Succinate dehydrogenase (mitochondrial complex II) is a source of reactive oxygen species in plants and regulates development and stress responses

Transcriptome analysis reveals the molecular mechanism of differences in growth between photoautotrophy and heterotrophy in Chlamydomonas reinhardtii

Background

The green alga Chlamydomonas reinhardtii can grow photoautotrophically utilizing light and CO2, and heterotrophically utilizing acetate. The physiological and biochemical responses of autotrophy and heterotrophy are different in C. reinhardtii. However, there is no complete understanding of the molecular physiology between autotrophy and heterotrophy. Therefore, we performed biochemical, molecular and transcriptome analysis of C. reinhardtii between autotrophy and heterotrophy.

Results

The cell growth characterization demonstrated that heterotrophic cell had enhanced growth rates, and autotrophic cell accumulated more chlorophyll. The transcriptome data showed that a total of 2,970 differentially expressed genes (DEGs) were identified from photoautotrophy 12h (P12h) to heterotrophy 12h (H12h). The DEGs were involved in photosynthesis, the tricarboxylic acid cycle (TCA), pyruvate and oxidative phosphorylation metabolisms. Moreover, the results of qRT-PCR revealed that the relative expression levels of malate dehydrogenase (MDH), succinate dehydrogenase (SDH), ATP synthase (ATPase), and starch synthase (SSS) were increased significantly from P12h and H12h. The protein activity of NAD-malate dehydrogenase (NAD-MDH) and succinate dehydrogenase (SDH) were significantly higher in the H12h group.

Conclusion

The above results indicated that the high growth rate observed in heterotrophic cell may be the effects of environmental or genetic regulation of photosynthesis. Therefore, the identification of novel candidate genes in heterotrophy will contribute to the development of microalga strains with higher growth capacity and better performance for biomass production.

Functional Differentiation of the Succinate Dehydrogenase Subunit SdhC Governs the Sensitivity to SDHI Fungicides, ROS Homeostasis, and Pathogenicity in Fusarium asiaticum

Succinate dehydrogenase (SDH) is an integral component of the tricarboxylic acid cycle (TCA) and respiratory electron transport chain (ETC), targeted by succinate dehydrogenase inhibitors (SDHIs). Fusarium asiaticum is a prominent phytopathogen causing Fusarium head blight (FHB) on wheat. Here, we characterized the functions of the FaSdhA, FaSdhB, FaSdhC1, FaSdhC2, and FaSdhD subunits. Deletion of FaSdhA, FaSdhB, or FaSdhD resulted in significant growth defects in F. asiaticum. The FaSdhC1 or FaSdhC2 deletion mutants exhibited substantial reductions in fungal growth, conidiation, virulence, and reactive oxygen species (ROS). The FaSdhC1 expression was significantly induced by pydiflumetofen (PYD). The ΔFaSdhC1 mutant displayed hypersensitivity to SDHIs, whereas the ΔFaSdhC2 mutant exhibited resistance against most SDHIs. The transmembrane domains of FaSdhC1 are essential for regulating mycelial growth, virulence, and sensitivity to SDHIs. These findings provided valuable insights into how the two SdhC paralogues regulated the functional integrity of SDH, ROS homeostasis, and the sensitivity to SDHIs in phytopathogenic fungi.

Malonate differentially affects cell survival and confers chemoresistance in cancer cells via the induction of p53-dependent autophagy

Metabolic network intertwines with cancerous signaling and drug responses. Malonate is a prevailing metabolite in cancer and a competitive inhibitor of succinate dehydrogenase (SDH). Recent studies showed that malonate induced reactive oxygen species (ROS)-dependent apoptosis in neuroblastoma cells, but protected cells from ischemia-reperfusion injury. We here revealed that malonate differentially regulated cell death and survival in cancer cells. While high-dose malonate triggered ROS-dependent apoptosis, the low-dose malonate induced autophagy and conferred resistance to multiple chemotherapeutic agents. Mechanistically, our results showed that malonate increased p53 stability and transcriptionally up-regulated autophagy modulator DRAM (damage-regulated autophagy modulator), thus promoting autophagy. We further proved that autophagy is required for malonate-associated chemoresistance. Collectively, our findings suggest that malonate plays a double-edge function in cancer response to stressors, and highlights a pro-cancer impact of p53-induced autophagy in response to malonate.

Assembly and comparative analysis of the complete mitochondrial genome of Trigonella foenum-graecum L

BACKGROUND

Trigonella foenum-graecum L. is a Leguminosae plant, and the stems, leaves, and seeds of this plant are rich in chemical components that are of high research value. The chloroplast (cp) genome of T. foenum-graecum has been reported, but the mitochondrial (mt) genome remains unexplored.

RESULTS

In this study, we used second- and third-generation sequencing methods, which have the dual advantage of combining high accuracy and longer read length. The results showed that the mt genome of T. foenum-graecum was 345,604 bp in length and 45.28% in GC content. There were 59 genes, including: 33 protein-coding genes (PCGs), 21 tRNA genes, 4 rRNA genes and 1 pseudo gene. Among them, 11 genes contained introns. The mt genome codons of T. foenum-graecum had a significant A/T preference. A total of 202 dispersed repetitive sequences, 96 simple repetitive sequences (SSRs) and 19 tandem repetitive sequences were detected. Nucleotide diversity (Pi) analysis counted the variation in each gene, with atp6 being the most notable. Both synteny and phylogenetic analyses showed close genetic relationship among Trifolium pratense, Trifolium meduseum, Trifolium grandiflorum, Trifolium aureum, Medicago truncatula and T. foenum-graecum. Notably, in the phylogenetic tree, Medicago truncatula demonstrated the highest level of genetic relatedness to T. foenum-graecum, with a strong support value of 100%. The interspecies non-synonymous substitutions (Ka)/synonymous substitutions (Ks) results showed that 23 PCGs had Ka/Ks < 1, indicating that these genes would continue to evolve under purifying selection pressure. In addition, setting the similarity at 70%, 23 homologous sequences were found in the mt genome of T. foenum-graecum.

CONCLUSIONS

This study explores the mt genome sequence information of T. foenum-graecum and complements our knowledge of the phylogenetic diversity of Leguminosae plants.

In situ self-induced electrical stimulation to plants: Modulates morphogenesis, photosynthesis and gene expression in Vigna radiata and Cicer arietinum

Specific stimuli to plants influence intracellular and intercellular communications, activation of ion channels, gene expression, growth and development. The functional role of self-induced in situ electrical stimuli at the rhizosphere of the plant by placing electrode assembly in a defined circuit mode was studied on the growth and development of Vigna radiata and Cicer arietinum plants. Experiments were designed with three-circuit mode configurational variations (CC-P, OC-P and SC-P) and compared with the relative performance of control system (non-potential). The plants cultivated under the in situ electrical stimuli (low-current) showed a marked influence on growth and photosynthetic performance of the plants. CC-P operation showed improved vegetative growth, characterized by increased roots, shoots and biomass along with accelerated plant growth from seed germination to vegetation, flowering and pod formation leading towards earlier and more robust flowering compared to control system. Plants also showed higher aquaporin gene expression levels in CC-P operation. The control operation showed 10 days additional maturation time compared to CC-P operation. The strategy can be beneficially applied to augment the bioremediation capacity of complex pollutants with reference to phytoremediation or constructed wetland systems where the plant and its roots are the main enabler apart from agriculture applications specific to nursery-raised or transplanted plants.

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.

The molecular chaperone mtHSC70-1 interacts with DjA30 to regulate female gametophyte development and fertility in Arabidopsis

Arabidopsis mitochondria-targeted heat shock protein 70 (mtHSC70-1) plays important roles in the establishment of cytochrome c oxidase-dependent respiration and redox homeostasis during the vegetative growth of plants. Here, we report that knocking out the mtHSC70-1 gene led to a decrease in plant fertility; the fertility defect of the mutant was completely rescued by introducing the mtHSC70-1 gene. mtHSC70-1 mutants also showed defects in female gametophyte (FG) development, including delayed mitosis, abnormal nuclear position, and ectopic gene expression in the embryo sacs. In addition, we found that an Arabidopsis mitochondrial J-protein gene (DjA30) mutant, j30+/- , had defects in FG development and fertility similar to those of mtHSC70-1 mutant. mtHSC70-1 and DjA30 had similar expression patterns in FGs and interacted in vivo, suggesting that these two proteins might cooperate during female gametogenesis. Further, respiratory chain complex IV activity in mtHSC70-1 and DjA30 mutant embryo sacs was markedly downregulated; this led to the accumulation of mitochondrial reactive oxygen species (ROS). Scavenging excess ROS by introducing Mn-superoxide dismutase 1 or catalase 1 gene into the mtHSC70-1 mutant rescued FG development and fertility. Altogether, our results suggest that mtHSC70-1 and DjA30 are essential for the maintenance of ROS homeostasis in the embryo sacs and provide direct evidence for the roles of ROS homeostasis in embryo sac maturation and nuclear patterning, which might determine the fate of gametic and accessory cells.

Comparative analysis of the complete mitogenome of Geoffroea decorticans: a native tree surviving in the Atacama Desert

Chañar (Geoffroea decorticans (Gill., ex Hook. & Arn.) Burkart) has been highly significant for indigenous people in the Atacama Desert for over 3,000 years. Through evolutionary processes, the G. decorticans mitogenome likely underwent changes facilitating its adaptation to the extreme conditions of the Atacama Desert. Here, we compare the mitochondrial genome of G. decorticans with those of other Papilionoideae family species. The complete mitogenome of G. decorticans was sequenced and assembled, making it the first in the genus Geoffroea. The mitogenome contained 383,963 base pairs, consisting of 33 protein coding genes, 21 transfer RNA genes, and 3 ribosomal RNA genes. The Chañar mitogenome is relatively compact, and has two intact genes (sdh4 and nad1) which were not observed in most other species. Additionally, Chañar possessed the highest amount of mitochondrial DNA of plastid origin among angiosperm species. The phylogenetic analysis of the mitogenomes of Chañar and 12 other taxa displayed a high level of consistency in taxonomic classification, when compared to those of the plastid genome. Atp8 was subjected to positive selection, while the ccmFc and rps1 were subjected to neutral selection. This study provides valuable information regarding its ability to survive the extreme environmental conditions of the Atacama Desert.

Deciphering the molecular basis of abiotic stress response in cucumber (Cucumis sativus L.) using RNA-Seq meta-analysis, systems biology, and machine learning approaches

Abiotic stress in cucumber (Cucumis sativus L.) may trigger distinct transcriptome responses, resulting in significant yield loss. More insight into the molecular underpinnings of the stress response can be gained by combining RNA-Seq meta-analysis with systems biology and machine learning. This can help pinpoint possible targets for engineering abiotic tolerance by revealing functional modules and key genes essential for the stress response. Therefore, to investigate the regulatory mechanism and key genes, a combination of these approaches was utilized in cucumber subjected to various abiotic stresses. Three significant abiotic stress-related modules were identified by gene co-expression network analysis (WGCNA). Three hub genes (RPL18, δ-COP, and EXLA2), ten transcription factors (TFs), one transcription regulator, and 12 protein kinases (PKs) were introduced as key genes. The results suggest that the identified PKs probably govern the coordination of cellular responses to abiotic stress in cucumber. Moreover, the C2H2 TF family may play a significant role in cucumber response to abiotic stress. Several C2H2 TF target stress-related genes were identified through co-expression and promoter analyses. Evaluation of the key identified genes using Random Forest, with an area under the curve of ROC (AUC) of 0.974 and an accuracy rate of 88.5%, demonstrates their prominent contributions in the cucumber response to abiotic stresses. These findings provide novel insights into the regulatory mechanism underlying abiotic stress response in cucumber and pave the way for cucumber genetic engineering toward improving tolerance ability under abiotic stress.

Oxidative stress and mitochondrial damage induced by a novel pesticide fluopimomide in Caenorhabditis elegans

Fluopimomide is a novel pesticide intensively used in agricultural pest control; however, its excessive use may have toxicological effects on non-target organisms. In this study, Caenorhabditis elegans was used to evaluate the toxic effects of fluopimomide and its possible mechanisms. The effects of fluopimomide on the growth, pharyngeal pumping, and antioxidant systems of C. elegans were determined. Furthermore, the gene expression levels associated with mitochondria in the nematodes were also investigated. Results indicated that fluopimomide at 0.2, 1.0, and 5.0 mg/L notably (p < 0.001) decreased body length, pharyngeal pumping, and body bends in the nematodes compared to the untreated control. Additionally, fluopimomide at 0.2, 1.0, and 5.0 mg/L notably (p < 0.05) increased the content of malondialdehyde by 3.30-, 21.24-, and 33.57-fold, respectively, while fluopimomide at 1.0 and 5.0 mg/L significantly (p < 0.001) increased the levels of reactive oxygen species (ROS) by 49.14% and 77.06% compared to the untreated control. In contrast, fluopimomide at 1.0 and 5.0 mg/L notably reduced the activities of target enzyme succinate dehydrogenase and at 5.0 mg/L reduced the activities of antioxidant enzyme superoxide dismutase. Further evidence revealed that fluopimomide at 1.0 and 5.0 mg/L significantly inhibited oxygen consumption and at 0.2, 1.0, and 5.0 mg/L significantly inhibited ATP level in comparison to the untreated control. The expression of genes related to the mitochondrial electron transport chain mev-1 and isp-1 was significantly downregulated. ROS levels in the mev-1 and isp-1 mutants after fluopimomide treatments did not change significantly compared with the untreated mutants, suggesting that mev-1 and isp-1 may play critical roles in the toxicity induced by fluopimomide. Overall, the results demonstrate that oxidative stress and mitochondrial damage may be involved in toxicity of fluopimomide in C. elegans.

Non-canonical and developmental roles of the TCA cycle in plants

Over recent years, our understanding of the tricarboxylic acid cycle (TCAC) in living organisms has expanded beyond its canonical role in cellular energy production. In plants, TCAC metabolites and related enzymes have important roles in physiology, including vacuolar function, chelation of metals and nutrients, photorespiration, and redox regulation. Research in other organisms, including animals, has demonstrated unexpected functions of the TCAC metabolites in a number of biological processes, including signaling, epigenetic regulation, and cell differentiation. Here, we review the recent progress in discovery of non-canonical roles of the TCAC. We then discuss research on these metabolites in the context of plant development, with a focus on research related to tissue-specific functions of the TCAC. Additionally, we review research describing connections between TCAC metabolites and phytohormone signaling pathways. Overall, we discuss the opportunities and challenges in discovering new functions of TCAC metabolites in plants.

Reciprocal Regulation of Peroxisome Biogenesis and Myogenic Factors Is Critical for Myogenesis

Mitochondria (MITO) and peroxisomes (PEXO) are the major organelles involved in the oxidative metabolism of cells, but detailed examination of their dynamics and functional adaptations during skeletal muscle (SKM) development (myogenesis) is still lacking. In this study, we found that during myogenesis, MITO DNA, ROS level, and redox ratio increased in myotubes, but the membrane potential (Δψm) and ATP content reduced, implying that the MITO efficiency might reduce during myogenesis. The PEXO number and density both increased during myogenesis, which probably resulted from the accumulation and increased biogenesis of PEXO. The expression of PEXO biogenesis factors was induced during myogenesis in vitro and in utero, and their promoters were also activated by MyoD. Knockdown of the biogenesis factors Pex3 repressed not only the PEXO density and functions but also the levels of MITO genes and functions, suggesting a close coupling between PEXO biogenesis and MITO functions. Surprisingly, Pex3 knockdown by the CRISPRi system repressed myogenic differentiation, indicating critical involvement of PEXO biogenesis in myogenesis. Taken together, these observations suggest that the dynamics and functions of both MITO and PEXO are coupled with each other and with the metabolic changes that occur during myogenesis, and these metabolic couplings are critical to myogenesis.

Iron nanoparticle regulate succinate dehydrogenase activity in canola plants under drought stress

Application of nutrients as nanoparticle (NP) is an operative manner of nutrient supply for plants, especially under stress conditions. The present study was designed to highlight the role of iron NP on drought tolerance and elucidate the underlying mechanisms in drought-stressed canola plants. Drought stress was imposed by polyethylene glycol different concentrations (0, 10 and 15% (W/V)) with or without iron NP (1.5 and 3 mg/l). A comparative study of several physiological and biochemical parameters have been carried out in canola plants treated by drought and iron NP. Stressed-canola plants showed a reduction in growth parameters, whereas iron NP mostly stimulated growth of stressed plants, which was accompanied by reinforcement in defense mechanisms. Regarding impacts on compatible osmolytes, the data revealed that iron NP was able to regulate osmotic potential by increasing protein, proline and soluble sugar contents. The iron NP application was activated the enzymatic defense system (catalase and polyphenol oxidase) and promoted the non-enzymatic antioxidants (phenol, flavonol and flavonoid). Both of these adaptive responses declined free radicals as well as lipid peroxidation and enhanced the membrane stability and drought tolerance of the plants. Enhanced chlorophyll accumulation via induction of protoporphyrin, magnesium protoporphyrin and protochlorophyllide, by iron NP also contributed towards better stress tolerance. Enzymes of Krebs cycle, namely succinate dehydrogenase and aconitase, were induced by iron NP in canola plants grown under drought stress. These results propose a multifaceted involvement of iron NP, through regulation of activity of respiratory enzymes and antioxidant enzymes, production of reactive oxygen species, osmoregulation and secondary metabolites metabolism, in response to drought stress.

The cellular response to ocean warming in Emiliania huxleyi

Marine phytoplankton contribute substantially to the global flux of carbon from the atmosphere to the deep ocean. Sea surface temperatures will inevitably increase in line with global climate change, altering the performance of marine phytoplankton. Differing sensitivities of photosynthesis and respiration to temperature, will likely shift the strength of the future oceanic carbon sink. To further clarify the molecular mechanisms driving these alterations in phytoplankton function, shotgun proteomic analysis was carried out on the globally-occurring coccolithophore Emiliania huxleyi exposed to moderate- (23°C) and elevated- (28°C) warming. Compared to the control (17°C), growth of E. huxleyi increased under elevated temperatures, with higher rates recorded under moderate- relative to elevated- warming. Proteomic analysis revealed a significant modification of the E. huxleyi cellular proteome as temperatures increased: at lower temperature, ribosomal proteins and photosynthetic machinery appeared abundant, as rates of protein translation and photosynthetic performance are restricted by low temperatures. As temperatures increased, evidence of heat stress was observed in the photosystem, characterized by a relative down-regulation of the Photosystem II oxygen evolving complex and ATP synthase. Acclimation to elevated warming (28°C) revealed a substantial alteration to carbon metabolism. Here, E. huxleyi made use of the glyoxylate cycle and succinate metabolism to optimize carbon use, maintain growth and maximize ATP production in heat-damaged mitochondria, enabling cultures to maintain growth at levels significantly higher than those recorded in the control (17°C). Based on the metabolic changes observed, we can predict that warming may benefit photosynthetic carbon fixation by E. huxleyi in the sub-optimal to optimal thermal range. Past the thermal optima, increasing rates of respiration and costs of repair will likely constrain growth, causing a possible decline in the contribution of this species to the oceanic carbon sink depending on the evolvability of these temperature thresholds.

Chemical imaging reveals diverse functions of tricarboxylic acid metabolites in root growth and development

Understanding how plants grow is critical for agriculture and fundamental for illuminating principles of multicellular development. Here, we apply desorption electrospray ionization mass spectrometry imaging (DESI-MSI) to the chemical mapping of the developing maize root. This technique reveals a range of small molecule distribution patterns across the gradient of stem cell differentiation in the root. To understand the developmental logic of these patterns, we examine tricarboxylic acid (TCA) cycle metabolites. In both Arabidopsis and maize, we find evidence that elements of the TCA cycle are enriched in developmentally opposing regions. We find that these metabolites, particularly succinate, aconitate, citrate, and α-ketoglutarate, control root development in diverse and distinct ways. Critically, the developmental effects of certain TCA metabolites on stem cell behavior do not correlate with changes in ATP production. These results present insights into development and suggest practical means for controlling plant growth.

A Trifolium repens flavodoxin-like quinone reductase 1 (TrFQR1) improves plant adaptability to high temperature associated with oxidative homeostasis and lipids remodeling

Maintenance of stable mitochondrial respiratory chains could enhance adaptability to high temperature, but the potential mechanism was not elucidated clearly in plants. In this study, we identified and isolated a TrFQR1 gene encoding the flavodoxin-like quinone reductase 1 (TrFQR1) located in mitochondria of leguminous white clover (Trifolium repens). Phylogenetic analysis indicated that amino acid sequences of FQR1 in various plant species showed a high degree of similarities. Ectopic expression of TrFQR1 protected yeast (Saccharomyces cerevisiae) from heat damage and toxic levels of benzoquinone, phenanthraquinone and hydroquinone. Transgenic Arabidopsis thaliana and white clover overexpressing TrFQR1 exhibited significantly lower oxidative damage and better photosynthetic capacity and growth than wild-type in response to high-temperature stress, whereas AtFQR1-RNAi A. thaliana showed more severe oxidative damage and growth retardation under heat stress. TrFQR1-transgenic white clover also maintained better respiratory electron transport chain than wild-type plants, as manifested by significantly higher mitochondrial complex II and III activities, alternative oxidase activity, NAD(P)H content, and coenzyme Q10 content in response to heat stress. In addition, overexpression of TrFQR1 enhanced the accumulation of lipids including phosphatidylglycerol, monogalactosyl diacylglycerol, sulfoquinovosyl diacylglycerol and cardiolipin as important compositions of bilayers involved in dynamic membrane assembly in mitochondria or chloroplasts positively associated with heat tolerance. TrFQR1-transgenic white clover also exhibited higher lipids saturation level and phosphatidylcholine:phosphatidylethanolamine ratio, which could be beneficial to membrane stability and integrity during a prolonged period of heat stress. The current study proves that TrFQR1 is essential for heat tolerance associated with mitochondrial respiratory chain, cellular reactive oxygen species homeostasis, and lipids remodeling in plants. TrFQR1 could be selected as a key candidate marker gene to screen heat-tolerant genotypes or develop heat-tolerant crops via molecular-based breeding.

Enantioselective toxic effects of the novel chiral antifungal agrochemical penthiopyrad in the early life stage of zebrafish (Danio rerio)

Penthiopyrad was extensively applied in agricultural production, however, the toxicities information of the penthiopyrad enantiomers on early life stages of aquatic organism were limited. This study investigated the enantioselective toxicity of penthiopyrad on the early life stage of zebrafish by acute toxicity, sublethal toxic effects and the mRNA relative expression levels of genes related to succinate dehydrogenase, cardiac development, and lipid metabolism. The results showed that the 96-h-LC₅₀ of penthiopyrad racemate and enantiomers to zebrafish embryos were Rac-: 2.784 mg/L; R-(-)-: 3.528 mg/L; S-(+)-: 1.882 mg/L. Penthiopyrad exposure induced autonomous movement abnormalities, slowed heart rate and delayed hatching in zebrafish embryos, and caused developmental toxic effects such as pericardial edema and yolk sac edema. The mRNA relative expression levels results showed that penthiopyrad exposure induced significant enantioselectivity effect for the expression of the Sdha, Pr1 and Nkx2.5 with a 1.94-4.98-fold difference between different enantiomers, and significantly affected succinate dehydrogenase (energy metabolism), lipid metabolism and cardiac development-related genes expression. In general, S-(+)-penthiopyrad induced higher toxic effects in zebrafish embryos, and mitochondrial dysfunction may be an important cause of abnormal development. This study contributed to improve the comprehensive risk assessment and enantiomeric research system of penthiopyrad to early life stage of zebrafish.

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.

Social isolation induces succinate dehydrogenase dysfunction in anxious mice

We have previously reported social isolation induces anxiety-like behavior, cognitive decline, and reduction in brain ATP levels in mice. These changes were ameliorated by treatment with dihydromyricetin (DHM), a compound that positively modulates γ-aminobutyric A (GABAA) receptor. To gain further insight into the subcellular mechanisms underlying these changes, we utilized a social isolation-induced anxiety mouse model and investigated changes in mitochondrial oxidative capacity via the electron transport chain. We found that 4 weeks of social isolation decreased ATP levels by 43% and succinate dehydrogenase capacity by 52% of the control, while daily DHM (2 mg/kg oral) administration restored succinate dehydrogenase capacity. These results suggest that social isolation decreased mitochondrial capacity to generate ATP. DHM can be developed to be a therapeutic against anxiety and mitochondrial stress.

INTERRELATION BETWEEN MITOCHONDRIAL ENZYME ACTIVITY AND ANTIOXIDANT ACTIVITY OF SECONDARY POLYPHENOL NATURE METABOLITES IN HEMIPARASITE VISCUM ALBUM L. LEAVES

Antioxidants are widely used in practical medicine. Not only the search for new plant antioxidants, but also the study of the factors affecting their accumulation in plants, are relevant.

The aim is to study the interrelation between the activity of mitochondrial enzymes and the antioxidant activity of the secondary polyphenolic nature metabolites in hemiparasite Viscum Album L. leaves.

Materials and methods. The sampling material was Viscum album L. leaves, collected in winter from a host tree, Malus domestica Borkh. The extraction of biologically active substances was carried out with ethyl alcohol of various concentrations (90%, 70% and 50%), or purified water. The amount of total antioxidants was estimated by the amperometric method. The amount of total phenols was evaluated in the reaction with the Folin-Ciocalteu reagent. The concentration of total flavonoids was estimated by the change in the optical density of the rutin with aluminum (III) chloride complex. The antioxidant properties of the analyzed extracts were determined in vitro in the induced lipid peroxidation test. The activity of aconitase was assessed by a conjugated aconitase-isocitrate dehydrogenase reaction, citrate synthase – by changing the color intensity of the Ellman reagent solution, succinate dehydrogenase were determined in the reaction of succinate-dependent oxidation of 2,6-dichlorophenolindophenol.

Results. The carried out study showed that the maximum amount of total phenols (2.39±0.05%) is observed in a 50% ethanol extract from Viscum album L. leaves, with the content of total flavonoids equal to 1.83±0.04%, and the antioxidants equal to 0.503±0.007 mg/g (a quercetin equivalent) and 0.322±0.006 mg/g (a gallic acid equivalent). A 50% ethanol extract suppressed lipid peroxidation in the model mixture with IC50=106.3±1.09 µg/ml. In Viscum album L. leaves, a high activity of aconitase which strongly correlated (r=0.88416) with changes in the concentration of flavonoids, has been notified.

Conclusion. The optimal extractant for obtaining extracts with a high antioxidant activity is 50% ethyl alcohol. The analysis of the mitochondrial enzymes activity showed that in Viscum album L. leaves collected in winter, a high activity of aconitase strongly correlated with changes in the concentration of flavonoids (r=0.88416).

Fluopyram activates systemic resistance in soybean

The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is a significant yield-limiting factor in soybean production in the Midwestern US. Several management practices are implemented to mitigate yield losses caused by SCN, including using SDHI (succinate dehydrogenase inhibitors) fungicides delivered as seed treatments. A set of studies was conducted to evaluate the effect of two seed-applied succinate dehydrogenase inhibitors (SDHI) compounds, fluopyram and pydiflumetofen, on SCN population densities, plant injury, and plant growth. Cyst counts in untreated control and pydiflumetofen treated plants were 3.44 and 3.59 times higher than fluopyram, respectively, while egg counts were 8.25 and 7.06 times higher in control and pydiflumetofen. Next-generation sequencing was later employed to identify transcriptomic shifts in gene expression profiles in fluopyram and pydiflumetofen -treated seedlings. RNA expression patterns of seed treatments clustered by sampling time (5 DAP vs. 10 DAP); therefore, downstream analysis was conducted by timepoint. At 5 DAP, 10,870 and 325 differentially expressed genes (DEG) were identified in fluopyram and pydiflumetofen, respectively. These same treatments generated 219 and 2 DEGs at 10 DAP. Multiple DEGs identified in soybean seedlings treated with fluopyram are linked to systemic resistance, suggesting a potential role of systemic resistance in the suppression of SCN by fluopyram, in addition to the known nematicidal activity. The non-target inhibition of soybean succinate dehydrogenase genes by fluopyram may be the origin of the phytotoxicity symptoms observed and potentially the source of the systemic resistance activation reported in the current study. This work helps to elucidate the mechanisms of suppression of SCN by fluopyram.

Mitochondrial HSC70-1 Regulates Polar Auxin Transport through ROS Homeostasis in Arabidopsis Roots

Arabidopsis mitochondrial-localized heat shock protein 70-1 (mtHSC70-1) modulates vegetative growth by assisting mitochondrial complex IV assembly and maintaining reactive oxygen species (ROS) homeostasis. In addition, mtHSC70-1 affects embryo development, and this effect is mediated by auxin. However, whether mtHSC70-1 regulates vegetative growth through auxin and knowledge of the link between ROS homeostasis and auxin distribution remain unclear. Here, we found that mtHSC70-1 knockout seedlings (mthsc70-1a) displayed shortened roots, decreased fresh root weight and lateral root number, increased root width and abnormal root morphology. The introduction of the mtHSC70-1 gene into mthsc70-1a restored the growth and development of roots to the level of the wild type. However, sugar and auxin supplementation could not help the mutant roots restore to normal. Moreover, mthsc70-1a seedlings showed a decrease in meristem length and activity, auxin transport carrier (PINs and AUX1) and auxin abundances in root tips. The application of exogenous reducing agents upregulated the levels of PINs in the mutant roots. The introduction of antioxidant enzyme genes (MSD1 or CAT1) into the mthsc70-1a mutant rescued the PIN and local auxin abundances and root growth and development. Taken together, our data suggest that mtHSC70-1 regulates polar auxin transport through ROS homeostasis in Arabidopsis roots.

Identification of resistance gene analogs of the NBS-LRR family through transcriptome probing and in silico prediction of the expressome of Dalbergia sissoo under dieback disease stress

Dalbergia sissoo is an important timber tree, and dieback disease poses a dire threat to it toward extinction. The genomic record of D. sissoo is not available yet on any database; that is why it is challenging to probe the genetic elements involved in stress resistance. Hence, we attempted to unlock the genetics involved in dieback resistance through probing the NBS-LRR family, linked with mostly disease resistance in plants. We analyzed the transcriptome of D. sissoo under dieback challenge through DOP-rtPCR analysis using degenerate primers from conserved regions of NBS domain-encoded gene sequences. The differentially expressed gene sequences were sequenced and in silico characterized for predicting the expressome that contributes resistance to D. sissoo against dieback. The molecular and bioinformatic analyses predicted the presence of motifs including ATP/GTP-binding site motif A (P-loop NTPase domain), GLPL domain, casein kinase II phosphorylation site, and N-myristoylation site that are the attributes of proteins encoded by disease resistance genes. The physicochemical characteristics of identified resistance gene analogs, subcellular localization, predicted protein fingerprints, in silico functional annotation, and predicted protein structure proved their role in disease and stress resistance.

A comparative study on the modulatory role of mesoporous silica nanoparticles MCM 41 and MCM 48 on growth and metabolism of dicot Vigna radiata

With the advent of nanoscience, nanotechnology and their applications in various fields, mesoporous silica nanoparticles have gained popularity due to their stability, biocompatibility, unique honeycomb-like structures - ordered and random by nature, large surface to volume ratio, porosity, active surfaces, high loading capacity, ease of interactions with solvent, solute and suspended particles. These multitudes of intrinsic properties have motivated us towards an interdisciplinary detailed study on applications of mesoporous silica with an intention in increasing efficacy of productivity, growth if any, in plant life. This study aims at finding modus operandi of the structural uniqueness and eccentricity of various types of mesoporous silica in maneuvering their own functionality as a potential regulator for growth of seedlings of model plant Vigna radiata. We undertook characterization of surface, morphology, epitome of porosity for MCM 41 and MCM 48 using various experimental techniques followed by application of the same to growing seedlings at various dosages. It turned out that mesoporous silica nanoparticles, inarguably have higher efficacy in promoting plant growth, reducing stress, and enhancing basic metabolic rates at optimum dosage. Optimal operation point was determined at effective dosages for MCM 41 and MCM 48 those are being much lower than that of conventional silica nanoparticles. This optimum dosage is attributed to the structures of the nanoparticles used and implied further that higher pore volume, higher surface to volume ratio in case of MCM 41 at higher dosage lead to better adsorption of ions and functionality in contrast to that of MCM 48.

Mitochondrial dysfunction associated with ascorbate synthesis in plants

Mitochondria are the major organelles of energy production; however, active mitochondria can decline their energetic role and show a dysfunctional status. Mitochondrial dysfunction was induced by high non-physiological level of L-galactone-1,4-lactone (L-GalL), the precursor of ascorbate (AsA), in plant mitochondria. The dysfunction induced by L-GalL was associated with the fault in the mitochondrial electron partition and reactive oxygen species (ROS) over-production. Using mitochondria from RNAi-plant lines harbouring silenced L-galactone-1,4-lactone dehydrogenase (L-GalLDH) activity, it was demonstrated that such dysfunction is dependent on this enzyme activity. The capacity of alternative respiration was strongly decreased by L-GalL, probably mediated by redox-inactivation of the alternative oxidase (AOX) enzyme. Although, alternative respiration was shown to be the key factor that helps support AsA synthesis in dysfunctional mitochondria. Experiments with respiratory inhibitors showed that ROS formation and mitochondrial dysfunction were more associated with the decline in the activities of COX (cytochrome oxidase) and particularly AOX than with the lower activities of respiratory complexes I and III. The application of high L-GalL concentrations induced proteomic changes that indicated alterations in proteins related to oxidative stress and energetic status. However, supra-optimal L-GalL concentration was not deleterious for plants. Instead, the L-GalLDH activity could be positive. Indeed, it was found that wild type plants performed better growth than L-GalLDH-RNAi plants in response to high non-physiological L-GalL concentrations.

Salicylic acid and adenine nucleotides regulate the electron transport system and ROS production in plant mitochondria

Although mitochondria have a central role in energy transduction and reactive oxygen species (ROS) production, the regulatory mechanisms and their involvement in plant stress signaling are not fully established. The phytohormone salicylic acid (SA) is an important regulator of mitochondria-mediated ROS production and defense signaling. The role of SA and adenine nucleotides in the regulation of the mitochondrial succinate dehydrogenase (SDH) complex activity and ROS production was analyzed using WT, RNAi SDH1-1 and disrupted stress response 1 (dsr1) mutants, which show a point mutation in SDH1 subunit and are defective in SA signaling. Our results showed that SA and adenine nucleotides regulate SDH complex activity by distinct patterns, contributing to increased SDH-derived ROS production. As previously demonstrated, SA induces the succinate-quinone reductase activity of SDH complex, acting at or near the ubiquinone binding site. On the other hand, here we demonstrated that adenine nucleotides, such as AMP, ADP and ATP, induce the SDH activity provided by the SDH1 subunit. The regulation of SDH activity by adenine nucleotides is dependent on mitochondrial integrity and is prevented by atractyloside, an inhibitor of adenine nucleotide translocator (ANT), suggesting that the regulatory mechanism occurs on the mitochondrial matrix side of the inner mitochondrial membrane, and not in the intermembrane space, as previously suggested. On the other hand, in the intermembrane space, ADP and ATP limit mitochondrial oxygen consumption by a mechanism that appears to be related to cytochrome bc1 complex inhibition. Altogether, these results indicate that SA signaling and adenine nucleotides regulate the mitochondrial electron transport system and mitochondria-derived ROS production by direct effect in the electron transport system complexes, bringing new insights into mechanisms with direct implications in plant development and responses to different environmental responses, serving as a starting point for future physiological explorations.

Succinate Dehydrogenase, Succinate, and Superoxides: A Genetic, Epigenetic, Metabolic, Environmental Explosive Crossroad

Research focused on succinate dehydrogenase (SDH) and its substrate, succinate, culminated in the 1950s accompanying the rapid development of research dedicated to bioenergetics and intermediary metabolism. This allowed researchers to uncover the implication of SDH in both the mitochondrial respiratory chain and the Krebs cycle. Nowadays, this theme is experiencing a real revival following the discovery of the role of SDH and succinate in a subset of tumors and cancers in humans. The aim of this review is to enlighten the many questions yet unanswered, ranging from fundamental to clinically oriented aspects, up to the danger of the current use of SDH as a target for a subclass of pesticides.

Metabolic and DNA checkpoints for the enhancement of Al tolerance

Acidic soils are a major limiting factor for food production in many developing countries. High concentrations of soluble Al cations, particularly Al³⁺, inhibit cell division and root elongation in plants. Al³⁺ damages several biomolecules, including DNA, impairing gene expression and cell cycle progression. Notably, the loss-of-function mutants of DNA checkpoints may mediate Al tolerance. Furthermore, mitochondrial organic acids play key roles in neutralizing Al³⁺ within the cell and around the rhizosphere. Here, we provide knowledge synthesis on interactions between checkpoints related to mitochondrial organic acid homeostasis and DNA integrity mediating Al tolerance in land plants. These interactions, coupled with remarkable advances in tools related to metabolism and cell cycle, may facilitate the development of next-generation productive crops under Al toxicity.

Low temperature tolerance is impaired by polystyrene nanoplastics accumulated in cells of barley (Hordeum vulgare L.) plants

With increasing plastic consumption, the large amount of polystyrene nanoplastics (PS-NPs) in agricultural soil may not only directly affect the plant growth, but also indirectly affect the abiotic stress tolerance in crops. In this study, the barley (Hordeum vulgare L.) was irrigated with 2 g L^-1 PS-NPs (65.776 ± 0.528 nm) solution for 7 days, then subjected to low temperature (2 ℃) for 24 h. The imaging of protoplasts indicated that polymethylmethacrylate nanoplastics could across the cell wall and accumulate in plant cells. The PS-NPs significantly decreased Rubisco activities and ATP production, hence limiting the photosynthetic carbon assimilation in barley under low temperature. The PS-NPs accumulated in cells also caused the significantly decreased activities of key enzymes involved in sucrolytic, glycolysis and starch metabolism pathways, including UDP-glucose pyrophorylase, ADP-Glucose pyrophosphorylase, phosphoglucomutase, glucose-6-phosphate dehydrogenase, phosphoglucoisomerase, fructokinase and phosphofructokinase. In addition, under low temperature, the PS-NPs presence significantly reduced the activities of superoxide dismutase, ascorbate peroxidase and catalase in chloroplasts, and significantly reduced the activities of ascorbate peroxidase and catalase in mitochondria. Thus, it is suggested that the PS-NPs accumulated in plant cells impaired the low temperature tolerance in barley mainly by the negative effects on photosynthetic carbon assimilation, carbohydrate metabolism and ROS homeostasis in sub-cellular level.

Integrated LC-MS and GC-MS-Based Metabolomics Reveal the Effects of Plant Competition on the Rye Metabolome

Plants compete with their neighbors about the limited resources available to them. Plants under induced stress resulting from competition may alter their metabolome to increase their resilience or enhance their defense mechanisms. In the present study, rye (Secale cereale) plants were cocultivated with different densities (3, 12, and 18 plants per pot) of Austrian pea (Pisum sativum subsp. arvense), hairy vetch (Vicia villosa), and Alexandrian clover (Trifolium alexandrinum L.) to elucidate the changes in the rye metabolome in response to the different levels of competition. Global metabolic profiling by liquid chromatography triple quadrupole tandem mass spectrometry (LC-QqQ-MS), liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS), and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS) was performed on rye plants, and the acquired data were analyzed using uni- and multivariate statistics. Targeted analysis showed that a high level of competition reduced the concentration of aglycone benzoxazinoids (BXs) and increased glycoside BXs in rye roots. Untargeted metabolomics analysis indicated an increase in the rye root content of the allelopathic compounds 4-hydroxybenzoic acid and uracil in response to competition. Untargeted analysis of rye shoots revealed that the plant competition increased the d-pyroglutamic acid, which is an elicitor of reactive oxygen species (ROS). Our results have enhanced the knowledge of the biochemical response of plant species to cocultivation.

Discovery of Novel Benzo[4,5]thiazolo(oxazolo)[3,2-a]pyrimidinone Mesoionic Derivatives as Potential Antibacterial Agents and Mechanism Research

A series of benzo[4,5]thiazole(oxazole)[3,2-a]pyrimidine mesoionic compounds were designed and synthesized. Antibacterial activity tests revealed that compound A23 showed good in vitro activities against Xanthomonas oryzae pv. Oryzicola (Xoc) and Xanthomonas oryzae pv. oryzae (Xoo), with half-maximal effective concentration (EC₅₀) values of 47.6 and 36.8 μM, respectively, which were better than positive control agents thiodiazole copper (281 and 259 μM) and bismerthiazol (245 and 220 μM). The protective activities of compound A23 anti-Xoc and anti-Xoo were 39.7% and 49.2%, respectively, which were better than those of bismerthiazol (31.5% and 40.7%). Compound A23 improved defensive enzyme activities in rice. In addition, compound A23 could upregulate the expression of succinate dehydrogenase (SDH) in the oxidative phosphorylation (OXPHOS) pathway through proteomics analysis, which was consistent with the result of the SDH activity test. Thus, compound A23 is a novel potential antibacterial agent that can be further developed.

Involvement of O2·- release in zearalenone-induced hormesis of intestinal porcine enterocytes: An electrochemical sensor-based analysis

Relationship between mycotoxin-induced hormesis and reactive oxygen species (ROS) has not been systematically investigated due to the lack of an effective analysis method. To monitor cellular release and intracellular level of O₂^·-, carboxymethyl cellulose-Mn₃(PO₄)₂ nanocomposite was synthesized to fabricate an electrochemical biosensor, which selectively detects O₂^·- over the range of 57.50 nM ∼ 2.95 μM (R² = 0.99) with the sensitivity of 78.67 μA μM^-1 cm^-2 and the detection limit of 8.47 nM. Transient exposure to zearalenone (ZEA) induces the enhancement on cell viability, immediate O₂^·- release from cells, and reduction of intracellular O₂^·- level. After post-treatment culture, intracellular O₂^·- initially increases to a high level and then decreases to the normal level. Concurrently, the ZEA-induced hormesis disappears. Based on the findings, we propose a mechanism, involving the ROS release, increase of succinate dehydrogenase activity and recovery of intracellular ROS, to explain the occurrence and disappearance of hormesis in intestinal porcine enterocytes.

Enantioselective bioaccumulation and toxicity of the novel chiral antifungal agrochemical penthiopyrad in zebrafish (Danio rerio)

Succinate dehydrogenase inhibitor (SDHI) fungicides has been extensively used in agricultural production, which are not easily degrade in the environment and have various toxic effects on aquatic organisms. However, the toxic effects information to non-target organisms were mostly at the racemate level, which were poorly understood at the enantiomers level. Thus, this study aimed to investigate the enantioselective bioaccumulation behavior and toxic effects of penthiopyrad in zebrafish. Significant enantioselective bioaccumulation was observed when exposed to penthiopyrad at two dose levels: S-(+)-penthiopyrad was preferentially accumulated. Moreover, S-(+)-penthiopyrad caused oxidative stress in zebrafish liver. The results of real-time RT-PCR analyses revealed that exposure to penthiopyrad also enantioselectivity interfered with the expression of mitochondrial respiratory complexes, mtDNA synthesis, lipid metabolism and apoptosis-related genes. S-(+)-penthiopyrad significantly decreased most of the expression of the above gene, which showed higher toxic effects. We inferred that the toxicity mechanism of penthiopyrad was caused by lipid metabolism disorder and mitochondrial dysfunction in zebrafish, and further leads to apoptosis even DNA damage. This study provides more accurate data to investigate the environmental impact of penthiopyrad at the enantiomer level.

Plant mitochondria - past, present and future

The study of plant mitochondria started in earnest around 1950 with the first isolations of mitochondria from animal and plant tissues. The first 35 years were spent establishing the basic properties of plant mitochondria and plant respiration using biochemical and physiological approaches. A number of unique properties (compared to mammalian mitochondria) were observed: (i) the ability to oxidize malate, glycine and cytosolic NAD(P)H at high rates; (ii) the partial insensitivity to rotenone, which turned out to be due to the presence of a second NADH dehydrogenase on the inner surface of the inner mitochondrial membrane in addition to the classical Complex I NADH dehydrogenase; and (iii) the partial insensitivity to cyanide, which turned out to be due to an alternative oxidase, which is also located on the inner surface of the inner mitochondrial membrane, in addition to the classical Complex IV, cytochrome oxidase. With the appearance of molecular biology methods around 1985, followed by genomics, further unique properties were discovered: (iv) plant mitochondrial DNA (mtDNA) is 10-600 times larger than the mammalian mtDNA, yet it only contains approximately 50% more genes; (v) plant mtDNA has kept the standard genetic code, and it has a low divergence rate with respect to point mutations, but a high recombinatorial activity; (vi) mitochondrial mRNA maturation includes a uniquely complex set of activities for processing, splicing and editing (at hundreds of sites); (vii) recombination in mtDNA creates novel reading frames that can produce male sterility; and (viii) plant mitochondria have a large proteome with 2000-3000 different proteins containing many unique proteins such as 200-300 pentatricopeptide repeat proteins. We describe the present and fairly detailed picture of the structure and function of plant mitochondria and how the unique properties make their metabolism more flexible allowing them to be involved in many diverse processes in the plant cell, such as photosynthesis, photorespiration, CAM and C4 metabolism, heat production, temperature control, stress resistance mechanisms, programmed cell death and genomic evolution. However, it is still a challenge to understand how the regulation of metabolism and mtDNA expression works at the cellular level and how retrograde signaling from the mitochondria coordinates all those processes.

Knockdown of Succinate Dehydrogenase Assembly Factor 2 Induces Reactive Oxygen Species-Mediated Auxin Hypersensitivity Causing pH-Dependent Root Elongation

Metabolism, auxin signaling and reactive oxygen species (ROS) all contribute to plant growth, and each is linked to plant mitochondria and the process of respiration. Knockdown of mitochondrial succinate dehydrogenase assembly factor 2 (SDHAF2) in Arabidopsis thaliana lowered succinate dehydrogenase activity and led to pH-inducible root inhibition when the growth medium pH was poised at different points between 7.0 and 5.0, but this phenomenon was not observed in wildtype (WT). Roots of sdhaf2 mutants showed high accumulation of succinate, depletion of citrate and malate and up-regulation of ROS-related and stress-inducible genes at pH 5.5. A change of oxidative status in sdhaf2 roots at low pH was also evidenced by low ROS staining in root tips and altered root sensitivity to H2O2. sdhaf2 had low auxin activity in root tips via DR5-GUS staining but displayed increased indole-3-acetic acid (IAA, auxin) abundance and IAA hypersensitivity, which is most likely caused by the change in ROS levels. On this basis, we conclude that knockdown of SDHAF2 induces pH-related root elongation and auxin hyperaccumulation and hypersensitivity, mediated by altered ROS homeostasis. This observation extends the existing evidence of associations between mitochondrial function and auxin by establishing a cascade of cellular events that link them through ROS formation, metabolism and root growth at different pH values.

Mitochondria: Key Organelles Accelerating Cell Wall Material Accumulation in Juice Sacs of Pummelo (Citrus grandis L. Osbeck) Fruits during Postharvest Storage

Granulation is a physiological disorder of juice sacs in citrus fruits, which develops through secondary cell wall formation. However, the synergistic changes in the cytoplasm of juice sac cells remain largely unknown. This study investigated the dynamic ultrastructure of juice sacs of “Guanxi” pummelo fruits by transmission electron microscopy and determined their cell wall material, soluble sugar, and organic acid contents. The results showed that lignin and hemicellulose are accumulated in juice sacs isolated from dorsal vascular bundles, while lignin and cellulose contribute to the granulation of juice sacs isolated from septal vascular bundles. The significant differences in lignin, cellulose, and hemicellulose contents between the two types of juice sacs began to be observed at 30 days of storage. Fructose levels were elevated in juice sacs isolated from the dorsal vascular bundles from 10 to 60 days. Sucrose contents significantly decreased in juice sacs isolated from the septal vascular bundles from 30 to 60 days. Meanwhile glucose, citric acid, and malic acid contents exhibited no apparent changes in both types of juice sacs. Based on the comprehensive analysis of the ultrastructure of both types of juice sacs, it was clearly found that plasma membrane ruptures induce cell wall material synthesis in intracellular spaces; however, cell wall substance contents did not significantly increase until the number of mitochondria sharply increased. In particular, sucrose contents began to decrease significantly just after the mitochondria amount largely increased in juice sacs isolated from the septal vascular bundles, indicating that mitochondria play a key role in regulating carbon source sugar partitioning for cell wall component synthesis.

The circadian-controlled PIF8-BBX28 module regulates petal senescence in rose flowers by governing mitochondrial ROS homeostasis at night

Reactive oxygen species (ROS) are unstable reactive molecules that are toxic to cells. Regulation of ROS homeostasis is crucial to protect cells from dysfunction, senescence, and death. In plant leaves, ROS are mainly generated from chloroplasts and are tightly temporally restricted by the circadian clock. However, little is known about how ROS homeostasis is regulated in nonphotosynthetic organs, such as petals. Here, we showed that hydrogen peroxide (H2O2) levels exhibit typical circadian rhythmicity in rose (Rosa hybrida) petals, consistent with the measured respiratory rate. RNA-seq and functional screening identified a B-box gene, RhBBX28, whose expression was associated with H2O2 rhythms. Silencing RhBBX28 accelerated flower senescence and promoted H2O2 accumulation at night in petals, while overexpression of RhBBX28 had the opposite effects. RhBBX28 influenced the expression of various genes related to respiratory metabolism, including the TCA cycle and glycolysis, and directly repressed the expression of SUCCINATE DEHYDROGENASE 1, which plays a central role in mitochondrial ROS (mtROS) homeostasis. We also found that PHYTOCHROME-INTERACTING FACTOR8 (RhPIF8) could activate RhBBX28 expression to control H2O2 levels in petals and thus flower senescence. Our results indicate that the circadian-controlled RhPIF8-RhBBX28 module is a critical player that controls flower senescence by governing mtROS homeostasis in rose.

Dose-dependent responses of metabolism and tissue injuries in clam Ruditapes philippinarum after subchronic exposure to cadmium

Marine cadmium (Cd) pollution has been globally occurring, which creates a pressing need to characterize toxicological effects and develop biomarkers for Cd. However, the dose-response relationships challenge toxicity characterization and biomarkers selection. Metabolic processes have been frequently targeted by Cd. In this work, we investigated the dose-dependent effects of Cd on metabolic endpoints in whole soft tissues as well as gill and hepatopancreas injuries in clam Ruditapes philippinarum, aiming to better understand the metabolic responses and develop biomarkers. Nuclear magnetic resonance (NMR)-based metabolomic analysis was conducted on clam whole soft tissues to identify metabolites. The enzymes and metabolites associated with tricarboxylic acid (TCA) cycle, glycolysis, and oxidative phosphorylation showed both monotonic and non-monotonic curves with the increase of Cd dose. In details, glutamine, glucose-1-phosphate, hexokinase (HK), and citrate synthase (CS) presented monotonic decreases with the increase of Cd dose, among which glutamine and CS were preferable biomarkers to Cd exposure based on lower benchmark dose (BMD) values. The monotonic decreases of HK and CS activities suggested Cd exposure potentially disrupted glycolysis and TCA cycle via inhibiting rate-limiting enzymes. In contrast, the non-monotonic responses of succinate dehydrogenase (SDH), alanine aminotransferase (ALT), and their substrates (succinate and alanine) were approximate to U- or J-shaped curves, suggesting the adaptive strategy of metabolic responses to different degrees of Cd stress, like induction of anaerobiosis as energy compensation. Especially, the alterations of succinate and SDH presented typical hormetic dose-response curves. What is more, clam hepatopancreas was more sensitive to Cd than gill in terms of injury occurrence. Overall, characterization of dose-dependent effect of Cd on metabolism and tissue injuries provides a new insight into understanding the metabolic adaptation in marine clams and risk assessment of Cd pollution.

Exogenous melatonin improves the salt tolerance of cotton by removing active oxygen and protecting photosynthetic organs

BACKGROUND

As damage to the ecological environment continues to increase amid unreasonable amounts of irrigation, soil salinization has become a major challenge to agricultural development. Melatonin (MT) is a pleiotropic signal molecule and indole hormone, which alleviates the damage of abiotic stress to plants. MT has been confirmed to eliminate reactive oxygen species (ROS) by improving the antioxidant system and reducing oxidative damage under adversity. However, the mechanism by which exogenous MT mediates salt tolerance by regulating the photosynthetic capacity and ion balance of cotton seedlings still remains unknown. In this study, the regulatory effects of MT on the photosynthetic system, osmotic modulators, chloroplast, and anatomical structure of cotton seedlings were determined under 0-500 μM MT treatments with salt stress induced by treatment with 150 mM NaCl.

RESULTS

Salt stress reduces the chlorophyll content, net photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate, PSII photochemical efficiency, PSII actual photochemical quantum yield, the apparent electron transfer efficiency, stomata opening, and biomass. In addition, it increases non-photochemical quenching. All of these responses were effectively alleviated by exogenous treatment with MT. Exogenous MT reduces oxidative damage and lipid peroxidation by reducing salt-induced ROS and protects the plasma membrane from oxidative toxicity. MT also reduces the osmotic pressure by reducing the salt-induced accumulation of Na⁺ and increasing the contents of K⁺ and proline. Exogenous MT can facilitate stomatal opening and protect the integrity of cotton chloroplast grana lamella structure and mitochondria under salt stress, protect the photosynthetic system of plants, and improve their biomass. An anatomical analysis of leaves and stems showed that MT can improve xylem and phloem and other properties and aides in the transportation of water, inorganic salts, and organic substances. Therefore, the application of MT attenuates salt-induced stress damage to plants. Treatment with exogenous MT positively increased the salt tolerance of cotton seedlings by improving their photosynthetic capacity, stomatal characteristics, ion balance, osmotic substance biosynthetic pathways, and chloroplast and anatomical structures (xylem vessels and phloem vessels).

CONCLUSIONS

Our study attributes help to protect the structural stability of photosynthetic organs and increase the amount of material accumulation, thereby reducing salt-induced secondary stress. The mechanisms of MT-induced plant tolerance to salt stress provide a theoretical basis for the use of MT to alleviate salt stress caused by unreasonable irrigation, fertilization, and climate change.

MEHP interferes with mitochondrial functions and homeostasis in skeletal muscle cells

Di (2-ethylhexyl) phthalate (DEHP) is a plasticizer frequently leached out from polyvinyl chloride (PVC) products and is quickly metabolized to its monoester equivalent mono(2-ethylhexyl) phthalate (MEHP) once enters organisms. Exposure to DEHP/MEHP through food chain intake has been shown to modified metabolism but its effect on the development of metabolic myopathy of skeletal muscle (SKM) has not been revealed so far. Here, we found that MEHP repressed myogenic terminal differentiation of proliferating myoblasts (PMB) and confluent myoblasts (CMB) but had weak effect on this process once it had been initiated. The transition of mitochondria (MITO) morphology from high efficient filamentary network to low efficient vesicles was triggered by MEHP, implying its negative effects on MITO functions. The impaired MITO functions was further demonstrated by reduced MITO DNA (mtDNA) level and SDH enzyme activity as well as highly increased reactive oxygen species (ROS) in cells after MEHP treatment. The expression of metabolic genes, including PDK4, CPT1b, UCP2, and HO1, was highly increased by MEHP and the promoters of PDK4 and CPT1b were also activated by MEHP. Additionally, the stability of some subunits in the oxidative phosphorylation system (OXPHOS) complexes was found to be reduced by MEHP, implying defective oxidative metabolism in MITO and which was confirmed by repressed palmitic acid oxidation in MEHP-treated cells. Besides, MEHP also blocked insulin-induced glucose uptake. Taken together, our results suggest that MEHP is inhibitory to myogenesis and is harmful to MITO functions in SKM, so its exposure should be avoided or limited.

Integrative analyses of transcriptomics and metabolomics in Raphidocelis subcapitata treated with clarithromycin

As a macrolide antibiotic, clarithromycin (CLA) has a high detection rate in surface water and sewage treatment plant effluents worldwide, posing a considerably high ecological risk to aquatic ecosystem. However, algal transcriptome and metabolome in response to CLA remains largely unknown. In this study, a model alga Raphidocelis subcapitata (R. subcapitata), was exposed to CLA at the concentrations of 0, 3, 10, and 15 μg L^-1. Transcriptomic analysis was performed for all the treatment groups, whereas metabolomics was merely applied to 0, 3, and 10 μg L^-1 groups because of the limited amount of algal biomass. After 7 d cultivation, the growth of R. subcapitata was significantly hindered at the concentrations above 10 μg L^-1. A total of 115, 1833, 2911 genes were differentially expressed in 3, 10, and 15 μg L^-1 groups, respectively; meanwhile, 134 and 84 differentially accumulated metabolites (DAMs) were found in the 3 and 10 μg L^-1 groups. Specifically, expression levels of DEGs and DAMs related to xenobiotic metabolism, electron transport and energy synthesis were dysregulated, leading to the produced reactive oxygen species (ROS). To confront the CLA-induced injury, the biosynthesis of unsaturated fatty acids and carotenoids of R. subcapitata in 3 μg L^-1 were up-regulated; although the photosynthesis was up-regulated in both 10 μg L^-1 and 15 μg L^-1 groups, the energy synthesis and the ability to resist ROS in these two groups were down-regulated. Overall, this study shed light on the mechanism underlying the inhibitory effects of macrolide antibiotics in algae.

Enhanced alkali tolerance of rhizobia-inoculated alfalfa correlates with altered proteins and metabolic processes as well as decreased oxidative damage

AIMS

Alkaline salt is one of the most devastating environmental factors limiting alfalfa productivity, however, the mechanisms underlying adaptation of alfalfa to alkaline remain unclear. Our aim is to investigate proteomic and metabolomic differences in growth and root of alfalfa under alkaline salt in Rhizobium-alfalfa symbiotic relationships.

METHODS

Rhizobium-inoculated and non-inoculated alfalfa plants were treated with 200 mmol/L NaHCO₃ to investigate physiological, metabolic, and proteomic responses of root-nodule symbiosis under alkaline-induced stress, using an integrated approach combining metabolome and proteome analysis with measurements of physiological parameters.

RESULTS

The improved tolerance to alkalinity was observed in RI-plants compared with NI-plants. RI-plants accumulated more proline and MDH, and had higher antioxidant activity and relatively high RWC but low MDA content and low Na⁺/K⁺ ratio. The stress-related genes (P5CS, GST13, H⁺-Ppase, NADP-Me, SDH, and CS) were actively upregulated in RI plants under alkaline stress. In RI-plants, damage caused by alkaline stress was mainly alleviated by decreasing oxidative damage, enhancing the organic acid and amino acid metabolic processes, and scavenging harmful ROS by activating the phenylpropanoid biosynthetic pathway.

CONCLUSIONS

We revealed distinct proteins and metabolites related to alkali tolerance in RI-plants compared to NI-plants. Alkali tolerance of rhizobia-inoculated alfalfa was enhanced by altered proteins and metabolic processes as well as decreased oxidative damage.

Integrative role of plant mitochondria facing oxidative stress: The case of ozone

Ozone is a secondary air pollutant, which causes oxidative stress in plants by producing reactive oxygen species (ROS) starting by an external attack of leaf apoplast. ROS have a dual role, acting as signaling molecules, regulating different physiological processes and response to stress, but also inducing oxidative damage. The production of ROS in plant cells is compartmented and regulated by scavengers and specific enzyme pathways. Chronic doses of ozone are known to trigger an important increase of the respiratory process while decreasing photosynthesis. Mitochondria, which normally operate with usual levels of intracellular ROS, would have to play a prominent role to cope with an enhanced ozone-derived ROS production. It is thus needed to compile the available literature on the effects of ozone on mitochondria to precise their strategy facing oxidative stress. An overview of the mitochondrial fate in three steps is proposed, i) starting with the initial responses of the mitochondria for alleviating the overproduction of ROS by the enhancement of existing antioxidant metabolism and adjustments of the electron transport chain, ii) followed by the setting up of detoxifying processes through exchanges between mitochondria and the cell, and iii) ending by an accelerated senescence initiated by mitochondrial membrane permeability and leading to programmed cell death.

Proteomics-Based Data Integration of Wheat Cultivars Facing Fusarium graminearum Strains Revealed a Core-Responsive Pattern Controlling Fusarium Head Blight

Fusarium head blight (FHB), mainly occurring upon Fusarium graminearum infection in a wide variety of small-grain cereals, is supposed to be controlled by a range of processes diverted by the fungal pathogen, the so-called susceptibility factors. As a mean to provide relevant information about the molecular events involved in FHB susceptibility in bread wheat, we studied an extensive proteome of more than 7,900 identified wheat proteins in three cultivars of contrasting susceptibilities during their interaction with three F. graminearum strains of different aggressiveness. No cultivar-specific proteins discriminated the three wheat genotypes, demonstrating the establishment of a core proteome regardless of unequivocal FHB susceptibility differences. Quantitative protein analysis revealed that most of the FHB-induced molecular adjustments were shared by wheat cultivars and occurred independently of the F. graminearum strain aggressiveness. Although subtle abundance changes evidenced genotype-dependent responses to FHB, cultivar distinction was found to be mainly due to basal abundance differences, especially regarding the chloroplast functions. Integrating these data with previous proteome mapping of the three F. graminearum strains facing the three same wheat cultivars, we demonstrated strong correlations between the wheat protein abundance changes and the adjustments of fungal proteins supposed to interfere with host molecular functions. Together, these results provide a resourceful dataset that expands our understanding of the specific molecular events taking place during the wheat-F. graminearum interaction.

LPS1, Encoding Iron-Sulfur Subunit SDH2-1 of Succinate Dehydrogenase, Affects Leaf Senescence and Grain Yield in Rice

The iron-sulfur subunit (SDH2) of succinate dehydrogenase plays a key role in electron transport in plant mitochondria. However, it is yet unknown whether SDH2 genes are involved in leaf senescence and yield formation. In this study, we isolated a late premature senescence mutant, lps1, in rice (Oryza sativa). The mutant leaves exhibited brown spots at late tillering stage and wilted at the late grain-filling stage and mature stage. In its premature senescence leaves, photosynthetic pigment contents and net photosynthetic rate were reduced; chloroplasts and mitochondria were degraded. Meanwhile, lps1 displayed small panicles, low seed-setting rate and dramatically reduced grain yield. Gene cloning and complementation analysis suggested that the causal gene for the mutant phenotype was OsSDH2-1 (LOC_Os08g02640), in which single nucleotide mutation resulted in an amino acid substitution in the encoded protein. OsSDH2-1 gene was expressed in all organs tested, with higher expression in leaves, root tips, ovary and anthers. OsSDH2-1 protein was targeted to mitochondria. Furthermore, reactive oxygen species (ROS), mainly H₂O₂, was excessively accumulated in leaves and young panicles of lps1, which could cause premature leaf senescence and affect panicle development and pollen function. Taken together, OsSDH2-1 plays a crucial role in leaf senescence and yield formation in rice.

Some data on the comparative and combined toxic activity of nanoparticles containing lead and cadmium with special attention to their vasotoxicity

Moderate subchronic intoxication was induced in rats by repeated intraperitoneal injections of PbO (49.6 ± 16.0 nm) and/or CdO (57.0 ± 13.0 nm) nanoparticles (NP) three times a week during 6 weeks. In particular, there was a reduction in arterial blood pressure and in blood concentrations of a number of factors controlling vasoconstriction and vasodilation, particularly of endothelin 1 (ET-1). This toxic effect was attenuated with a bioprotective complex administered in the background. The study confirmed as well that the combined binary action typology varies depending on which effect it is estimated by.

Comparative Physiological and Proteomic Analysis Reveals Different Involvement of Proteins during Artificial Aging of Siberian Wildrye Seeds

Seed aging has an important effect on the germplasm preservation and industrialized production of Siberian wildrye (Elymus sibiricus) in the Qinghai-Tibet Plateau. However, so far its underlying molecular mechanisms still largely remain unknown. To shed light on this topic, one-year stored seeds of E. sibiricus were exposed to artificial aging treatments (AAT), followed by seed vigor characteristics and physiological status monitoring. Then global proteomics analysis was undertaken by the tandem mass tags (TMT) technique, and the proteins were quantified with liquid chromatography-tandem mass spectrometry on three aging time points (0 h, 36 h and 72 h). Finally, we verified the expression of related proteins by parallel reaction monitoring (PRM). Our results demonstrated that the seed vigor decreased remarkably in response to artificial aging, but the relative ion-leakage and malondialdehyde content, superoxide anion and hydrogen peroxide showed the opposite situation. Proteomic results showed that a total of 4169 proteins were identified and quantified. Gene Ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis indicated that a series of key pathways including carbohydrate metabolism, lipid metabolism, and antioxidant activity were severely damaged by aging treatments. Numerous key proteins such as glyceraldehyde triphosphate glyceraldehyde dehydrogenase, succinate dehydrogenase, lipoxygenase, peroxidase, glutathione-s-transferase and late embryogenesis abundant proteins were significantly down-regulated. However, the up-regulation of the heat shock protein family has made a positive contribution to oxidative stress resistance in seeds. This study provides a useful catalog of the E. sibiricus proteomes with insights into the future genetic improvement of seed storability.

Exogenous supplementation of melatonin alters representative organic acids and enzymes of respiratory cycle as well as sugar metabolism during arsenic stress in two contrasting indica rice cultivars

The objective of the present investigation was to understand the impact of exogenously applied melatonin on mitochondrial respiration and sugar metabolism in two contrasting rice cultivars, viz., Khitish (arsenic-susceptible) and Muktashri (arsenic-tolerant) under arsenic-stress. Melatonin effectively restored the level of organic acids like pyruvic acid, malic acid and more particularly citric acid by 33 % in Khitish which were lowered during arsenic-stress, whereas their levels were further elevated in Muktashri to provide energy for defence against arsenic-induced injury. Arsenic-exposure led to a significant inhibition in enzyme activities as well as corresponding transcript level of key respiratory enzymes, viz., pyruvate dehydrogenase, citrate synthase, isocitrate dehydrogenase, succinate dehydrogenase and malate dehydrogenase, intriguingly more prominently in case of Khitish. Conversely, melatonin supplementation, irrespective of cultivars, considerably improved the activity of the above enzymes and corresponding gene expressions during stress, indicating acceleration in the rate of Krebs cycle. Melatonin supplementation also stimulated the accumulation of total soluble sugars by 62 % and 25 %, reducing sugars by 50 % and 44 % and non-reducing sugars by 75 % and 14 % in Khitish and Muktashri respectively, concomitant with higher activities of acid invertase, sucrose synthase and sucrose phosphate synthase enzymes, along with the expression of corresponding genes. Enhanced starch accumulation via regulation of alpha amylase and starch phosphorylase activities and gene expression, by melatonin also contributed towards better stress tolerance. Overall, this work illustrated the efficacy of melatonin in the regulation of representative organic acids and enzymes of respiratory cycle along with starch and sugar metabolism in rice cultivars under arsenic toxicity.

A mitochondria-targeted coenzyme Q peptoid induces superoxide dismutase and alleviates salinity stress in plant cells

Salinity is a serious challenge to global agriculture and threatens human food security. Plant cells can respond to salt stress either by activation of adaptive responses, or by programmed cell death. The mechanisms deciding the respective response are far from understood, but seem to depend on the degree, to which mitochondria can maintain oxidative homeostasis. Using plant PeptoQ, a Trojan Peptoid, as vehicle, it is possible to transport a coenzyme Q10 (CoQ10) derivative into plant mitochondria. We show that salinity stress in tobacco BY-2 cells (Nicotiana tabacum L. cv Bright Yellow-2) can be mitigated by pretreatment with plant PeptoQ with respect to numerous aspects including proliferation, expansion, redox homeostasis, and programmed cell death. We tested the salinity response for transcripts from nine salt-stress related-genes representing different adaptive responses. While most did not show any significant response, the salt response of the transcription factor NtNAC, probably involved in mitochondrial retrograde signaling, was significantly modulated by the plant PeptoQ. Most strikingly, transcripts for the mitochondrial, Mn-dependent Superoxide Dismutase were rapidly and drastically upregulated in presence of the peptoid, and this response was disappearing in presence of salt. The same pattern, albeit at lower amplitude, was seen for the sodium exporter SOS1. The findings are discussed by a model, where plant PeptoQ modulates retrograde signalling to the nucleus leading to a strong expression of mitochondrial SOD, what renders mitochondria more resilient to perturbations of oxidative balance, such that cells escape salt induced cell death and remain viable.

Impact of Up- and Downregulation of Metabolites and Mitochondrial Content on pH and Color of the Longissimus Muscle from Normal-pH and Dark-Cutting Beef

Limited knowledge is currently available on the biochemical basis for the development of dark-cutting beef. The objective of this research was to determine the metabolite profile and mitochondrial content differences between normal-pH and dark-cutting beef. A gas chromatography-mass spectrometer-based nontargeted metabolomic approach indicated downregulation of glycolytic metabolites, including glucose-1- and 6-phosphate and upregulation of tricarboxylic substrates such as malic and fumaric acids occurred in dark-cutting beef when compared to normal-pH beef. Neurotransmitters such as 4-aminobutyric acid and succinate semialdehyde were upregulated in dark-cutting beef than normal-pH beef. Immunohistochemistry indicated a more oxidative fiber type in dark-cutting beef than normal-pH beef. In support, the mitochondrial protein and DNA content were greater in dark-cutting beef. This increased mitochondrial content, in part, could influence oxygen consumption and myoglobin oxygenation/appearance of dark-cutting beef. The current results demonstrate that the more tricarboxylic metabolites and mitochondrial content in dark-cutting beef impact muscle pH and color.