Oxidized fatty acids as inter-kingdom signaling molecules

Lipoxygenases at the Intersection of Infection and Carcinogenesis

The persisting presence of opportunistic pathogens like Pseudomonas aeruginosa poses a significant threat to many immunocompromised cancer patients with pulmonary infections. This review highlights the complexity of interactions in the host's defensive eicosanoid signaling network and its hijacking by pathogenic bacteria to their own advantage. Human lipoxygenases (ALOXs) and their mouse counterparts are integral elements of the innate immune system, mostly operating in the pro-inflammatory mode. Taking into account the indispensable role of inflammation in carcinogenesis, lipoxygenases have counteracting roles in this process. In addition to describing the structure-function of lipoxygenases in this review, we discuss their roles in such critical processes as cancer cell signaling, metastases, death of cancer and immune cells through ferroptosis, as well as the roles of ALOXs in carcinogenesis promoted by pathogenic infections. Finally, we discuss perspectives of novel oncotherapeutic approaches to harness lipoxygenase signaling in tumors.

The metabolites of light: Untargeted metabolomic approaches bring new clues to understand light-driven acclimation of intertidal mudflat biofilm

The microphytobenthos (MPB), a microbial community of primary producers, play a key role in coastal ecosystem functioning, particularly in intertidal mudflats. These mudflats experience challenging variations of irradiance, forcing the micro-organisms to develop photoprotective mechanisms to survive and thrive in this dynamic environment. Two major adaptations to light are well described in literature: the excess of light energy dissipation through non-photochemical quenching (NPQ), and the vertical migration in the sediment. These mechanisms trigger considerable scientific interest, but the biological processes and metabolic mechanisms involved in light-driven vertical migration remain largely unknown. To our knowledge, this study investigates for the first time metabolomic responses of a migrational mudflat biofilm exposed for 30 min to a light gradient of photosynthetically active radiation (PAR) from 50 to 1000 μmol photons m-2 s-1. The untargeted metabolomic analysis allowed to identify metabolites involved in two types of responses to light irradiance levels. On the one hand, the production of SFAs and MUFAs, primarily derived from bacteria, indicates a healthy photosynthetic state of MPB under low light (LL; 50 and 100 PAR) and medium light (ML; 250 PAR) conditions. Conversely, when exposed to high light (HL; 500, 750 and 1000 PAR), the MPB experienced light-induced stress, triggering the production of alka(e)nes and fatty alcohols. The physiological and ecological roles of these compounds are poorly described in literature. This study sheds new light on the topic, as it suggests that these compounds may play a crucial and previously unexplored role in light-induced stress acclimation of migrational MPB biofilms. Since alka(e)nes are produced from FAs decarboxylation, these results thus emphasize for the first time the importance of FAs pathways in microphytobenthic biofilms acclimation to light.

Mutational Analysis of Aspergillus fumigatus Volatile Oxylipins in a Drosophila Eclosion Assay

Aspergillus fumigatus is a ubiquitous opportunistic pathogen. We have previously reported that volatile organic compounds (VOCs) produced by A. fumigatus cause delays in metamorphosis, morphological abnormalities, and death in a Drosophila melanogaster eclosion model. Here, we developed A. fumigatus deletion mutants with blocked oxylipin biosynthesis pathways (∆ppoABC) and then exposed the third instar larvae of D. melanogaster to a shared atmosphere with either A. fumigatus wild-type or oxylipin mutant cultures for 15 days. Fly larvae exposed to VOCs from wild-type A. fumigatus strains exhibited delays in metamorphosis and toxicity, while larvae exposed to VOCs from the ∆ppoABC mutant displayed fewer morphogenic delays and higher eclosion rates than the controls. In general, when fungi were pre-grown at 37 °C, the effects of the VOCs they produced were more pronounced than when they were pre-grown at 25 °C. GC-MS analysis revealed that the wild-type A. fumigatus Af293 produced more abundant VOCs at higher concentrations than the oxylipin-deficient strain Af293∆ppoABC did. The major VOCs detected from wild-type Af293 and its triple mutant included isopentyl alcohol, isobutyl alcohol, 2-methylbutanal, acetoin, and 1-octen-3-ol. Unexpectedly, compared to wild-type flies, the eclosion tests yielded far fewer differences in metamorphosis or viability when flies with immune-deficient genotypes were exposed to VOCs from either wild-type or ∆ppoABC oxylipin mutants. In particular, the toxigenic effects of Aspergillus VOCs were not observed in mutant flies deficient in the Toll (spz⁶) pathway. These data indicate that the innate immune system of Drosophila mediates the toxicity of fungal volatiles, especially via the Toll pathway.

Transcriptomic and metabolic signatures of diatom plasticity to light fluctuations

Unlike in terrestrial and freshwater ecosystems, light fields in oceans fluctuate due to both horizontal current and vertical mixing. Diatoms thrive and dominate the phytoplankton community in these fluctuating light fields. However, the molecular mechanisms that regulate diatom acclimation and adaptation to light fluctuations are poorly understood. Here, we performed transcriptome sequencing, metabolome profiling, and 13C-tracer labeling on the model diatom Phaeodactylum tricornutum. The diatom acclimated to constant light conditions was transferred to six different light conditions, including constant light (CL5d), short-term (1 h) high light (sHL1h), and short-term (1 h) and long-term (5 days) mild or severe light fluctuation conditions (mFL1h, sFL1h, mFL5d, and sFL5d) that mimicked land and ocean light levels. We identified 2,673 transcripts (25% of the total expressed genes) expressed differentially under different fluctuating light regimes. We also identified 497 transcription factors, 228 not reported previously, which exhibited higher expression under light fluctuations, including 7 with a light-sensitive PAS domain (Per-period circadian protein, Arnt-aryl hydrocarbon receptor nuclear translocator protein, Sim-single-minded protein) and 10 predicted to regulate genes related to light-harvesting complex proteins. Our data showed that prolonged preconditioning in severe light fluctuation enhanced photosynthesis in P. tricornutum under this condition, as evidenced by increased oxygen evolution accompanied by the upregulation of Rubisco and light-harvesting proteins. Furthermore, severe light fluctuation diverted the metabolic flux of assimilated carbon preferentially toward fatty acid storage over sugar and protein. Our results suggest that P. tricornutum use a series of complex and different responsive schemes in photosynthesis and carbon metabolism to optimize their growth under mild and severe light fluctuations. These insights underscore the importance of using more intense conditions when investigating the resilience of phytoplankton to light fluctuations.

First report of chemical composition and cytotoxicity evaluation of Foraminispora rugosa basidiomata from Brazil

BACKGROUND

Foraminispora rugosa is a species reported from Brazil, Venezuela, French Guiana, Costa Rica and Cuba. It is a basidiomycete in the Ganodermataceae family. In this study, both chemical composition and cytotoxicity of the ethanolic extract of F. rugosa were investigated for the first time.

RESULTS

Phylogenetic analysis confirmed the identification of the specimens, and the results of cytotoxicity assays showed that at concentrations of 7.8-500.0 µg/mL the ethanolic extract displayed weak cytotoxicity against the tested cell lines. Five oxylipins were identified by ultra high performance liquid chromatography coupled with quadrupole time-of-flight and mass spectrometry (UHPLC-QTOF-MS).

CONCLUSIONS

This study provides new insights into the current knowledge of bioactive compounds produced by macrofungi, and provides data for future biological assays with relative selectivity and safety.

Antifungal Activity and Biochemical Profiling of Exudates from Germinating Maize Nostrano di Storo Local Variety

Plant pathogens are responsible for important damages to valuable crops causing important economic losses. Agrobiodiversity protection is crucial for the valorization of local varieties that could possess higher resistance to biotic and abiotic stress. At the beginning of germination, seeds are susceptible to pathogens attacks, thus they can release endogenous antimicrobial compounds of different natures in the spermosphere, to contrast proliferation of microorganisms. The work aimed at characterizing the maize of local variety Nostrano di Storo seed exudates secreted during the first phases of germination, to identify compounds active in the defense towards pathogens. Storo seed exudates were proven to inhibit F. verticilloides germination. In order to investigate the cause of the described effect, compositional profiling of the exudates was performed through NMR, lipidomic, and proteomic analyses. This study suggests an important role of microbial endophytic communities in the protection of the seed during the early phases of the germination process and their interplay with fatty acids released by the seeds, rather than a specific antifungal compound. The valorization of agronomically acceptable maize lines with pre-harvest enhanced resistances to pathogens contamination could lead, in the near future, to commercially available varieties potentially requiring more limited chemical protective treatments.

Fungal and bacterial oxylipins are signals for intra- and inter-cellular communication within plant disease

Lipids are central at various stages of host-pathogen interactions in determining virulence and modulating plant defense. Free fatty acids may act as substrates for oxidizing enzymes [e.g., lipoxygenases (LOXs) and dioxygenases (DOXs)] that synthesize oxylipins. Fatty acids and oxylipins function as modulators of several pathways in cell-to-cell communication; their structural similarity among plant, fungal, and bacterial taxa suggests potential in cross-kingdom communication. We provide a prospect of the known role of fatty acids and oxylipins in fungi and bacteria during plant-pathogen interactions. In the pathogens, oxylipin-mediated signaling pathways are crucial both in development and host infection. Here, we report on case studies suggesting that oxylipins derived from oleic, linoleic, and linolenic acids are crucial in modulating the pathogenic lifestyle in the host plant. Intriguingly, overlapping (fungi-plant/bacteria-plant) results suggest that different inter-kingdom pathosystems use similar lipid signals to reshape the lifestyle of the contenders and occasionally determine the outcome of the challenge.

Marine Compounds for Melanoma Treatment and Prevention

Melanoma is considered a multifactorial disease etiologically divided into melanomas related to sun exposure and those that are not, but also based on their mutational signatures, anatomic site, and epidemiology. The incidence of melanoma skin cancer has been increasing over the past decades with 132,000 cases occurring globally each year. Marine organisms have been shown to be an excellent source of natural compounds with possible bioactivities for human health applications. In this review, we report marine compounds from micro- and macro-organisms with activities in vitro and in vivo against melanoma, including the compound Marizomib, isolated from a marine bacterium, currently in phase III clinical trials for melanoma. When available, we also report active concentrations, cellular targets and mechanisms of action of the mentioned molecules. In addition, compounds used for UV protection and melanoma prevention from marine sources are discussed. This paper gives an overview of promising marine molecules which can be studied more deeply before clinical trials in the near future.

Bleaching physiology: who's the 'weakest link' - host vs. symbiont?

Environmental stress, such as an increase in the sea surface temperature, triggers coral bleaching, a profound dysfunction of the mutualist symbiosis between the host cnidarians and their photosynthetic dinoflagellates of the Family Symbiodiniaceae. Because of climate change, mass coral bleaching events will increase in frequency and severity in the future, threatening the persistence of this iconic marine ecosystem at global scale. Strategies adapted to coral reefs preservation and restoration may stem from the identification of the succession of events and of the different molecular and cellular contributors to the bleaching phenomenon. To date, studies aiming to decipher the cellular cascade leading to temperature-related bleaching, emphasized the involvement of reactive species originating from compromised bioenergetic pathways (e.g. cellular respiration and photosynthesis). These molecules are responsible for damage to various cellular components causing the dysregulation of cellular homeostasis and the breakdown of symbiosis. In this review, we synthesize the current knowledge available in the literature on the cellular mechanisms caused by thermal stress, which can initiate or participate in the cell cascade leading to the loss of symbionts, with a particular emphasis on the role of each partner in the initiating processes.

Development, validation, and application of an HPLC-MS/MS method for quantification of oxidized fatty acids in plants

Oxylipins constitute a huge class of compounds produced by oxidation of long-chain unsaturated fatty acids either chemically (by radicals such as reactive oxygen species, ROS) or enzymatically (by lipoxygenases, LOX; cyclooxygenases, COX; or cytochrome P450 pathways). This process generates fatty acids peroxides, which can then be further modified in a broad range to epoxy, hydroxy, keto, ether fatty acids, and also hydrolyzed to generate small aldehydes and alcohols. In general, oxylipins are present in almost all living organisms and have a wide range of signaling, metabolic, physiological, and ecological roles depending on the particular organism and on their structure. In plants, oxylipins have been extensively studied over the past 35 years. However, these studies have focused mainly on the jasmonates and so-called green leaves volatiles. The function of early LOX products (like keto and hydroxy fatty acids) is yet not well understood in plants, where they are mainly analyzed by indirect methods or by GC-MS what requires a laborious sample preparation. Here, we developed and validated a straightforward, precise, accurate, and sensitive method for quantifying oxylipins in plant tissues using HPLC-MS/MS, with a one-step extraction procedure using low amount of plant tissues. We successfully applied this method to quantify the oxylipins in different plant species and Arabidopsis thaliana plants treated with various biotic and abiotic stress conditions.

Pentadecanoic acid against Candida albicans-Klebsiella pneumoniae biofilm: towards the development of an anti-biofilm coating to prevent polymicrobial infections

The ability to form biofilms is a common feature of microorganisms, which can colonize a variety of surfaces, such as host tissues and medical devices, resulting in infections highly resistant to conventional drugs. This aspect is particularly critical in polymicrobial biofilms involving both fungi and bacteria, therefore, to eradicate such severe infections, new and effective anti-biofilm strategies are needed. The efficacy of pentadecanal and pentadecanoic acid as anti-biofilm agents has been recently reported against different bacterial strains. Their chemical similarity with diffusible signal factors (DSFs), plus the already known ability of fatty acids to act as anti-biofilm agents, suggested to explore their use against Candida albicans and Klebsiella pneumoniae mixed biofilm. In this work, we demonstrated the ability of both molecules to prevent the formation and destabilize the structure of the dual-species biofilm. Moreover, the pentadecanoic acid anti-biofilm coating, previously developed through the adsorption of the fatty acid on polydimethylsiloxane (PDMS), was proved to prevent the polymicrobial biofilm formation in dynamic conditions by confocal laser scanning microscopy analysis. Finally, the evaluation of the expression levels of some biofilm-related genes of C. albicans and K. pneumoniae treated with pentadecanoic acid provided some insights into the molecular mechanisms underpinning its anti-biofilm effect.

Metabolomic profiling of active and inactive liver cystic echinococcosis

Cystic Echinococcosis (CE) is one of the life-threatening diseases worldwide. It is a parasitic zoonosis caused by tapeworms of the species Echinococcus granulosus sensu lato (s.l). The treatment options of CE vary from simple "watch and wait" approach to invasive treatment, based on the type and especially the nature of the cyst (active/inactive). Serological tests are inadequate to distinguish between active and inactive CE. A diagnostic reference that can determine whether the cyst is active or inactive can easily guide the treatment strategy. We aimed to test whether gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-quadropole time of flight mass spectrometry (LC-qTOF-MS) based metabolomics can establish a plasma metabolic fingerprint of CE patients and identify a diagnostic reference to discriminate active and inactive CE cysts. Metabolite concentrations were measured in plasma samples of 36 active CE patients, 17 inactive CE patients and 31 healthy controls. Multivariate statistical analysis on 232 identified metabolites obtained from two analytical platforms was performed by using principle component analysis (PCA) and partial least square-discriminant analysis (PLS-DA) methods. The PLS-DA scores plot of the combined data set demonstrated a good separation between the groups. Compared to the healthy control group, decreased levels of squalene and increased levels of glyceric acid, 3-phosphoglycerate, glutamic acid, palmitoleic acid and oleic acid were determined in the CE patients. However, decreased levels of 3-phosphoglycerate and increased levels of 4-hydroxyphenylacetylglutamine, docosahexanoic acid were determined in active CE patients compared to the inactive CE patients. Determination of differences in metabolites may provide detailed understandings of potential metabolic process associated with active and inactive CE patients, and altered specific metabolic changes may provide some clues to obtain diagnostic reference for CE. This study has certain limitations: a. various factors affecting results of metabolomic studies such as lifestyle and dietary habits of the patients could not be fully controlled b. other infectious or malignant diseases of the liver should also be included as a positive control to evaluate the specificity of the diagnostic references.

Fatty acid export protein BnFAX6 functions in lipid synthesis and axillary bud growth in Brassica napus

Sugar is considered as the primary regulator of plant apical dominance, whereby the outgrowth of axillary buds is inhibited by the shoot tip. However, there are some deficiencies in this theory. Here, we reveal that Fatty Acid Export 6 (BnFAX6) functions in FA transport, and linoleic acid or its derivatives acts as a signaling molecule in regulating apical dominance of Brassica napus. BnFAX6 is responsible for mediating FA export from plastids. Overexpression of BnFAX6 in B. napus heightened the expression of genes involved in glycolysis and lipid biosynthesis, promoting the flow of photosynthetic products to the biosynthesis of FAs (including linoleic acid and its derivatives). Enhancing expression of BnFAX6 increased oil content in seeds and leaves and resulted in semi-dwarf and increased branching phenotypes with more siliques, contributing to increased yield per plant relative to wild-type. Furthermore, decapitation led to the rapid flow of the carbon from photosynthetic products to FA biosynthesis in axillary buds, consistent with the overexpression of BnFAX6 in B. napus. In addition, free FAs, especially linoleic acid, were rapidly transported from leaves to axillary buds. Increasing linoleic acid in axillary buds repressed expression of a key transcriptional regulator responsible for maintaining bud dormancy, resulting in bud outgrowth. Taken together, we uncovered that BnFAX6 mediating FA export from plastids functions in lipid biosynthesis and in axillary bud dormancy release, possibly through enhancing linoleic acid level in axillary buds of B. napus.

Plant-associated fungal biofilms-knowns and unknowns

Nearly all microbes, including fungi, grow firmly attached to surfaces as a biofilm. Yet, attention toward fungal interactions with plants and the environment is dedicated to free-floating (planktonic) cells. Fungal biofilms are generally thought to configure interactions across and among plant populations. Despite this, plant fungal biofilm research lags far behind the research on biofilms of medically important fungi. The deficit in noticing and exploring this research avenue could limit disease management and plant improvement programs. Here, we provide the current state of knowledge of fungal biofilms and the different pivotal ecological roles they impart in the context of disease, through leveraging evidence across medically important fungi, secondary metabolite production, plant beneficial functions and climate change. We also provide views on several important information gaps potentially hampering plant fungal biofilm research, and propose a way forward to address these gaps.

Lyophilized extracts from vegetable flours as valuable alternatives to purified oxygenases for the synthesis of oxylipins

In this work, the whole aqueous extracts of soybean flour and oat flour have been used as valuable alternatives to purified oxygenase enzymes for the preparation of oxylipins derived from (5Z,8Z,11Z,14Z,17Z)-eicosapentaenoic acid (EPA). The lipoxygenase activity in the aqueous extracts of soybean (Glycine max. L.) flour was monitored with linoleic acid as substrate and compared with the commercially available purified enzyme (LOX-1). Oat flour extracts (Avena sativa L.) were evaluated for their peroxygenase activity by comparing different enzyme preparations in the epoxidation of methyl oleate. It was found that lyophilization of the aqueous extracts from these vegetable flours offers advantages in terms of enzyme stability, reproducibility and applicability to preparative organic synthesis. The lyophilized enzyme preparations were tested for the oxyfunctionalization of EPA and the formed products were isolated in satisfactory yields. In the presence of lyophilized extract from soybean, EPA gave 15S-hydroxy-(5Z,8Z,11Z,13E,17Z)-eicosapentaenoic acid in enantiopure form as exclusive product. Peroxygenase from oat flour was less selective and catalyzed the formation of different epoxides of EPA. However, the biocatalyzed epoxidation of EPA under controlled conditions allowed to obtain optically active (17R,18S)-epoxy-(5Z,8Z,11Z,14Z)-eicosatetraenoic acid (65% ee) as the main monoepoxide, among the five possible ones.

Beyond Antagonism: The Interaction Between Candida Species and Pseudomonas aeruginosa

There are many examples of the interaction between prokaryotes and eukaryotes. One such example is the polymicrobial colonization/infection by the various opportunistic pathogenic yeasts belonging to the genus Candida and the ubiquitous bacterium, Pseudomonas aeruginosa. Although this interaction has simplistically been characterized as antagonistic to the yeast, this review highlights the complexity of the interaction with various factors influencing both microbes. The first section deals with the interactions in vitro, looking specifically at the role of cell wall components, quorum sensing molecules, phenazines, fatty acid metabolites and competition for iron in the interaction. The second part of this review places all these interactions in the context of various infection or colonization sites, i.e., lungs, wounds, and the gastrointestinal tract. Here we see that the role of the host, as well as the methodology used to establish co-infection, are important factors, influencing the outcome of the disease. Suggested future perspectives for the study of this interaction include determining the influence of newly identified participants of the QS network of P. aeruginosa, oxylipin production by both species, as well as the genetic and phenotypic plasticity of these microbes, on the interaction and outcome of co-infection.

Oxylipins mediate cell-to-cell communication in Pseudomonas aeruginosa

Oxygenated unsaturated fatty acids, known as oxylipins, are signaling molecules commonly used for cell-to-cell communication in eukaryotes. However, a role for oxylipins in mediating communication in prokaryotes has not previously been described. Bacteria mainly communicate via quorum sensing, which involves the production and detection of diverse small molecules termed autoinducers. Here we show that oleic acid-derived oxylipins produced by Pseudomonas aeruginosa function as autoinducers of a novel quorum sensing system. We found that this system controls the cell density-dependent expression of a gene subset independently of the quorum sensing systems thus far described in this bacterium. We identified a LysR-type transcriptional regulator as the primary receptor of the oxylipin signal. The discovery of this oxylipin-dependent quorum sensing system reveals that prokaryote-derived oxylipins also mediate cell-to-cell communication in bacteria.

Eriel Martínez et al. report that the bacterial pathogen Pseudomonas aeruginosa can convert oleic acids into oxylipins for use in cell-cell communication. This quorum sensing system is regulated by the bacterial protein called oxylipin-dependent diol synthase regulator OdsR.

"Only a Life Lived for Others Is Worth Living": Redox Signaling by Oxygenated Phospholipids in Cell Fate Decisions

SIGNIFICANCE

Oxygenated polyunsaturated lipids are known to play multi-functional roles as essential signals coordinating metabolism and physiology. Among them are well-studied eicosanoids and docosanoids that are generated via phospholipase A2 hydrolysis of membrane phospholipids and subsequent oxygenation of free polyunsaturated fatty acids (PUFA) by cyclooxygenases and lipoxygenases. Recent Advances: There is an emerging understanding that oxygenated PUFA-phospholipids also represent a rich signaling language with yet-to-be-deciphered details of the execution machinery-oxygenating enzymes, regulators, and receptors. Both free and esterified oxygenated PUFA signals are generated in cells, and their cross-talk and inter-conversion through the de-acylation/re-acylation reactions is not sufficiently explored.

CRITICAL ISSUES

Here, we review recent data related to oxygenated phospholipids as important damage signals that trigger programmed cell death pathways to eliminate irreparably injured cells and preserve the health of multicellular environments. We discuss the mechanisms underlying the trans-membrane redistribution and generation of oxygenated cardiolipins in mitochondria by cytochrome c as pro-apoptotic signals. We also consider the role of oxygenated phosphatidylethanolamines as proximate pro-ferroptotic signals.

FUTURE DIRECTIONS

We highlight the importance of sequential processes of phospholipid oxygenation and signaling in disease contexts as opportunities to use their regulatory mechanisms for the identification of new therapeutic targets.

The Various Roles of Fatty Acids

Lipids comprise a large group of chemically heterogeneous compounds. The majority have fatty acids (FA) as part of their structure, making these compounds suitable tools to examine processes raging from cellular to macroscopic levels of organization. Among the multiple roles of FA, they have structural functions as constituents of phospholipids which are the "building blocks" of cell membranes; as part of neutral lipids FA serve as storage materials in cells; and FA derivatives are involved in cell signalling. Studies on FA and their metabolism are important in numerous research fields, including biology, bacteriology, ecology, human nutrition and health. Specific FA and their ratios in cellular membranes may be used as biomarkers to enable the identification of organisms, to study adaptation of bacterial cells to toxic compounds and environmental conditions and to disclose food web connections. In this review, we discuss the various roles of FA in prokaryotes and eukaryotes and highlight the application of FA analysis to elucidate ecological mechanisms. We briefly describe FA synthesis; analyse the role of FA as modulators of cell membrane properties and FA ability to store and supply energy to cells; and inspect the role of polyunsaturated FA (PUFA) and the suitability of using FA as biomarkers of organisms.

Cyclooxygenases and lipoxygenases are used by the fungus Podospora anserina to repel nematodes

Oxylipins are secondary messengers used universally in the living world for communication and defense. The paradigm is that they are produced enzymatically for the eicosanoids and non-enzymatically for the isoprostanoids. They are supposed to be degraded into volatile organic compounds (VOCs) and to participate in aroma production. Some such chemicals composed of eight carbons are also envisoned as alternatives to fossil fuels. In fungi, oxylipins have been mostly studied in Aspergilli and shown to be involved in signalling asexual versus sexual development, mycotoxin production and interaction with the host for pathogenic species. Through targeted gene deletions of genes encoding oxylipin-producing enzymes and chemical analysis of oxylipins and volatile organic compounds, we show that in the distantly-related ascomycete Podospora anserina, isoprostanoids are likely produced enzymatically. We show the disappearance in the mutants lacking lipoxygenases and cyclooxygenases of the production of 10-hydroxy-octadecadienoic acid and that of 1-octen-3-ol, a common volatile compound. Importantly, this was correlated with the inability of the mutants to repel nematodes as efficiently as the wild type. Overall, our data show that in this fungus, oxylipins are not involved in signalling development but may rather be used directly or as precursors in the production of odors against potential agressors.

SIGNIFICANCE

We analyzse the role in inter-kingdom communication of lipoxygenase (lox) and cyclooxygenase (cox) genes in the model fungus Podospora anserina. Through chemical analysis we define the oxylipins and volatile organic compounds (VOCs)produce by wild type and mutants for cox and lox genes, We show that the COX and LOX genes are required for the production of some eight carbon VOCs. We show that COX and LOX genes are involved in the production of chemicals repelling nematodes. This role is very different from the ones previously evidenced in other fungi.

Priming plant resistance by activation of redox-sensitive genes

Priming by natural compounds is an interesting alternative for sustainable agriculture, which also contributes to explore the molecular mechanisms associated with stress tolerance. Although hosts and stress types eventually determine the mode of action of plant-priming agents, it highlights that many of them act on redox signalling. These include vitamins thiamine, riboflavin and quercetin; organic acids like pipecolic, azelaic and hexanoic; volatile organic compounds such as methyl jasmonate; cell wall components like chitosans and oligogalacturonides; H₂O₂, etc. This review provides data on how priming inducers promote stronger and faster responses to stress by modulating the oxidative environment, and interacting with signalling pathways mediated by salycilic acid, jasmonic acid and ethylene. The histone modifications involved in priming that affect the transcription of defence-related genes are also discussed. Despite the evolutionary distance between plants and animals, and the fact that the plant innate immunity takes place in each plant cell, they show many similarities in the molecular mechanisms that underlie pathogen perception and further signalling to activate defence responses. This review highlights the similarities between priming through redox signalling in plants and in mammalian cells. The strategies used by pathogens to manipulate the host´s recognition and the further activation of defences also show similarities in both kingdoms. Moreover, phytochemicals like sulforaphane and 12-oxo-phytodienoic acid prime both plant and mammalian responses by activating redox-sensitive genes. Hence research data into the priming of plant defences can provide additional information and a new viewpoint for priming mammalian defence, and vice versa.

Microalgae-derived oxylipins decrease inflammatory mediators by regulating the subcellular location of NFκB and PPAR-γ

Oxylipins (OXLs) are bioactive molecules generated by the oxidation of fatty acids that promote the resolution of acute inflammation and prevent chronic inflammatory processes through molecular mechanisms that are not well known. We have previously reported the anti-inflammatory activity of microalgae-derived OXLs and OXL-containing biomass in two inflammatory bowel disease (IBD) models: 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced acute colitis and TNBS-induced recurrent colitis. In this study, we examined the in vitro anti-inflammatory mechanism of action of the most abundant OXLs isolated from Chlamydomonas debaryana (13S-HOTE and 13S-HODE) and Nannochloropsis gaditana (15S-HEPE). These OXLs decreased IL-1β and IL-6 pro-inflammatory cytokines production as well as iNOS and COX-2 expression levels in THP-1 macrophages. In addition, OXLs decreased IL-8 production in HT-29 colon cells, the major chemokine produced by these cells. The interaction of OXLs with NFκB and PPAR-γ signaling pathways was studied by confocal microscopy. In THP-1 macrophages and HT-29 colon cells, stimulated by LPS and TNFα respectively, a pre-treatment with 13S-HOTE, 13S-HODE and 15S-HEPE (100μM) resulted in a lower nuclear presence of NFκB in both cell lines. The study of the subcellular localization of PPAR-γ showed that the treatment of THP-1 and HT-29 cells with these OXLs caused the migration of PPAR-γ into the nucleus. Colocalization analysis of both transcription factors in LPS-stimulated THP-1 macrophages showed that the pre-treatment with 13S-HOTE, 13S-HODE or 15S-HEPE lowered nuclear colocalization similar to control value, and increased cytosolic localization above control level. These results indicate that these OXLs could act as agonist of PPAR-γ and consequently inhibit NFκB signaling pathway activation, thus lowering the production of inflammatory markers, highlighting the therapeutic potential of these OXLs in inflammatory diseases such as IBD.

De novo Transcriptome Assembly of Phomopsis liquidambari Provides Insights into Genes Associated with Different Lifestyles in Rice (Oryza sativa L.)

The mechanisms that trigger the switch from endophytic fungi to saprophytic fungi are largely unexplored. Broad host range Phomopsis liquidambari is established in endophytic and saprophytic systems with rice (Oryza sativa L.). Endophytic P. liquidambari promotes rice growth, increasing rice yield and improving the efficiency of nitrogen fertilizer. This species's saprophytic counterpart can decompose rice litterfall, promoting litter organic matter cycling and the release of nutrients and improving the soil microbial environment. Fluorescence microscopy, confocal laser scanning microscopy and quantitative PCR investigated the colonization dynamics and biomass of P. liquidambari in rice in vivo. P. liquidambari formed infection structures similar to phytopathogens with infected vascular tissues that systematically spread to acrial parts. However, different from pathogenic infection, P. liquidambari colonization exhibits space restriction and quantity restriction. Direct comparison of a fungal transcriptome under three different habitats provided a better understanding of lifestyle conversion during plant-fungi interactions. The isolated total RNA of Ck (pure culture), EP (endophytic culture) and FP (saprophytic culture) was subjected to Illumina transcriptome sequencing. To the best of our knowledge, this study is the first to investigate Phomopsis sp. using RNA-seq technology to obtain whole transcriptome information. A total of 27,401,258 raw reads were generated and 22,700 unigenes were annotated. Functional annotation indicated that carbohydrate metabolism and biosynthesis of secondary metabolites played important roles. There were 2522 differentially expressed genes (DEGs) between the saprophytic and endophytic lifestyles. Quantitative PCR analysis validated the DEGs of RNA-seq. Analysis of DEGs between saprophytic and endophytic lifestyles revealed that most genes from amino acids metabolism, carbohydrate metabolism, fatty acid biosynthesis, secondary metabolism and terpenoid and steroid biosynthesis were up-regulated in EP. Secondary metabolites of these pathways may affect fungal growth and development and contribute to signaling communication with the host. Most pathways of xenobiotic biodegradation and metabolism were upregulated in FP. Cytochrome P450s play diverse vital roles in endophytism and saprophytism, as their highly specialized functions are evolutionarily adapted to various ecological niches. These results help to characterize the relationship between fungi and plants, the diversity of fungi for ecological adaptations and the application prospects for fungi in sustainable agriculture.

Anti-inflammatory effects of an oxylipin-containing lyophilised biomass from a microalga in a murine recurrent colitis model

Diet and nutritional factors have emerged as possible interventions for inflammatory bowel diseases (IBD), which are characterised by chronic uncontrolled inflammation of the intestinal mucosa. Microalgal species are a promising source of n-3 PUFA and derived oxylipins, which are lipid mediators with a key role in the resolution of inflammation. The aim of the present study was to investigate the effects of an oxylipin-containing lyophilised biomass from Chlamydomonas debaryana on a recurrent 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis mice model. Moderate chronic inflammation of the colon was induced in BALB/c mice by weekly intracolonic instillations of low dose of TNBS. Administration of the lyophilised microalgal biomass started 2 weeks before colitis induction and was continued throughout colitis development. Mice were killed 48 h after the last TNBS challenge. Oral administration of the microalgal biomass reduced TNBS-induced intestinal inflammation, evidenced by an inhibition of body weight loss, an improvement in colon morphology and a decrease in pro-inflammatory cytokines TNF-α, IL-1β, IL-6 and IL-17. This product also down-regulated colonic expressions of inducible nitric oxide, cyclo-oxygenase 2 and NF-κB, as well as increased PPAR-γ. In addition, lyophilised microalgal biomass up-regulated the expressions of the antioxidant transcription factor nuclear factor E2-related factor 2 and the target gene heme oxygenase 1. This study describes for the first time the prophylactic effects of an oxylipin-containing lyophilised microalgae biomass from C. debaryana in the acute phase of a recurrent TNBS-induced colitis model in mice. These findings suggest the potential use of this microalga, or derived oxylipins, as a nutraceutical in the treatment of IBD.

Cytotoxic Activity of Microalgal-derived Oxylipins against Human Cancer Cell lines and their Impact on ATP Levels

Oxylipins are metabolites derived from lipid peroxidation. The plant oxylipin methyl jasmonate (MJ) shows cytotoxic activity against cancer cell lines of various origins, with ATP-depletion being one of the mechanisms responsible for this effect. The cytotoxic activity of oxylipins (OXLs) isolated from the microalgae Chlamydomonas debaryana (13-HOTE) and Nannochloropsis gaditana (15-HEPE) was higher against UACC-62 (melanoma) than towards HT-29 (colon adenocarcinoma) cells. OXLs lowered the ATP levels of HT-29 and UACC-62 cells, but the effect was higher on the second cell line, which had higher basal ATP. This result proves a link between the cytotoxicity and the capability of these compounds to deplete ATP. In addition, the combination of 13-HOTE with the anticancer drug 5-fluorouracil (5-FU) induced a synergistic toxicity against HT-29 cells. These results highlight the therapeutic potential of oxylipins derived from microalgae.

Nitric oxide triggers a transient metabolic reprogramming in Arabidopsis

Nitric oxide (NO) regulates plant growth and development as well as responses to stress that enhanced its endogenous production. Arabidopsis plants exposed to a pulse of exogenous NO gas were used for untargeted global metabolomic analyses thus allowing the identification of metabolic processes affected by NO. At early time points after treatment, NO scavenged superoxide anion and induced the nitration and the S-nitrosylation of proteins. These events preceded an extensive though transient metabolic reprogramming at 6 h after NO treatment, which included enhanced levels of polyamines, lipid catabolism and accumulation of phospholipids, chlorophyll breakdown, protein and nucleic acid turnover and increased content of sugars. Accordingly, lipid-related structures such as root cell membranes and leaf cuticle altered their permeability upon NO treatment. Besides, NO-treated plants displayed degradation of starch granules, which is consistent with the increased sugar content observed in the metabolomic survey. The metabolic profile was restored to baseline levels at 24 h post-treatment, thus pointing up the plasticity of plant metabolism in response to nitroxidative stress conditions.

Quantitative analysis of 3-OH oxylipins in fermentation yeast

Despite the ubiquitous distribution of oxylipins in plants, animals, and microbes, and the application of numerous analytical techniques to study these molecules, 3-OH oxylipins have never been quantitatively assayed in yeasts. The formation of heptafluorobutyrate methyl ester derivatives and subsequent analysis with gas chromatography - negative chemical ionization - mass spectrometry allowed for the first determination of yeast 3-OH oxylipins. The concentration of 3-OH 10:0 (0.68-4.82 ng/mg dry cell mass) in the SMA strain of Saccharomyces pastorianus grown in laboratory-scale beverage fermentations was elevated relative to oxylipin concentrations in plant tissues and macroalgae. In fermenting yeasts, the onset of 3-OH oxylipin formation has been related to fermentation progression and flocculation initiation. When the SMA strain was grown in laboratory-scale fermentations, the maximal sugar consumption rate preceded the lowest concentration of 3-OH 10:0 by ∼4.5 h and a distinct increase in 3-OH 10:0 concentration by ∼16.5 h.

Lipid signalling in plant responses to abiotic stress

Lipids are one of the major components of biological membranes including the plasma membrane, which is the interface between the cell and the environment. It has become clear that membrane lipids also serve as substrates for the generation of numerous signalling lipids such as phosphatidic acid, phosphoinositides, sphingolipids, lysophospholipids, oxylipins, N-acylethanolamines, free fatty acids and others. The enzymatic production and metabolism of these signalling molecules are tightly regulated and can rapidly be activated upon abiotic stress signals. Abiotic stress like water deficit and temperature stress triggers lipid-dependent signalling cascades, which control the expression of gene clusters and activate plant adaptation processes. Signalling lipids are able to recruit protein targets transiently to the membrane and thus affect conformation and activity of intracellular proteins and metabolites. In plants, knowledge is still scarce of lipid signalling targets and their physiological consequences. This review focuses on the generation of signalling lipids and their involvement in response to abiotic stress. We describe lipid-binding proteins in the context of changing environmental conditions and compare different approaches to determine lipid-protein interactions, crucial for deciphering the signalling cascades.

Fatty acid esters produced by Lasiodiplodia theobromae function as growth regulators in tobacco seedlings

The Botryosphaeriaceae are a family of trunk disease fungi that cause dieback and death of various plant hosts. This work sought to characterize fatty acid derivatives in a highly virulent member of this family, Lasiodiplodia theobromae. Nuclear magnetic resonance and gas chromatography-mass spectrometry of an isolated compound revealed (Z, Z)-9,12-ethyl octadecadienoate, (trivial name ethyl linoleate), as one of the most abundant fatty acid esters produced by L. theobromae. A variety of naturally produced esters of fatty acids were identified in Botryosphaeriaceae. In comparison, the production of fatty acid esters in the soil-borne tomato pathogen Fusarium oxysporum, and the non-phytopathogenic fungus Trichoderma asperellum was found to be limited. Ethyl linoleate, ethyl hexadecanoate (trivial name ethyl palmitate), and ethyl octadecanoate, (trivial name ethyl stearate), significantly inhibited tobacco seed germination and altered seedling leaf growth patterns and morphology at the highest concentration (0.2 mg/mL) tested, while ethyl linoleate and ethyl stearate significantly enhanced growth at low concentrations, with both still inducing growth at 98 ng/mL. This work provides new insights into the role of naturally esterified fatty acids from L. theobromae as plant growth regulators with similar activity to the well-known plant growth regulator gibberellic acid.

Arabidopsis lipoxygenase 2 is essential for formation of green leaf volatiles and five-carbon volatiles

Plants biosynthesize a variety of bioactive lipid derivatives, such as green leaf volatiles (GLVs) and jasmonates (JAs). Here we identify a lipoxygenase 2 (LOX2) involved in GLV biosynthesis in Arabidopsis using mutant lines for each of the six LOX isoforms present in Arabidopsis. We found that formation of five carbon volatiles was also dependent on LOX2. LOX2 is known to be involved in formation of JA; thus, LOX2 is apparently versatile in function. The results in this study suggested that LOX2 activity is suppressed in intact cells but activated upon tissue damage to support the rapid GLV-burst observed in wounded leaves.

Targeting of the hydrophobic metabolome by pathogens

The hydrophobic molecules of the metabolome – also named the lipidome – constitute a major part of the entire metabolome. Novel technologies show the existence of a staggering number of individual lipid species, the biological functions of which are, with the exception of only a few lipid species, unknown. Much can be learned from pathogens that have evolved to take advantage of the complexity of the lipidome to escape the immune system of the host organism and to allow their survival and replication. Different types of pathogens target different lipids as shown in interaction maps, allowing visualization of differences between different types of pathogens. Bacterial and viral pathogens target predominantly structural and signaling lipids to alter the cellular phenotype of the host cell. Fungal and parasitic pathogens have complex lipidomes themselves and target predominantly the release of polyunsaturated fatty acids from the host cell lipidome, resulting in the generation of eicosanoids by either the host cell or the pathogen. Thus, whereas viruses and bacteria induce predominantly alterations in lipid metabolites at the host cell level, eukaryotic pathogens focus on interference with lipid metabolites affecting systemic inflammatory reactions that are part of the immune system. A better understanding of the interplay between host–pathogen interactions will not only help elucidate the fundamental role of lipid species in cellular physiology, but will also aid in the generation of novel therapeutic drugs.

Freshwater dispersion stability of PAA-stabilised cerium oxide nanoparticles and toxicity towards Pseudokirchneriella subcapitata

An aqueous dispersion of poly (acrylic acid)-stabilised cerium oxide (CeO₂) nanoparticles (PAA-CeO₂) was evaluated for its stability in a range of freshwater ecotoxicity media (MHRW, TG 201 and M7), with and without natural organic matter (NOM). In a 15 day dispersion stability study, PAA-CeO₂ did not undergo significant aggregation in any media type. Zeta potential varied between media types and was influenced by PAA-CeO₂ concentration, but remained constant over 15 days. NOM had no influence on PAA-CeO₂ aggregation or zeta potential. The ecotoxicity of the PAA-CeO₂ dispersion was investigated in 72 h algal growth inhibition tests using the freshwater microalgae Pseudokirchneriella subcapitata. PAA-CeO₂ EC₅₀ values for growth inhibition (GI; 0.024 mg/L) were 2-3 orders of magnitude lower than pristine CeO₂ EC₅₀ values reported in the literature. The concentration of dissolved cerium (Ce(3+)/Ce(4+)) in PAA-CeO₂ exposure suspensions was very low, ranging between 0.5 and 5.6 μg/L. Free PAA concentration in the exposure solutions (0.0096-0.0384 mg/L) was significantly lower than the EC10 growth inhibition (47.7 mg/L) value of pure PAA, indicating that free PAA did not contribute to the observed toxicity. Elemental analysis indicated that up to 38% of the total Cerium becomes directly associated with the algal cells during the 72 h exposure. TOF-SIMS analysis of algal cell wall compounds indicated three different modes of action, including a significant oxidative stress response to PAA-CeO₂ exposure. In contrast to pristine CeO₂ nanoparticles, which rapidly aggregate in standard ecotoxicity media, PAA-stabilised CeO₂ nanoparticles remain dispersed and available to water column species. Interaction of PAA with cell wall components, which could be responsible for the observed biomarker alterations, could not be excluded. This study indicates that the increased dispersion stability of PAA-CeO₂ leads to an increase in toxicity compared to pristine non-stabilised forms.