Waterborne Signaling Primes the Expression of Elicitor-Induced Genes and Buffers the Oxidative Responses in the Brown Alga Laminaria digitata

As marine sessile organisms, seaweeds must respond efficiently to biotic and abiotic challenges in their natural environment to reduce the fitness consequences of wounds and oxidative stress. This study explores the early steps of the defense responses of a large marine brown alga (the tangle kelp Laminaria digitata) and investigates its ability to transmit a warning message to neighboring conspecifics. We compared the early responses to elicitation with oligoguluronates in laboratory-grown and harvested wild individuals of L. digitata. We followed the release of H2O2 and the concomitant production of volatile organic compounds. We also monitored the kinetics of expression of defense-related genes following the oxidative burst. Laboratory-grown algae were transplanted in kelp habitats to further evaluate their responses to elicitation after a transient immersion in natural seawater. In addition, a novel conditioning procedure was established to mimic field conditions in the laboratory. Our experiments showed that L. digitata integrates waterborne cues present in the kelp bed and/or released from elicited neighboring plants. Indeed, the exposure to elicited conspecifics changes the patterns of oxidative burst and volatile emissions and potentiates this kelp for faster induction of genes specifically regulated in response to oligoguluronates. Thus, waterborne signals shape the elicitor-induced responses of kelps through a yet unknown mechanism reminiscent of priming in land plants

Mass Spectrometry-Based Metabolomics to Elucidate Functions in Marine Organisms and Ecosystems

Marine systems are very diverse and recognized as being sources of a wide range of biomolecules. This review provides an overview of metabolite profiling based on mass spectrometry (MS) approaches in marine organisms and their environments, focusing on recent advances in the field. We also point out some of the technical challenges that need to be overcome in order to increase applications of metabolomics in marine systems, including extraction of chemical compounds from different matrices and data management. Metabolites being important links between genotype and phenotype, we describe added value provided by integration of data from metabolite profiling with other layers of omics, as well as their importance for the development of systems biology approaches in marine systems to study several biological processes, and to analyze interactions between organisms within communities. The growing importance of MS-based metabolomics in chemical ecology studies in marine ecosystems is also illustrated

Identification et dosage de dérivés oxydés d'acides gras polyinsaturés dans les milieux biologiques par une approche métabolomique ciblée

Les oxylipides/oxylipines, dérivés oxydés d'acides gras polyinsaturés, jouent un rôle important dans la signalisation lipidique, en réponse à un stress biotique ou abiotique, chez les animaux comme chez les végétaux. Nous avons mis au point des méthodes spécifiques de dosage des oxylipides dans des échantillons biologiques d'origine humaine et phycologique (algues). Ces méthodes font appel à la spectrométrie de masse couplée à la chromatographie en phase gazeuse ou liquide (GC/MS/NCI et LC/MS). Ainsi, nous avons : -établi une méthode de dosage des EETs dans le sang humain par GC/MS/NCI. Ces métabolites époxydés de l'acide arachidonique (AA) par les cytochromes P450 ont des propriétés de vasorelaxation. -mis en évidence la production de 20-HETE, métabolite de l'AA, par le CYFP dans une lignée hépatomateuse humaine, HepaRG. -étudié la formation des énantiomères du 19,20-époxyde de l'acide docosahaénoïque (DHA) après incubation de cytochromes P450 recombinants humains avec du [14C]-DHA, ainsi que leur séparation sur colonne chirale. -identifié une signature oxylipidique de la réponse de l'algue brune Laminaria digitata au stress induit par le cuivre, révélant des voies de synthèse enzymatique et chimique ainsi qu'un nouveau composé : l'acide 18-hydroxy, 17-oxo-eicosatétranoïque. -mis en évidence l'émission d'aldéhydes polyinsaturés par les algues en réponse à un stress. Ces composés sont impliqués dans la communication interplante menant à une potentialisation des défenses face au stress biotique mimé par les oligoguluronates. Ces résultats devraient contribuer à une meilleure compréhension du rôle des oxylipides chez l'homme comme chez l'algue.Oxylipids/oxylipins, oxidized derivatives of polyunsaturated fatty acids, play a major role in lipid signalization, during biotic or abiotic stress, in both mammals ans in higher plants. We established specific methods for quantifying oxylipids in biological samples of human or phycologic (algae) origin. These methods are based on mass spectrometry coupled with gas or liquid chromatography (GC/MS/NCI and LC/MS). Thus, we have : -established a quantification method of EETs from human blood by GC/MS/NCI. These arachidonic acid (AA) metabolites by the action of cytochromes P450, have vasorelaxation properties. -highlighted the specific production of 20-HETE, an AA metabolite, by the CYP4F3B in a human hepatoma cell line, HepaRG. -studied the formation of docosahexaenoic acid (DHA) 19,20-epoxide enantiomers after incubation of recombinant human cytochromes P450 with [14C]-DHA and their separation on a chiral column. -identified an oxylipin signature of the response of the brown marine alga Laminaria digitata during abiotic stress, induced by copper, revealing enzymatic and chemical synthesis pathways. The presence of a new compound, the 18-hydroxy, 17-oxo-eicosatetraenoic acid has been described. -highlighted the polyinsaturated aldehyde emission in response to stress in this alga. These compounds are involved in distance signaling and inter-plant communication leading to a priming of defenses during a biotic stress mimicked by oligoguluronates. These results could allow a better comprehension of the oxylipid role in man as algae.BREST-BU Médecine-Odontologie (290192102) / SudocSudocFranceF

Microbiota Influences Morphology and Reproduction of the Brown Alga Ectocarpus sp.

International audienceAssociated microbiota play crucial roles in health and disease of higher organisms. For macroalgae, some associated bacteria exert beneficial effects on nutrition, morphogenesis and growth. However, current knowledge on macroalgae–microbiota interactions is mostly based on studies on green and red seaweeds. In this study, we report that when cultured under axenic conditions, the filamentous brown algal model Ectocarpus sp. loses its branched morphology and grows with a small ball-like appearance. Nine strains of periphytic bacteria isolated from Ectocarpus sp. unialgal cultures were identified by 16S rRNA sequencing, and assessed for their effect on morphology, reproduction and the metabolites secreted by axenic Ectocarpus sp. Six of these isolates restored morphology and reproduction features of axenic Ectocarpus sp. Bacteria-algae co-culture supernatants, but not the supernatant of the corresponding bacterium growing alone, also recovered morphology and reproduction of the alga. Furthermore, colonization of axenic Ectocarpus sp. with a single bacterial isolate impacted significantly the metabolites released by the alga. These results show that the branched typical morphology and the individuals produced by Ectocarpus sp. are strongly dependent on the presence of bacteria, while the bacterial effect on the algal exometabolome profile reflects the impact of bacteria on the whole physiology of this alga

Constitutive or Inducible Protective Mechanisms against UV-B Radiation in the Brown Alga Fucus vesiculosus? A Study of Gene Expression and Phlorotannin Content Responses.

A role as UV sunscreens has been suggested for phlorotannins, the phenolic compounds that accumulate in brown algae in response to a number of external stimuli and take part in cell wall structure. After exposure of the intertidal brown alga Fucus vesiculosus to artificial UV-B radiation, we examined its physiological responses by following the transcript level of the pksIII gene encoding a phloroglucinol synthase, likely to be involved in the first step of phlorotannins biosynthesis. We also monitored the expression of three targeted genes, encoding a heat shock protein (hsp70), which is involved in global stress responses, an aryl sulfotransferase (ast), which could be involved in the sulfation of phlorotannins, and a vanadium bromoperoxidase (vbpo), which can potentially participate in the scavenging of Reactive Oxygen Species (ROS) and in the cross-linking and condensation of phlorotannins. We investigated whether transcriptional regulation of these genes is correlated with an induction of phlorotannin accumulation by establishing metabolite profiling of purified fractions of low molecular weight phlorotannins. Our findings demonstrated that a high dose of UV-B radiation induced a significant overexpression of hsp70 after 12 and 24 hours following the exposure to the UV-B treatment, compared to control treatment. The physiological performance of algae quantified by the photosynthetic efficiency (Fv/Fm) was slightly reduced. However UV-B treatment did not induce the accumulation of soluble phlorotannins in F. vesiculosus during the kinetics of four weeks, a result that may be related to the lack of induction of the pksIII gene expression. Taken together these results suggest a constitutive accumulation of phlorotannins occurring during the development of F.vesiculosus, rather than inducible processes. Gene expression studies and phlorotannin profiling provide here complementary approaches to global quantifications currently used in studies of phenolic compounds in brown algae

Differential induction of oxylipin pathway in potato and tobacco cells by bacterial and oomycete elicitors

International audiencePotato and tobacco cells are differentially suited to study oxylipin pathway and elicitor-induced responses. Synthesis of oxylipins via the lipoxygenase (LOX) pathway provides plant cells with an important class of signaling molecules, related to plant stress responses and innate immunity. The aim of this study was to evaluate the induction of LOX pathway in tobacco and potato cells induced by a concentrated culture filtrate (CCF) from Phytophthora infestans and lipopolysaccharide (LPS) from Pectobacterium atrosepticum. Oxylipin activation was evaluated by the measurement of LOX activity and metabolite quantification. The basal levels of oxylipins and fatty acids showed that potato cells contained higher amounts of linoleic (LA), linolenic (LnA) and stearic acids than tobacco cells. The major oxylipin in potato cells, 9(S),10(S),11(R)-trihydroxy-12(Z),15(Z)-octadecadienoic acid (9,10,11-THOD), was not detected in tobacco cells. CCF induced a sharp increase of LA and LnA at 8 h in tobacco cells. In contrast they decreased in potato cells. In CCF-treated tobacco cells, colneleic acid increased up to 24 h, colnelenic acid and 9(S)-hydroxyoctadecatrienoic acid (9(S)-HOT) increased up to 16 h. In potato cells, only colneleic acid increased slightly until 16 h. A differential induction of LOX activity was measured in both cells treated by CCF. With LPS treatment, only 9,10,11-THOD accumulation was significantly induced at 16 h in potato cells. Fatty acids were constant in tobacco but decreased in potato cells over the studied time period. These results showed that the two elicitors were differently perceived by the two Solanaceae and that oxylipin pathway is strongly induced in tobacco with the CCF. They also revealed that elicitor-induced responses depended on both cell culture and elicitor

Impact of abiotic stresses on the protection efficacy of defence elicitors and on metabolic regulation in tomato leaves infected by Botrytis cinerea

International audienceFinding sustainable plant protection strategies is a major challenge for agriculture. Taking advantage of the plant natural immune system by using plant defence elicitors is an interesting avenue to explore. However, transfer to field application is often difficult, mostly due to the complexity of interactions between plants and their environment, involving biotic and abiotic stresses. The protection efficacy against gray mold and the modes of action of potential elicitors were studied on tomato. Modulation of plant defense was studied using both global and targeted metabolic profiling. We identified seven potential elicitors showing good plant protection efficacy and able to trigger the oxylipin pathway, including jasmonic acid production, after inoculation with Botrytis cinerea. Following preliminary assays, seven elicitors including two well-studied elicitors (Bion 50WG® and BABA) showing good plant protection efficacy and low fungitoxic effect were selected to assay the effect of abiotic stresses (wounding, water stress and nitrogen deficiency) on their protection efficacy. Our results showed that the protection efficacy of all products was reduced when plants were exposed to abiotic stresses, suggesting an antagonistic interaction between the tomato responses to abiotic stresses and product treatments. We found that responses to leaf cuttings and product treatments induced metabolic changes in a time-dependent manner, and that both of which mainly activated the oxylipin and JA pathway. However, the negative effects of wounding on tomato protection efficacy of defence elicitors suggest that interplay with other antagonistic signalling pathways is also involved in the tomato responses to this combination of stress