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3-Hydroxy-3-methylglutaryl CoA reductase (HMGR, EC 1.1.1.34) catalyzes the reaction from hydroxymethylglutaryl CoA to mevalonate in the isoprenoid pathway. In solanaceous plants, one class of endproducts of the pathway are sesquiterpenoid phytoalexins, antibiotic compounds produced by plants in response to pathogens. We are interested in the role of the defense-inducible isoforms of HMGR in phytoalexin production and disease resistance. Transgenic tobacco, constitutively expressing the defense-inducible tomato hmgr isogene, hmg2, showed fewer and smaller lesions following tobacco mosaic virus (TMV) inoculation. There is little evidence of phytoalexins acting directly against viruses, but they may reduce the spread of viruses as part of the hypersensitive response resulting in death of the host cell. Transmission electron microscopy of leaf cells of the transgenic plants revealed a larger volume of cytosol and accumulation of electron-dense inclusion bodies within the vacuoles. No structures resembling crystalloid ER or karmellae, caused by overexpression of hmgr in mammalian or yeast cells, respectively, were observed. Similar inclusion bodies were found in the vacuoles of wild-type tobacco leaf cells adjacent to necrotic cells in a TMV lesion. Tobacco expressing a truncated (membrane domain) form of hmg2 did not show enhanced resistance to TMV or any ultrastructural changes, indicating the importance of catalytically active HMG2 in mediating these changes. Sesquiterpene cyclase (a key branch point enzyme controlling sesquiterpene phytoalexin biosynthesis) was not induced and the amount of capsidiol, the tobacco phytoalexin, was not elevated by expression of hmg2. After TMV-inoculation, HMGR activity and the amount of capsidiol were higher in the wild-type than in the transgenic plants. Consequently, the enhanced resistance to TMV was not due to constitutive capsidiol production. The transgenic plants may have been able to produce sesquiterpenoid phytoalexins faster due to constitutive hmg2- expression and restricted the spread of the virus earlier, so that only a few cells were sacrificed. The subcellular localization of the defense-specific HMG2 isoform was determined by tagging tomato hmg2 with a c-myc epitope, and constitutively expressing the construct in transgenic tobacco plants. In non-induced leaves, MYC-HMG2 was found localized in small clusters associated with the ER. In TMV-inoculated leaves MYC-HMG2 co-localized with sesquiterpene cyclase to the vacuolar inclusion bodies suggesting that they may contain a defense-induced, membrane-associated multienzyme complex dedicated to sesquiterpene production. Our results support the hypothesis of the multibranched plant isoprenoid pathway being partly regulated by pathway partitioning. / Ph. D.

Un des principaux acteurs impliqués dans la régulation du statut redox intracellulaire, permettant aux plantes de s’adapter aux contraintes environnementales, est une famille multigénique de petites (12-14 kDa) oxydoréductases ubiquistes appelées thiorédoxines (TRX). Le génome d’Arabidopsis code une vingtaine de TRX canoniques dont neuf sont plastidiales (TRX f, m, x et y). Très étudiées dans notre laboratoire par des approches biochimiques, les TRX de types f et m apparaissent réguler majoritairement l’activité d’enzymes impliquées dans le métabolisme primaire tandis que les types x et y servir principalement de substrats réducteurs d’enzymes antioxydantes. Plus récemment, une dixième TRX, proposée plastidiale et nommée TRX z, a été identifiée. Au cours de ma thèse, j’ai caractérisé cette nouvelle TRX chloroplastique montrant des propriétés physico-chimiques inhabituelles, la rendant unique. En effet, la TRX z semble interagir, via des interactions électrostatiques, avec des protéines pour former des complexes de masses moléculaires élevées, potentiellement liés aux acides nucléiques. De plus, la TRX z, dont l’expression est induite à la lumière, principalement dans les tissus photosynthétiques, est la première TRX chloroplastique qui n’est pas réduite par le système FTR à la lumière mais qui peut être réduite par les autres TRX plastidiales, suggérant une interconnexion entre ces différentes TRX. D’autre part, une recherche exhaustive de cibles de la TRX z, par deux approches spécifiques et complémentaires (protéomique et double hybride), ont révélé 90 cibles putatives de la TRX z. La plupart de ces cibles, jamais identifiées comme cibles des TRX, sont impliquées dans la réponse de défense des plantes mise en place lors de stress biotiques. Ces résultats suggèrent que la TRX z pourrait être un élément clé dans la mise en place de ces réponses. L’analyse fonctionnelle préliminaire de la TRX z au cours de la réponse immune innée conforte cette hypothèse. L’ensemble de ces résultats indique que la TRX z pourrait jouer le rôle d’une protéine senseur de l’état d’oxydoréduction de la cellule. / One of the main actors involved in regulation of the cellular redox state, which allow plant adaptation to stress environmental conditions, is a multigenic family of small (12-14 kDa) ubiquitous oxidoreductases named thioredoxins (TRX). Arabidopsis encodes around twenty canonical TRX, including nine plastidial isoforms (TRX f, m, x and y). Extensively studied in our laboratory by biochemical approaches, TRX f and m was found to mainly redox regulate the activity of enzymes involved in the primary metabolism whereas TRX x and y serve as reducing substrates for antioxidant enzymes. More recently, a tenth TRX, predicted plastidial and named TRX z, was identified. During my PhD, I have characterized this new plastidial TRX showing unusual physicochemical properties, making it unique. Indeed, TRX z seems to interact, via electrostatic bonds, with proteins to form high molecular weight complexes, potentially linked to nucleic acids. Moreover, TRX z, which is expressed in green tissues in the light, is the first plastidial TRX which is not reduced by the FTR system but which can be reduced by other plastidial TRX, suggesting an interconnection between these TRX. Furthermore, a large scale inventory of TRX z targets, by two specific and complementary approaches (proteomic and yeast two hybrid), revealed 90 putative TRX z targets. Most of these, which have never been identified as TRX targets before, are implicated in plant defense response to biotic stresses. These results suggest that TRX z might be a key player in these responses. Preliminary functional analysis of TRX z during immune innate response reinforces this hypothesis. Altogether, these results indicate that TRX z appears as an important sensor of the redox status of the cell.

Le fer est un élément essentiel pour presque tous les êtres vivants cependant, il est peu biodisponible et est toxique dans sa forme libre car il engendre des formes réactives de l'oxygène via la réaction de Fenton. Pour se procurer le fer, les microorganismes sécrètent de petites molécules nommées sidérophores ayant une très forte affinité pour Fe3+. Les sidérophores sont requis pour la pathogénie de plusieurs agents pathogènes sur hôtes animaux ou végétaux, mais ce sont également des éliciteurs de défense. Des travaux antérieurs ont montré que les sidérophores activent les défenses et les gènes de réponse à la carence en fer chez Arabidopsis thaliana. L’activation de réponses de défense par le sidérophore requiert un niveau physiologique de fer dans la plante indiquant que le fer participe à la mise en place de ce processus. Au cours de ma thèse, les réponses globales de la plante A. thaliana au sidérophore deferrioxamine (DFO) ont été étudiées par une approche transcriptome. Les résultats obtenus montrent que le principal processus activé est l’immunité. En utilisant des chélateurs de fer différents, j’ai montré que l’effet chélation du fer est responsable de l’activation de l’immunité. Le traitement sidérophore provoque également une perturbation de l’homéostasie du fer et d’autres métaux dans la plante. Dans un mutant irt1 affecté dans le transport de plusieurs métaux lourds dont le fer, l’activation des défenses par la DFO est compromise. Par ailleurs, j’ai étudié l’effet du statut en fer de la plante sur sa sensibilité à la bactérie pathogène Dickeya dadantii et sur l’expression des défenses. Il apparait que le fer est requis pour la mise en place de plusieurs processus de défense en réponse à D. dadantii. Les plantes carencées en fer sont plus résistantes à l’infection. Une quantité de fer physiologique dans la plante est requise pour la multiplication bactérienne et pour l’expression des facteurs de pathogénie, les pectate lyases. Le marquage du fer par la méthode Perls’-DAB-H2O2 montre que celui–ci est très peu abondant dans les tissues végétaux contenant les bactéries qui, elles, sont chargées de fer. Dans l’ensemble, nos résultats montrent que le fer est requis dans l’arsenal défensif de la plante mais qu’il est également un facteur limitant pour le cycle infectieux de D. dadantii. / Iron is an essential element for almost all living organisms, however, it is not bioavailable and is toxic in its free form as it generates reactive oxygen species via the Fenton reaction. To obtain iron, microorganisms secrete small molecules named siderophores with very high affinity for Fe3 +. Siderophores are required for the pathogenesis of several pathogens on animals or plants, but they also are elicitors of defenses. Previous work has shown that siderophores activate defenses and iron deficiency response genes in Arabidopsis thaliana. The activation of defense responses by the siderophore requires a physiological level of iron in the plant indicating that iron is involved in the activation of this process. In my thesis, the global response of the plant A. thaliana to the siderophore deferrioxamine (DFO) has been studied by a transcriptomic approach. The results obtained show that the main process being activated is immunity. By using different iron chelating agents, I have shown that the iron chelation effect is responsible for the activation of immunity. The siderophore treatment also causes disturbance in the homeostasis of iron and other metals in the plant. In an irt1 mutant affected in the transport of heavy metals including iron, activation of defenses by the DFO is compromised. In addition, I studied the effect of iron status of the plant on its susceptibility to the pathogenic bacteria Dickeya dadantii and on the expression of defenses. It appears that iron is required for the establishment of several defense processes in response to D. dadantii. The iron deficient plants are more resistant to infection. A physiological amount of iron in the plant is required for bacterial growth and for expression of the virulence factors, pectate lyases. Iron staining by the Perls' -DAB - H2O2 method shows that low abundance of this metal in plant tissue coincides with the presence of bacteria, which contain high amounts of iron. Overall, our results show that iron is required in the defense arsenal of the plant but it is also a limiting factor for the infectious cycle of D. dadantii.

L'utilisation de biofongicides et de molécules stimulatrices des défenses des plantes (SDP) constituent des stratégies de lutte alternative permettant la réduction de l'utilisation des fongicides conventionnels. Toutefois, il n'existe que peu de produits homologués et appliqués sur blé et encore moins contre la septoriose. Dans le cadre de cette étude, nous avons testés et mis en évidence l'efficacité de protection du blé contre Zymoseptoria tritici de plusieurs molécules. En effet, 29 molécules biosourcées dérivées de la fonctionnalisation de l'acide pyroglutamique (PGA), contenu dans les mélasses de la betterave sucrière, ont été évaluées en plus de l'acide y-aminobutyrique GABA, pour la première fois contre Z. tritici. Le GABA et 16 molécules fonctionnalisées ont réduit significativement les pourcentages de la maladie. L'absence d'effets directs sur Z. tritici vérifiée in vitro confirme que ces protections sont dues exclusivement à un effet SDP. Pour ces molécules, l'étude de la relation structure activité a mis en évidence l'importance des différents groupements chimiques impliqués dans les protections observées. D'autre part, la conjugaison du PGA avec l'acide salicylique (SA) a permis l'obtention de 5 nouvelles molécules parmi lesquelles 4 étaient plus efficaces que les molécules mères et cette efficacité semble être également due à un effet SDP. Enfin, la saccharine ainsi que trois lipopeptides cycliques produits par Bacillus subtilis (mycosubtiline, surfactine et fengycine seuls ou en mélange) ont été évalués pour la première fois sur le pathosystème blé - Z. tritici et ont conféré des protections significatives dues à des propriétés SDP, à des activités antifongiques directes ou à des effets combinés. Cette étude a donc permis d'identifier de nouvelles molécules possédant différents modes d'action et qui pourraient être envisageables en lutte alternative contre la septoriose du blé, toutefois, des analyses complémentaires sont requises. / The use of biofungicides and elicitors of plant defenses are alternative control stategies that can reduce the use of conventional fungicides. However, there are few products registered and applied on wheat and even less against Septoria tritici blotch. As part of this study, we tested and demonstrated the protective efficacity of several molecules on wheat against Zymoseptoria tritici. In fact, 29 biosourced molecules derived from the functionalization of pyroglutamic acid (PGA) contained in the molasses of sugar beet were evaluated with y-aminobutyric acid GABA, for the first time against Z. tritici. GABA and 16 functionalized molecules significantly reduced the percentages of the disease. The absence of direct effects on the fungus tested in vitro confirms that these protections are due exclusively to an elicitation of plant defense mechanisms. For these molecules, the study of the structure activity relationship has highlighted the importance of different chemical groups involved in the observed protections. On the other hand, the conjugation of PGA with salicylic acid (SA) allowed the obtention of 5 new molecules among which 4 were more effective than the parent molecules and this efficiency seems to be also due to an eliciting effect. Finally, saccharin and three cyclic lipopeptides produced by Bacillus subtilis (mycosubtilin, surfactin and fengycin alone or as mixtures) were evaluated for the first time on the pathosystem wheat - Z. tritici and conferred significant protection due to eliciting properties, direct antifungal activities or combined effects. This study has thus made it possible to identify new molecules with different modes of action and which could be considered in alternative control against wheat leaf blotch, however, additional analyses are required.

Orchids are characterized by producing minute endosperm-lacking seeds, which depend on mycorrhizal fungi for germination and embryo development. Some aclorophyllous orchids remain dependent on the mycorrhizal association for carbon acquisition during their whole life history, whereasother orchids develop photosynthesis. Despite the biological significance of orchid mycorrhiza, gene expression studies are lacking. We have used different highthroughput approaches in order to understanding the mechanisms regulating orchid mycorrhiza development and functioning. Firstly, we have used a 2D-LC-MS/MS approach coupled to isobaric tagging for relative and absolute quantification (iTRAQ) to identify proteins with differential accumulation in Oncidium sphacelatum at different stages of mycorrhizal protocorm development (achlorophyllous and green protocorms) after seed inoculation with a Ceratobasidium sp. isolate. Quantitative analysis showed that the expected changes in carbon metabolism in green protocorms were accompanied by enhanced accumulation of proteins involved in the modulation of reactive oxygen species homeostasis, defense related responses, phytoalexins and carotenoid biosynthesis, suggesting that orchid protocorms undergo profound metabolic changes during the switch from the fully mycoheterotrophic to the photosynthethic stage. Secondly, three different proteomic techniques were carried out in independent experiments aiming to identify changes in protein accumulation in mycorrhizal roots of the terrestrial orchid Oeceoclades maculata.Finally, O. maculatamycorrhizal roots were used for transcriptome analyses. The data revealed a strong increase in general stress responses, accompanied by changes in signaling pathways possibly related to fungal recognition and establishment of a compatible interaction. Some of the upregulated genes may be involved in the reorganization of cell structure, likely related to accommodation of the fungal symbiont in the plant roots. We have also observed in mycorrhizal roots up-regulation of genes involved in carbon metabolism, including glycolysis/gluconeogenesis and amino sugars metabolism, as well as genes involved innitrogen assimilation. The down-regulation of genes involved in the jasmonate and ABA transduction pathways, and key genes encoding anti-fungal proteins, such as chitinase and a mannose-specific binding lectin, strongly suggests an alleviation of plant defense responses in O. maculata mycorrhizal roots. In general, our data suggest that the physiology of an orchid mycorrhiza is more similar to a compatible interaction than to an arm-race between plant and fungi. Overall orchid mycorrhiza have proved to be a promising model for investigating plantfungal interactions and further studies should now address the specific roles of the genes showing differential regulation in this study. / As orquídeas são caracterizadas por produzirem sementes diminutas, que não possuem endosperma. Necessitam, portanto, da interação com fungos micorrízicos para germinação e desenvolvimento do embrião. Algumas orquídeas aclorofiladas se mantêm dependentes dos fungos micorrízicos para a aquisição de carbono, enquanto outras desenvolvem a maquinaria fotossintética. Apesar do significado biológico das micorrizas de orquídeas, alterações na expressão gênica e no acúmulo de proteínas foram altamente negligenciads nos últimos anos. Neste trabalho, foram utilizadas diferentes técnicas sequenciamento e identificação de genes e proteínas em larga-escala para acessar as alterações moleculares responsáveis pela regulação das micorrizas de orquídeas. Uma abordagem baseada em 2D-LC MS/MS acoplada a técnica de quantificação absoluta e relativa iTRAQ, foiutilizada para identificar proteínas com acúmulo diferencial em Oncidium sphacelatum em diferentes estágios do desenvolvimento do protocormo (protocormos aclorofilados versus protocormos fotossintetizantes), após inoculação com um fungo do gênero Ceratobasidium. As análises mostraram que, as alterações esperadas no metabolismo do carbono foram acompanhadas de um acúmulo aumentado de proteínas envolvidas na modulação de espécies reativas de oxigênio, respostas de defesa, biossíntese de fitoalexinas e carotenóides, sugerindo que os protocormos de orquídeas passam por profundas alterações metabolicas durante a transição do metabolismo micoheterotrófico para o fotossintético. Posteriormente foram utilizadas três diferentes técnicas de proteômica quantitativa para explorar alterações fisiológicas em raízes micorrizadas e não-micorrizadas de Oeceoclades maculata.Este estudo foi ampliado, pela utilização de uma abordagem transcritômica ao mesmo modelo biológico. Em conjunto, os dados revelaram um forte aumento em respostas relacionadas ao estresse, acompanhadas de alterações em vias de transdução de sinal possivelmente relacionadas ao reconhecimento do simbionte fúngico e estabelecimento de uma interação compatível. Alguns genes com expressão aumentada devem estar envolvidos na reorganização celular, provavelmente ligada a acomodação do simbionte fúngico nas raízes das plantas. Também foi observado o aumento de genes envolvidos no metabolismo do carbono e de açúcares aminados, juntamente a genes relacionados a assimilação de nitrogênio em raízes micorrizadas. A expressão diminuída de genes envolvidas nas vias do jasmonato e ácido abscícico, juntamente a genes-chave que codificam para proteínas anti-fúngicas sugerem fortemente uma atenuação das respostas de defesa da planta em raízes micorrizadas de Oeceoclades maculata. No geral, parece que as micorrizas de orquídeas são fisiológicamente mais próximas de uma simbiose compatível do que de uma interação unilateral em favor da planta. Sobretudo, este sistema biológico provou ser promissor para investigação de interações planta-fungo e, próximas pesquisas devem agora ser focadas em funções específicas dos genes que mostraram regulação diferencial neste estudo.

Orchids are characterized by producing minute endosperm-lacking seeds, which depend on mycorrhizal fungi for germination and embryo development. Some aclorophyllous orchids remain dependent on the mycorrhizal association for carbon acquisition during their whole life history, whereasother orchids develop photosynthesis. Despite the biological significance of orchid mycorrhiza, gene expression studies are lacking. We have used different highthroughput approaches in order to understanding the mechanisms regulating orchid mycorrhiza development and functioning. Firstly, we have used a 2D-LC-MS/MS approach coupled to isobaric tagging for relative and absolute quantification (iTRAQ) to identify proteins with differential accumulation in Oncidium sphacelatum at different stages of mycorrhizal protocorm development (achlorophyllous and green protocorms) after seed inoculation with a Ceratobasidium sp. isolate. Quantitative analysis showed that the expected changes in carbon metabolism in green protocorms were accompanied by enhanced accumulation of proteins involved in the modulation of reactive oxygen species homeostasis, defense related responses, phytoalexins and carotenoid biosynthesis, suggesting that orchid protocorms undergo profound metabolic changes during the switch from the fully mycoheterotrophic to the photosynthethic stage. Secondly, three different proteomic techniques were carried out in independent experiments aiming to identify changes in protein accumulation in mycorrhizal roots of the terrestrial orchid Oeceoclades maculata.Finally, O. maculatamycorrhizal roots were used for transcriptome analyses. The data revealed a strong increase in general stress responses, accompanied by changes in signaling pathways possibly related to fungal recognition and establishment of a compatible interaction. Some of the upregulated genes may be involved in the reorganization of cell structure, likely related to accommodation of the fungal symbiont in the plant roots. We have also observed in mycorrhizal roots up-regulation of genes involved in carbon metabolism, including glycolysis/gluconeogenesis and amino sugars metabolism, as well as genes involved innitrogen assimilation. The down-regulation of genes involved in the jasmonate and ABA transduction pathways, and key genes encoding anti-fungal proteins, such as chitinase and a mannose-specific binding lectin, strongly suggests an alleviation of plant defense responses in O. maculata mycorrhizal roots. In general, our data suggest that the physiology of an orchid mycorrhiza is more similar to a compatible interaction than to an arm-race between plant and fungi. Overall orchid mycorrhiza have proved to be a promising model for investigating plantfungal interactions and further studies should now address the specific roles of the genes showing differential regulation in this study. / As orquídeas são caracterizadas por produzirem sementes diminutas, que não possuem endosperma. Necessitam, portanto, da interação com fungos micorrízicos para germinação e desenvolvimento do embrião. Algumas orquídeas aclorofiladas se mantêm dependentes dos fungos micorrízicos para a aquisição de carbono, enquanto outras desenvolvem a maquinaria fotossintética. Apesar do significado biológico das micorrizas de orquídeas, alterações na expressão gênica e no acúmulo de proteínas foram altamente negligenciads nos últimos anos. Neste trabalho, foram utilizadas diferentes técnicas sequenciamento e identificação de genes e proteínas em larga-escala para acessar as alterações moleculares responsáveis pela regulação das micorrizas de orquídeas. Uma abordagem baseada em 2D-LC MS/MS acoplada a técnica de quantificação absoluta e relativa iTRAQ, foiutilizada para identificar proteínas com acúmulo diferencial em Oncidium sphacelatum em diferentes estágios do desenvolvimento do protocormo (protocormos aclorofilados versus protocormos fotossintetizantes), após inoculação com um fungo do gênero Ceratobasidium. As análises mostraram que, as alterações esperadas no metabolismo do carbono foram acompanhadas de um acúmulo aumentado de proteínas envolvidas na modulação de espécies reativas de oxigênio, respostas de defesa, biossíntese de fitoalexinas e carotenóides, sugerindo que os protocormos de orquídeas passam por profundas alterações metabolicas durante a transição do metabolismo micoheterotrófico para o fotossintético. Posteriormente foram utilizadas três diferentes técnicas de proteômica quantitativa para explorar alterações fisiológicas em raízes micorrizadas e não-micorrizadas de Oeceoclades maculata.Este estudo foi ampliado, pela utilização de uma abordagem transcritômica ao mesmo modelo biológico. Em conjunto, os dados revelaram um forte aumento em respostas relacionadas ao estresse, acompanhadas de alterações em vias de transdução de sinal possivelmente relacionadas ao reconhecimento do simbionte fúngico e estabelecimento de uma interação compatível. Alguns genes com expressão aumentada devem estar envolvidos na reorganização celular, provavelmente ligada a acomodação do simbionte fúngico nas raízes das plantas. Também foi observado o aumento de genes envolvidos no metabolismo do carbono e de açúcares aminados, juntamente a genes relacionados a assimilação de nitrogênio em raízes micorrizadas. A expressão diminuída de genes envolvidas nas vias do jasmonato e ácido abscícico, juntamente a genes-chave que codificam para proteínas anti-fúngicas sugerem fortemente uma atenuação das respostas de defesa da planta em raízes micorrizadas de Oeceoclades maculata. No geral, parece que as micorrizas de orquídeas são fisiológicamente mais próximas de uma simbiose compatível do que de uma interação unilateral em favor da planta. Sobretudo, este sistema biológico provou ser promissor para investigação de interações planta-fungo e, próximas pesquisas devem agora ser focadas em funções específicas dos genes que mostraram regulação diferencial neste estudo.

Salicylic acid binding protein 2 (SABP2) is known to play a key role in Salicylic acid mediated defense pathway. SBIP-470 is SABP2 interacting protein that might be putatively involved in transfer of lipids. SBIP-470 was cloned without the signal peptide and expressed in E. coli. In vitro lipid binding assay using recombinant SBIP-470 failed to detect lipid binding. In vitro lipid transfer assay showed recombinant SBIP-470 does not transfer phospholipid. Study has shown that SBIP-470 is highly inducible upon infection with viral as well as bacterial pathogens. Induction of SBIP-470 expression upon the TMV infection most likely depends upon the SABP2 while its expression upon non-host bacterial pathogens is most probably inhibited by the SABP2. A study of Arabidopsis knockout mutants (ltp12 mutant and ltp2 mutant) lacking the SBIP-470 homolog genes showed defects in growth phenotype, and they were found susceptible to bacterial pathogens.

Made available in DSpace on 2015-03-26T13:30:36Z (GMT). No. of bitstreams: 1 texto completo.pdf: 798885 bytes, checksum: 61e83d94af55596a24b1ca546bd339ca (MD5) Previous issue date: 2011-07-21 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The tomato is one of the most important vegetables produced in Brazil, playing an important role in the economy and creating jobs. In countries of South America, Europe and Africa, the mite Tetranychus evansi is considered an important pest of this crop. Recent studies have shown that this mite manipulates the defense of the plant reducing its defensive products. The objective of this study was to investigate whether endosymbiotic bacteria associated with the mite T. evansi play a role in manipulating the defenses of the tomato plant. The mite T. urticae was used as a standard, which is known to induce plant defense response. Bacterial DNA was extracted from T. evansi and T. urticae with subsequent denaturing gradient gel electrophoresis to compare bacterial diversity between these species, observing that T. evansi has a higher bacterial diversity than T. urticae. To determine if bacteria associated with T. evansi provide some advantage for its development and reproduction, as well as contributing to suppress the defenses of plants, mites were obtained without endosymbionts by treating them with a tetracycline solution. Mites treated with tetracycline showed no significant differences (p> 0.05) in development, oviposition and mortality. However, plants attacked by treated mites showed higher lipoxygenase activity and increased inhibition of trypsin (p <0.05) compared to clean plants and plants attacked by mites not treated with tetracycline. These results show that plants attacked by T. evansi without endosymbiotic bacteria activated their defense mechanism. Thus, these results suggest that bacteria may assist the mites in manipulating plant defense, making them more susceptible to attack. / A cultura do tomateiro é uma das mais importantes hortaliças produzidas no Brasil, apresentando destacada influência na economia e geração de empregos. Em países da América do Sul, Europa e África, o ácaro Tetranychus evansi é considerado uma importante praga dessa cultura. Recentes estudos demonstraram que este ácaro manipula a defesa da planta reduzindo seus produtos de defesa. O objetivo deste trabalho foi investigar se bactérias endossimbiontes associadas ao ácaro T. evansi tem função na manipulação de defesa de T.evansi no tomateiro. Para isso foi utilizado também o ácaro T. urticae como padrão, que é conhecido por induzir resposta de defesa de planta. Foi realizada a extração de DNA bacteriano de T. evansi e T. urticae com posterior corrida eletroforética em gel com gradiente desnaturante para comparar a diversidade bacteriana entre estas espécies, foi observado que T. evansi possui uma diversidade bacteriana superior ao T. urticae. Para avaliar se as bactérias associadas ao T. evansi proporcionam alguma vantagem ao seu desenvolvimento e reprodução, bem como na contribuição de suprimir as defesas das plantas, foram obtidos ácaros sem endossimbiontes através do tratamento destes, com solução de tetraciclina. Ácaros tratados com tetraciclina não apresentaram diferenças significativas (p > 0,05) no desenvolvimento, oviposição e mortalidade. Entretanto, as plantas atacadas por ácaros tratados apresentaram maior atividade de lipoxigenase e maior inibição de tripsina (p<0,05), comparado com plantas limpas e plantas atacadas por ácaros não tratados com tetraciclina. Estes resultados evidenciam que plantas atacadas por T. evansi sem endossimbiontes bacterianos ativaram seu mecanismo de defesa. Sendo assim, estes resultados sugerem que as bactérias podem auxiliar os ácaros na manipulação da defesa da planta, deixando-as mais susceptíveis ao ataque e à alimentação.