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The oxygenated derivatives of fatty acids, known as oxylipins, are pivotal signaling molecules in animals and terrestrial plants. In animal systems, eicosanoids regulate cell differentiation, immune responses, and homeostasis. In contrast, terrestrial plants use derivatives of C18 and C16 fatty acids as developmental or defense hormones. Marine algae have emerged early in the evolution of eukaryotes as several distinct phyla, independent from the animal and green-plant lineages. The occurrence of oxylipins of the eicosanoid family is well documented in marine red algae, but their biological roles remain an enigma. Here we address the hypothesis that they are involved with the defense mechanisms of the red alga Chondrus crispus. By investigating its association with a green algal endophyte Acrochaete operculata, which becomes invasive in the diploid generation of this red alga, we showed that (1) when challenged by pathogen extracts, the resistant haploid phase of C. crispus produced both C20 and C18 oxylipins, (2) elicitation with pathogen extracts or methyl jasmonate activated the metabolism of C20 and C18 polyunsaturated fatty acids to generate hydroperoxides and cyclopentenones such as prostaglandins and jasmonates, and (3) C20 and C18 hydroperoxides as well as methyl jasmonate did induce shikimate dehydrogenase and Phe ammonialyase activities in C. crispus and conferred an induced resistance to the diploid phase, while inhibitors of fatty acid oxidation reduced the natural resistance of the haploid generation. The dual nature of oxylipin metabolism in this alga suggests that early eukaryotes featured both animal-(eicosanoids) and plant-like (octadecanoids) oxylipins as essential components of innate immunity mechanisms.Signaling cascades involving compounds derived from the oxidative metabolism of polyunsaturated fatty acids (PUFAs) are known to operate in response to external stimuli in both terrestrial plants and animals. In animal systems, eicosanoids, i.e. hydroperoxides derived from C20 PUFAs, regulate cell differentiation, immune responses, and homeostasis (Funk, 2001). In contrast, terrestrial plants use derivatives of C18 (octadecanoids) and C16 (hexadecanoids) fatty acids as developmental or defense hormones (Weber, 2002). The biosynthesis of these so-called oxylipins involves lipoxygenases (LOXs), which are multifunctional enzymes that catalyze the oxygenation of PUFAs into hydroperoxy derivatives, then on to other secondary products (Funk, 2001;Howe and Schilmiller, 2002). In terrestrial higher plants, this leads to the synthesis of the cyclopentenone jasmonic acid (JA), a key defense hormone described in a variety of crops or cell cultures (Heitz et al., 1997;Ishiguro et al., 2001;Seo et al., 2001;Turner et al., 2002). In animals, an alternative pathway involving cyclooxygenases also leads to the synthesis of important hormones with a cyclopentenone structure, known as prostaglandins (Funk, 2001). Another pathway derived from phospholipase-released arachidonic acid, involving 5-LOX, generates oth...

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Summary To better understand the toxicity and the orchestration of antioxidant defenses of marine brown algae in response to copper‐induced stress, lipid peroxidation processes were investigated in the brown alga Laminaria digitata. The expression of genes involved in cell protection and anti‐oxidant responses were monitored by semi‐quantitative reverse transcriptase polymerase chain reaction and the lipid peroxidation products were further characterized by profiling oxylipin signatures using high‐pressure liquid chromatography–mass spectrometry. Exposure to copper excess triggers lipoperoxide accumulation and upregulates the expression of stress related genes. It also increases the release of free polyunsaturated fatty acids, leading to an oxidative cascade through at least two distinct mechanisms. Incubations in presence of inhibitors of lipoxygenases and cycloxygenases showed that in addition to the reactive oxygen species‐mediated processes, copper stress induces the synthesis of oxylipins through enzymatic mechanisms. Among complex oxylipins, cyclopentenones from C18 and C20 fatty acids such as 12‐oxo‐PDA and prostaglandins were detected for the first time in brown algae, as well as unique compounds such as the 18‐hydroxy‐17‐oxo‐eicosatetraenoic acid. These results suggest that lipid peroxidation participates in the toxic effects of copper and that lipid peroxidation derivatives may regulate protective mechanisms by employing plant‐like octadecanoid signals but also eicosanoid oxylipins which are absent in vascular plants.

Arachidonic acid, linolenic acid and methyl jasmonate (MeJA) were found to be strong triggers of an oxidative burst in the kelp Laminaria digitata. These findings constitute the first report of an oxidative burst in an algal system induced by free fatty acids. The source of reactive oxygen species can be at least partially inhibited by diphenylene iodonium (DPI). Treatment with arachidonic acid increases the levels of a number of free fatty acids [including myristic (C14:0), linoleic (C18:2), linolenic (C18:3) and eicosapentaeneoic (C20:5) acids] and hydroxylated derivatives [such as 15-hydroxyeicosatetraenoic acid (15-HETE), 13-hydroxyoctadecatrienoic acid (13-HOTE) and 15-hydroxyeicosapentaenoic acid (15-HEPE)]. Similar to a previous report of the function of an alginate oligosaccharide-triggered oxidative burst in the establishment of resistance in L. digitata against infection by its brown algal endophyte Laminariocolax tomentosoides, C20:4- and MeJA-induced oxidative bursts seem to be involved in establishing the same protection in L. digitata. Altogether, this study supports the notion that lipid oxidation signaling plays a key role in defense induction in marine brown algae.

The chemical tagging of a cytochrome P-450-dependent lauric acid omega-hydroxylase from clofibrate-treated Vicia sativa seedlings with [1-14C]11-dodecynoic acid allowed the isolation of a full-length cDNA designated CYP94A1. We describe here the functional expression of this novel P-450 in two Saccharomyces cerevisiae strains overproducing their own NADPH-cytochrome P-450 reductase or a reductase from Arabidopsis thaliana. The results show a much higher efficiency of the yeast strain overproducing the plant reductase compared with the yeast strain overproducing its own reductase for expressing CYP94A1. The methyl end of saturated (from C-10 to C-16) and unsaturated (C18:1, C18:2 and C18:3) fatty acids was mainly oxidized by CYP94A1. Both E/Z and Z/E configurations of 9, 12-octadecadienoic acids were omega-hydroxylated. Lauric, myristic and linolenic acids were oxidized with the highest turnover rate (24 min-1). The strong regioselectivity of CYP94A1 was clearly shifted with sulphur-containing substrates, since both 9- and 11-thia laurate analogues were sulphoxidized. Similar to animal omega-hydroxylases, this plant enzyme was strongly induced by clofibrate treatment. Rapid CYP94A1 transcript accumulation was detected less than 20 min after exposure of seedlings to the hypolipidaemic drug. The involvement of CYP94A1 in the synthesis of cutin monomers and fatty acid detoxification is discussed.

Human CYP450 v-hydroxylases of the CYP4 family are known to convert arachidonic acid (AA) to its metabolite . This study deals with hydroxylations of four PUFAs, eicosatrienoic acid (ETA), AA, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) by either human recombinant CYP4s enzymes or human liver microsomal preparations. CYP4F3A and CYP4F3B were the most efficient v-hydroxylases of these PUFAs. Moreover, the differences in the number of unsaturations of ETA, AA, and EPA allowed us to demonstrate a rise in the metabolic rate of hydroxylation when the double bond in 14-15 or 17-18 was missing. With the CYP4F enzymes, the main pathway was always the v-hydroxylation of PUFAs, whereas it was the (v-1)-hydroxylation with CYP1A1, CYP2C19, and CYP2E1. Finally, we demonstrated that the v9 and v3 PUFAs (ETA, EPA, and DHA) could all be used as alternative substrates in AA metabolism by human CYP4F2 and -4F3B. Thus, they decreased the ability of these enzymes to convert AA to 20-HETE. However, although ETA was the most hydroxylated substrate, EPA and DHA were the most potent inhibitors of the conversion of AA to 20-HETE. These findings suggest that some physiological effects of v3 FAs could partly result from a shift in the generation of active hydroxylated metabolites of AA through a CYP-mediated catalysis.-Fer, M., L. Corcos, Y. Dréano, E. Plée-Gautier, J-P. Salaün, F. Berthou, and Y. Amet. Cytochromes P450 from family 4 are the main omega hydroxylating enzymes in humans: CYP4F3B is the prominent player in PUFA metabolism. J. Lipid Res. 2008Res. . 49: 2379Res. -2389