Orientador: Anselmo Nogueira / Resumo: Muitas características fenotípicas das plantas mudam drasticamente ao longo do desenvolvimento vegetal e podem influenciar as interações ecológicas. Dado que existe um custo energético associado a manutenção de diferentes mutualismos, investigamos a relação entre os estádios de desenvolvimento vegetal e o estabelecimento de três mutualismos, assim como a possível interferência do mutualismo raiz-rizóbio sobre os mutualismos nectário extrafloral-formiga e flor-abelha. No campo selecionamos 30 plantas da espécie de leguminosa de Cerrado, Chamaecrista desvauxii var. latistipula, com diferentes tamanhos, de indivíduos juvenis a maiores reprodutivos, para avaliar a ocorrência e intensidade das interações mutualistas raiz-rizóbio, nectário extrafloral-formiga e flor-abelha. Em casa de vegetação montamos um experimento manipulando as bactérias do tipo rizóbio e o tipo de solo em que as plantas foram cultivadas, no qual investigamos a interferência da interação raiz-rizóbio sobre os recursos vegetais disponíveis para outros mutualismos. As plantas amostradas em campo variaram entre 4 a 1300 unidade de tamanho. A interação raiz-rizóbio e nectário extrafloral-formiga ocorreu em plantas ainda muito pequenas, enquanto a interação flor-abelha se estabeleceu em plantas maiores. A intensidade da interação teve padrão exponencial para os nódulos radiculares e visitação das abelhas, e quadrático para as formigas. Esses padrões distintos na intensidade dos mutualismos sugeriram possível interf... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Plant phenotypic traits change drastically throughout plant development and can modify ecological interactions. Whereas there is an energy cost associated with maintenance of different mutualisms on the same plant, we investigated the relationship between plant development and the establishment of multiple mutualisms. Besides, we evaluated the possible interference of the root-rhizobia mutualism on extrafloral nectary-ant and flower-bee mutualisms. In the field, we selected 30 plants of Cerrado legume species, Chamaecrista desvauxii var. latistipula, with different sizes, from juvenile to reproductive individuals, to evaluate the occurrence and intensity of root-rhizobia, extrafloral nectary-ant and flower-bee interactions. In a greenhouse, we manipulate the rhizobia bacteria and soil type, investigating the interference of root-rhizobia on plant resources available for other mutualisms. Plants sampled in field ranged from 4 to 1300 plant size. Root-rhizobia and extrafloral nectary-ant interactions occurred on tiny plants, while flower-bee interaction was established on larger plants. The strength of interactions had an exponential pattern for root nodules and bee visitation, and quadratic for ant visitation. These distinct patterns suggested a possible interference between mutualisms since the number of root nodules and the flower-bee interaction increased and the extrafloral nectary-ant interaction decreased. Moreover, in the rhizobium exclusion experiment, plants with inoc... (Complete abstract click electronic access below) / Mestre

Na indução de resistência a planta possui mecanismos de defesa físicos e químicos para impedir a entrada e o desenvolvimento de patógenos e parasitas, incluindo fungos, bactérias, vírus, nematóides e até insetos. Estes mecanismos são ativados por infecções prévias ou pelo tratamento com agentes indutores (eliciadores) bióticos ou abióticos. Entre os agentes indutores bióticos, destaca-se a S. cerevisiae, que além da importância biotecnológica, tem demonstrado em estudos prévios potencial para o controle de doenças em várias plantas de importância econômica. Produtos à base de S. cerevisiae, como por exemplo o Agro-Mos® (carboidratos da parede celular da levedura) estão disponíveis no mercado, mas não como indutores de resistência. Já o indutor químico registrado como Bion® vem sendo comercializado e utilizado na indução de resistência em diversas espécies de plantas contra vários patógenos. Os objetivos deste trabalho foram purificar parcialmente frações de S. cerevisiae indutoras de resistência em pepineiro contra antracnose, causada por Colletotrichum lagenarium, e avaliar o efeito do extrato bruto autoclavado de S. cerevisiae, Agro-Mos® e Bion® na indução de resistência contra o inseto T. absoluta em tomateiro, o nematóide M. incognita em pepineiro, como também, verificar o efeito destes agentes na interação simbiótica entre soja e B. elkanii. Os resultados mostraram que o extrato bruto aquoso de S. cerevisiae autoclavado por 4 h foi o mais efetivo na redução da antracnose. Dessa maneira, o mesmo foi submetido à precipitação etanólica e o sobrenadante da precipitação foi fracionado utilizando-se Cromatografia de Troca Aniônica - CTA. Obtiveram-se quatro picos, sendo que os picos I (frações não ligada à resina DEAE-celulose) e II (frações ligadas à resina DEAE-celulose) foram os mais efetivos na proteção de plântulas de pepineiro reduzindo a severidade de antracnose em 80% e 72%, respectivamente. A aplicação foliar do extrato bruto aquoso de S. cerevisiae, Agro-Mos® e Bion® não afetou o desenvolvimento do inseto em tomateiro, como também, não interferiu significativamente na multiplicação do nematóide em raízes de pepineiro. Na interação simbiótica da soja com B. elkanii, os agentes testados não afetaram a nodulação por B. elkanii em raízes e o desenvolvimento vegetativo das plantas. Porém, a aplicação foliar do extrato bruto autoclavado de S. cerevisiae aumentou a quantidade de nitrogênio total da parte aérea das plantas. Finalmente, conclui-se que frações de S. cerevisiae induziram resistência em pepineiro contra C. lagenarium. Por sua vez, os agentes testados são foram eficientes no controle do inseto herbívoro e do nematóide e não demonstraram efeito negativo na interação soja - rizóbio. / In the resistance induction, the plant has physical and chemical defense mechanisms to avoid the entrance and the development of pathogens and parasites, including fungi, bacteria, virus, nematodes and even insects. These mechanisms are activated by previous infections or by the treatment with biotic and abiotic inducer agents. Among the biotic agents there is S. cerevisiae, that besides the biotechnological importance, was shown in previous studies to control diseases in several plants of economical importance. Products made of S. cerevisiae, as for exemple, the Agro-Mos® (formulated with carbohydrates from the cellular wall of the yeast) are available in the market, but not resistance inducers. The chemical inducer known as Bion® is already marketed and used to induced resistance in several plant species against several pathogens. The objectives of this work were to partially purify fractions of S. cerevisiae able to induce resistance in cucumber against anthracnose, caused by Colletotrichum lagenarium, and also evaluate the effect of the autoclaved crude aqueous extract from S. cerevisiae, Agro-Mos® and Bion® in the resistance induction against the insect T. absoluta in tomato plants, the nematode M. incognita in cucumber plants, as well as to verify the effect of the agents in the symbiotic interaction envolving soybean and B. elkanii. The results showed that the crude aqueous extract of S. cerevisiae autoclaved for 4 h was the most effective out in the reduction of cucumber anthracnose. Thus, the same extract was submitted to ethanolic precipitation and the obtained supernatant was fractioned by using Anion Exchange Chromatography - AEC. For peaks were obtained and peak I (non-adsorbed fraction to DEAE-Cellulose) and II (fraction adsorbed to DEAE-Cellulose) were the most effective out in the protection of the cucumber seedling by reducing anthracnose severity in 81% and 72% ,respectively. The application of the autoclaved extract of S. cerevisiae, Agro-Mos® and Bion® did not affect the development of the insect in tomato plants as well as did not interfere significantly in the multiplication of the nematode in cucumber roots. In the symbiotic interaction of soybean and B. elkanii, the tested agents did not affect the formation of nodules in soybean roots and the vegetative development of the plants. However, the foliar application of the autoclaved crude extract of S. cerevisiae significantly increased the amount of total nitrogen in the aerial part of the plants. Finally, it is concluded that the fractions (peaks I and II) of S. cerevisiae induced resistance of the cucumber plants. However the tested agents were not efficient in the control of the herbivore insect and the nematode and did not exhibit negative effects in the symbiotic interaction soybean and rhizobium.

Les légumineuses sont connues pour leurs capacités à établir une relation symbiotique avec des bactéries du sol fixatrices de l'azote atmosphérique. Cette interaction aboutit à la formation d'un nouvel organe au niveau des racines, la nodosité, au sein duquel le symbiote convertit l'azote atmosphérique (N2) en ammoniac, qui peut être directement consommé par les plantes. A l’intérieur de cette nodosité, la concentration en oxygène (O2) est maintenue à un très faible niveau car la réaction de réduction du N2 par l’enzyme bactérienne nitrogénase est inhibée par des traces d’oxygène. Un mécanisme de perception directe de l'O2 impliquant des membres de la famille des facteurs de transcription « Ethylene Responsive Factors » (ERFs) du groupe VII a récemment été découvert chez Arabidopsis thaliana. Ces facteurs de transcription (FT) possèdent une extrémité N-terminale caractéristique avec un résidu de cystéine à la seconde position. Dans des conditions normales d'O2, les FT sont conduit à la dégradation suivant une voie spécifique du protéasome. En condition de stress hypoxique, les TFs sont stabilisés et peuvent activer l’expression des gènes de réponse à l'hypoxie. Il a été démontré que la présence d’O2 et de NO était nécessaire pour déstabiliser ces protéines, et qu'une réduction de la disponibilité de l'un ou l'autre des gaz est suffisante pour protéger le résidu cystéine N-terminale de l'oxydation. L’objectif de cette thèse a été d'étudier le rôle de la famille ERF-VII dans la perception et l'adaptation au manque d'O2 chez M. truncatula. Des travaux ont aussi été menés pour déterminer l’importance du NO dans le fonctionnement en microoxie de la nodosité. Quatre gènes codant pour des facteurs de transcription de la famille ERF-VII ont été identifiés dans le génome de M. truncatula. La caractérisation de cette famille au niveau transcriptionnel a révélé que seul MtERF-B2.2 était induit par le stress hypoxique et au cours du développement des nodosités. Les trois autres, MtERF-B1.1, MtERF-B1.11 et MtERF-B2.3, sont constitutivement exprimés dans les feuilles, les racines et les nodosités. Pour étudier la stabilité de la protéine MtERF-B2.1, l’orthologue de RAP2.12 principal ERF-VII décrit dans la perception de l’O2 chez Arabidopsis, en fonction de la disponibilité de O2/NO, nous avons réalisé une protéine de fusion entre l’extrémité N-terminale de notre protéine et la protéine rapporteur luciférase. Les résultats obtenus sur des protoplastes d'Arabidopsis montrent l’implication la partie N-terminale de MtERF-B2.1 dans la régulation de la stabilité de la protéine, mais en contradiction avec les résultats obtenus en plantes composites de M. truncatula. La fonction de MtERF-B2.1 et MtERF-B2.11 a également été étudiée dans le cadre de la réponse au stress hypoxique et au cours du processus de nodulation en utilisant une stratégie d'interférence ARN. Des racines transgéniques dérégulées sur l’expression de MtERF-B2.1 et MtERF-B2.11 ont montré un défaut d’activation de plusieurs gènes de réponses à l'hypoxie tels que l’alcool déshydrogénase (ADH1) ou la pyruvate décarboxylase (PDC1). Ces racines transgéniques ARNi-MtERF-B2.1/B2.11 sont également affectées dans l'interaction symbiotique avec une réduction significative de la capacité de nodulation et de l'activité de fixation de l'azote dans les nodules matures. En conclusion, ces travaux révèlent que le mécanisme de détection d'O2 est médié par les ERF-VII dans les nodosités de M. truncatula et que ce mécanisme, associé aux cibles moléculaires régulées en aval, participe au développement de cet organe et au maintien de la capacité de fixatrice de celui-ci. De plus, les résultats indiquent que MtERF-B2.1/B2.11 sont des régulateurs positifs du métabolisme anaérobie et que les gènes associés au cycle hémoglobine-NO sont susceptibles d'activer d'autres voies de génération d'ATP. / Legume crops are known for their capacities to establish a symbiotic relationship with nitrogen fixing soil bacteria. This mutualism culminates in the formation of a new plant organ, the root nodule, in which the symbiont converts atmospheric nitrogen (N2) into ammonia, which can be directly consumed by plants. In nodules, bacterial nitrogenase enzyme is inhibited by traces of oxygen (O2) so different mechanisms maintain this organ at low O2 level. At the same time, nodules need to maintain a high ATP level to support the nitrogenase activity, which is highly energy demanding. Thus, a balance between a tight protection from O2 and an efficient energy production, referred as the “O2 paradox” of N2-fixing legume nodules, has to be reached. In Arabidopsis thaliana, a direct oxygen sensing mechanism has recently been discovered involving members of the ethylene responsive factors (ERFs) group VII. These transcription factors (TFs) possess a characteristic N-terminal amino acid with a cysteine residue at the second position that, under normal O2 conditions, leads to protein degradation following a specific pathway called the N-end rule pathway. Furthermore, it was shown that both O2 and nitric oxide (NO) are required to destabilize the ERFs VII and that a reduction in the availability of either gas is sufficient to stabilize these proteins. Therefore, the goal of this thesis was to investigated the role of ERF-VII family in O2 sensing and adaptation to hypoxia in M. truncatula, model plant for legumes, and to understand how NO interacts with O2 in hypoxic signalization in the microoxic environment that characterizes the nodule. We identified four genes belonging to the ERF-VII TF family in the M. truncatula genome, which present a strong similarity with ERF-VII of Arabidopsis. The characterization of this family at the transcriptional level revealed that only MtERF-B2.2 is up-regulated by hypoxia stress and during nodule development. The three others, MtERF-B1.1, MtERF-B1.11 and MtERF-B2.3 are found constitutively expressed in leaves, roots and nodules. To investigated the protein stability of MtERF-B2.1, the closest orthologous to AtRAP2.12 described as O2-sensors in Arabidopsis, in function of O2/NO availability, we realized a fusion protein with the luciferase reporter protein. Our results on Arabidopsis protoplasts indicated that the N-terminal part of MtERF-B2.1 drives its O2-dependent degradation by the N-end rule pathway. The function of MtERF-B2.1 and MtERF-B2.11 was also investigated both in response to hypoxia stress and during the nodulation process using an RNA interference strategy. Silencing of MtERFB2.1 and MtERF-2.11 showed a significant lower activation of several core hypoxia-responsive genes such as ADH1, PDC1, nsHb1 and AlaAT. These double knock-down transgenic roots were also affected in symbiotic interaction with a significant reduction of the nodulation capacity and nitrogen fixation activity in mature nodules. Overall, the results reveal that O2 sensing mechanism is mediated by ERF-VIIs in M. truncatula roots and nodules and that this mechanism, together with downstream targets, is involved in the organ development and ability to efficiently fix nitrogen. Furthermore, results indicated that MtERF-B2.1/B2.11 are positive regulator of the anaerobic metabolism and the Hb-NO cycle– related genes likely in order to activate alternative ATP generation pathways.