses and in epigenetic modifications. Plants that have been silenced for OsGPX3 (gpx3i) present substantial changes in the accumulation of proteins related to these processes. These plants also have several altered ABA responses, such as germination, ROS accumulation, stomatal closure, and dark-induced senescence. This study is the first to demonstrate that OsGPX3 plays a role in ABA signaling and corroborate that redox homeostasis enzymes can act in different and complex pathways in plant cells. SIGNIFICANCE: This work proposes the mitochondrial glutathione peroxidase (OsGPX3) as a novel ABA regulatory pathway component. Our results suggest that this antioxidant enzyme is involved in ABA-responses, highlighting the complex pathways that these proteins can participate beyond the regulation of cellular redox status.

Root response in Pisum sativum under naproxen stress: Morpho-anatomical, cytological, and biochemical traits

Non-steroidal anti-inflammatory drugs as an important group of emerging environmental contaminants in irrigation water and soils can influence biochemical and physiological processes essential for growth and development in plants as non-target organisms. Plants are able to take up, transport, transform, and accumulate drugs in the roots. Root biomass in ten-days old pea plants was lowered by 6% already under 0.1 mg/L naproxen (NPX) due to a lowered number of lateral roots, although 0.5 mg/L NPX stimulated the total root length by 30% as against control. Higher section area (by 40%) in root tip, area of xylem (by 150%) or stele-to-section ratio (by 10%) in zone of maturation, and lower section area in zone of lateral roots (by 18%) prove the changes in primary root anatomy and its earlier differentiation at 10 mg/L NPX. Accumulated NPX (up to 10 μg/g DW at 10 mg/L) and products of its metabolization in roots increased the amounts of hydrogen peroxide (by 33%), and superoxide (by 62%), which was reflected in elevated lipid peroxidation (by 32%), disruption of membrane integrity (by 89%) and lowering both oxidoreductase and dehydrogenase activities (by up to 40%). Elevated antioxidant capacity (SOD, APX, and other molecules) under low treatments decreased at 10 mg/L NPX (both by approx. 30%). Naproxen was proved to cause changes at both cellular and tissue levels in roots, which was also reflected in their anatomy and morphology. Higher environmental loading through drugs thus can influence even the root function.

Stress signalling dynamics of the mitochondrial electron transport chain and oxidative phosphorylation system in higher plants

BACKGROUND

Mitochondria play a diversity of physiological and metabolic roles under conditions of abiotic or biotic stress. They may be directly subjected to physico-chemical constraints, and they are also involved in integrative responses to environmental stresses through their central position in cell nutrition, respiration, energy balance and biosyntheses. In plant cells, mitochondria present various biochemical peculiarities, such as cyanide-insensitive alternative respiration, and, besides integration with ubiquitous eukaryotic compartments, their functioning must be coupled with plastid functioning. Moreover, given the sessile lifestyle of plants, their relative lack of protective barriers and present threats of climate change, the plant cell is an attractive model to understand the mechanisms of stress/organelle/cell integration in the context of environmental stress responses.

SCOPE

The involvement of mitochondria in this integration entails a complex network of signalling, which has not been fully elucidated, because of the great diversity of mitochondrial constituents (metabolites, reactive molecular species and structural and regulatory biomolecules) that are linked to stress signalling pathways. The present review analyses the complexity of stress signalling connexions that are related to the mitochondrial electron transport chain and oxidative phosphorylation system, and how they can be involved in stress perception and transduction, signal amplification or cell stress response modulation.

CONCLUSIONS

Plant mitochondria are endowed with a diversity of multi-directional hubs of stress signalling that lead to regulatory loops and regulatory rheostats, whose functioning can amplify and diversify some signals or, conversely, dampen and reduce other signals. Involvement in a wide range of abiotic and biotic responses also implies that mitochondrial stress signalling could result in synergistic or conflicting outcomes during acclimation to multiple and complex stresses, such as those arising from climate change.

Melatonin: Awakening the Defense Mechanisms during Plant Oxidative Stress

Melatonin is a multifunctional signaling molecule that is ubiquitously distributed in different parts of a plant and responsible for stimulating several physio-chemical responses to adverse environmental conditions. In this review, we show that, although plants are able to biosynthesize melatonin, the exogenous application of melatonin to various crops can improve plant growth and development in response to various abiotic and biotic stresses (e.g., drought, unfavorable temperatures, high salinity, heavy metal contamination, acid rain, and combined stresses) by regulating antioxidant machinery of plants. Current knowledge suggests that exogenously applied melatonin can enhance the stress tolerance of plants by regulating both the enzymatic and non-enzymatic antioxidant defense systems. Enzymic antioxidants upregulated by exogenous melatonin include superoxide dismutase, catalase, glutathione peroxidase, and enzymes involved in the ascorbate–glutathione cycle (ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, and glutathione reductase), whereas levels of non-enzymatic antioxidants such as ascorbate, reduced glutathione, carotenoids, tocopherols, and phenolics are also higher under stress conditions. The enhanced antioxidant system consequently exhibits lower lipid peroxidation and greater plasma membrane integrity when under stress. However, these responses vary greatly from crop to crop and depend on the intensity and type of stress, and most studies to date have been conducted under controlled conditions. This means that a wider range of crop field trials and detailed transcriptomic analysis are required to reveal the gene regulatory networks involved in the between melatonin, antioxidants, and abiotic stress.

Overexpression of the Arabidopsis and winter squash superoxide dismutase genes enhances chilling tolerance via ABA-sensitive transcriptional regulation in transgenic Arabidopsis

The winter squash (Cucurbita moschata, Cm) superoxide dismutase (SOD) CmSOD gene and Arabidopsis thaliana (At)SOD gene were transferred under a ubiquitin promoter into Arabidopsis via Agrobacterium tumefaciens. The expression and amount of SOD and the SOD activities in the AtSOD and CmSOD transgenic lines were significantly higher than those of non-transgenic (NT) plants exposed to 23 or 4°C treatment for 6 ~ 192-h periods. Furthermore, expressions of the cold-inducible gene (AtCBF2) and desiccation-responsible transcription factors (AtRD29A/B) were also activated in all transgenic lines compared to NT plants after chilling treatments. Compared to NT plants under chilling stress, superoxide (•O2^-) accumulation was significantly lower, and chlorophyll (Chl) contents were significantly higher in all transgenic lines with higher SOD activity. Moreover, Arabidopsis seedlings overexpressing AtSOD and CmSOD also displayed greater resistance to chilling and less oxidative injury than NT plants under chilled conditions, indicating that the overexpression of AtSOD and CmSOD in Arabidopsis enhanced chilling tolerance by eliminating •O2^-. The expression of AtRD29A was strongly up-regulated only in AtSOD transgenic plants treated with abscisic acid (ABA), while it was repressed in other transgenic plants, indicating ABA-sensitive AtCBF2 and AtRD29A/B transcriptional regulation signaling pathways in transgenic Arabidopsis under chilling conditions.

Cloning and overexpression of the ascorbate peroxidase gene from the yam (Dioscorea alata) enhances chilling and flood tolerance in transgenic Arabidopsis

Minghuai 1 (MH1) is a yam (Dioscorea alata) cultivar with high tolerance to flooding but sensitivity to chilling. MH1 responded differently to chilling and flooding according to various physiological parameters and antioxidant enzymes. Flooding led to an increase in ascorbate peroxidase (APX) activity in both roots and leaves, while chilling did not affect APX activity. The full length DaAPX ORF sequence from MH1 (750 bp) was then cloned. Phylogenetic analysis showed that plant cytosolic APXs into four major clusters and DaAPX was closely related to Oncidium. The DaAPX gene driven by a 35S promoter was transferred into Arabidopsis. The gene expression and enzyme activity of APX in the DaAPX transgenic lines 1-3 were significantly higher than in wild type (WT) plants. Compared to WT plants, seedling growth characteristics were significantly better in all transgenic lines under chilling, flooding, and oxidative stresses, indicating that the overexpression of DaAPX in Arabidopsis enhanced tolerance to several abiotic stresses. MH1 plants supplied with H₂O₂ presented an increase in the activity of APX leading to enhanced tolerance to chilling. Functional characterization of the APX gene should improve our understanding of the chilling- and flood-response mechanism in the yam.

Fibroin Delays Chilling Injury of Postharvest Banana Fruit via Enhanced Antioxidant Capability during Cold Storage

storage Banana fruit after harvest is susceptible to chilling injury, which is featured by peel browning during cold, and it easily loses its nutrition and economic values. This study investigated the role of fibroin treatment in delaying peel browning in association with the antioxidant capability of postharvest banana fruit during cold storage. Compared to the control fruit, fibroin-treated fruit contained higher amounts of Pro and Cys during overall storage as well as higher glutathione (GSH) during the middle of storage. Conversely, fibroin-treated fruit exhibited a lower peel browning index and reactive oxygen species (ROS) level during overall storage as well as lower contents of hexadecanoic acid and octadecanoic acid by the end of storage compared to control fruit. In addition, fibroin-treated banana fruit showed higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in relation to upregulation SOD, CAT, and GR as well as peroxiredoxins (MT3 and GRX) during the middle of storage. These results highlighted the role of fibroin treatment in reducing peel browning by enhancing the antioxidant capability of harvested banana fruit during cold storage.

Genome-wide association study reveals significant genomic regions for improving yield, adaptability of rice under dry direct seeded cultivation condition

BACKGROUND

Puddled transplanted system of rice cultivation despite having several benefits, is a highly labor, water and energy intensive system. In the face of changing climatic conditions, a successful transition from puddled to dry direct seeded rice (DDSR) cultivation system looks must in future. Genome-wide association study was performed for traits including, roots and nutrient uptake (14 traits), plant-morphological (5 traits), lodging-resistance (4 traits) and yield and yield attributing traits (7 traits) with the aim to identify significant marker-trait associations (MTAs) for traits enhancing rice adaptability to dry direct-seeded rice (DDSR) system.

RESULTS

Study identified a total of 37 highly significant MTAs for 20 traits. The false discovery rate (FDR) ranged from 0.264 to 3.69 × 10- 4, 0.0330 to 1.25 × 10- 4, and 0.0534 to 4.60 × 10- 6 in 2015WS, 2016DS and combined analysis, respectively. The percent phenotypic variance (PV) explained by SNPs ranged from 9 to 92%. Among the identified significant MTAs, 15 MTAs associated with the traits including nodal root, root hair length, root length density, stem and culm diameter, plant height and grain yield were reported to be located in the proximity of earlier identified candidate gene. The significant positive correlation of grain-yield with seedling establishment traits, root morphological and nutrient-uptake related traits and grain yield attributing traits pointing towards combining target traits to increase rice yield and adaptability under DDSR. Seven promising progenies with better root morphology, nutrient-uptake and higher grain yield were identified that can further be used in genomics assisted breeding for DDSR varietal development.

CONCLUSIONS

Once validated, the identified MTAs and the SNPs linked with trait of interest could be of direct use in genomic assisted breeding (GAB) to improve grain yield and adaptability of rice under DDSR.

Differential response of Indian mustard (Brassica juncea L., Czern and Coss) under salinity: photosynthetic traits and gene expression

To explore the effect of salt stress on photosynthetic traits and gene expression in Indian mustard, four genotypes CS 54 (national check for salinity), CS 52-SPS-1-2012 (salt tolerant mutant), CS 614-4-1-4-100-13 (salt sensitive mutant) and Pusa bold (high yielding variety) were evaluated under irrigation water salinity (ECiw 12, and 15 dS m-1). Results suggest genotype CS 52-SPS-1-2012 followed by CS 54 performed better under imposed salt stress due to differential regulation of Na+ accumulation in the roots and main stem, restriction of Na+ influx from root to shoot, maintaining higher net photosynthetic traits under saline stress compared to CS 614-4-1-4-100-13 and Pusa bold. Further, overexpression of antiporters (SOS1, SOS2, SOS3, ENH1 and NHX1) and antioxidant (APX1, APX4, DHAR1 and MDHAR) genes in salt tolerant genotypes CS 52-SPS-1-2012 and CS 54 demonstrated their significant role in imparting salt tolerance in Indian mustard.

Effect of Gpx3 gene silencing by siRNA on apoptosis and autophagy in chicken cardiomyocytes

Glutathione peroxidase 3 (Gpx3), as an important selenoprotein, is the most crucial antioxidant defense in cardiomyocytes. However, the role of Gpx3 in Se-deficient cardiomyocyte damage still less reported. Here, we developed Gpx3 silence cardiomyocytes culture model (small interfering RNA; siRNA) for research the crosstalk between autophagy and apoptosis. Quantitative real-time PCR and western blot analysis are performed to detect the expression of apoptosis and autophagy-related genes. MDC stain, flow cytometry, AO/EB stain, and electron microscope were performed to observe the changes of cell morphology. Our results reveal that Gpx3 suppression can significant increases in ROS (p < 0.05) levels, which further induced apoptosis through upregulated the expression of Caspase-3 in cardiomyocytes. Meanwhile, we also found that the whole process is accompanied by the occurrence of autophagy, which are promoted by inhibiting the mTOR, and increasing the expression of ATG-7, ATG-10, and ATG-12. Altogether, we conclude that the apoptotic and autophagic response machineries share antagonistic function in Gpx3 knockdown cardiomyocytes.