Caleosin/Peroxygenases:multifunctional proteins in plants

BACKGROUND: Caleosin/peroxygenases (CLO/PXGs) are a family of multifunctional proteins that are ubiquitous in land plants and also found in some fungi and green algae. CLO/PXGs were initially described as a class of plant lipid-associated proteins with some similarities to the oleosins that stabilize lipid droplets (LDs) in storage tissues such as seeds. However, we now know that CLO/PXGs have more complex structure, distribution and functions than oleosins. Structurally, CLO/PXGs share conserved domains that confer specific biochemical features with diverse localizations and functions.SCOPE: This review surveys the structural properties of CLO/PXGs and their biochemical roles. In addition to their highly conserved structures, CLO/PXGs have peroxygenase activities and are involved in several aspects of oxylipin metabolism in plants. The enzymatic activities and the spatiotemporal expression of CLO/PXGs are described and linked with their wider involvement in plant physiology. Plant CLO/PXGs have many roles in both biotic and abiotic stress responses in plants and in their responses to environmental toxins. Finally, some intriguing developments in the biotechnological uses of CLO/PXGs are addressed.CONCLUSIONS: It is now two decades since caleosin/peroxygenases (CLO/PXGs) were first recognized as a new class of lipid-associated proteins, and only 15 years since their additional enzymatic functions as a novel class of peroxygenases was discovered. There are many interesting research questions that remain to be addressed in future physiological studies of plant CLO/PXGs and also their recently discovered roles in the sequestration and possibly detoxification of a wide variety of lipidic xenobiotics that can challenge plant welfare.</p

Biochemical, Transcriptional, and Bioinformatic Analysis of Lipid Droplets from Seeds of Date Palm (Phoenix dactylifera L.) and Their Use as Potent Sequestration Agents against the Toxic Pollutant, 2,3,7,8-Tetrachlorinated Dibenzo-p-Dioxin

Contamination of aquatic environments with dioxins, the most toxic group of persistent organic pollutants (POPs), is a major ecological issue. Dioxins are highly lipophilic and bioaccumulate in fatty tissues of marine organisms used for seafood where they constitute a potential risk for human health. Lipid droplets (LDs) purified from date palm, Phoenix dactylifera, seeds were characterized and their capacity to extract dioxins from aquatic systems was assessed. The bioaffinity of date palm LDs toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins was determined. Fractioned LDs were spheroidal with mean diameters of 2.5 µm, enclosing an oil-rich core of 392.5 mg mL(-1). Isolated LDs did not aggregate and/or coalesce unless placed in acidic media and were strongly associated with three major groups of polypeptides of relative mass 32–37, 20–24, and 16–18 kDa. These masses correspond to the LD-associated proteins, oleosins, caleosins, and steroleosins, respectively. Efficient partitioning of TCDD into LDs occurred with a coefficient of log K(LB/w,TCDD) = 7.528 ± 0.024; it was optimal at neutral pH and was dependent on the presence of the oil-rich core, but was independent of the presence of LD-associated proteins. Bioinformatic analysis of the date palm genome revealed nine oleosin-like, five caleosin-like, and five steroleosin-like sequences, with predicted structures having putative lipid-binding domains that match their LD stabilizing roles and use as bio-based encapsulation systems. Transcriptomic analysis of date palm seedlings exposed to TCDD showed strong up-regulation of several caleosin and steroleosin genes, consistent with increased LD formation. The results suggest that the plant LDs could be used in ecological remediation strategies to remove POPs from aquatic environments. Recent reports suggest that several fungal and algal species also use LDs to sequester both external and internally derived hydrophobic toxins, which indicates that our approach could be used as a broader biomimetic strategy for toxin removal

ALPHA-OXYDATION D'ACIDES GRAS DANS LE SOJA

STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Peroxygénase végétale (Double localisation d'une oxygénase originale)

L'intérêt pour le métabolisme et les rôles physiologiques des oxylipines s'est accru ces dernières années puisque ces composés semblent être impliqués dans les phénomènes d'infection. Chez la plante, les phytooxylipines dérivent essentiellement de l'acide linoléique (C18:2) et de l'acide linolénique (C18:3) par la voie de la lipoxygénase. Les hydroperoxydes formés par la lipoxygénase sont rapidement métabolisés en composés physiologiquement actifs, sous l'action de CYP74s et d'une peroxygénase (PXG). Cette enzyme, qui catalyse des réactions d'oxydation, est une hémoprotéine membranaire, unique par son mécanisme catalytique puisqu'elle ne présente aucune homologie de séquence avec des oxydases. Métabolisant aussi bien des hydroperoxydes d'acides gras, substrats de CYP74, que l'eau oxygénée, substrat des peroxydases, j'ai recherché les caractéristiques moléculaires qui confèrent son originalité à la peroygénase en identifiant le mode de coordination de son hème. J'ai pu montrer que chez AtPXG1, ce groupement prosthétique n'était pas lié par l'intermédiaire d'une cystéine comme chez les CYP74s, mais à un résidu histidine. Ces résultats, obtenus par mutagenèse dirigée et confirmés par RPE identifient chez AtPXG1 un hème dont le fer est coordonné via un résidu histidine. J'ai montré que les différentes isoformes possédaient des spécificités de réactions différentes. Afin d'apporter des éléments réponses aux rôles physiologiques de la peroxygénase, j'ai localisé, par fusion à la GFP, AtPXG1 et AtPXG3 dans le réticulum endoplasmique et les oléosomes, des organites constitués d'un noyau de lipides neutres entourés d'une monocouche phospholipidique et protéique. J'ai montré qu'une signature de type FFAT ciblait la peroxygénase vers le RE et qu'une signature de type DXE permettait son export du RE vers les oléosomes. Cet export serait dépendant de la protéine Sar1, un élément du complexe COPII qui permet l'export des protéines du réticulum vers l'appareil de Golgi.During the last decade, increasing interest in oxygenated fatty acids, collectively named oxylipins, has been generated as these metabolites are considered to be involved in infection. In plants, oxylipins mainly derive from linole(n)ic acid via the lipoxygenase pathway. Fatty acids hydroperoxyds produced by lipoxygenase are rapidly metabolised in a variety of physiologically active derivatives by CYP74s and by peroxygénase (PXG). This later membrane bound hemoprotein catalyses reaction of oxydation by a mechanism which seems to be quite unique and surprisingly, it do not presents any homology with presently known oxidases. Peroxygenase is able to metabolise fatty acid hydroperoxyds (CYP74's substrate) as good as hydrogen peroxyd (peroxydase's substrate), raising questions about peroxygenase original mechanism origin which I try to characterize in studying the mode of linking of the heme iron. By site-directed mutagenesis experiments on AtPXG1, I found that the heme was not coordinated by cysteine residues like in CYP74s but to a histidine residue like in peroxydases. These results were confirmed by EPR, identifying an heme in which iron is coordinated via an histidine residue. In a second time, I have demonstrated that different isoforms differ from each other by various reactions specificity. In order to find some answer concerning plant peroxygénase physiological function, I have localized, by GFP fused strategy, AtPXG1 and AtPXG3 isoforms in endoplasmic reticulum and in lipid bodies, which are organelles constituted by a neutral lipid core surrounded by a proteic and phospholipid monolayer. I demonstrated that an FFAT motif was responsible of peroxygénase targeting to reticulum and that a DXE motif permit its export from RE to lipid bodies. First experiment round seems to demonstrate that this export is dependant from Sar1, an element of COPII complex, responsible of protein export from RE to Golgi apparatus.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

LIPIDES DES PLANTES Symposium « Lipides des plantes et oxylipines » : compte rendu et mise en place d’un réseau lipides des plantes

Un colloque sur les lipides de plantes et les oxylipines s’est tenu à Strasbourg les 10 et 11 juillet 2001, dans le cadre des Journées de la Société Française de Physiologie Végétale. Plus de 85 chercheurs ont participé à ce colloque et 45 communications ont été faites. La plupart ont porté sur la synthèse des stérols et des isoprénoïdes, le métabolisme des lipides, les relations entre le stress thermique et les lipides membranaires ainsi que sur les oxylipines. Les conférences plénières ont été données par le Pr Heinz sur les cérébrosides et les stérols glucosides, le Dr R. Verger sur les lipases et le Dr I. Feussner sur les oxylipines. Une table ronde s’est tenue pour discuter de la constitution d’un réseau réunissant les spécialistes des lipides des plantes en France. L’idée a été accueillie favorablement par tous les participants et il a été envisagé de créer un site « web » contenant un annuaire des chercheurs, des cahiers de protocoles et une base de données bibliographiques. Ceci se fera en collaboration étroite avec les chercheurs européens et américains de la spécialité

LIPIDES DES PLANTES Symposium « Lipides des plantes et oxylipines » : compte rendu et mise en place d’un réseau lipides des plantes

Un colloque sur les lipides de plantes et les oxylipines s’est tenu à Strasbourg les 10 et 11 juillet 2001, dans le cadre des Journées de la Société Française de Physiologie Végétale. Plus de 85 chercheurs ont participé à ce colloque et 45 communications ont été faites. La plupart ont porté sur la synthèse des stérols et des isoprénoïdes, le métabolisme des lipides, les relations entre le stress thermique et les lipides membranaires ainsi que sur les oxylipines. Les conférences plénières ont été données par le Pr Heinz sur les cérébrosides et les stérols glucosides, le Dr R. Verger sur les lipases et le Dr I. Feussner sur les oxylipines. Une table ronde s’est tenue pour discuter de la constitution d’un réseau réunissant les spécialistes des lipides des plantes en France. L’idée a été accueillie favorablement par tous les participants et il a été envisagé de créer un site « web » contenant un annuaire des chercheurs, des cahiers de protocoles et une base de données bibliographiques. Ceci se fera en collaboration étroite avec les chercheurs européens et américains de la spécialité

Biochemical, transcriptional, and bioinformatic analysis of lipid droplets from seeds of date palm ('Phoenix dactylifera' L.) and their use as potent sequestration agents against the toxic pollutant, 2,3,7,8-tetrachlorinated dibenzo-p-dioxin

Contamination of aquatic environments with dioxins, the most toxic group of persistent organic pollutants (POPs), is a major ecological issue. Dioxins are highly lipophilic and bioaccumulate in fatty tissues of marine organisms used for seafood where they constitute a potential risk for human health. Lipid droplets (LDs) purified from date palm, 'Phoenix dactylifera', seeds were characterized and their capacity to extract dioxins from aquatic systems was assessed. The bioaffinity of date palm LDs toward 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the most toxic congener of dioxins was determined. Fractioned LDs were spheroidal with mean diameters of 2.5 µm, enclosing an oil-rich core of 392.5 mg mL-1. Isolated LDs did not aggregate and/or coalesce unless placed in acidic media and were strongly associated with three major groups of polypeptides of relative mass 32–37, 20–24, and 16–18 kDa. These masses correspond to the LD-associated proteins, oleosins, caleosins, and steroleosins, respectively. Efficient partitioning of TCDD into LDs occurred with a coefficient of log KLB/w,TCDD = 7.528 ± 0.024; it was optimal at neutral pH and was dependent on the presence of the oil-rich core, but was independent of the presence of LD-associated proteins. Bioinformatic analysis of the date palm genome revealed nine oleosin-like, five caleosin-like, and five steroleosin-like sequences, with predicted structures having putative lipid-binding domains that match their LD stabilizing roles and use as bio-based encapsulation systems. Transcriptomic analysis of date palm seedlings exposed to TCDD showed strong up-regulation of several caleosin and steroleosin genes, consistent with increased LD formation. The results suggest that the plant LDs could be used in ecological remediation strategies to remove POPs from aquatic environments. Recent reports suggest that several fungal and algal species also use LDs to sequester both external and internally derived hydrophobic toxins, which indicates that our approach could be used as a broader biomimetic strategy for toxin removal