Flavin-Dependent Monooxygenases as a Detoxification Mechanism in Insects: New Insights from the Arctiids (Lepidoptera)

Insects experience a wide array of chemical pressures from plant allelochemicals and pesticides and have developed several effective counterstrategies to cope with such toxins. Among these, cytochrome P450 monooxygenases are crucial in plant-insect interactions. Flavin-dependent monooxygenases (FMOs) seem not to play a central role in xenobiotic detoxification in insects, in contrast to mammals. However, the previously identified senecionine N-oxygenase of the arctiid moth Tyria jacobaeae (Lepidoptera) indicates that FMOs have been recruited during the adaptation of this insect to plants that accumulate toxic pyrrolizidine alkaloids. Identification of related FMO-like sequences of various arctiids and other Lepidoptera and their combination with expressed sequence tag (EST) data and sequences emerging from the Bombyx mori genome project show that FMOs in Lepidoptera form a gene family with three members (FMO1 to FMO3). Phylogenetic analyses suggest that FMO3 is only distantly related to lepidopteran FMO1 and FMO2 that originated from a more recent gene duplication event. Within the FMO1 gene cluster, an additional gene duplication early in the arctiid lineage provided the basis for the evolution of the highly specific biochemical, physiological, and behavioral adaptations of these butterflies to pyrrolizidine-alkaloid-producing plants. The genes encoding pyrrolizidine-alkaloid-N-oxygenizing enzymes (PNOs) are transcribed in the fat body and the head of the larvae. An N-terminal signal peptide mediates the transport of the soluble proteins into the hemolymph where PNOs efficiently convert pro-toxic pyrrolizidine alkaloids into their non-toxic N-oxide derivatives. Heterologous expression of a PNO of the generalist arctiid Grammia geneura produced an N-oxygenizing enzyme that shows noticeably expanded substrate specificity compared with the related enzyme of the specialist Tyria jacobaeae. The data about the evolution of FMOs within lepidopteran insects and the functional characterization of a further member of this enzyme family shed light on this almost uncharacterized detoxification system in insects

Chemical defence of larvae of Chrysomela tremulae (Chrysomelidae)

Larven der Blattkäfer (Chrysomeliden) schützen sich durch chemische Substanzen vor Fraßfeinden. Spezies der Unterfamilie Chrysomelina produzieren Substanzen in Wehrdrüsen, die sich im Meso- und Metathorax sowie den sieben Abdominalsegmenten befinden. Bei Störung wird die Wehrsubstanz nach außen gedrückt, so dass auf der Körperoberfläche der Larve ein Tropfen erscheint. Diese leicht flüchtigen Substanzen umgeben die Larve wie eine Duftwolke, die einen Kontakt mit dem Fraßfeind verhindert. Chemische Analysen haben drei verschiedene Wehrsekret-Zusammensetzungen identifiziert. Viele Larven synthetisieren iridoide Monoterpene unabhängig von ihrer Wirtspflanze. Die meisten Chrysomela Arten und Phratora vitellinae verwenden Phenolglucoside der Salicaceen, um Salicylaldehyd zu bilden. Die dritte Gruppe produziert Ester der Isobutter- und 2-Methylbuttersäure, um Fraßfeinde abzuschrecken. C. tremulae frisst auf Salicaceen und verwendet Salicin aus der Wirtspflanze als Vorstufe zur Bildung von Salicylaldehyd. Dabei wird Salicin in die Wehrdrüse aufgenommen und von einer β-Glucosidase zu Salicylalkohol hydrolisiert, welches von einer extrazellulären Oxidase, der Salicylalkoholoxidase (SAO), zu Salicylaldehyd oxidiert wird. Das dabei entstehende Wasserstoffperoxid wird durch eine Katalase entgiftet. In vorangegangenen Studien wurde vermutet, dass die autogene Strategie der iridoiden Monoterpene den ursprünglichen Weg darstellt. Daraus hat sich die wirtspflanzenabhängige Strategie entwickelt, die aufgrund der Verwendung pflanzlicher Vorstufen im Gegensatz zur autogenen Strategie energetisch günstiger ist. Um diese phylogenetische Entwicklung zu rekonstruieren, wurde in vorangegangenen Arbeiten unserer Arbeitsgruppe die SAO biochemisch charakterisiert. In der vorliegenden Arbeit haben wir eine putative SAO codierende cDNA aus C. tremulae identifiziert. Eine Katalase und eine β-Glucosidase wurden ebenfalls gefunden.A huge number of larvae belonging to the leaf beetles (Coleoptera) defend themselves against predators by using toxins from their host plants. Species of the subtribe Chrysomelina release volatile secretions from specialized exocrine glands which are located in the meso- and metathorax and also in the seven abdominal segments. When the larvae are disturbed the glands everse and the secretion appears as a drop at the tip of the glands, deterring predators from a distance before contact. Chemical analysis identified three different kinds of larval defence secretions: many larvae produce autogenous iridoid aldehydes independent from the host plant. Most Chrysomela species and Phratora vitellinae use phenol glucosides from Salicaceae host plant to build salicylaldehyde. The third group uses esters of isobutyric and 2-methylbutyric acids to deter predators. Chrysomela tremulae feeds on Salicaceae, and uses Salicin from its host plant as a precursor for salicylaldehyde that is produced in the defensive secretions. Salicin is hydrolyzed by a β-glucosidase into salicylic alcohol which is oxidased by an extracellular oxidase, named salicyl alcohol oxidase (SAO), to salicylaldehyde. The produced hydrogen peroxide is detoxified by a catalase. In previous studies it was suggested that the autogenous synthesis of iridoid monoterpenes is the ancestral character state, the host-plant derived strategy being a secondary biogenetic route. The shift from autogenous to host-derived defenses is explained by being energetically advantegous due to the uptake of host-derived precursors. To reconstruct the phylogeny of the ability to use plant-derived salicin to produce salicylaldehyde, the enzyme SAO was identified and purified in previous studies. In this work we identify the putative cDNA coding for SAO from C. tremulae. Also the concerned enzymes catalase and β-glucosidase were identified

L'immunothérapie anti-tumorale à base de cellules dendritiques.

SCOPUS: re.jinfo:eu-repo/semantics/publishe

Salicyl alcohol oxidase of the chemical defense secretion of two chrysomelid leaf beetles: Molecular and functional characterization of two new members of the glucose-methanol-choline oxidoreductase gene family

SCOPUS: ar.jinfo:eu-repo/semantics/publishe