Antagonistic role of 9-lipoxygenase-derived oxylipins and ethylene in the control of oxidative stress, lipid peroxidation and plant defence

Deciphering Aphanomyces euteiches-pea-biocontrol bacterium interactions through untargeted metabolomics

Aphanomyces euteiches causes root rot in pea, leading to significant yield losses. However, the metabolites involved in this pathosystem have not been thoroughly studied. This study aimed to fill this gap and explore mechanisms of bacterial suppression of A. euteiches via untargeted metabolomics using pea grown in a controlled environment. Chemical isotope labeling (CIL), followed by liquid chromatography-mass spectrometry (LC-MS), was used for metabolite separation and detection. Univariate and multivariate analyses showed clear separation of metabolites from pathogen-treated pea roots and roots from other treatments. A three-tier approach positively or putatively identified 5249 peak pairs or metabolites. Of these, 403 were positively identified in tier 1; 940 were putatively identified with high confidence in tier 2. There were substantial changes in amino acid pool, and fatty acid and phenylpropanoid pathway products. More metabolites, including salicylic and jasmonic acids, were upregulated than downregulated in A. euteiches-infected roots. 1-aminocyclopropane-1-carboxylic acid and 12-oxophytodienoic acid were upregulated in A. euteiches + bacterium-treated roots compared to A. euteiches-infected roots. A great number of metabolites were up- or down-regulated in response to A. euteiches infection compared with the control and A. euteiches + bacterium-treated plants. The results of this study could facilitate improved disease management.

Nuclear lamina component KAKU4 regulates chromatin states and transcriptional regulation in the Arabidopsis genome

BACKGROUND

The nuclear lamina links the nuclear membrane to chromosomes and plays a crucial role in regulating chromatin states and gene expression. However, current knowledge of nuclear lamina in plants is limited compared to animals and humans.

RESULTS

This study mainly focused on elucidating the mechanism through which the putative nuclear lamina component protein KAKU4 regulates chromatin states and gene expression in Arabidopsis leaves. Thus, we constructed a network using the association proteins of lamin-like proteins, revealing that KAKU4 is strongly associated with chromatin or epigenetic modifiers. Then, we conducted ChIP-seq technology to generate global epigenomic profiles of H3K4me3, H3K27me3, and H3K9me2 in Arabidopsis leaves for mutant (kaku4-2) and wild-type (WT) plants alongside RNA-seq method to generate gene expression profiles. The comprehensive chromatin state-based analyses indicate that the knockdown of KAKU4 has the strongest effect on H3K27me3, followed by H3K9me2, and the least impact on H3K4me3, leading to significant changes in chromatin states in the Arabidopsis genome. We discovered that the knockdown of the KAKU4 gene caused a transition between two types of repressive epigenetics marks, H3K9me2 and H3K27me3, in some specific PLAD regions. The combination analyses of epigenomic and transcriptomic data between the kaku4-2 mutant and WT suggested that KAKU4 may regulate key biological processes, such as programmed cell death and hormone signaling pathways, by affecting H3K27me3 modification in Arabidopsis leaves.

CONCLUSIONS

In summary, our results indicated that KAKU4 is directly and/or indirectly associated with chromatin/epigenetic modifiers and demonstrated the essential roles of KAKU4 in regulating chromatin states, transcriptional regulation, and diverse biological processes in Arabidopsis.

Integrated small RNA, transcriptome and physiological approaches provide insight into Taxodium hybrid 'Zhongshanshan' roots in acclimation to prolonged flooding

Although Taxodium hybrid 'Zhongshanshan' 406 (Taxodium mucronatum Tenore × Taxodium distichum; Taxodium 406) is an extremely flooding-tolerant woody plant, the physiological and molecular mechanisms underlying acclimation of its roots to long-term flooding remain largely unknown. Thus, we exposed saplings of Taxodium 406 to either non-flooding (control) or flooding for 2 months. Flooding resulted in reduced root biomass, which is in line with lower concentrations of citrate, α-ketoglutaric acid, fumaric acid, malic acid and adenosine triphosphate (ATP) in Taxodium 406 roots. Flooding led to elevated activities of pyruvate decarboxylase, alcohol dehydrogenase and lactate dehydrogenase, which is consistent with higher lactate concentration in the roots of Taxodium 406. Flooding brought about stimulated activities of superoxide dismutase and catalase and elevated reduced glutathione (GSH) concentration and GSH/oxidized glutathione, which is in agreement with reduced concentrations of O2- and H2O2 in Taxodium 406 roots. The levels of starch, soluble protein, indole-3-acetic acid, gibberellin A4 and jasmonate were decreased, whereas the concentrations of glucose, total non-structural carbohydrates, most amino acids and 1-aminocyclopropane-1-carboxylate (ACC) were improved in the roots of flooding-treated Taxodium 406. Underlying these changes in growth and physiological characteristics, 12,420 mRNAs and 42 miRNAs were significantly differentially expressed, and 886 miRNA-mRNA pairs were identified in the roots of flooding-exposed Taxodium 406. For instance, 1-aminocyclopropane-1-carboxylate synthase 8 (ACS8) was a target of Th-miR162-3p and 1-aminocyclopropane-1-carboxylate oxidase 4 (ACO4) was a target of Th-miR166i, and the downregulation of Th-miR162-3p and Th-miR166i results in the upregulation of ACS8 and ACO4, probably bringing about higher ACC content in flooding-treated roots. Overall, these results indicate that differentially expressed mRNA and miRNAs are involved in regulating tricarboxylic acid cycle, ATP production, fermentation, and metabolism of carbohydrates, amino acids and phytohormones, as well as reactive oxygen species detoxification of Taxodium 406 roots. These processes play pivotal roles in acclimation to flooding stress. These results will improve our understanding of the molecular and physiological bases underlying woody plant flooding acclimation and provide valuable insights into breeding-flooding tolerant trees.

Mutant noxy8 exposes functional specificities between the chloroplast chaperones CLPC1 and CLPC2 in the response to organelle stress and plant defence

Chloroplast function is essential for growth, development, and plant adaptation to stress. Organelle stress and plant defence responses were examined here using noxy8 (nonresponding to oxylipins 8) from a series of Arabidopsis mutants. The noxy8 mutation was located at the CLPC2 gene, encoding a chloroplast chaperone of the protease complex CLP. Although its CLPC1 paralogue is considered to generate redundancy, our data reveal significant differences distinguishing CLPC2 and CLPC1 functions. As such, clpc1 mutants displayed a major defect in housekeeping chloroplast proteostasis, leading to a pronounced reduction in growth and pigment levels, enhanced accumulation of chloroplast and cytosol chaperones, and resistance to fosmidomycin. Conversely, clpc2 mutants showed severe susceptibility to lincomycin inhibition of chloroplast translation and resistance to Antimycin A inhibition of mitochondrial respiration. In the response to Pseudomonas syringae pv. tomato, clpc2 but not clpc1 mutants were resistant to bacterial infection, showing higher salicylic acid levels, defence gene expression and 9-LOX pathway activation. Our findings suggest CLPC2 and CLPC1 functional specificity, with a preferential involvement of CLPC1 in housekeeping processes and of CLPC2 in stress responses.

KAKU4 regulates leaf senescence through modulation of H3K27me3 deposition in the Arabidopsis genome

Lamins are the major components of the nuclear lamina, which regulate chromatin structure and gene expression. KAKU4 is a unique nuclear lamina component in the nuclear periphery, modulates nuclear shape and size in Arabidopsis. The knowledge about the regulatory role of KAKU4 in leaf development remains limited. Here we found that knockdown of KAKU4 resulted in an accelerated leaf senescence phenotype, with elevated levels of H2O2 and hormones, particularly SA, JA, and ABA. Our results demonstrated the importance of KAKU4 as a potential negative regulator in age-triggered leaf senescence in Arabidopsis. Furthermore, we conducted combination analyses of transcriptomic and epigenomic data for the kaku4 mutant and WT leaves. The knockdown of KAKU4 lowered H3K27me3 deposition in the up-regulated genes associated with hormone pathways, programmed cell death, and leaf senescence, including SARD1, SAG113/HAI1, PR2, and so forth. In addition, we found the functional crosstalks between KAKU4 and its associated proteins (CRWN1/4, PNET2, GBPL3, etc.) through comparing multiple transcriptome datasets. Overall, our results indicated that KAKU4 may inhibit the expression of a series of genes related to hormone signals and H2O2 metabolism by affecting the deposition of H3K27me3, thereby suppressing leaf senescence.

9,10-KODA, an α-ketol produced by the tonoplast-localized 9-lipoxygenase ZmLOX5, plays a signaling role in maize defense against insect herbivory

13-Lipoxygenases (LOXs) initiate the synthesis of jasmonic acid (JA), the best-understood oxylipin hormone in herbivory defense. However, the roles of 9-LOX-derived oxylipins in insect resistance remain unclear. Here, we report a novel anti-herbivory mechanism mediated by a tonoplast-localized 9-LOX, ZmLOX5, and its linolenic acid-derived product, 9-hydroxy-10-oxo-12(Z),15(Z)-octadecadienoic acid (9,10-KODA). Transposon-insertional disruption of ZmLOX5 resulted in the loss of resistance to insect herbivory. lox5 knockout mutants displayed greatly reduced wound-induced accumulation of multiple oxylipins and defense metabolites, including benzoxazinoids, abscisic acid (ABA), and JA-isoleucine (JA-Ile). However, exogenous JA-Ile failed to rescue insect defense in lox5 mutants, while applications of 1 μM 9,10-KODA or the JA precursor, 12-oxo-phytodienoic acid (12-OPDA), restored wild-type resistance levels. Metabolite profiling revealed that exogenous 9,10-KODA primed the plants for increased production of ABA and 12-OPDA, but not JA-Ile. While none of the 9-oxylipins were able to rescue JA-Ile induction, the lox5 mutant accumulated lower wound-induced levels of Ca2+, suggesting this as a potential explanation for lower wound-induced JA. Seedlings pretreated with 9,10-KODA exhibited rapid or more robust wound-induced defense gene expression. In addition, an artificial diet supplemented with 9,10-KODA arrested fall armyworm larvae growth. Finally, analysis of single and double lox5 and lox10 mutants showed that ZmLOX5 also contributed to insect defense by modulating ZmLOX10-mediated green leaf volatile signaling. Collectively, our study uncovered a previously unknown anti-herbivore defense and hormone-like signaling activity for a major 9-oxylipin α-ketol.

Faba Bean Flavor Effects from Processing to Consumer Acceptability

Faba beans as an alternative source of protein have received significant attention from consumers and the food industry. Flavor represents a major driving force that hinders the utilization faba beans in various products due to off-flavor. Off-flavors are produced from degradation of amino acids and unsaturated fatty acids during seed development and post-harvest processing stages (storage, dehulling, thermal treatment, and protein extraction). In this review, we discuss the current state of knowledge on the aroma of faba bean ingredients and various aspects, such as cultivar, processing, and product formulation that influence flavour. Germination, fermentation, and pH modulation were identified as promising methods to improve overall flavor and bitter compounds. The probable pathway in controlling off-flavor evolution during processing has also been discussed to provide efficient strategies to limit their impact and to encourage the use of faba bean ingredients in healthy food design.

The MYB59 transcription factor negatively regulates salicylic acid- and jasmonic acid-mediated leaf senescence

Leaf senescence is the final stage of leaf development and is affected by various exogenous and endogenous factors. Transcriptional regulation is essential for leaf senescence, however, the underlying molecular mechanisms remain largely unclear. In this study, we report that the transcription factor MYB59, which was predominantly expressed in early senescent rosette leaves, negatively regulates leaf senescence in Arabidopsis (Arabidopsis thaliana). RNA sequencing revealed a large number of differentially expressed genes involved in several senescence-related biological processes in myb59-1 rosette leaves. Chromatin immunoprecipitation and transient dual-luciferase reporter assays demonstrated that MYB59 directly repressed the expression of SENESCENCE ASSOCIATED GENE 18 and indirectly inhibited the expression of several other senescence-associated genes to delay leaf senescence. Moreover, MYB59 was induced by salicylic acid (SA) and jasmonic acid (JA). MYB59 inhibited SA production by directly repressing the expression of ISOCHORISMATE SYNTHASE 1 and PHENYLALANINE AMMONIA-LYASE 2 and restrained JA biosynthesis by directly suppressing the expression of LIPOXYGENASE 2, thus forming two negative feedback regulatory loops with SA and JA and ultimately delaying leaf senescence. These results help us understand the novel function of MYB59 and provide insights into the regulatory network controlling leaf senescence in Arabidopsis.

Transcriptomics Reveals the Effect of Short-Term Freezing on the Signal Transduction and Metabolism of Grapevine

Low temperature is an important factor limiting plant growth. Most cultivars of Vitis vinifera L. are sensitive to low temperatures and are at risk of freezing injury or even plant death during winter. In this study, we analyzed the transcriptome of branches of dormant cv. Cabernet Sauvignon exposed to several low-temperature conditions to identify differentially expressed genes and determine their function based on Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG)enrichment analyses. Our results indicated that exposure to subzero low temperatures resulted in damage to plant cell membranes and extravasation of intracellular electrolytes, and that this damage increased with decreasing temperature or increasing duration. The number of differential genes increased as the duration of stress increased, but most of the common differentially expressed genes reached their highest expression at 6 h of stress, indicating that 6 h may be a turning point for vines to tolerate extreme low temperatures. Several pathways play key roles in the response of Cabernet Sauvignon to low-temperature injury, namely: (1) the role of calcium/calmodulin-mediated signaling; (2) carbohydrate metabolism, including the hydrolysis of cell wall pectin and cellulose, decomposition of sucrose, synthesis of raffinose, and inhibition of glycolytic processes; (3) the synthesis of unsaturated fatty acids and metabolism of linolenic acid; and (4) the synthesis of secondary metabolites, especially flavonoids. In addition, pathogenesis-related protein may also play a role in plant cold resistance, but the mechanism is not yet clear. This study reveals possible pathways for the freezing response and leads to new insights into the molecular basis of the tolerance to low temperature in grapevine.

DNA methylation is enhanced during Cd hyperaccumulation in Noccaea caerulescens ecotype Ganges

In this study, we assess the DNA damage occurring in response to cadmium (Cd) in the Cd hyperaccumulator Noccaea caerulescens Ganges (GA) vs the non-accumulator and close-relative species Arabidopsis thaliana. At this purpose, the alkaline comet assay was utilized to evaluate the Cd-induced variations in nucleoids and the methy-sens comet assay, and semiquantitative real-time (qRT)-PCR were also performed to associate nucleus variations to possible DNA modifications. Cadmium induced high DNA damages in nuclei of A. thaliana while only a small increase in DNA migration was observed in N. caerulescens GA. In addition, in N. caerulescens GA, CpG DNA methylation increase upon Cd when compared to control condition, along with an increase in the expression of MET1 gene, coding for the DNA-methyltransferase. N. caerulescens GA does not show any oxidative stress under Cd treatment, while A. thaliana Cd-treated plants showed an upregulation of transcripts of the respiratory burst oxidase, accumulation of reactive oxygen species, and enhanced superoxide dismutase activity. These data suggest that epigenetic modifications occur in the N. caerulescens GA exposed to Cd to preserve genome integrity, contributing to Cd tolerance.

Cold stress-induced changes in metabolism of carbonyl compounds and membrane fatty acid composition in chickpea

In this study, changes in membrane fatty acid (FA) composition and damage indices contents as well as the transcript patterns of carbonyl-detoxifying genes were evaluated in two chickpea (Cicer arietinum L.) genotypes, cold-tolerant Sel96th11439 and cold-sensitive ILC533 under cold stress (CS; 4 °C). During CS, H2O2 and malondialdehyde (MDA) contents increased (by 47% and 57%, respectively) in the sensitive genotype, while these contents remained unchanged in the tolerant genotype. In tolerant plants, higher content of linoleic, linolenic, unsaturated FAs (UFAs), total FAs and double bond index (DBI) (by 23, 21, 19, 17 and 9%, respectively) was observed at 6 days after stress (DAS) compared to sensitive plants, which, along with alterations of the damage indices, indicate their enhanced tolerance to CS. Compared with the sensitive genotype, less lipoxygenase (LOX) activity (by 59%) in the tolerant genotype was accompanied by decreased MDA and increased levels of UFAs and DBI during CS, particularly at 6 DAS. Upregulation of aldehyde dehydrogenase and aldo-keto reductase genes (by 9- and 10-fold, respectively) at 1 DAS, along with the enhanced transcript levels of aldehyde reductase and 2-alkenal reductase (by 3- and 14.7-fold, respectively) at 6 DAS were accompanied by increased UFAs and reduced MDA contents in the tolerant genotype. Overall, the results suggest that cold tolerance in chickpea was partly associated with regulation of membrane FA compositions and the potential metabolic networks involved in synthesis and degradation of carbonyl compounds.

Transcriptome analysis of mulberry (Morus alba L.) leaves to identify differentially expressed genes associated with post-harvest shelf-life elongation

Present study deals with molecular expression patterns responsible for post-harvest shelf-life extension of mulberry leaves. Quantitative profiling showed retention of primary metabolite and accumulation of stress markers in NS7 and CO7 respectively. The leaf mRNA profiles was sequenced using the Illumina platform to identify DEGs. A total of 3413 DEGs were identified between the treatments. Annotation with Arabidopsis database has identified 1022 DEGs unigenes. STRING generated protein-protein interaction, identified 1013 DEGs nodes with p < 1.0e-16. KEGG classifier has identified genes and their participating biological processes. MCODE and BiNGO detected sub-networking and ontological enrichment, respectively at p ≤ 0.05. Genes associated with chloroplast architecture, photosynthesis, detoxifying ROS and RCS, and innate-immune response were significantly up-regulated, responsible for extending shelf-life in NS7. Loss of storage sucrose, enhanced activity of senescence-related hormones, accumulation of xenobiotics, and development of osmotic stress inside tissue system was the probable reason for tissue deterioration in CO7. qPCR validation of DEGs was in good agreement with RNA sequencing results, indicating the reliability of the sequencing platform. Present outcome provides a molecular insight regarding involvement of genes in self-life extension, which might help the sericulture industry to overcome their pre-existing problems related to landless farmers and larval feeding during monsoon.

A successful defense of the narrow-leafed lupin against anthracnose involves quick and orchestrated reprogramming of oxidation-reduction, photosynthesis and pathogenesis-related genes

Narrow-leafed lupin (NLL, Lupinus angustifolius L.) is a legume plant cultivated for grain production and soil improvement. Worldwide expansion of NLL as a crop attracted various pathogenic fungi, including Colletotrichum lupini causing a devastating disease, anthracnose. Two alleles conferring improved resistance, Lanr1 and AnMan, were exploited in NLL breeding, however, underlying molecular mechanisms remained unknown. In this study, European NLL germplasm was screened with Lanr1 and AnMan markers. Inoculation tests in controlled environment confirmed effectiveness of both resistance donors. Representative resistant and susceptible lines were subjected to differential gene expression profiling. Resistance to anthracnose was associated with overrepresentation of "GO:0006952 defense response", "GO:0055114 oxidation-reduction process" and "GO:0015979 photosynthesis" gene ontology terms. Moreover, the Lanr1 (83A:476) line revealed massive transcriptomic reprogramming quickly after inoculation, whereas other lines showed such a response delayed by about 42 h. Defense response was associated with upregulation of TIR-NBS, CC-NBS-LRR and NBS-LRR genes, pathogenesis-related 10 proteins, lipid transfer proteins, glucan endo-1,3-beta-glucosidases, glycine-rich cell wall proteins and genes from reactive oxygen species pathway. Early response of 83A:476, including orchestrated downregulation of photosynthesis-related genes, coincided with the successful defense during fungus biotrophic growth phase, indicating effector-triggered immunity. Mandelup response was delayed and resembled general horizontal resistance.

IQD1 Involvement in Hormonal Signaling and General Defense Responses Against Botrytis cinerea

IQ Domain 1 (IQD1) is a novel Arabidopsis thaliana calmodulin-binding protein, which was found to be a positive regulator of glucosinolate (GS) accumulation and plant defense responses against insects. We demonstrate here that the IQD1 overexpressing line (IQD1 ^OXP ) was also more resistant also to the necrotrophic fungus Botrytis cinerea, whereas an IQD1 knockout line (iqd1-1) was much more sensitive. Furthermore, we showed that IQD1 is up-regulated by jasmonic acid (JA) and downregulated by salicylic acid (SA). A comparison of whole transcriptome expression between iqd1-1 and wild type plants revealed a substantial downregulation of genes involved in plant defense and hormone regulation. Further examination revealed a marked reduction of SA and increases in the levels of ethylene, JA and abscisic acid response genes in the iqd1-1 line. Moreover, quantification of SA, JA, and abscisic acids in IQD1 ^OXP and iqd1-1 lines relative to the wild type, showed a significant reduction in endogenous JA levels in the knockout line, simultaneously with increased SA levels. Relations between IQD1 ^OXP and mutants defective in plant-hormone response indicated that IQD1 cannot rescue the absence of NPR1 or impaired SA accumulation in the NahG line. IQD1 cannot rescue ein2 or eto1 mutations connected to the ethylene pathway involved in both defense responses against B. cinerea and in regulating GS accumulation. Furthermore, IQD1cannot rescue the aos, coi1 or jar1mutations, all involved in the defense response against B. cinerea and it depends on JAR1 to control indole glucosinolate accumulation. We also found that in the B. cinerea, which infected the iqd1-1 mutant, the most abundant upregulated group of proteins is involved in the degradation of complex carbohydrates, as correlated with the sensitivity of this mutant. In summary, our results suggest that IQD1 is an important A. thaliana defensive protein against B. cinerea that is integrated into several important pathways, such as those involved in plant defense and hormone responses.

Hypoxia-Induced Aquaporins and Regulation of Redox Homeostasis by a Trans-Plasma Membrane Electron Transport System in Maize Roots

In plants, flooding-induced oxygen deficiency causes severe stress, leading to growth reduction and yield loss. It is therefore important to understand the molecular mechanisms for adaptation to hypoxia. Aquaporins at the plasma membrane play a crucial role in water uptake. However, their role during hypoxia and membrane redox changes is still not fully understood. The influence of 24 h hypoxia induction on hydroponically grown maize (Zea mays L.) was investigated using an oil-based setup. Analyses of physiological parameters revealed typical flooding symptoms such as increased ethylene and H₂O₂ levels, an increased alcohol dehydrogenase activity, and an increased redox activity at the plasma membrane along with decreased oxygen of the medium. Transcriptomic analysis and shotgun proteomics of plasma membranes and soluble fractions were performed to determine alterations in maize roots. RNA-sequencing data confirmed the upregulation of genes involved in anaerobic metabolism, biosynthesis of the phytohormone ethylene, and its receptors. Transcripts of several antioxidative systems and other oxidoreductases were regulated. Mass spectrometry analysis of the plasma membrane proteome revealed alterations in redox systems and an increased abundance of aquaporins. Here, we discuss the importance of plasma membrane aquaporins and redox systems in hypoxia stress response, including the regulation of plant growth and redox homeostasis.

Specific Roles of Lipoxygenases in Development and Responses to Stress in Plants

Lipoxygenases (LOXs), naturally occurring enzymes, are widely distributed in plants and animals. LOXs can be non-sulfur iron, non-heme iron, or manganese-containing dioxygenase redox enzymes. LOXs catalyze the oxidation of polyunsaturated fatty acids into fatty acid hydroperoxides. Linolenic acid, a precursor in the jasmonic acid (JA) biosynthesis, is converted to 12-oxo-phytodienoic acid through oxygenation with LOX, allene oxide synthase, and allene oxide cyclase. Moreover, JA participates in seed germination, fruit ripening, senescence, and many other physio-biochemical processes. LOXs also play crucial roles in defense responses against biotic stress, i.e., insects, pests, pathogenic attacks, and abiotic stress, such as wounding, UV-rays, extreme temperature, oxidative stress, and drought.

Identification of Key Gene Networks and Deciphering Transcriptional Regulators Associated With Peanut Embryo Abortion Mediated by Calcium Deficiency

Peanut embryo development is easily affected by a variety of nutrient elements in the soil, especially the calcium level. Peanut produces abortive embryos in calcium-deficient soil, but underlying mechanism remains unclear. Thus, identifying key transcriptional regulators and their associated regulatory networks promises to contribute to a better understanding of this process. In this study, cellular biology and gene expression analyses were performed to investigate peanut embryo development with the aim to discern the global architecture of gene regulatory networks underlying peanut embryo abortion under calcium deficiency conditions. The endomembrane systems tended to disintegrate, impairing cell growth and starch, protein and lipid body accumulation, resulting in aborted seeds. RNA-seq analysis showed that the gene expression profile in peanut embryos was significantly changed under calcium deficiency. Further analysis indicated that multiple signal pathways were involved in the peanut embryo abortion. Differential expressed genes (DEGs) related to cytoplasmic free Ca²⁺ were significantly altered. DEGs in plant hormone signaling pathways tended to be associated with increased IAA and ethylene but with decreased ABA, gibberellin, cytokinin, and brassinosteroid levels. Certain vital genes, including apoptosis-inducing factor, WRKYs and ethylene-responsive transcription factors, were up-regulated, while key regulators of embryo development, such as TCP4, WRI1, FUS3, ABI3, and GLK1 were down-regulated. Weighted gene co-expression network analysis (WGCNA) identified 16 significant modules associated with the plant hormone signaling, MAPK signaling, ubiquitin mediated proteolysis, reserve substance biosynthesis and metabolism pathways to decipher regulatory network. The most significant module was darkolivegreen2 and FUS3 (AH06G23930) had the highest connectivity among this module. Importantly, key transcription factors involved in embryogenesis or ovule development including TCP4, GLK1, ABI3, bHLH115, MYC2, etc., were also present in this module and down regulated under calcium deficiency. This study presents the first global view of the gene regulatory network involved in peanut embryo abortion under calcium deficiency conditions and lays foundation for improving peanut tolerances to calcium deficiency by a targeted manipulation of molecular breeding.

Oxylipin signaling in salt-stressed soybean is modulated by ligand-dependent interaction of Class II acyl-CoA-binding proteins with lipoxygenase

Plant lipoxygenases (LOXs) oxygenate linoleic and linolenic acids, creating hydroperoxy derivatives, and from these, jasmonates and other oxylipins are derived. Despite the importance of oxylipin signaling, its activation mechanism remains largely unknown. Here, we show that soybean ACYL-COA-BINDING PROTEIN3 (ACBP3) and ACBP4, two Class II acyl-CoA-binding proteins, suppressed activity of the vegetative LOX homolog VLXB by sequestering it at the endoplasmic reticulum. The ACBP4-VLXB interaction was facilitated by linoleoyl-CoA and linolenoyl-CoA, which competed with phosphatidic acid (PA) for ACBP4 binding. In salt-stressed roots, alternative splicing produced ACBP variants incapable of VLXB interaction. Overexpression of the variants enhanced LOX activity and salt tolerance in Arabidopsis and soybean hairy roots, whereas overexpressors of the native forms exhibited reciprocal phenotypes. Consistently, the differential alternative splicing pattern in two soybean genotypes coincided with their difference in salt-induced lipid peroxidation. Salt-treated soybean roots were enriched in C32:0-PA species that showed high affinity to Class II ACBPs. We conclude that PA signaling and alternative splicing suppress ligand-dependent interaction of Class II ACBPs with VLXB, thereby triggering lipid peroxidation during salt stress. Hence, our findings unveil a dual mechanism that initiates the onset of oxylipin signaling in the salinity response.

Volatile Compounds in Pulses: A Review

The worldwide demand for pulse-based products is increasing in the face of climate change, but their acceptability is limited due to the presence of off-flavours. Off-notes contribute to negative perceptions of pulses (beany notes). Volatile compounds belong to a large variety of chemical classes. They are mainly produced from the oxidation of unsaturated free fatty acids and the degradation of amino acids during seed development, storage, and transformation (dehulling, milling, and starch or protein production). This review aims to provide an overview highlighting the identification of these molecules in different pulses, their potential origins, and their impact on perceptions. However, data on odour-active compounds in pulses are sparse, as they are limited to those of two studies on peas and lupins. A better knowledge of the volatile compounds involved in the off-notes and their origins should allow for drawing efficient strategies to limit their impact on overall perception for more acceptable healthy food design.

The Responses of the Lipoxygenase Gene Family to Salt and Drought Stress in Foxtail Millet (Setaria italica)

Plant lipoxygenases (LOXs), a kind of non-heme iron-containing dioxygenases, participate plant physiological activities (especially in response to biotic and abiotic stresses) through oxidizing various lipids. However, there was few investigations on LOXs in foxtail millet (Setaria italica). In this study, we identified the LOX gene family in foxtail millet, and divided the total 12 members into three sub-families on the basis of their phylogenetic relationships. Under salt and drought stress, LOX genes showed different expression patterns. Among them, only SiLOX7 showed up-regulated expression in Yugu1 (YG1) and Qinhuang2 (QH2), two stress-tolerant varieties, indicating that SiLOX7 may play an important role in responses to abiotic stress. Our research provides a basis for further investigation of the role of LOX genes in the adaptation to abiotic stresses and other possible biological functions in foxtail millet.

Intestinal and Hepatic Uptake of Dietary Peroxidized Lipids and Their Decomposition Products, and Their Subsequent Effects on Apolipoprotein A1 and Paraoxonase1

Both pro- and antiatherosclerotic effects have been ascribed to dietary peroxidized lipids. Confusion on the role of peroxidized lipids in atherosclerotic cardiovascular disease is punctuated by a lack of understanding regarding the metabolic fate and potential physiological effects of dietary peroxidized lipids and their decomposition products. This study sought to determine the metabolic fate and physiological ramifications of 13-hydroperoxyoctadecadienoic acid (13-HPODE) and 13-HODE (13-hydroxyoctadecadienoic acid) supplementation in intestinal and hepatic cell lines, as well as any effects resulting from 13-HPODE or 13-HODE degradation products. In the presence of Caco-2 cells, 13-HPODE was rapidly reduced to 13-HODE. Upon entering the cell, 13-HODE appears to undergo decomposition, followed by esterification. Moreover, 13-HPODE undergoes autodecomposition to produce aldehydes such as 9-oxononanoic acid (9-ONA). Results indicate that 9-ONA was oxidized to azelaic acid (AzA) rapidly in cell culture media, but AzA was poorly absorbed by intestinal cells and remained detectable in cell culture media for up to 18 h. An increased apolipoprotein A1 (ApoA1) secretion was observed in Caco-2 cells in the presence of 13-HPODE, 9-ONA, and AzA, whereas such induction was not observed in HepG2 cells. However, 13-HPODE treatments suppressed paraoxonase 1 (PON1) activity, suggesting the induction of ApoA1 secretion by 13-HPODE may not represent functional high-density lipoprotein (HDL) capable of reducing oxidative stress. Alternatively, AzA induced both ApoA1 secretion and PON1 activity while suppressing ApoB secretion in differentiated Caco-2 cells but not in HepG2. These results suggest oxidation of 9-ONA to AzA might be an important phenomenon, resulting in the accumulation of potentially beneficial dietary peroxidized lipid-derived aldehydes.

Oxylipins From Different Pathways Trigger Mitochondrial Stress Signaling Through Respiratory Complex III

Plant oxylipins are signaling molecules produced from fatty acids by oxidative pathways, mainly initiated by 9- and 13-lipoxygenases (9-LOX and 13-LOX), alpha-dioxygenases or non-enzymatic oxidation. Oxylipins from the 9-LOX pathway induce oxidative stress and control root development and plant defense. These activities have been associated with mitochondrial processes, but precise cellular targets and pathways remain unknown. In order to study oxylipin signaling, we previously generated a collection of Arabidopsis thaliana mutants that were insensitive to the 9-LOX products 9(S)-hydroxy-10,12, 15-octadecatrienoic acid (9-HOT) and its ketone derivative 9-KOT (noxy mutants). Here, we describe noxy1, noxy3, noxy5, noxy23, and noxy54 mutants, all affected in nucleus-encoded mitochondrial proteins, and use them to study the role of mitochondria in oxylipin signaling. Functional and phenotypic analyses showed that noxy plants displayed mitochondrial aggregation, reduced respiration rates and resistance to the complex III inhibitor Antimycin A (AA), thus indicating a close similarity of the oxylipin signaling and mitochondrial stress. Application of 9-HOT and 9-KOT protected plants against subsequent mitochondrial stress, whereas they boosted root growth reduction when applied in combination with complex III inhibitors but did not with inhibitors of other respiratory complexes. A similar effect was caused by linear-chain oxylipins from 13-LOX or non-enzymatic pathways having α,β-unsaturated hydroxyl or keto groups in their structure. Studies to investigate 9-HOT and 9-KOT activity indicated that they do not reduce respiration rates, but their action is primarily associated with enhanced ROS responses. This was supported by the results showing that 9-HOT or 9-KOT combined with AA amplified the expression of oxylipin- and ROS-responding genes but not of the AA marker AOX1a, thus implying the activation of a specific mitochondria retrograde signaling pathway. Our results implicate mitochondrial complex III as a hub in the signaling activity of multiple oxylipin pathways and point at downstream ROS responses as components of oxylipin function.

Functional involvement of caleosin/peroxygenase PdPXG4 in the accumulation of date palm leaf lipid droplets after exposure to dioxins

Dioxins are highly injurious environmental pollutants with proven toxicological effects on both animals and humans, but to date their effects on plants still need to be studied in detail. We identified a dioxin-inducible caleosin/peroxygenase isoform, PdPXG4, that is mostly expressed in leaves of date palm seedlings and exhibits a specific reductase activity towards the 13-hydroperoxide of C18:2 and C18:3 (HpODE and HpOTrE, respectively). After exposure to TCDD, lipid droplets (LDs) isolated from TCDD-exposed leaves were about 6.5-15.7-fold more active in metabolizing 13-HpOTrE compared with those isolated from non-exposed leaves. A characteristic spectrum of leaf dioxin-responsive oxylipins (LDROXYL) was detected in dioxin-exposed seedlings. Of particular importance, a group of these oxylipins, referred to as Class I, comprising six congeners of hydroxides fatty acids derived from C18:2 and C18:3, was exclusively found in leaves after exposure to TCDD. The TCDD-induced oxylipin pattern was confirmed in vitro using terbufos, a typical inhibitor towards the PdPXG4 peroxygenase activity. Of particular interest, the response of terbufos-pretreated protoplasts to TCDD was drastically reduced. Together, these findings suggest that PdPXG4 is implicated in the establishment of a dioxin-specific oxylipin signature in date palm leaves soon after their exposure to these pollutants.

The Resistance of Narrow-Leafed Lupin to Diaporthe toxica Is Based on the Rapid Activation of Defense Response Genes

Narrow-leafed lupin (Lupinus angustifolius L.) is a grain legume crop that is advantageous in animal nutrition due to its high protein content; however, livestock grazing on stubble may develop a lupinosis disease that is related to toxins produced by a pathogenic fungus, Diaporthe toxica. Two major unlinked alleles, Phr1 and PhtjR, confer L. angustifolius resistance to this fungus. Besides the introduction of these alleles into modern cultivars, the molecular mechanisms underlying resistance remained unsolved. In this study, resistant and susceptible lines were subjected to differential gene expression profiling in response to D. toxica inoculation, spanning the progress of the infection from the early to latent phases. High-throughput sequencing of stem transcriptome and PCR quantification of selected genes were performed. Gene Ontology term analysis revealed that an early (24 h) response in the resistant germplasm encompassed activation of genes controlling reactive oxygen species and oxylipin biosynthesis, whereas in the susceptible germplasm, it comprised induction of xyloglucan endotransglucosylases/hydrolases. During the first five days of the infection, the number of genes with significantly altered expressions was about 2.6 times higher in resistant lines than in the susceptible line. Global transcriptome reprogramming involving the activation of defense response genes occurred in lines conferring Phr1 and PhtjR resistance alleles about 4–8 days earlier than in the susceptible germplasm.

New Insights Into the Role of Seed Oil Body Proteins in Metabolism and Plant Development

Oil bodies (OBs) are ubiquitous dynamic organelles found in plant seeds. They have attracted increasing attention recently because of their important roles in plant physiology. First, the neutral lipids stored within these organelles serve as an initial, essential source of energy and carbon for seed germination and post-germinative growth of the seedlings. Secondly, they are involved in many other cellular processes such as stress responses, lipid metabolism, organ development, and hormone signaling. The biological functions of seed OBs are dependent on structural proteins, principally oleosins, caleosins, and steroleosins, which are embedded in the OB phospholipid monolayer. Oleosin and caleosin proteins are specific to plants and mainly act as OB structural proteins and are important for the biogenesis, stability, and dynamics of the organelle; whereas steroleosin proteins are also present in mammals and play an important role in steroid hormone metabolism and signaling. Significant progress using new genetic, biochemical, and imaging technologies has uncovered the roles of these proteins. Here, we review recent work on the structural or metabolic roles of these proteins in OB biogenesis, stabilization and degradation, lipid homeostasis and mobilization, hormone signal transduction, stress defenses, and various aspects of plant growth and development.

Acquiring control: The evolution of ROS-Induced oxidative stress and redox signaling pathways in plant stress responses

Reactive oxygen species (ROS) - the byproducts of aerobic metabolism - influence numerous aspects of the plant life cycle and environmental response mechanisms. In plants, ROS act like a double-edged sword; they play multiple beneficial roles at low concentrations, whereas at high concentrations ROS and related redox-active compounds cause cellular damage through oxidative stress. To examine the dual role of ROS as harmful oxidants and/or crucial cellular signals, this review elaborates that (i) how plants sense and respond to ROS in various subcellular organelles and (ii) the dynamics of subsequent ROS-induced signaling processes. The recent understanding of crosstalk between various cellular compartments in mediating their redox state spatially and temporally is discussed. Emphasis on the beneficial effects of ROS in maintaining cellular energy homeostasis, regulating diverse cellular functions, and activating acclimation responses in plants exposed to abiotic and biotic stresses are described. The comprehensive view of cellular ROS dynamics covering the breadth and versatility of ROS will contribute to understanding the complexity of apparently contradictory ROS roles in plant physiological responses in less than optimum environments.

Photoinhibition of Photosystem I Provides Oxidative Protection During Imbalanced Photosynthetic Electron Transport in Arabidopsis thaliana

Photosynthesis involves the conversion of sunlight energy into stored chemical energy, which is achieved through electron transport along a series of redox reactions. Excess photosynthetic electron transport might be dangerous due to the risk of molecular oxygen reduction, generating reactive oxygen species (ROS) over-accumulation. Avoiding excess ROS production requires the rate of electron transport to be coordinated with the capacity of electron acceptors in the chloroplast stroma. Imbalance between the donor and acceptor sides of photosystem I (PSI) can lead to inactivation, which is called PSI photoinhibition. We used a light-inducible PSI photoinhibition system in Arabidopsis thaliana to resolve the time dynamics of inhibition and to investigate its impact on ROS production and turnover. The oxidation state of the PSI reaction center and rates of CO2 fixation both indicated strong and rapid PSI photoinhibition upon donor side/acceptor side imbalance, while the rate of inhibition eased during prolonged imbalance. PSI photoinhibition was not associated with any major changes in ROS accumulation or antioxidant activity; however, a lower level of lipid oxidation correlated with lower abundance of chloroplast lipoxygenase in PSI-inhibited leaves. The results of this study suggest that rapid activation of PSI photoinhibition under severe photosynthetic imbalance protects the chloroplast from over-reduction and excess ROS formation.

Functional diversity of glycerolipid acylhydrolases in plant metabolism and physiology

Most current knowledge about plant lipid metabolism has focused on the biosynthesis of lipids and their transport between different organelles. However, lipid composition changes during development and in response to environmental cues often go beyond adjustments of lipid biosynthesis. When lipids have to be removed to adjust the extent of membranes during down regulation of photosynthesis, or lipid composition has to be adjusted to alter the biophysical properties of membranes, or lipid derived chemical signals have to be produced, lipid-degrading enzymes come into play. This review focuses on glycerolipid acylhydrolases that remove acyl groups from glycerolipids and will highlight their roles in lipid remodeling and lipid-derived signal generation. One emerging theme is that these enzymes are involved in the dynamic movement of acyl groups through different lipid pools, for example from polar membrane lipids to neutral lipids sequestered in lipid droplets during de novo triacylglycerol synthesis. Another example of acyl group sequestration in the form of triacylglycerols in lipid droplets is membrane lipid remodeling in response to abiotic stresses. Fatty acids released for membrane lipids can also give rise to potent signaling molecules and acylhydrolases are therefore often the first step in initiating the formation of these lipid signals.

Identification of a dioxin-responsive oxylipin signature in roots of date palm: involvement of a 9-hydroperoxide fatty acid reductase, caleosin/peroxygenase PdPXG2

Dioxins are highly hazardous pollutants that have well characterized impacts on both animal and human health. However, the biological effects of dioxins on plants have yet to be described in detail. Here we describe a dioxin-inducible caleosin/peroxygenase isoform, PdPXG2, that is mainly expressed in the apical zone of date palm roots and specifically reduces 9-hydroperoxide fatty acids. A characteristic spectrum of 18 dioxin-responsive oxylipin (DROXYL) congeners was also detected in date palm roots after exposure to dioxin. Of particular interest, six oxylipins, mostly hydroxy fatty acids, were exclusively formed in response to TCDD. The DROXYL signature was evaluated in planta and validated in vitro using a specific inhibitor of PdPXG2 in a root-protoplast system. Comparative analysis of root suberin showed that levels of certain monomers, especially the mono-epoxides and tri-hydroxides of C16:3 and C18:3, were significantly increased after exposure to TCDD. Specific inhibition of PdPXG2 activity revealed a positive linear relationship between deposition of suberin in roots and their permeability to TCDD. The results highlight the involvement of this peroxygenase in the plant response to dioxin and suggest the use of dioxin-responsive oxylipin signatures as biomarkers for plant exposure to this important class of xenobiotic contaminants.

A Novel Mechanism for Atherosclerotic Calcification: Potential Resolution of the Oxidation Paradox

AIM

In this study, we tested the hypothesis that lipid peroxide-derived dicarboxylic acids (DCAs), by virtue of their ability to bind to calcium (Ca), might be involved in atherosclerotic calcification. We determined the ability of azelaic acid (AzA) to promote calcification in human aortic smooth muscle cells (HASMCs), identified AzA in human calcified atherosclerotic lesions, and compared its levels with control and noncalcified atherosclerotic lesions.

RESULTS

HASMCs efficiently converted 9-oxononanoic acid (ONA), a lipid peroxide-derived monocarboxylic aldehyde, to AzA. In vitro incubations of AzA micelles with HASMC resulted in the formation of Ca deposits, which contained AzA. Liquid chromatography-mass spectrometry analysis of human control uninvolved artery, noncalcified, and calcified lesions showed significant increase of AzA in calcified lesions compared with noncalcified and control tissues. Calcified mouse atherosclerotic lesions also showed substantial presence of AzA in Ca complexes.

INNOVATION

This study identifies a DCA, AzA, as an integral part of the Ca complex. The study also demonstrates the conversion of a lipid peroxidation product, ONA, as a potential source of AzA, and establishes the presence of AzA in calcified materials isolated from human and mouse lesions.

CONCLUSION

The presence of AzA as a Ca sequestering agent in atherosclerotic lesions (i) might indicate participation of oxidized low-density lipoprotein (Ox-LDL) derived products in calcification, (ii) explain the potential correlation between calcification and overall plaque burden (as Ox-LDL has been suggested to be involved in atherogenesis), (iii) could contribute to plaque stabilization via its anti-inflammatory actions, and (iv) might explain why antioxidants failed to affect atherosclerosis in clinical studies. Antioxid. Redox Signal. 29, 471-483.

Genome-wide identification of lipoxygenase gene family in cotton and functional characterization in response to abiotic stresses

BACKGROUND

Plant lipoxygenase (LOX) genes are members of the non-haeme iron-containing dioxygenase family that catalyze the oxidation of polyunsaturated fatty acids into functionally diverse oxylipins. The LOX family genes have been extensively studied under biotic and abiotic stresses, both in model and non-model plant species; however, information on their roles in cotton is still limited.

RESULTS

A total of 64 putative LOX genes were identified in four cotton species (Gossypium (G. hirsutum, G. barbadense, G. arboreum, and G. raimondii)). In the phylogenetic tree, these genes were clustered into three categories (9-LOX, 13-LOX type I, and 13-LOX type II). Segmental duplication of putative LOX genes was observed between homologues from A2 to At and D5 to Dt hinting at allopolyploidy in cultivated tetraploid species (G. hirsutum and G. barbadense). The structure and motif composition of GhLOX genes appears to be relatively conserved among the subfamilies. Moreover, many cis-acting elements related to growth, stresses, and phytohormone signaling were found in the promoter regions of GhLOX genes. Gene expression analysis revealed that all GhLOX genes were induced in at least two tissues and the majority of GhLOX genes were up-regulated in response to heat and salinity stress. Specific expressions of some genes in response to exogenous phytohormones suggest their potential roles in regulating growth and stress responses. In addition, functional characterization of two candidate genes (GhLOX12 and GhLOX13) using virus induced gene silencing (VIGS) approach revealed their increased sensitivity to salinity stress in target gene-silenced cotton. Compared with controls, target gene-silenced plants showed significantly higher chlorophyll degradation, higher H2O2, malondialdehyde (MDA) and proline accumulation but significantly reduced superoxide dismutase (SOD) activity, suggesting their reduced ability to effectively degrade accumulated reactive oxygen species (ROS).

CONCLUSION

This genome-wide study provides a systematic analysis of the cotton LOX gene family using bioinformatics tools. Differential expression patterns of cotton LOX genes in different tissues and under various abiotic stress conditions provide insights towards understanding the potential functions of candidate genes. Beyond the findings reported here, our study provides a basis for further uncovering the biological roles of LOX genes in cotton development and adaptation to stress conditions.

Arabidopsis nonresponding to oxylipins locus NOXY7 encodes a yeast GCN1 homolog that mediates noncanonical translation regulation and stress adaptation

Stress adaptation and translational regulation was studied using noxy7 (nonresponding to oxylipins7) from a series of Arabidopsis thaliana mutants. We identified the noxy7 mutation in At1g64790, which encodes a homolog of the yeast translational regulator General Control Nonderepressible1 (GCN1) that activates the GCN2 kinase; GCN2 in turn phosphorylates the α subunit of the translation initiation factor eIF2. This regulatory circuit is conserved in yeast and mammals, in which phosphorylated eIF2α (P-eIF2α) facilitates stress adaptation by inhibiting protein synthesis. In phenotypic and de novo protein synthesis studies with Arabidopsis mutants, we found that NOXY7/GCN1 and GCN2 mediate P-eIF2α formation and adaptation to amino acid deprivation; however, P-eIF2α formation is not linked to general protein synthesis arrest. Additional evidence suggested that NOXY7/GCN1 but not GCN2 regulates adaptation to mitochondrial dysfunction, high boron concentration, and activation of plant immunity to infection by Pseudomonas syringae pv tomato (Pst). In these responses, NOXY7/GCN1 acts with GCN20 to regulate translation in a noncanonical pathway independently of GCN2 and P-eIF2α. These results show the lesser functional relevance of GCN2 and P-eIF2α in plants relative to other eukaryotes and highlight the prominent role of NOXY7/GCN1 and GCN20 in regulation of translation and stress adaptation in plants.

The Oxylipin Pathways: Biochemistry and Function

Plant oxylipins form a constantly growing group of signaling molecules that comprise oxygenated fatty acids and metabolites derived therefrom. In the last decade, the understanding of biosynthesis, metabolism, and action of oxylipins, especially jasmonates, has dramatically improved. Additional mechanistic insights into the action of enzymes and insights into signaling pathways have been deepened for jasmonates. For other oxylipins, such as the hydroxy fatty acids, individual signaling properties and cross talk between different oxylipins or even with additional phytohormones have recently been described. This review summarizes recent understanding of the biosynthesis, regulation, and function of oxylipins.

Genome mining of Streptomyces scabrisporus NF3 reveals symbiotic features including genes related to plant interactions

Endophytic bacteria are wide-spread and associated with plant physiological benefits, yet their genomes and secondary metabolites remain largely unidentified. In this study, we explored the genome of the endophyte Streptomyces scabrisporus NF3 for discovery of potential novel molecules as well as genes and metabolites involved in host interactions. The complete genomes of seven Streptomyces and three other more distantly related bacteria were used to define the functional landscape of this unique microbe. The S. scabrisporus NF3 genome is larger than the average Streptomyces genome and not structured for an obligate endosymbiotic lifestyle; this and the fact that can grow in R2YE media implies that it could include a soil-living stage. The genome displays an enrichment of genes associated with amino acid production, protein secretion, secondary metabolite and antioxidants production and xenobiotic degradation, indicating that S. scabrisporus NF3 could contribute to the metabolic enrichment of soil microbial communities and of its hosts. Importantly, besides its metabolic advantages, the genome showed evidence for differential functional specificity and diversification of plant interaction molecules, including genes for the production of plant hormones, stress resistance molecules, chitinases, antibiotics and siderophores. Given the diversity of S. scabrisporus mechanisms for host upkeep, we propose that these strategies were necessary for its adaptation to plant hosts and to face changes in environmental conditions.

Integrated analysis of zone-specific protein and metabolite profiles within nitrogen-fixing Medicago truncatula-Sinorhizobium medicae nodules

Symbiotic nitrogen fixation (SNF) between rhizobia and legumes requires metabolic coordination within specialized root organs called nodules. Nodules formed in the symbiosis between S. medicae and barrel medic (M. truncatula) are indeterminate, cylindrical, and contain spatially distinct developmental zones. Bacteria in the infection zone II (ZII), interzone II-III (IZ), and nitrogen fixation zone III (ZIII) represent different stages in the metabolic progression from free-living bacteria into nitrogen fixing bacteroids. To better understand the coordination of plant and bacterial metabolism within the nodule, we used liquid and gas chromatography coupled to tandem mass spectrometry (MS) to observe protein and metabolite profiles representative of ZII, IZ, ZIII, whole-nodule, and primary root. Our MS-based approach confidently identified 361 S. medicae proteins and 888 M. truncatula proteins, as well as 160 metabolites from each tissue. The data are consistent with several organ- and zone-specific protein and metabolite localization patterns characterized previously. We used our comprehensive dataset to demonstrate how multiple branches of primary metabolism are coordinated between symbionts and zones, including central carbon, fatty acid, and amino acid metabolism. For example, M. truncatula glycolysis enzymes accumulate from zone I to zone III within the nodule, while equivalent S. medicae enzymes decrease in abundance. We also show the localization of S. medicae's transition to dicarboxylic acid-dependent carbon metabolism within the IZ. The spatial abundance patterns of S. medicae fatty acid (FA) biosynthesis enzymes indicate an increased demand for FA production in the IZ and ZIII as compared to ZI. These observations provide a resource for those seeking to understand coordinated physiological changes during the development of SNF.

Specific Caleosin/Peroxygenase and Lipoxygenase Activities Are Tissue-Differentially Expressed in Date Palm (Phoenix dactylifera L.) Seedlings and Are Further Induced Following Exposure to the Toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin

Two caleosin/peroxygenase isoforms from date palm, Phoenix dactylifera L., PdCLO2 and PdCLO4, were characterized with respect to their tissue expression, subcellular localization, and oxylipin pathway substrate specificities in developing seedlings. Both PdCLO2 and PdCLO4 had peroxygenase activities that peaked at the mid-stage (radicle length of 2.5 cm) of seedling growth and were associated with the lipid droplet (LD) and microsomal fractions. Recombinant PdCLO2 and PdCLO4 proteins heterologously expressed in yeast cells were localized in both LD and microsomal fractions. Each of the purified recombinant proteins exhibited peroxygenase activity but they were catalytically distinct with respect to their specificity and product formation from fatty acid epoxide and hydroxide substrates. We recently showed that date palm CLO genes were upregulated following exposure to the potent toxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (Hanano et al., 2016), and we show here that transcripts of 9- and 13-lipoxygenase (LOX) genes were also induced by TCDD exposure. At the enzyme level, 9-LOX and 13-LOX activities were present in a range of seedling tissues and responded differently to TCDD exposure, as did the 9- and 13-fatty acid hydroperoxide reductase activities. This demonstrates that at least two branches of the oxylipin pathway are involved in responses to the environmental organic toxin, TCDD in date palm.

Screen Identifying Arabidopsis Transcription Factors Involved in the Response to 9-Lipoxygenase-Derived Oxylipins

13-Lipoxygenase-derived oxylipins, such as jasmonates act as potent signaling molecules in plants. Although experimental evidence supports the impact of oxylipins generated by the 9-Lipoxygenase (9-LOX) pathway in root development and pathogen defense, their signaling function in plants remains largely elusive. Based on the root growth inhibiting properties of the 9-LOX-oxylipin 9-HOT (9-hydroxy-10,12,15-octadecatrienoic acid), we established a screening approach aiming at identifying transcription factors (TFs) involved in signaling and/or metabolism of this oxylipin. Making use of the AtTORF-Ex (ArabidopsisthalianaTranscription Factor Open Reading Frame Expression) collection of plant lines overexpressing TF genes, we screened for those TFs which restore root growth on 9-HOT. Out of 6,000 lines, eight TFs were recovered at least three times and were therefore selected for detailed analysis. Overexpression of the basic leucine Zipper (bZIP) TF TGA5 and its target, the monoxygenase CYP81D11 reduced the effect of added 9-HOT, presumably due to activation of a detoxification pathway. The highly related ETHYLENE RESPONSE FACTORs ERF106 and ERF107 induce a broad detoxification response towards 9-LOX-oxylipins and xenobiotic compounds. From a set of 18 related group S-bZIP factors isolated in the screen, bZIP11 is known to participate in auxin-mediated root growth and may connect oxylipins to root meristem function. The TF candidates isolated in this screen provide starting points for further attempts to dissect putative signaling pathways involving 9-LOX-derived oxylipins.

Facilitation of Fusarium graminearum Infection by 9-Lipoxygenases in Arabidopsis and Wheat

Fusarium graminearum causes Fusarium head blight, an important disease of wheat. F. graminearum can also cause disease in Arabidopsis thaliana. Here, we show that the Arabidopsis LOX1 and LOX5 genes, which encode 9-lipoxygenases (9-LOXs), are targeted during this interaction to facilitate infection. LOX1 and LOX5 expression were upregulated in F. graminearum-inoculated plants and loss of LOX1 or LOX5 function resulted in enhanced disease resistance in the corresponding mutant plants. The enhanced resistance to F. graminearum infection in the lox1 and lox5 mutants was accompanied by more robust induction of salicylic acid (SA) accumulation and signaling and attenuation of jasmonic acid (JA) signaling in response to infection. The lox1- and lox5-conferred resistance was diminished in plants expressing the SA-degrading salicylate hydroxylase or by the application of methyl-JA. Results presented here suggest that plant 9-LOXs are engaged during infection to control the balance between SA and JA signaling to facilitate infection. Furthermore, since silencing of TaLpx-1 encoding a 9-LOX with homology to LOX1 and LOX5, resulted in enhanced resistance against F. graminearum in wheat, we suggest that 9-LOXs have a conserved role as susceptibility factors in disease caused by this important fungus in Arabidopsis and wheat.

Maize death acids, 9-lipoxygenase-derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators

Plant damage promotes the interaction of lipoxygenases (LOXs) with fatty acids yielding 9-hydroperoxides, 13-hydroperoxides, and complex arrays of oxylipins. The action of 13-LOX on linolenic acid enables production of 12-oxo-phytodienoic acid (12-OPDA) and its downstream products, termed "jasmonates." As signals, jasmonates have related yet distinct roles in the regulation of plant resistance against insect and pathogen attack. A similar pathway involving 9-LOX activity on linolenic and linoleic acid leads to the 12-OPDA positional isomer, 10-oxo-11-phytodienoic acid (10-OPDA) and 10-oxo-11-phytoenoic acid (10-OPEA), respectively; however, physiological roles for 9-LOX cyclopentenones have remained unclear. In developing maize (Zea mays) leaves, southern leaf blight (Cochliobolus heterostrophus) infection results in dying necrotic tissue and the localized accumulation of 10-OPEA, 10-OPDA, and a series of related 14- and 12-carbon metabolites, collectively termed "death acids." 10-OPEA accumulation becomes wound inducible within fungal-infected tissues and at physiologically relevant concentrations acts as a phytoalexin by suppressing the growth of fungi and herbivores including Aspergillus flavus, Fusarium verticillioides, and Helicoverpa zea. Unlike previously established maize phytoalexins, 10-OPEA and 10-OPDA display significant phytotoxicity. Both 12-OPDA and 10-OPEA promote the transcription of defense genes encoding glutathione S transferases, cytochrome P450s, and pathogenesis-related proteins. In contrast, 10-OPEA only weakly promotes the accumulation of multiple protease inhibitor transcripts. Consistent with a role in dying tissue, 10-OPEA application promotes cysteine protease activation and cell death, which is inhibited by overexpression of the cysteine protease inhibitor maize cystatin-9. Unlike jasmonates, functions for 10-OPEA and associated death acids are consistent with specialized roles in local defense reactions.

The Pepper Lipoxygenase CaLOX1 Plays a Role in Osmotic, Drought and High Salinity Stress Response

In plants, lipoxygenases (LOXs) are involved in various physiological processes, including defense responses to biotic and abiotic stresses. Our previous study had shown that the pepper 9-LOX gene, CaLOX1, plays a crucial role in cell death due to pathogen infection. Here, the function of CaLOX1 in response to osmotic, drought and high salinity stress was examined using CaLOX1-overexpressing (CaLOX1-OX) Arabidopsis plants. Changes in the temporal expression pattern of the CaLOX1 gene were observed when pepper leaves were treated with drought and high salinity, but not when treated with ABA, the primary hormone in response to drought stress. During seed germination and seedling development, CaLOX1-OX plants were more tolerant to ABA, mannitol and high salinity than wild-type plants. In contrast, expression of the ABA-responsive marker genes RAB18 and RD29B was higher in CaLOX1-OX Arabidopsis plants than in wild-type plants. In response to high salinity, CaLOX1-OX plants exhibited enhanced tolerance, compared with the wild type, which was accompanied by decreased accumulation of H2O2 and high levels of RD20, RD29A, RD29B and P5CS gene expression. Similarly, CaLOX1-OX plants were also more tolerant than wild-type plants to severe drought stress. H2O2 production and the relative increase in lipid peroxidation were lower, and the expression of COR15A, DREB2A, RD20, RD29A and RD29B was higher in CaLOX1-OX plants, relative to wild-type plants. Taken together, our results indicate that CaLOX1 plays a crucial role in plant stress responses by modulating the expression of ABA- and stress-responsive marker genes, lipid peroxidation and H2O2 production.

The involvement of wheat F-box protein gene TaFBA1 in the oxidative stress tolerance of plants

As one of the largest gene families, F-box domain proteins have been found to play important roles in abiotic stress responses via the ubiquitin pathway. TaFBA1 encodes a homologous F-box protein contained in E3 ubiquitin ligases. In our previous study, we found that the overexpression of TaFBA1 enhanced drought tolerance in transgenic plants. To investigate the mechanisms involved, in this study, we investigated the tolerance of the transgenic plants to oxidative stress. Methyl viologen was used to induce oxidative stress conditions. Real-time PCR and western blot analysis revealed that TaFBA1 expression was up-regulated by oxidative stress treatments. Under oxidative stress conditions, the transgenic tobacco plants showed a higher germination rate, higher root length and less growth inhibition than wild type (WT). The enhanced oxidative stress tolerance of the transgenic plants was also indicated by lower reactive oxygen species (ROS) accumulation, malondialdehyde (MDA) content and cell membrane damage under oxidative stress compared with WT. Higher activities of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD), were observed in the transgenic plants than those in WT, which may be related to the upregulated expression of some antioxidant genes via the overexpression of TaFBA1. In others, some stress responsive elements were found in the promoter region of TaFBA1, and TaFBA1 was located in the nucleus, cytoplasm and plasma membrane. These results suggest that TaFBA1 plays an important role in the oxidative stress tolerance of plants. This is important for understanding the functions of F-box proteins in plants' tolerance to multiple stress conditions.

Lipids and proteins--major targets of oxidative modifications in abiotic stressed plants

Stress factors provoke enhanced production of reactive oxygen species (ROS) in plants. ROS that escape antioxidant-mediated scavenging/detoxification react with biomolecules such as cellular lipids and proteins and cause irreversible damage to the structure of these molecules, initiate their oxidation, and subsequently inactivate key cellular functions. The lipid- and protein-oxidation products are considered as the significant oxidative stress biomarkers in stressed plants. Also, there exists an abundance of information on the abiotic stress-mediated elevations in the generation of ROS, and the modulation of lipid and protein oxidation in abiotic stressed plants. However, the available literature reflects a wide information gap on the mechanisms underlying lipid- and protein-oxidation processes, major techniques for the determination of lipid- and protein-oxidation products, and on critical cross-talks among these aspects. Based on recent reports, this article (a) introduces ROS and highlights their relationship with abiotic stress-caused consequences in crop plants, (b) examines critically the various physiological/biochemical aspects of oxidative damage to lipids (membrane lipids) and proteins in stressed crop plants, (c) summarizes the principles of current technologies used to evaluate the extent of lipid and protein oxidation, (d) synthesizes major outcomes of studies on lipid and protein oxidation in plants under abiotic stress, and finally, (e) considers a brief cross-talk on the ROS-accrued lipid and protein oxidation, pointing to the aspects unexplored so far.

Oxylipins and plant abiotic stress resistance

Oxylipins are signaling molecules formed enzymatically or spontaneously from unsaturated fatty acids in all aerobic organisms. Oxylipins regulate growth, development, and responses to environmental stimuli of organisms. The oxylipin biosynthesis pathway in plants includes a few parallel branches named after first enzyme of the corresponding branch as allene oxide synthase, hydroperoxide lyase, divinyl ether synthase, peroxygenase, epoxy alcohol synthase, and others in which various biologically active metabolites are produced. Oxylipins can be formed non-enzymatically as a result of oxygenation of fatty acids by free radicals and reactive oxygen species. Spontaneously formed oxylipins are called phytoprostanes. The role of oxylipins in biotic stress responses has been described in many published works. The role of oxylipins in plant adaptation to abiotic stress conditions is less studied; there is also obvious lack of available data compilation and analysis in this area of research. In this work we analyze data on oxylipins functions in plant adaptation to abiotic stress conditions, such as wounding, suboptimal light and temperature, dehydration and osmotic stress, and effects of ozone and heavy metals. Modern research articles elucidating the molecular mechanisms of oxylipins action by the methods of biochemistry, molecular biology, and genetics are reviewed here. Data on the role of oxylipins in stress signal transduction, stress-inducible gene expression regulation, and interaction of these metabolites with other signal transduction pathways in cells are described. In this review the general oxylipin-mediated mechanisms that help plants to adjust to a broad spectrum of stress factors are considered, followed by analysis of more specific responses regulated by oxylipins only under certain stress conditions. New approaches to improvement of plant resistance to abiotic stresses based on the induction of oxylipin-mediated processes are discussed.

The Physcomitrella patens unique alpha-dioxygenase participates in both developmental processes and defense responses

BACKGROUND

Plant α-dioxygenases catalyze the incorporation of molecular oxygen into polyunsaturated fatty acids leading to the formation of oxylipins. In flowering plants, two main groups of α-DOXs have been described. While the α-DOX1 isoforms are mainly involved in defense responses against microbial infection and herbivores, the α-DOX2 isoforms are mostly related to development. To gain insight into the roles played by these enzymes during land plant evolution, we performed biochemical, genetic and molecular analyses to examine the function of the single copy moss Physcomitrella patens α-DOX (Ppα-DOX) in development and defense against pathogens.

RESULTS

Recombinant Ppα-DOX protein catalyzed the conversion of fatty acids into 2-hydroperoxy derivatives with a substrate preference for α-linolenic, linoleic and palmitic acids. Ppα-DOX is expressed during development in tips of young protonemal filaments with maximum expression levels in mitotically active undifferentiated apical cells. In leafy gametophores, Ppα-DOX is expressed in auxin producing tissues, including rhizoid and axillary hairs. Ppα-DOX transcript levels and Ppα-DOX activity increased in moss tissues infected with Botrytis cinerea or treated with Pectobacterium carotovorum elicitors. In B. cinerea infected leaves, Ppα-DOX-GUS proteins accumulated in cells surrounding infected cells, suggesting a protective mechanism. Targeted disruption of Ppα-DOX did not cause a visible developmental alteration and did not compromise the defense response. However, overexpressing Ppα-DOX, or incubating wild-type tissues with Ppα-DOX-derived oxylipins, principally the aldehyde heptadecatrienal, resulted in smaller moss colonies with less protonemal tissues, due to a reduction of caulonemal filament growth and a reduction of chloronemal cell size compared with normal tissues. In addition, Ppα-DOX overexpression and treatments with Ppα-DOX-derived oxylipins reduced cellular damage caused by elicitors of P. carotovorum.

CONCLUSIONS

Our study shows that the unique α-DOX of the primitive land plant P. patens, although apparently not crucial, participates both in development and in the defense response against pathogens, suggesting that α-DOXs from flowering plants could have originated by duplication and successive functional diversification after the divergence from bryophytes.

Involvement of the caleosin/peroxygenase RD20 in the control of cell death during Arabidopsis responses to pathogens

Caleosins, mostly found in lipid droplets of seeds and leaves, are believed to play physiological roles through their enzymatic capacities to produce oxylipins. We recently identified the caleosin RD20 as a peroxygenase reducing endogenous fatty acid hydroperoxides into their corresponding alcohols. Such oxylipins confer tolerance to oxidative stress by decreasing reactive oxygen species accumulation and by minimizing cell death. RD20 expression being induced by pathogens, we have examined the mode of action of this caleosin in response to biotic stress. Plants overexpressing RD20 exhibited an alteration of their leaf cuticle wax components and an increased resistance to the fungus Alternaria brassicicola. Conversely, silencing RD20 led to an enhanced propagation of the fungus and to reduced severity of the damages caused by the inoculation of the bacteria Pseudomonas syringae pv tomato. We discuss these findings and propose that the major function of RD20 is to generate oxylipins modulating oxidative status and cell death.

Oxylipins in moss development and defense

Oxylipins are oxygenated fatty acids that participate in plant development and defense against pathogen infection, insects, and wounding. Initial oxygenation of substrate fatty acids is mainly catalyzed by lipoxygenases (LOXs) and α-dioxygenases but can also take place non-enzymatically by autoxidation or singlet oxygen-dependent reactions. The resulting hydroperoxides are further metabolized by secondary enzymes to produce a large variety of compounds, including the hormone jasmonic acid (JA) and short-chain green leaf volatiles. In flowering plants, which lack arachidonic acid, oxylipins are produced mainly from oxidation of polyunsaturated C18 fatty acids, notably linolenic and linoleic acids. Algae and mosses in addition possess polyunsaturated C20 fatty acids including arachidonic and eicosapentaenoic acids, which can also be oxidized by LOXs and transformed into bioactive compounds. Mosses are phylogenetically placed between unicellular green algae and flowering plants, allowing evolutionary studies of the different oxylipin pathways. During the last years the moss Physcomitrella patens has become an attractive model plant for understanding oxylipin biosynthesis and diversity. In addition to the advantageous evolutionary position, functional studies of the different oxylipin-forming enzymes can be performed in this moss by targeted gene disruption or single point mutations by means of homologous recombination. Biochemical characterization of several oxylipin-producing enzymes and oxylipin profiling in P. patens reveal the presence of a wider range of oxylipins compared to flowering plants, including C18 as well as C20-derived oxylipins. Surprisingly, one of the most active oxylipins in plants, JA, is not synthesized in this moss. In this review, we present an overview of oxylipins produced in mosses and discuss the current knowledge related to the involvement of oxylipin-producing enzymes and their products in moss development and defense.

The novel monocot-specific 9-lipoxygenase ZmLOX12 is required to mount an effective jasmonate-mediated defense against Fusarium verticillioides in maize

Fusarium verticillioides is a major limiting factor for maize production due to ear and stalk rot and the contamination of seed with the carcinogenic mycotoxin fumonisin. While lipoxygenase (LOX)-derived oxylipins have been implicated in defense against diverse pathogens, their function in maize resistance against F. verticillioides is poorly understood. Here, we functionally characterized a novel maize 9-LOX gene, ZmLOX12. This gene is distantly related to known dicot LOX genes, with closest homologs found exclusively in other monocot species. ZmLOX12 is predominantly expressed in mesocotyls in which it is strongly induced in response to F. verticillioides infection. The Mutator transposon-insertional lox12-1 mutant is more susceptible to F. verticillioides colonization of mesocotyls, stalks, and kernels. The infected mutant kernels accumulate a significantly greater amount of the mycotoxin fumonisin. Reduced resistance to the pathogen is accompanied by diminished levels of the jasmonic acid (JA) precursor 12-oxo phytodienoic acid, JA-isoleucine, and expression of jasmonate-biosynthetic genes. Supporting the strong defense role of jasmonates, the JA-deficient opr7 opr8 double mutant displayed complete lack of immunity to F. verticillioides. Unexpectedly, the more susceptible lox12 mutant accumulated higher levels of kauralexins, suggesting that F. verticillioides is tolerant to this group of antimicrobial phytoalexins. This study demonstrates that this unique monocot-specific 9-LOX plays a key role in defense against F. verticillioides in diverse maize tissues and provides genetic evidence that JA is the major defense hormone against this pathogen.