Cardenolides in nectar may be more than a consequence of allocation to other plant parts: a phylogenetic study of Asclepias

The primary function of secondary plant metabolites is thought to be defence against herbivores. The frequent occurrence of these same noxious compounds in floral nectar, which functions primarily to attract pollinators, has been seen as paradoxical. Although these compounds may have an adaptive purpose in nectar, they may also occur as a nonadaptive consequence of chemical defence in other plant parts. If nectar chemistry reflects physiological constraints or passive leakage from other tissues, we expect that the identity and relative concentration of nectar cardenolides to be correlated with those of other plant parts; in contrast, discordant distributions of compounds in nectar and other tissues may suggest adaptive roles in nectar. We compared the concentrations and identities of cardenolides in the nectar, leaves and flowers of 12 species from a monophyletic clade of Asclepias. To measure putative toxicity of nectar cardenolides, we then examined the effects of a standard cardenolide (digoxin) on the behaviour of bumblebees, a common generalist pollinator of Asclepias. We found that the average cardenolide concentrations in nectar, leaves and flowers of the 12 Asclepias species were positively correlated as predicted by nonadaptive hypotheses. However, significant differences in the identities and concentrations of individual cardenolides between nectar and leaves suggest that the production or allocation of cardenolides may be independently regulated at each plant part. In addition, cardenolide concentrations in leaves and nectar exhibited no phylogenetic signal. Surprisingly, bumblebees did not demonstrate an aversion to digoxin-rich nectar, which may indicate that nectar cardenolides have little effect on pollination. Although the idea that discordant patterns of secondary metabolites across tissue types may signal adaptive functions is attractive, there is evidence to suggest constraint contributes to nectar secondary chemistry. Further work testing the ecological impacts of such patterns will be critical in determining the functional significance of nectar cardenolides

Characterisation of "fou2", a constitutive wound-activated mutant and analysis of the proteome and leaf physiology in the region proximal to wounds in Arabidopsis

Résumé : Les jasmonates (JA), une famille d'hor1none végétale, jouent un rôle central dans la réponse à la blessure, et aux attaques d'insectes et de pathogènes. Les JA sont principalement dérivés d'un acide gras, l'acide linolénique. L'addition par une lipoxygénase d'une molécule d'oxygène à l'acide linolénique initie la synthèse de JA. Cependant les mécanismes régulant l'activation de la biosynthèse de JA ne sont pas encore connus. C'est pour cette raison que dans ce travail, nous avons caractérisé chez Arabidopsis thaliana (l'Arabette des Dames) un mutant fou2 dont l'activité lipoxygénase est plus élevée que celle d'une plante sauvage. Les niveaux de JA sont constitutivement plus élevés et l'activation de la synthèse de JA après blessure est fortement plus induite chez fou2 que chez le type sauvage. En outre, fou2 est plus résistant au pathogène Botrytis cinerea et à la chenille Spodoptera littoralis. Afin de comprendre quel mécanisme chez fou2 génére ce phénotype, nous avons cloné le gène responsable du phénotype de fou2. Le mutant fou2 porte une mutation dans le gène d'un canal à deux pores transportant probablement du potassium, du lumen de la vacuole végétale vers le compartiment cytosolique. L'analyse du protéome de fou2 a permis d'identifier une expression plus élevée de sept protéines régulées par les JA ou le stress. La découverte de l'implication d'un canal dans le phénotype de fou2 renforce l'hypothèse que les flux de cations pourraient être impliqués dans les étapes précoces de la synthèse des JA. Nous avons également étudié le protéome et la physiologie d'une feuille blessée, Pour évaluer les changements d'expression protéique en réponse à la blessure et contrôlés par les JA, nous avons quantifié l'expression de 5937 protéines chez une plante d'Arabidopsis sauvage et chez un mutant incapable de synthétiser des JA. Parmi ces 5937 protéines, nous avons identifié 99 protéines régulées par la blessure chez le type sauvage. Nous avons observé pour 65% des protéines dont l'expression protéique changeait après blessure une bonne corrélation entre la quantité de transcrits et de protéines. Plusieurs enzymes de la voie des chorismates impliquées dans la biosynthèse des acides aminés phénoliques étaient induites par les JA après blessure. Une quantification des acides aminés a montré que les niveaux d'acides aminés phénoliques augmentaient significativement après blessure. La blessure induisait aussi des changements dans l'expression de protéines impliquées dans la réponse au stress et particulièrement au stress oxydatif. Nous avons quantifié l'état réduit et oxydé du glutathion, un tripeptide qui, sous sa forme réduite, est l'antioxydant majeur des cellules. Nous avons trouvé une quantité significativement plus élevée de glutathion oxydé chez le type sauvage blessé que chez la plante aus blessée. Ce résultat suggère que la génération d'un stress oxydatif et la proportion relative de glutathions réduits et oxydés sont contrôlés par les JA après blessure. Abstract : Plants possess a family of potent fatty acid-derived wound-response and developmental regulators: the jasmonates. These compounds are derived from the tri?unsaturated fatty acid a-linolenic-acid (18:3). Addition of an oxygen molecule to 18:3 by 13-lipoxygenases (13-LOX) initiates JA biosynthesis. Actually components regulating the activation of JA biosynthesis are poorly defined. Therefore we characterized in Arabidopsis thaliana the fatty acid Qxygenation upregulated 2 (fou2) mutant, which was previously isolated in a screen for mutants with an enhanced 13-LOX activity. As a consequence of this increased 13-LOX activity, JA levels in fou2 are higher than in wild type (WT) and wounding strongly increased JA biosynthesis compared to WT. fou2 was more resistant to the fungus Botrytis cinerea and the generalist caterpillar Spodaptera littomlis, The fou2 mutant carries a missense mutation in the Two Pore Channel 1 gene (TPCJ), which encodes a vacuolar cation channel transporting probably K* into the cytosol. Patchclamp analysis of fou2 vacuolar membranes showed faster time-dependent conductivity and activation of the mutated channel at lower membrane potentials than wild-type. Proteomic analysis of fou2 leaves identified increased levels of seven biotic stress- and JA- inducible proteins. The discovery of the implication of a channel in the fou2 phenotype strenghtens the hypothesis that cation fluxes might be implicated in early steps of JA synthesis. We further concentrated on the proteome and leaf physiology in the region proximal to wounds in Arabidopsis using the WT and the aos JA-biosynthesis deficient mutant in order to find JA- induced proteins changes. We used two successive proteomic methods to assess protein changes in response to wounding Arabidopsis leaves, two dimensional electrophoresis (2DE) and linear trap quadrupole ion-trap mass spectrometry. In total 5937 proteins were quantified. We identified 99 wound-regulated proteins in the WT. Most these proteins were also wound-regulated at the transcript level showing a good correlation between transcript and protein abundance. We identified several wound-regulated enzymes involved in amino acid biosynthesis and confirmed this result by amino acid quantification. Proteins involved in stress reponses were upregulated, particularly in redox species regulation. We found a significantly higher quantity of oxidized glutathione in wounded WT relative to wounded aos leaves. This result suggests that levels of reduced glutathione are controlled by JA after wounding.

Developmental, metabolic and immunological costs of flea infestation in the common vole

Parasites use resources from their hosts, which can indirectly affect a number of host functions because of trade-offs in resource allocation. In order to get a comprehensive view of the costs imposed by blood sucking parasites to their hosts, it is important to monitor multiple components of the development and physiology of parasitized hosts over long time periods. The effect of infestation by fleas on body mass, body length growth, haematocrit, resistance to oxidative stress, resting metabolic rate and humoral immune response were experimentally evaluated. During a 3-month period, male common voles, Microtus arvalis, were either parasitized by rat fleas (Nosopsyllus fasciatus), which are naturally occurring generalist ectoparasites of voles, or reared without fleas. Then voles were challenged twice by injecting Keyhole Limpet Haemocyanin (KLH) to assess whether the presence of fleas affects the ability of voles to produce antibodies against a novel antigen. During the immune challenge we measured the evolution of body mass, haematocrit, resistance to oxidative stress and antibody production. Flea infestation negatively influenced the growth of voles. Moreover, parasitized voles had reduced haematocrit, higher resting metabolic rate and lower production of antibodies against the KLH. Resistance to oxidative stress was not influenced by the presence of fleas. During the immune challenge with KLH, body mass decreased in both groups, while the resistance to oxidative stress remained stable. In contrast, the haematocrit decreased only in parasitized voles. Our experiment shows that infestation by a haematophageous parasite negatively affects multiple traits like growth, energy consumption and immune response. Fleas may severely reduce the survival probability and reproductive success of their host in natural conditions.

Differential contribution of transcription factors to Arabidopsis thaliana defense against Spodoptera littoralis

In response to insect herbivory, Arabidopsis plants activate the synthesis of the phytohor- mone jasmonate-isoleucine, which binds to a complex consisting of the receptor COI1 and JAZ repressors. Upon proteasome-mediated JAZ degradation, basic helix-loop-helix tran- scription factors (TFs) MYC2, MYC3, and MYC4 become activated and this results in the expression of defense genes. Although the jasmonate (JA) pathway is known to be essen- tial for the massive transcriptional reprogramming that follows herbivory, there is however little information on other TFs that are required for defense against herbivores and whether they contribute significantly to JA-dependent defense gene expression. By transcriptome profiling, we identified 41TFs that were induced in response to herbivory by the generalist Spodoptera littoralis. Among them, nine genes, including WRKY18, WRKY40, ANAC019, ANAC055, ZAT10, ZAT12, AZF2, ERF13, and RRTF1, were found to play a significant role in resistance to S. littoralis herbivory. Compared to the triple mutant myc234 that is as sensitive as coi1-1 to herbivory, knockout lines of these nine TFs were only partially more sensitive to S. littoralis but, however, some displayed distinct gene expression changes at the whole-genome level. Data thus reveal that MYC2, MYC3, and MYC4 are master regu- lators of Arabidopsis resistance to a generalist herbivore and identify new genes involved in insect defense.

Diversity, prevalence and virulence of fungal entomopathogens in colonies of the ant Formica selysi

The richness of the parasitic community associated with social insect colonies has rarely been investigated. Moreover, understanding how hosts and pathogens interact in nature is important to interpret results from laboratory experiments. Here, we assessed the diversity, prevalence and virulence of fungal entomopathogens present around and within colonies of the ant Formica selysi. We detected eight fungal species known to be entomopathogenic in soil sampled from the habitat of ants. Six of these entomopathogens were found in active nests, abandoned nests, and corpses from dump piles or live ants. A systematic search for the presence of three generalist fungal entomopathogens in ant colonies revealed a large variation in their prevalence. The most common of the three pathogens, Paecilomyces lilacinus, was detected in 44% of the colonies. Beauveria bassiana occurred in 17% of the colonies, often in association with P. lilacinus, whereas we did not detect Metarhizium brunneum (formerly M. anisopliae) in active colonies. The three fungal species caused significant mortality to experimentally challenged ants, but varied in their degree of virulence. There was a high level of genetic diversity within B. bassiana isolates, which delineated three genetic strains that also differed significantly in their virulence. Overall, our study indicates that the ants encounter a diversity of fungal entomopathogens in their natural habitat. Moreover, some generalist pathogens vary greatly in their virulence and prevalence in ant colonies, which calls for further studies on the specificity of the interactions between the ant hosts and their fungal pathogens.

Loss of interactions with ants under cold climate in a regional myrmecophilous butterfly fauna

Aim Specialized mutualistic clades may revert and thus increase their autonomy and generalist characteristics. However, our understanding of the drivers that trigger reductions in mutualistic traits and of the consequences for the tolerance of these species to various environmental conditions remains limited. This study investigates the relationship between the environmental niche and the degree of myrmecophily (i.e. the ability to interact with ants) among members of the Lycaenidae. Location The western Swiss Alps. Methods We measured the tolerance of Lycaenidae species to low temperatures by comparing observations from a random stratified field sampling with climatic maps. We then compared the species-specific degree of myrmecophily with the species range limits at colder temperatures while controlling for phylogenetic dependence. We further evaluated whether the community-averaged degree of myrmecophily increases with temperature, as would be expected in the case of environmental filters acting on myrmecophilous species. Results Twenty-nine Lycaenidae species were found during sampling. Ancestral state reconstruction indicated that the 24 species of Polyommatinae displayed both strong myrmecophily and secondary loss of mutualism; these species were used in the subsequent statistical analyses. Species with a higher degree of ant interaction were, on average, more likely to inhabit warmer sites. Species inhabiting the coldest environments displayed little or no interaction with ants. Main conclusions Colder climates at high elevations filter out species with a high degree of myrmecophily and may have been the direct evolutionary force that promoted the loss of mutualism. A larger taxon sampling across the Holarctic may help to distinguish between the ecological and evolutionary effects of climate.

Differential effectiveness of microbially induced resistance against herbivorous insects in Arabidopsis.

Rhizobacteria-induced systemic resistance (ISR) and pathogen-induced systemic acquired resistance (SAR) have a broad, yet partly distinct, range of effectiveness against pathogenic microorganisms. Here, we investigated the effectiveness of ISR and SAR in Arabidopsis against the tissue-chewing insects Pieris rapae and Spodoptera exigua. Resistance against insects consists of direct defense, such as the production of toxins and feeding deterrents and indirect defense such as the production of plant volatiles that attract carnivorous enemies of the herbivores. Wind-tunnel experiments revealed that ISR and SAR did not affect herbivore-induced attraction of the parasitic wasp Cotesia rubecula (indirect defense). By contrast, ISR and SAR significantly reduced growth and development of the generalist herbivore S. exigua, although not that of the specialist P. rapae. This enhanced direct defense against S. exigua was associated with potentiated expression of the defense-related genes PDF1.2 and HEL. Expression profiling using a dedicated cDNA microarray revealed four additional, differentially primed genes in microbially induced S. exigua-challenged plants, three of which encode a lipid-transfer protein. Together, these results indicate that microbially induced plants are differentially primed for enhanced insect-responsive gene expression that is associated with increased direct defense against the generalist S. exigua but not against the specialist P. rapae.

TRANSCRIPTION FACTORS INVOLVED IN PLANT DEFENCE AGAINST INSECT HERBIVORES IN ARABIDOPSIS THALIANA

Afin de pouvoir se défendre contre les insectes nuisibles, les plantes ont développé plusieurs stratégies leur permettant de maximiser leurs chances de survie et de reproduction. Parmi elles, les plantes sont souvent pourvues de barrières physiques telles que les poils urticants, les épines et la cuticule. En plus, les plantes sont capables de produire des protéines anti-digestives et des métabolites secondaires insecticides tels que la nicotine, les tannins ou les glucosinolates (GS). La mise en place de ces barrières physiques et chimiques comporte un coût énergétique au détriment de la croissance et de la reproduction. Par conséquent, en absence d'insectes, la plante investit la majeure partie de son énergie dans le développement et la croissance. A l'inverse, une blessure causée par un insecte provoquera une croissance ralentie, une augmentation de la densité de poils urticants ainsi que la synthèse de défenses chimiques. Au niveau moléculaire, cette défense inductible est régulée par l'hormone végétale acide jamsonique (AJ). En réponse à l'attaque d'un insecte, la plante produit cette hormone en grande quantité, ce qui se traduira par une forte expression de gènes de défense. Pendant ma thèse, j'ai essayé de découvrir quels étaient les facteurs de transcription (FT) responsables de l'expression des gènes de défense dans Arabidopsis thaliana. J'ai ainsi pu démontrer que des plantes mutées dans les FTs comme MYC2, MYC3, MYC4, ZAT10, ZAT12, AZF2, WRKY18, WRKY40, WRKY6, ANAC019, ANAC55, ERF13 et RRTF1 deviennent plus sensibles aux insects de l'espèce Spodoptera littoralis. Par la suite, j'ai également pu montrer que MYC2, MYC3 et MYC4 sont probablement la cible principale de la voie de signalisation du AJ et qu'ils sont nécessaires pour l'expression de la majorité des gènes de défense dont la plupart sont essentiels à la biosynthèse des GS. Une plante mutée simultanément dans ces trois protéines est par conséquent incapable de synthétiser des GS et devient hypersensible aux insectes. J'ai également pu démontrer que les GS sont uniquement efficaces contre les insectes généralistes tels S. littoralis et Heliothis virescens alors que les insectes spécialisés sur les Brassicaceae comme Pieris brassicae et Plutella xylostella se sont adaptés en développant des mécanismes de détoxification. - In response to herbivore insects, plants have evolved several defence strategies to maximize their survival and reproduction. For example, plants are often endowed with trichomes, spines and a thick cuticule. In addition, plants can produce anti-digestive proteins and toxic secondary metabolites like nicotine, tannins and glucosinolates (GS). These physical and chemical barriers have an energetic cost to the detriment of growth and reproduction. As a consequence, in absence of insects, plants allocate their energy to development and growth. On the contrary, an attack by herbivore insects will affect plant growth, increase trichome density and induce the production of anti-digestive proteins and secondary metabolites. At the molecular level, this inducible defence is regulated by the phytohormone jasmonic acid (JA). Thus, an attack by herbivores will be followed by a burst of JA that will induce the expression of defence genes. The aim of my thesis was to characterize which transcription factors (TF) regulate the expression of these defence genes in Arabidopsis thaliana. I could show that plants mutated in various TFs like MYC2, MYC3, MYC4, ZAT10, ZAT12, AZF2, WRKY18, WRKY40, WRKY6, ANAC019, ANAC55, ERF 13 and RRTFl were more susceptible to the herbivore Spodoptera littoralis. Furthermore, I could demonstrate that MYC2, MYC3 and MYC4 are probably the main target of the JA-signalling pathway and that they are necessary for the insect-mediated induction of most defence genes including genes involved in the biosynthesis of GS. A triple mutant myc2myc3myc4 is depleted of GS and consequently hypersensitive to insects. Moreover, I showed that GS are only efficient against generalist herbivores like S. littoralis and Heliothis virescens whereas specialized insects like Pieris brassicae and Plutella xylostella have evolved detoxification mechanisms against GS.

Ectoparasite affects choice and use of roost sites in the great tit, Parus major

Many diurnal bird species roost at night in holes. As a regular visitor of a hole they are therefore a welcome host for several species of ectoparasites. The interactions of ectoparasites with the behaviour, life-history traits and population demography of their hosts are largely unknown. In the present study the effects of the haematophagous hen flea, Ceratophyllus gallinae , on the great tit's choice of winter roost site were investigated experimentally. Three experiments tested (1) whether great tits prefer a clean nestbox to one containing an old, but parasite-free nest, (2) whether they prefer a parasite-free nestbox to one infested with the haematophagous hen flea, and (3) whether they prefer not to use a nestbox when there is only an infested box available in their territory. In the first experiment there was no discrimination and both kinds of boxes were used equally often. In the second experiment the great tits clearly preferred to roost in the box without ectoparasites. In the third experiment a significantly higher proportion of the infested nestboxes were not used for roosting compared with the parasite-free boxes. Recently the validity of the conclusions drawn from nestbox studies where the naturally occurring detrimental ectoparasites are eliminated by the routine removal of old nests between breeding seasons has been questioned. This study shows that ectoparasites affect host behaviour and therefore lends support to that criticism.

Animal Toxins: How is Complexity Represented in Databases?

Peptide toxins synthesized by venomous animals have been extensively studied in the last decades. To be useful to the scientific community, this knowledge has been stored, annotated and made easy to retrieve by several databases. The aim of this article is to present what type of information users can access from each database. ArachnoServer and ConoServer focus on spider toxins and cone snail toxins, respectively. UniProtKB, a generalist protein knowledgebase, has an animal toxin-dedicated annotation program that includes toxins from all venomous animals. Finally, the ATDB metadatabase compiles data and annotations from other databases and provides toxin ontology.

Potential hosts number in cuckoo bees (Psithyrus subgen.) increases toward higher elevations

In severe and variable conditions, specialized resource selection strategies should be less fre‐ quent because extinction risks increase for species that depend on a single and unstable resource. Psithyrus (Bombus subgenus Psithyrus) are bumblebee parasites that usurp Bombus nests and display inter‐specific variation in the number of hosts they parasitize. Using a phylogenetic comparative frame‐ work, we show that Psithyrus species at higher elevations display a higher number of hosts species com‐ pared with species restricted to lower elevations. Species inhabiting high elevations also cover a larger temperature range, suggesting that species able to occur in colder conditions may benefit from recruit‐ ment from populations occurring in warmer conditions. Our results provide evidence for an 'altitudinal niche breadth hypothesis' in parasitic species, showing a decrease in the parasites' specialization along the elevational gradient, and also suggesting that Rapoport's rule might apply to Psithyrus.

Animal Toxins: How is Complexity Represented in Databases?

Peptide toxins synthesized by venomous animals have been extensively studied in the last decades. To be useful to the scientific community, this knowledge has been stored, annotated and made easy to retrieve by several databases. The aim of this article is to present what type of information users can access from each database. ArachnoServer and ConoServer focus on spider toxins and cone snail toxins, respectively. UniProtKB, a generalist protein knowledgebase, has an animal toxin-dedicated annotation program that includes toxins from all venomous animals. Finally, the ATDB metadatabase compiles data and annotations from other databases and provides toxin ontology.

Plants and tortoises: mutations in the Arabidopsis jasmonate pathway increase feeding in a vertebrate herbivore.

Photosynthetic tissues, the major food source of many invertebrates and vertebrates, are well defended. Many defence traits in leaves are controlled via the jasmonate signalling pathway in which jasmonate acts as a hormone by binding to a receptor to activate responses that lead to increased resistance to invertebrate folivores. We predicted that mutations in jasmonate synthesis might also increase the vulnerability of leaves to vertebrate folivores and tested this hypothesis using the Eastern Hermann's tortoise (Eurotestudo boettgeri) and an Arabidopsis thaliana (Brassicaceae) allene oxide synthase (aos) mutant unable to synthesize jasmonate. Tortoises preferred the aos mutant over the wild type (WT). Based on these results, we then investigated the effect of mutating jasmonate perception using a segregating population of the recessive A. thaliana jasmonate receptor mutant coronatine insensitive1-1 (coi1-1). Genotyping of these plants after tortoise feeding revealed that the homozygous coi1-1 receptor mutant was consumed more readily than the heterozygous mutant or the WT. Therefore, the plant's ability to synthesize or perceive jasmonate reduces feeding by a vertebrate herbivore. We also tested whether or not tortoise feeding behaviour was influenced by glucosinolates, the principal defence chemicals in Arabidopsis leaves with known roles in defence against many generalist insects. However, in contrast to what has been observed with such insects, leaves in which the levels of these compounds were reduced genetically were consumed at a similar rate to those of the WT.

" Arabidopsis Thaliana " response to insect feeding : new components controlling defense gene expression and plant resistance

Abstract: Plants cannot run away to escape attacking herbivores, but they defend themselves by producing anti-digestive proteins and toxic compounds (for example glucosinolates). The first goal of this thesis was to study changes in gene expression after insect attack using microarrays. The responses of Arabidopsis thaliana to feeding by the specialist Pieris rapae and the generalist Spodoptera liffora is were compared. We found that the transcript profiles after feeding by the two chewing insects were remarkably similar, although the generalist induced a slightly stronger response. The second goal was to evaluate the implication of the four signals jasmonic acid (JA), salicylic acid (SA), ethylene (ET), and abscisic acid (ABA) in the control of insect-regulated gene expression. Using signaling mutants, we observed that JA was the predominant signal and that ABA modulated defense gene expression. In contrast, SA and ET appeared to control slightly gene expression, but only after feeding by S. litforalis. The third goal was to establish whether plant responses are really effective against insects. In accordance with the transcript profile, both insects were affected by the JA-dependent defenses, as they performed better on the JA-insensitive mutant. S. littoralis also performed better on ABA-deficient mutants, providing evidence for the role of ABA in defense against insects. When testing indole or aliphatic glucosinolate deficient mutants, we found that they were also more susceptible to insect feeding, providing some of the first genetic evidence for the defensive role of glucosinolates in planta. Finally, a glutathione-deficient mutant, pad2-1, was also more susceptible to insect feeding and we could attribute this phenotype to a lowered accumulation of the major indole glucosinolate. In this thesis, we provide a comprehensive list of insect-regulated genes, including many transcription factors that constitute interesting candidate genes for the further study of insect-induced expression changes. Understanding how the plant responses to insects are regulated will provide tools for a better management of insect pest in the field. Résumé: Les plantes ne peuvent s'échapper pour fuir les insectes qui les attaquent, mais elles se défendent en produisant des protéines anti-digestives et des composés toxiques (par exemple des glucosinolates). Le premier but de cette thèse était d'étudier les changements de l'expression génétique lors d'attaque par des insectes en utilisant des puces à ADN. Nous avons comparé la réponse d'Arabidopsis thaliana à deux espèces d'insectes avec des habitudes alimentaires différentes : le spécialiste Pieris rapae et le généraliste Spodoptera littoralis. Nous avons trouvé que les profils de transcription après l'attaque par les deux insectes sont remarquablement similaires, bien que le généraliste induise une réponse légèrement plus forte. Le deuxième but était de déterminer l'implication de quatre signaux dans le contrôle de la réponse :l'acide jasmonique (JA), l'acide salicylique (SA), l'éthylène (ET), et l'acide abscissique (ABA). En utilisant de mutants de signalisation, nous avons montré que l'acide jasmonique était le signal prédominant et que l'acide abscissique modulait l'expression génétique. D'autre part, l'acide salicylique et l'éthylène contrôlent à un degré moindre l'expression génétique, mais seulement après l'attaque par S. littoralís. Le troisième but était d'établir si les réponses des plantes sont efficaces contre les insectes. En accord avec le profil de transcription, les deux espèces d'insectes se sont mieux développées sur un mutant insensible au JA, indiquant que les défenses contrôlées par ce signal sont cruciales pour la plante. De plus, les larves de S. littorales se sont mieux développées sur des mutants déficients en ABA, ce qui fournit une preuve du rôle de l'acide abscissique dans la défense contre les insectes. En testant des mutants déficients en glucosinolates de type indole ou aliphatique, nous avons trouvé qu'ils étaient plus sensibles aux insectes, démontrant ainsi le rôle défensif des glucosinolates in planta. Finalement, le mutant déficient en glutathion pad2-1 était aussi plus sensible à l'attaque des insectes, et nous avons pu attribuer ce phénotype à une plus faible augmentation d'un indole glucosinolate dans ce mutant. Dans cette thèse, nous avons mis en évidence un nombre important de gènes contrôlés par les insectes, comprenant de nombreux facteurs de transcription qui constituent des candidats intéressants pour`étudier plus en détail les changements d'expression génétique induits par les insectes. Une meilleure compréhension de la réponse des plantes contre l'attaque des insectes devrait nous permettre de développer de nouvelles stratégies pour mieux gérer les ravageurs des cultures.