Maize anthracnose, caused by the fungus Colletotrichum graminicola, is an economically important species contributing to major yield losses. C. graminicola is a hemibiotroph; initially it invades its host while it is alive, and then it switches to destructive necrotrophic growth and the host is killed. Establishment of compatible interactions by biotrophic pathogens is usually associated with suppression of host defenses and cell death, while necrotrophic pathogens typically secrete phytotoxic compounds and induce cell death. To understand the relationship of hemibiotrophy in C. graminicola to biotrophy and necrotrophy, I compared a compatible and an incompatible interaction, utilizing a non-pathogenic mutant strain that is very similar to the wild type in vitro. I developed an assay to visualize in detail living fungal and host cells during pathogenic and nonpathogenic interactions. My results provided evidence that C. graminicola produces diffusible substances during colonization that predispose nearby living host cells for fungal invasion. My observations further suggested that the mutant is nonpathogenic because it fails to produce these substances. To explore the possibility that the C. graminicola mutant is impaired in the production and/or secretion of one or more secondary metabolites (SM), I characterized the range of SM-associated genes in C. graminicola. C. graminicola has a large and diverse repetoire of these genes, indicating significant capacity for the production of SM. I then characterized the global expression of fungal genes during different developmental phases in both compatible and incompatible interactions. I found that SM-associated genes are expressed during early and late stages of maize infection. Secreted proteins and putative effectors were overrepresented among differentially regulated predicted gene products. There were relatively few differences in expression between the mutant and wild type, suggesting that differences between them may relate to post-transcriptional events. The transcriptional analysis indicated that the mutant was defective very early in biotrophy. This study indicates that biotrophy and necrotrophy coexist in this pathosystem in different cells, and that arrays of differentially regulated and locally expressed genes are involved in maintaining this balance. Understanding the nature of induced susceptibility may lead to new therapeutic targets for management of this damaging disease.

Bionanotechnology is an intersection between biology and nanotechnology, a field in which novel applications for very small materials are being realised at an alarming rate. Nanoparticles have 3 dimensions that can be measured in nanometers, their small size conferring upon them different properties from individual atoms or the bulk material. The interactions between these unique materials and microorganisms are often toxic, thus have been exploited for antimicrobial applications. However, there is a considerable paucity of data for the underlying molecular mechanisms. This study has been carried out to investigate the interactions that occur between nanoparticles and bacteria with the objective of identifying these toxicological mechanisms and novel nanoparticle effects, using the model Gram negative organism Escherichia coli K12. This study has identified metal nanoparticles that are a superior vehicle for the delivery of toxic metal ions to E. coli. The nanoparticles associate with the bacterial surface, but do not cross the cell wall. They then dissolve, releasing a concentration of metal ions that accumulate at the bacterial-nanoparticle interface, enhancing the antibacterial efficacy compared to the concentration of metal ions in the bulk solution phase. Measurement of the whole transcriptome response to silver nanoparticles in comparison to the silver ion indicates that the different modes of ion delivery may induce a differential stress response. Moreover, this data identifies molecular mechanisms that are involved in the toxicity of this metal that is now becoming increasingly prevalent in society. The dissolution based toxic effects of zinc oxide nanoparticles are augmented by an interaction with ultra-violet light, offering an alternative mode for nanoparticle toxicity.

Résumé: De nos jours, les bactériophages (c.-à-d. des virus bactériens, ou phages) sont reconnus comme un des principaux facteurs qui influencent l’évolution et la biologie bactérienne. De plus, la nature dynamique des relations phage-hôte engendre des adaptations mutuelles au niveau des stratégies d’infection et de défense, phénomène communément appelé « course à l’armement ». Malgré une importance démontrée chez de nombreuses espèces bactériennes, l’étude du rôle des phages dans la biologie du pathogène Clostridium difficile est demeurée très limitée. Or, les infections à C. difficile sont considérées comme étant la principale cause des diarrhées associées à la prise d’antibiotiques. Alors, l’objectif de la présente étude avait pour but de mieux caractériser l’implication des phages dans la biologie de C. difficile. Des travaux préalables ont montré que la lysogénisation par le phage tempéré φCD38-2 pouvait mener à une augmentation de la production de toxines chez certaines souches de C. difficile suggérant une implication des phages dans la virulence bactérienne. En utilisant cette étude comme point de départ, nous avons évalué l’influence de la lysogénisation du phage φCD38-2 sur le transcriptome global d’une souche de C. difficile d’importance clinique. Ainsi, nous avons montré que la lysogénisation par le phage φCD38-2 a un impact significatif sur la transcription de 39 gènes bactériens dont près de la moitié encodent des protéines reliées au métabolisme des sucres, suggérant une implication du phage dans les processus métaboliques de l’hôte. Cependant, le gène présentant la plus grande altération transcriptionnelle encode une protéine de surface nommée CwpV. À partir de sa localisation sur la surface bactérienne, nous avons démontré que son expression a un effet protecteur sur les cellules face aux infections par les phages. Les expériences subséquentes ont permis de lier l’activité antiphage au domaine carboxy-terminale variable de la protéine. Étant donné que l’adsorption virale n’est pas affectée par la présence de CwpV, nous avons établi que le mode d’action du système consiste à bloquer l’injection d’ADN virale dans la cellule bactérienne. De plus, l’effet antiphage est plus prononcé envers les siphophages comparé aux myophages suggérant un mode d’action dépendant de la morphologie virale. Finalement, les expériences préliminaires suggèrent que les cellules qui expriment la CwpV ont un avantage sélectif par rapport aux cellules qui ne l’expriment pas dans un essai de co-culture soumise à une infection virale. / Abstract: Bacteriophages (or simply phages) are viruses that specifically infect and kill bacteria. They are omnipresent in every niche where bacteria thrive and as such are considered as the most abundant biological entities in the biosphere. Their massive impact on bacterial biology has incited scientific community to consider the phages as the major driving force in bacterial evolution. Nowadays, it is also assumed that phages act as the principal vectors for horizontal transfer of genetic information among prokaryotes. Moreover, highly dynamic nature of phage host relationships usually results in mutual adaptations that effectively stimulates acquisition of new offensive and defensive strategies. This phenomenon is generally described as the “phage-host arms race”. Despite their obvious importance, the contribution of phages to the biology of Clostridium difficile, the main cause of nosocomial infectious diarrhea, has not been extensively explored. Thus, the main objective of this study was to assess the overall impact of phages to C. difficile lifestyle. Our previous work has revealed the potential of a specific C. difficile phage termed φCD38-2 to stimulate the production of bacterial toxins. Based on those results, we have performed a global study of the impact of the φCD38-2 lysogeny on the bacterial transcriptome. Thus, we have found a total of 39 genes whose expression was altered during the lysogeny of φCD38- 2 with near half of them encoding proteins implicated in bacterial sugar metabolism. This suggests phage implication in the regulation of bacterial utilization of carbon sources. However, the largest transcriptional alteration has been observed for cwpV which encodes a phase-variable surface-anchored protein. Owing to its variable nature, we have hypothesized that CwpV might play a role in phage infection and indeed, we have shown that CwpV expression protects bacterial cells from phage infection. Moreover, variable C-terminal domain of CwpV was found to be essential for antiphage phenotype since its deletion restored bacterial susceptibility to infection. Additionally, CwpV did not significantly affect phage adsorption, but phage DNA replication was prevented suggesting that CwpV act as a superinfection exclusion system. Interestingly, the antiphage effect was more pronounced against phages from Siphoviridae family compared to phages from Myoviridae family suggesting that structural differences are important for the antiphage phenotype. Finally, our preliminary data suggest that CwpV expression confers selective advantage when mixed cocultures are challenged by phage infection.

Background: The pink bollworm Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) is one of the world's most important pests of cotton. Insecticide sprays and transgenic cotton producing toxins of the bacterium Bacillus thuringiensis (Bt) are currently used to manage this pest. Bt toxins kill susceptible insects by specifically binding to and destroying midgut cells, but they are not toxic to most other organisms. Pink bollworm is useful as a model for understanding insect responses to Bt toxins, yet advances in understanding at the molecular level have been limited because basic genomic information is lacking for this cosmopolitan pest. Here, we have sequenced, de novo assembled and annotated a comprehensive larval midgut transcriptome from a susceptible strain of pink bollworm. Findings: A de novo transcriptome assembly for the midgut of P. gossypiella was generated containing 46,458 transcripts (average length of 770 bp) derived from 39,874 unigenes. The size of the transcriptome is similar to published midgut transcriptomes of other Lepidoptera and includes up to 91 % annotated contigs. The dataset is publicly available in NCBI and GigaDB as a resource for researchers. Conclusions: Foundational knowledge of protein-coding genes from the pink bollworm midgut is critical for understanding how this important insect pest functions. The transcriptome data presented here represent the first large-scale molecular resource for this species, and may be used for deciphering relevant midgut proteins critical for xenobiotic detoxification, nutrient digestion and allocation, as well as for the discovery of protein receptors important for Bt intoxication.

Microalgae are widely viewed as a potential source of renewable biofuels. Microalgae are highly productive and can be cultured in recycled water on margial or non-agricultural land. Despite their advantages, the industrial scale deployment of microalgae faces numerous challenges including relatively little knowledge of the algae themselves and the comparatively expensive infrastructures required for culture. The green microalga, Botryococcus braunii is particularly interesting because it synthesizes long-chain (C30- C40) hydrocarbons that can be converted to liquid fuel by hydrogenation and catalytic cracking. Moreover, B. braunii is the major fossil present in the Ordovician oil shales and kerogen deposits. Although studied since the 1970s, very little is known regarding critical aspects of B. braunii, notably its molecular biology. In higher plants molecular clocks have been well defined and transcript profiling has revealed a sophisticated network of circadian scheduling of metabolic processes. Characterization of temporal controls over hydrocarbon synthesis is therefore of importance to optimization of biofuel production from B. braunii. In this project B. braunii (Race B, strain Guadeloupe) were cultured in a 12-hour photoperiod and either maintained in that regime or transferred to constant light. Algae were sampled every 4 hours, during a 28-hour time-course and mRNA extracted. mRNA was reverse-transcribed to cDNA and sequenced using a paired-end protocol on an Illumina HiSeq 2000 platform. Over 2 billion sequence reads of 100 bp were generated and assembled de novo, into a complete transcriptome for B. braunii. The transcriptome was comprehensively annotated using global and targeted protocols and differential expression and co-expression analyses were performed. Metabolic pathway analysis confirmed the presence, and photoperiodic regulation of the MEP/DOXP Terpenoid Backbone synthesis pathway. Targeted annotation and expression analysis revealed two predicted B. braunii circadian clock components, which were incorporated into a B. braunii circadian clock model. In non-hierarchical cluster analysis, contigs of the B. braunii transcriptome clustered under four distinct patterns of diel expression. Networks of co- and anti-expressed contigs were elucidated by hierarchical clustering. These results demonstrate the exquisite control over metabolism in B. braunii. Such knowledge is essential for the industrial applications of B. braunii, either directly or through the engineering of selected B. braunii genes or molecular pathways into alternative chassis.

La cornification est la dernière étape de la différenciation terminale de l'épiderme. Elle est caractérisée par de profonds remaniements morphologiques et biochimiques du kératinocyte et aboutit à la formation d'une couche cornée solide, résistante, imperméable et hydratée, responsable de la fonction " barrière " de l'épiderme. Certaines génodermatoses rares, appelées ichtyoses, sont dues à des mutations de gènes impliqués dans la cornification. Le " Peeling Skin Disease " (PSD, OMIM 270300) est une ichtyose inflammatoire généralisée, caractérisée par une importante desquamation, de l'eczéma et un prurit souvent sévère et insomniant. Cette maladie chronique entraine une altération importante de la qualité de vie du patient. A ce jour, aucune thérapie efficace n'est disponible. Le PSD est dû à des mutations homozygotes du gène Cornéodesmosine (CDSN), qui code une protéine adhésive de l'épiderme essentielle à la cohésion du stratum corneum (SC) et à l'homéostasie de la barrière épidermique. La physiopathologie du PSD est encore mal connue. Le décollement du SC conduit à une rupture de la barrière épidermique, qui déclenche à son tour érythème, atopie et prurit, par des mécanismes non élucidés. Afin de décortiquer ces mécanismes, j'ai utilisé deux modèles murins d'invalidation du gène Cdsn (knock-out, KO) dans l'épiderme. Le premier mime le stade précoce du PSD (décollement du SC chez l'embryon E18.5 Cdsnep-/-) et le second, qui est inductible, reproduit le stade chronique (défaut persistant de la barrière épidermique chez la souris adulte Cdsniep-/-). J'ai réalisé l'étude comparative du transcriptome cutané de ces deux modèles à l'aide de puces à ADN. Des signatures d'expression génique distinctes, en lien avec une réponse de restauration de la barrière cutanée, ont été obtenues : induction principalement de gènes de l'inflammation et de la prolifération (Cdsnep-/-) vs des gènes de défenses de l'hôte et de la cornification (Cdsniep-/-). En particulier, une forte expression de gènes codant des inhibiteurs de protéases à cystéine de la famille des stéfines A (cystatine A chez l'homme) et des protéases à sérine de la famille des kallikréines (KLKs), caractérise le modèle adulte Cdsniep-/-. Ceci a été secondairement confirmé dans l'épiderme de patients atteints de PSD. Parmi les KLKs, KLK13 est apparue la plus fortement exprimée, contrairement à KLK5 dont l'expression reste faible et stable. KLK13 pourrait donc intervenir dans la réponse inflammatoire et/ou la desquamation, mécanismes dans lesquels jusqu'à présent seule KLK5 a été décrite comme jouant un rôle central. Une surexpression de KLK13 avait déjà été décrite dans l'épiderme de patients atteints de PSD et au niveau de lésions psoriasiques, ce qui conforte notre hypothèse. Ainsi, mes résultats mettent en lumière KLK13, dont la fonction dans l'épiderme est encore très peu connue. En parallèle, dans le cadre d'un travail collaboratif, j'ai participé à une étude centrée sur la composante inflammatoire de la maladie, réalisée à l'aide de notre modèle de souris adultes Cdsniep-/-. Les résultats obtenus montrent un développement simultané des voies inflammatoires de type Th2 et Th17, ainsi qu'une contre-régulation entre ces deux axes au cours de la maladie chez la souris. En conclusion, mon travail contribue à mieux comprendre les mécanismes physiopathologiques du PSD. Notamment, le modèle adulte Cdsniep-/- apparaît comme particulièrement pertinent pour étudier la maladie humaine. L'exploration du rôle, dans le contexte du PSD, des gènes candidats identifiés pourrait déboucher sur la découverte de nouvelles cibles thérapeutiques. Enfin, nos résultats seront certainement bénéfiques à l'étude d'autres maladies dermatologiques inflammatoires rares (syndrome de Netherton, syndrome SAM) ou fréquentes (psoriasis, dermatite atopique), qui présentent un défaut de barrière épidermique. / Cornification is the final step of epidermal differentiation. It is characterized by structural and biochemical modifications of keratinocytes and leads to the formation of a solid, resistant, impermeable and moisturized cornified layer, responsible for the "barrier" function of the epidermis. Some rare genodermatoses, called ichthyoses, are caused by mutations of genes involved in cornification. The Peeling Skin Disease (PSD, OMIM 270300) is a generalized inflammatory ichthyosis characterized by important desquamation, eczema and severe itching. This chronic disease severely affects patients 'quality of life and no specific therapy is currently available. PSD is due to homozygous mutations in the Corneodesmosin (CDSN) gene, which codes an adhesive epidermal protein crucial for the cohesion of the stratum corneum (SC) and the epidermal barrier homeostasis. The pathophysiology of PSD is still poorly understood. The detachment of the SC leads to an impairment of the epidermal barrier which could in turn trigger erythema, atopic manifestations and pruritus by so far unidentified mechanisms. In order to dissect these mechanisms, I used two epidermis-specific Cdsn-deficient mouse models (knock-out, KO). The first mimics the early phase of PSD (detachment of the SC in Cdsnep-/- E18.5 embryos) and the second, inducible, reproduces the chronic phase (permanent permeability defect in Cdsniep-/- adult mice). I performed a comparative analysis of the skin transcriptome between these two models using DNA microarrays. Distinct molecular signatures related to a skin barrier repair response were highlighted: increased expression of inflammatory and proliferative genes (Cdsnep-/-) vs antimicrobial defense and cornification genes (Cdsniep-/-). In particular, a strong expression of genes coding for inhibitors of cysteine proteases from the stefin A family (cystatin A in humans), and serine proteases of the kallikrein (KLK) family, was distinguishable in Cdsniep-/- mice. This was secondarily confirmed in the epidermis of PSD patients. Among the KLKs, KLK13 was the most strongly up-regulated, contrary to KLK5 whose expression remains low and constant. Thus, KLK13 could take part into the inflammatory response and/or the desquamation when until now only KLK5 was described as playing a central role in these mechanisms. An up-regulation of KLK13 has already been described in the epidermis from PSD patients and from chronic psoriatic plaques, reinforcing our hypothesis. Thus, my results highlight KLK13, whose epidermal function is still poorly characterized. At the same time, I was part of a collaborative study focusing on the inflammatory component of the disease carried out with our Cdsniep-/- adult mouse model. The results showed a simultaneous development of type 2 and type 17 T lymphocytes responses as well as a counter-regulation between these two inflammatory axes. In conclusion, my work contributes to a better understanding of PSD pathophysiology. Notably, the Cdsniep-/- adult mouse model seems especially relevant to study the human disease. A further exploration, in the context of PSD, of the role of the candidate genes we identified could lead to the discovery of new therapeutic targets. Finally, our results will certainly be helpful for the understanding of other inflammatory skin diseases with epidermal barrier defects, whether they are rare (Netherton syndrome, SAM syndrome) or frequent (psoriasis, atopic dermatitis).

Circadian rhythms are ubiquitous among organisms, influencing a wide array of physiological processes and behaviors including aggression. While many neurophysiological mechanisms are involved in the regulation of aggressive behaviors, relatively few studies have investigated the underlying components involved in the interplay between circadian rhythms and aggression. Spiders are an ideal model system for studying circadian regulation of aggression as they are ecologically both predators and prey. Recent studies have revealed a nocturnal orb- weaving spider Larinioides cornutus exhibits a diel and circadian rhythm in anti-predator behavior (i.e. boldness) that can be manipulated by administration of octopamine (OA) and serotonin (5- HT). Dosing of OA increases boldness of an individual while 5-HT decreases boldness levels. Thus, it appears the serotonergic and octopaminergic system are playing a key role in the daily fluctuations of boldness. This study took a holistic approach to investigate OA and 5-HT levels of head tissue and hemolymph (i.e. blood) as well as the genes involved in synthesis, signaling, and degradation of these monoamines throughout the day (0100, 0700, 1300, and 1900 hours) using HPLC-ED and RNA-sequencing. Although endogenous and circulating levels of OA did not significantly fluctuate, putative transcripts involved in synthesis and signaling did increase in relative expression levels at dusk when L. cornutus begins to actively forage for prey. Endogenous and circulating levels of 5-HT also did not significantly change at the four different time points, but clear patterns of upregulation of 5-HT synthesis enzymes as well as some receptor transcripts were upregulated during the day when L. cornutus would be mostly inactive in its retreat. Lastly, monoamine oxidase, a major catabolic enzyme of monoamines in vertebrates and some invertebrates, was identified in L. cornutus and exhibited substrate specificity for OA compared to 5-HT. Together with the higher enzymatic activity at mid-day compared to dusk, MAO appears to be playing a significant role in regulating the OA and 5-HT signaling in L. cornutus. In conclusion, these results allow a unique preliminary perspective on how OA and 5-HT are influencing the diel shifts in aggression-related behaviors in an ecologically dynamic arthropod.

<p>Iron is an essential micronutrient for plant growth, development and productivity. Although it is abundant in soil, the bio-availability of iron is often low for plants in many areas of the world. The insufficient quantity of usable iron in plants causes reduction in chlorophyll synthesis, reduced photosynthesis rate and decreased growth and yield. Two major strategies, Strategy I and II, have been discovered to be involved in response to low iron and a complex network of biochemical and molecular pathways participate in the processes. </p> <p> </p> <p>Cellular transcriptional regulation is associated with iron deficiency responses. Multiple genes and pathways involved in iron-deficiency responses have been identified in plants in the past decade. Here, we measured different physiological parameters and used RNA-Seq to elucidate the physiological and molecular responses in early stage of iron deficiency in the whole leaf of model plant species Arabidopsis thaliana. In this study, Arabidopsis showed reduced chlorophyll content, increased ferric reductase activity and reduced antioxidant enzyme activities when stressed by iron deficiency. In addition, we have identified multiple pathways that may play promising roles in the response to iron deficiency, e.g., 1) we found that the auxin biosynthesis under iron deficiency is preferentially depended on the TAA-YUC pathway rather than the CYP79 pathways; 2) TCA cycle is involved in mediating the acclimation process to the stress condition; 3) glucosinolate synthesis could be a limiting factor for iron deficiency response due to its negative relationship with hormone and energy metabolism.</p> <p> </p> Systemic signals generated from leaves are critical for triggering iron deficiency responses in roots. Due to the physiological characteristic and cellular ultrastructure of companion cells (CCs), we hypothesize that the CCs located in phloem play essential roles in regulating systemic nutrient signaling. In this study, by using a cell-specific TRAP-Seq, we discovered that not only CCs respond more drastically than the other cells in leaf, the altered molecular pathways in the CCs are also more diverse during early iron deficiency response. In particular, we found that auxin and sucrose transport and metabolism in the CCs may be two of the key regulatory processes that plants use to exert the shoot-to-root signaling process. Our discoveries have collectively suggested that CCs may function as the central machinery in the systemic signaling in response to iron deficiency. A comparison between whole leaf transcriptome and translatome also suggested that translatomic analysis is a more sensitive method for gene profiling than conventional transcriptomic analysis.

Os insetos são capazes de sobreviver em diversos ecossistemas do planeta e, mesmo estando constantemente expostos à ameaça de infecção microbiana, permanecem livres de infecções na maior parte do tempo. Essa capacidade de sobrevivência aliada à larga distribuição dos insetos em regiões totalmente diferentes tem estimulado a pesquisa de novos agentes terapêuticos nesta classe devido à descoberta de diversos componentes de mecanismos inespecíficos de combate à infecção, sendo possível sua aplicação no controle de diversas doenças. Todavia, apesar de um grande número de moléculas de defesa ter sido identificado a partir de vários insetos, pouca informação sobre suas aplicações está disponível. Desta forma, o presente trabalho elucida o perfil transcriptômico geral e dos genes de defesa do tegumento de Podalia orsilochus durante sua fase larval. Como consequência, os transcritos e os dados obtidos permitirão o auxílio em pesquisas posteriores, seja para comparação, citação, conhecimento biológico e das respostas de defesa ou das relações de filogenia do animal. / The insects are able to survive in diverse ecosystems on earth, and even being constantly exposed to the threat of microbial infections, remain free of infection for most of the time. This survivability combined with the wide distribution of insects in totally different regions has stimulated the search for new therapeutic agents in this class due to the discovery of several components of nonspecific mechanisms to fight infection, and possible implementation in the control of various diseases. However, despite a large number of defense molecules have been identified from various insects, little information is available on their applications. Thus, this paper elucidates the general transcriptomic profile and integument of defense gene Podalia orsilochus during their larval stage. As a result, the transcripts and the data obtained will aid in further research, to compare, reference, biological knowledge and defense or animal phylogeny relationships.

Diversos estudos elucidaram mecanismos envolvidos com a organogênese in vitro, porém pouco é conhecido a respeito da fase de aquisição de competência, fundamental para que a regeneração ocorra. Alguns genes já foram identificados por interferirem na fase de aquisição de competência em tomateiro (Solanum lycopersicum), mas ainda existem diversas lacunas a serem esclarecidas. Para investigar a expressão de genes e o controle hormonal na fase de aquisição de competência, foram utilizados os mutantes de tomateiro, sob o background genético da cultivar Micro-Tom (MT), MT-Rg1 e MT-pro (procera), os quais afetam positiva ou negativamente a organogênese in vitro, respectivamente. Embora a resposta constitutiva a giberelina no mutante MT-pro seja conhecida, a identidade molecular do gene RG1 permanece indefinida. O mutante MT-Rg1 apresenta aumento tanto na formação de gemas caulinares quanto de raízes e reduz o tempo necessário para a indução desses órgãos, devido à diminuição do período para a aquisição de competência. A partir do estabelecimento das fases de aquisição de competência e indução da organogênese in vitro para MT e MT-Rg1, foram identificados genes diferencialmente expressos entre estes genótipos. Entre estes genes, CELL DIVISION CYCLE ASSOCIATED 7 e LACCASE 1A estão regulados positivamente em MT-Rg1 e todos estão fortemente relacionados à fase de aquisição de competência, e a alterações na proliferação de células do protoxilema durante o início da organogênese. Por outro lado, a resposta constitutiva à giberelina no mutante MT-pro reduz a formação de gemas caulinares e raízes e aumenta a formação de calos in vitro, sem afetar o tempo requerido para a indução de gemas caulinares e raízes. De forma oposta a MT-Rg1, o gene CDCA7 apresenta expressão reduzida durante a fase de aquisição de competência em MT-pro, diminuindo o número de células do protoxilema em divisão. Outro fator importante para a divisão celular no mutante MT-pro é o aumento da expressão do gene WUS, causando um aumento da proliferação das stem cells, que são células indiferenciadas relacionadas à formação de novos órgãos. Esta proliferação celular inadequada, somada a uma alteração desfavorável na homeostase das citocininas, justifica o efeito negativo do alelo pro na formação de gemas caulinares, o que permitiu a criação de um novo modelo para organogênese in vitro / Several studies have enabled the discovery of mechanisms to achieve in vitro organogenesis; however, little is known about the phase of acquisition of competence, essential for regeneration. A few genes have been identified to interfere in the acquisition of the competence phase in tomato (Solanum lycopersicum), but there are still many gaps to be filled. We have used the mutants, under the genetic background of the Micro-Tom cultivar, MT-Rg1 and MT-pro (procera), which positively or negatively affect in vitro organogenesis, respectively, to investigate gene expression and the hormonal control in the phase of acquisition of competence. Despite the fact that the constitutive gibberellin response in the procera mutant is well-established, the molecular identity of RG1 gene remains unknown. The MT-Rg1 mutant presents an increase in the formation of both shoot and roots and a reduced period for the induction of these organs, because of the reduced time required for acquisition of competence.We searched for the identity of differentially expressed genes between MT and MT-Rg1 after the establishment of the competence acquisition phase and organogenesis induction stages. Among those genes, CDCA7 and LAC1A are upregulated in MT-Rg1 and these genes appear to be strongly related with the acquisition of competence phase and changes in proliferation of protoxylem cells during early organogenesis. The constitutive response to gibberellin in the MT-pro mutant decreases the formation of shoot and roots and increase in vitro calli formation, without reducing the induction phase of shoots and roots. Unlike MT-Rg1, MT-pro reduces the CDCA7L expression during the acquisition of competence phase, causing a reduction of the protoxylem dividing cells. Another important factor for cell division in MT-pro mutant is the increased expression of the WUS gene, leading to an abnormal proliferation of stem cells. Thereby, this abnormal cell proliferation, in addition to an unfavorable change in the cytokinin homeostasis, justify the negative effect of the pro allele in the shoot formation, which enabled the proposal of a new model for in vitro organogenesis