The control of cellular tyrosine phosphorylation levels is of great importance in many biological systems. Among the kinases and phosphatases that modulate these levels, the LAR-RPTPs have been suggested to act in several key aspects of neural development, and in a dysfunctional manner in various pathologies from diabetes to cancer. The aim of this thesis is to describe the physiological functions of one of the members of this subfamily of RPTPs, namely RPTPsigma. First, we showed that glucose homeostasis is altered in RPTPsigma null mice. They are hypoglycemic and more sensitive to exogenous insulin and we proposed that the insulin hypersensitivity observed in RPTPsigma-null mice is likely secondary to their neuroendocrine dysplasia and GH/IGF-1 deficiency. In addition to regulating nervous system development, RPTPsigma was previously shown to regulate axonal regeneration after injury. In the absence of RPTPsigma, axonal regeneration in the sciatic, facial and optical nerves was enhanced following nerve crush. However, myelin-associated growth inhibitory proteins and components of the glial scar such as CSPGs (chondroitin sulfate proteoglycans) have long been known to inhibit axonal regeneration in the CNS, making spinal cord injury irreversible. In collaboration with Dr Samuel David, we unveiled that RPTPsigma null mice are able to regenerate their corticospinal tract following spinal cord hemisections as opposed to their WT littermates. We then isolated primary neurons from both sets of animals and found that the absence of RPTPsigma promotes the ability of the neurons to adhere to certain inhibitory substrates. Finally, in order to better understand the physiological role of RPTPsigma, we used a yeast substrate-trapping approach, to screen a murine embryonic library for new substrates. This screen identified the RhoGAP p250GAP as a new substrate, suggesting a downstream role for RPTPsigma in RhoGTPase signaling. We also identified p130Cas and Fyn as new binding partners. All these proteins have clear functional links to neurite extension. The characterization of RPTPsigma and its signaling partners is essential for understanding its role in neurological development and may one day translate into treatments of neural diseases and injuries.

Cholinergic inputs from mesopontine tegmentum activate midbrain dopamine (DA) neurons via M5 muscarinic receptors. The M5 receptor is important for mesopontine stimulation-induced accumbal or striatal DA efflux, brain stimulation reward or morphine-induced conditioned place preference (CPP). M5 receptor knockout (KO) mice show 40-50% less morphine-induced locomotion. Pedunculopontine tegmental nucleus (PPT) lesions in rodents block morphine CPP, but are ineffective after 18 hours food deprivation, opiate dependence, or intra-VTA BDNF. Based on these findings, we investigated whether acute food deprivation or intra-VTA BDNF alters morphine-induced locomotion (3 and 10 mg/kg, i.p.) in C57BL/6 M5 KO mice. Non-deprived M5 KOs showed reduced morphine-induced locomotion, suggesting M5 receptors partly mediate morphine-induced locomotion. Morphine-induced locomotion was reversed in food-deprived mice, suggesting the stimulant effects of morphine were altered to bypass the PPT. Unexpectedly, intra-VTA BDNF infusions were ineffective in altering morphine-induced locomotion. Additionally, M5 KOs receiving intra-VTA saline showed no deficits in morphine-induced locomotion.

Cholinergic inputs from mesopontine tegmentum activate midbrain dopamine (DA) neurons via M5 muscarinic receptors. The M5 receptor is important for mesopontine stimulation-induced accumbal or striatal DA efflux, brain stimulation reward or morphine-induced conditioned place preference (CPP). M5 receptor knockout (KO) mice show 40-50% less morphine-induced locomotion. Pedunculopontine tegmental nucleus (PPT) lesions in rodents block morphine CPP, but are ineffective after 18 hours food deprivation, opiate dependence, or intra-VTA BDNF. Based on these findings, we investigated whether acute food deprivation or intra-VTA BDNF alters morphine-induced locomotion (3 and 10 mg/kg, i.p.) in C57BL/6 M5 KO mice. Non-deprived M5 KOs showed reduced morphine-induced locomotion, suggesting M5 receptors partly mediate morphine-induced locomotion. Morphine-induced locomotion was reversed in food-deprived mice, suggesting the stimulant effects of morphine were altered to bypass the PPT. Unexpectedly, intra-VTA BDNF infusions were ineffective in altering morphine-induced locomotion. Additionally, M5 KOs receiving intra-VTA saline showed no deficits in morphine-induced locomotion.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Reducing the production cost of industrial biofuels will greatly facilitate their proliferation and co-integration with fossil fuels. The cost of feedstock is the largest cost in most fermentation bioprocesses and therefore represents an important target for cost reduction. Meanwhile, the biorefinery concept advocates revenue growth through complete utilization of by-products generated during biofuel production. Taken together, the production of biofuels from low-cost crude glycerol, available in oversupply as a by-product of bioethanol production, in the form of thin stillage, and biodiesel production, embodies a remarkable opportunity to advance affordable biofuel development. However, few bacterial species possess the natural capacity to convert glycerol as a sole source of carbon and energy into value-added bioproducts. Of particular interest is the anaerobe Clostridium pasteurianum, the only microorganism known to convert glycerol alone directly into butanol, which currently holds immense promise as a high-energy biofuel and bulk chemical. Unfortunately, genetic and metabolic engineering of C. pasteurianum has been fundamentally impeded due to a complete lack of genetic tools and techniques available for the manipulation of this promising bacterium. This thesis encompasses the development of fundamental genetic tools and techniques that will permit extensive genetic and metabolic engineering of C. pasteurianum. We initiated our genetic work with the development of an electrotransformation protocol permitting high-level DNA transfer to C. pasteurianum together with accompanying selection markers and vector components. The CpaAI restriction-modification system was found to be a major barrier to DNA delivery into C. pasteurianum which we overcame by in vivo methylation of the recognition site (5’-CGCG-3’) using the M.FnuDII methyltransferase. Systematic investigation of various parameters involved in the cell growth, washing and pulse delivery, and outgrowth phases of the electrotransformation procedure significantly elevated the electrotransformation efficiency up to 7.5 × 104 transformants µg-1 DNA, an increase of approximately three orders of magnitude. Key factors affecting the electrotransformation efficiency include cell-wall-weakening using glycine, ethanol-mediated membrane solubilization, field strength of the electric pulse, and sucrose osmoprotection. Following development of a gene transfer methodology, we next aimed to sequence the entire genome of C. pasteurianum. Using a hybrid approach involving 454 pyrosequencing, Illumina dye sequencing, and single molecule real-time sequencing platforms, we obtained a near-complete genome sequence comprised of 12 contigs, 4,420,100 bp, and 4,056 candidate protein-coding genes with a GC content of 30.0%. No extrachromosomal elements were detected. We provide an overview of the genes and pathways involved in the organism’s central fermentative metabolism. We used our developed electrotransformation procedure to investigate the use of established clostridial group II intron biology for constructing chromosomal gene knockout mutants of C. pasteurianum. Through methylome analysis of C. pasteurianum genome sequencing data and transformation assays of various vector deletion constructs, we identified a new Type I restriction-modification system that inhibits transfer of vectors harboring group II intron gene knockout machinery. We designated the new restriction system CpaAII and proposed a recognition sequence of 5’-AAGNNNNNCTCC-3’. Overcoming restriction by CpaAII, in addition to low intron retrohoming efficiency, allowed the isolation of a gene knockout mutant of C. pasteurianum with a disrupted CpaAI Type II restriction system. The resulting mutant strain should be efficienty transformed with plasmid DNA lacking M.FnuDII methylation. Lastly, we investigated the use of plasmid-based gene overexpression and chromosomal gene downregulation to alter gene expression in C. pasteurianum. Using a β-galactosidase reporter gene, we characterized promoters corresponding to the ferredoxin and thiolase genes of C. pasteurianum and show that both promoters permitted high-level, constitutive gene expression. The thiolase promoter was then utilized to drive transcription of an antisense RNA molecule possessing complementarity to mRNA of our β-galactosidase reporter gene. Our antisense RNA system demonstrated 52-58% downregulation of plasmid encoded β-galactosidase activity throughout the duration of growth. In an attempt to perturb the central fermentative metabolism of C. pasteurianum and enhance butanol titers, we prepared several antisense RNA constructs for downregulation of 1,3-propanediol, butyrate, and hydrogen production pathways. The resulting downregulation strains are expected to exhibit drastically altered central fermentative metabolism and product distribution. Taken together, we have demonstrated that C. pasteurianum is amendable to genetic manipulation through the development of methods for plasmid DNA transfer and gene overexpression, knockdown, and knockout. Further, our genome sequence should provide valuable nucleotide sequence information for the application of our genetic tools. Thus, the genome sequence, electrotransformation method, and associated genetic tools and techniques reported here should promote extensive genetic manipulation and metabolic engineering of this biotechnologically important bacterium.

El NFAT5 es un factor de transcripción de la familia Rel, la cual incluye a los NFATc y los NF-[kappa]B. Hasta ahora, el NFAT5 había sido caracterizado principalmente como un factor de respuesta a estrés osmótico ya que regula la expresión de genes osmoprotectores y citoquinas en respuesta a hipertonicidad. En este trabajo hemos identificado y caracterizado una nueva función del NFAT5, la regulación de genes (TNF[alfa], IL6, iNOS) activados por la vía de los receptores de tipo Toll (TLR), importantes para la respuesta inmunitaria innata y adaptativa a una amplia variedad de estímulos patogénicos. Nuestros resultados muestran que el NFAT5 es un regulador importante en la ruta de los TLR, jugando un papel en la actividad de varios miembros de esta familia de receptores, tal y como lo hacen los factores de transcripción NF[kappa]B e IRF5. / NFAT5 is a transcription factor of the Rel family, which includes NFATc and NF-[kappa]B. NFAT5 has been mainly characterized as a hypertonicity responsive factor, since it regulates the expression of osmoprotective genes and cytokines in response to osmotic stress. In this work we have identified and characterized a novel role for NFAT5, the regulation of genes (TNF[alfa], IL6, iNOS) activated by the Toll-like receptor pathway (TLR), important for innate and adaptive immunity responses to a wide variety of pathogenic molecules. Our results show that NFAT5 is an important transcription factor of the TLR pathway, playing a role in the activity of several members of this receptor family, like other transcription factors such as NF-[kappa]B and IRF5.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

Thesis (Ph.D.) -- University of Texas Southwestern Medical Center at Dallas, 2005. / Embargoed. Vita. Bibliography: 97-112.

Η ανάπτυξη του ανοσοποιητικού συστήματος ξεκινά από πολυδύναμα αρχέγονα αιμοποιητικά κύτταρα, τα οποία διαδοχικά δίνουν γένεση σε ενδιάμεσους πληθυσμούς προγονικών κυττάρων οι οποίοι σταδιακά χάνουν την ικανότητά τους για αυτοανανέωση και τελικά δίνουν γένεση στα πλήρως διαφοροποιημένα κύτταρα της μυελικής και λεμφικής σειράς. Η συγκεκριμένη διαδικασία στηρίζεται στο λεπτό συντονισμό της αυτοανανέωσης, αλλά και της διαφοροποίησης, απαιτεί δε την έκφραση διαφορετικών γονιδίων που σχετίζονται με τη ρύθμιση του κυτταρικού κύκλου, τη μεταγραφική ρύθμιση γονιδίων, αλλά και συμπλόκων αναδιοργάνωσης της δομής της χρωματίνης που εμπλέκονται στη διαφοροποίηση. Η geminin έχει προταθεί ότι ρυθμίζει την απόφαση ενός κυττάρου για πολλαπλασιασμό ή διαφοροποίηση. Αλληλεπιδρά με μεταγραφικούς παράγοντες, με σύμπλοκα αναδιάταξης της δομής της χρωματίνης, ρυθμίζοντας την έκφραση γονιδίων που ελέγχουν τη νευρωνική διαφοροποίηση. Παράλληλα, δρα σαν αναστολέας του κυτταρικού κύκλου, προσδενόμενη στο παράγοντα αδειοδότησης της αντιγραφής του DNA, CDT1. Στόχος μας ήταν να διερευνήσουμε τον in vivo ρόλο της Geminin στη διαφοροποίηση και τον πολλαπλασιασμό, στο ανοσοποιητικό σύστημα. Στα πλαίσια της διδακτορικής διατριβής, βασιζόμενοι στο σύστημα Cre-loxP, δημιουργήσαμε μύες που επιτρέπουν την υπό συνθήκη εξάλειψη (knockout) του γονιδίου της geminin, πλαισιώνοντας τα εξώνια 3 και 4 του γονιδίου της με θέσεις loxP. Η στόχευση του γονιδίου και η παρεμβολή των 3 loxP θέσεων πραγματοποιήθηκε σε pc3 εμβρυικά πολυδύναμα κύτταρα μυός, χρησιμοποιώντας κατάλληλο πλασμιδιακό knockout φορέα, που έφερε τη κασέτα επιλογής TKneo. Μετά από ένεση των ορθά ανασυνδυασμένων pc3 κλώνων σε βλαστοκύστεις, τη δημιουργία χιμαιρικών μυών που εκφράζουν την Cre ρεκομπινάση στη γαμετική σειρά, και την επακόλουθη διασταύρωσή τους με μύες αγρίου τύπου, δημιουργήθηκαν ετερόζυγοι μύες για το πλαισιωμένο με loxP θέσεις αλληλόμορφο της Geminin, που παράλληλα έφερε και τη κασέτα επιλογής TKneo («floxed-ΤΚneo»), το πλαισιωμένο με loxP θέσεις αλληλόμορφο της Geminin, που στερούνταν της κασέτας επιλογής TKneo (floxed), καθώς επίσης και το αλληλόμορφο που στερούνταν των εξωνίων 3 και 4 και είναι το πλήρες knockout (ΔGEM ΚΟ -null) αλληλόμορφο). Από διασταυρώσεις ετερόζυγων για το ΔGEM ΚΟ αλληλόμορφο της geminin, δεν προέκυψαν ομόζυγοι μύες για το ΔGEM ΚO αλληλόμορφο (-/-), τόσο μεταγεννητικά όσο και in utero. Η μειωμένη αντιπροσώπευση των ΔGEM+/- μυών σε συνδυασμό με την αύξηση των Thy1-/B220- κυττάρων σε σπλήνα και λεμφαδένες ενήλικων μυών, η σημαντική αύξηση των Thy1+ και ειδικότερα των CD8+ Τ κυττάρων, καθώς επίσης και η αισθητή μείωση των CD4+ Τ κυττάρων του σπλήνα σε ζώα ηλικίας 5 μηνών, προτείνει ένα είδος απλοανεπάρκειας των ετερόζυγων για Geminin μυών. Σε παραπλήσια αποτελέσματα οδηγηθήκαμε και μετά από την ανάλυση των GT KO για το γονίδιο της Geminin (GT) μυών με τη μεθοδολογία της παγίδευσης γονιδίων. Τα ετερόζυγα GT ζώα διασταυρώθηκαν με ετερόζυγα ζώα για το πλήρες ΚΟ του BRG1 (BRG) και με ετερόζυγα ζώα που υπερεκφράζουν μια επικρατούσα κατασταλτική μορφή του BAF57 (BAFΔΝ, BAF), προκειμένου να διαπιστωθεί εάν υπάρχει γενετική αλληλεπίδραση μεταξύ της Geminin και των μελών του συμπλέγματος αναδιοργάνωσης της δομής της χρωματίνης SWI/SNF, BRG1 και BAF57 που έχει δειχθεί ότι παίζουν σημαντικό ρόλο κατά την ανάπτυξη και διαφοροποίηση του ανοσοποιητικού συστήματος. Ιστοειδικά, χρησιμοποιώντας την floxedΤΚneo σειρά μυών σε συνδυασμό με την CD2-Cre, που επιτρέπει την εξάλειψη του γονιδίου από το στάδιο των DN κυττάρων του θύμου και μετά, είδαμε ότι η ανάπτυξη του θύμου δεν φαίνεται να επηρεάζεται κατά την απουσία της Geminin, ενώ αντίθετα ο ολικός αριθμός των σπληνοκυττάρων μειώνεται στα FlTKneo/KO;CD2 σε σχέση με τα WT. Μιτωγονική διέγερση με ConA εναιωρήματος σπληνοκυττάρων από FlTKneo/KO;CD2 και WT ζώα, έδειξε ότι τα FlTKneo/KO;CD2 Τ λεμφοκύτταρα αδυνατούν να διαιρεθούν. Τέλος, έγινε προσπάθεια για ιστοειδική υπερέκφραση στο ανοσοποιητικό σύστημα της ανθρώπινης Geminin συντηγμένης με τη πράσινη φθορίζουσα χρωστική (GFP). Το συγκεκριμένο σύστημα επιτρέπει την υψηλή έκφραση του διαγονιδίου κυρίως στα Τ κύτταρα. Ενώ προέκυψαν ιδρυτές για όλες τις πιο πάνω σειρές τόσο με χαμηλή όσο και με υψηλή ενσωμάτωση του διαγονιδίου, η έκφραση της GFP δεν κατέστη δυνατόν να ανιχνευθεί με FACS. Συνοψίζοντας, τα αποτελέσματά μας καταδεικνύουν ότι η Geminin είναι ιδιαίτερα σημαντική κατά τα αρχικά στάδια ανάπτυξης του εμβρύου μυός, ενώ ιστοειδικά στο ανοσοποιητικό σύστημα η πλήρης εξάλειψή της δεν έχει καμία επίπτωση στην ανάπτυξη του θύμου αδένα, ενώ αντίθετα στη σπλήνα εμφανίζονται μειωμένοι οι πληθυσμοί των ώριμων CD4 και CD8 Τ λεμφοκυττάρων. Τέλος, φαίνεται να συνεργάζεται με το σύμπλεγμα αναδιοργάνωσης της δομής της χρωματίνης SWI/SNF στη ρύθμιση των CD4 κυττάρων του θύμου αδένα και των CD8 του σπλήνα. / Immune system development initiates from a multipotent hematopoietic stem cell that consecutively generates intermediate progenitors that concomitantly lose their self-renewal ability and finally generate the fully differentiated cells of the myeloid and lymphoid lineage. The whole procedure is based on the fine tuning of the processes of both self-renewal and differentiation, and requires the expression of diverse genes that are implicated in the processes of cell cycle regulation, transcriptional regulation, and are constituents of chromatin remodeling complexes that operate during differentiation. Geminin has been proposed to control a cell’s decision to proliferate or differentiate. It interacts with transcription factors, with chromatin remodeling complexes, regulating neurospecific gene transcription. At the same time, Geminin acts as a cell cycle inhibitor through direct binding to the DNA licensing factor CDT1. Our goal was to investigate Geminin’s in vivo role in differentiation and cell cycle regulation in the immune system. In this thesis, using Cre-loxP system, we generated conditional knockout mice for Geminin’s gene, flanking exons 3 and 4 with loxP sites. Gene targeting and the insertion of the three loxP sites was performed in pc3 mouse embryonic stem cells, using a suitable knockout plasmid vector, which bared the TKneo cassette selection marker. Upon injection of the homologously recombined pc3 clones into blastocysts, the generation of chimeric mice that expressed Cre recombinase in their germ line, and their subsequent cross to wild type mice, we were able to generate heterozygote mice for the flanked by loxP sites allele of Geminin that also bared TKneo selection marker (“floxed-TKneo” allele), the flanked by loxP sites allele of Geminin that was deprived of the TKneo selection marker (the floxed allele) and the complete knockout allele of Geminin (ΔGEM KO (null) allele) that was deprived of exons 3 and 4. From ΔGEM+/- intercrosses we didn’t recover any homozygote knockout mice, both postnatally and in utero. The reduced number of the ΔGEM+/- obtained, in combination with the dramatic increase of Thy1-B220- cells from spleen and lymph nodes from ΔGEM+/- adult mice, the significant increase in Thy1+ and CD8+ from lymph nodes and the discernible decrease of spleenic CD4 T cells in ΔGEM+/- aged 5 months suggest that ΔGEM+/- mice are haploinsufficient. Similar results were obtained from the analysis of the GT knockout that we generated, using a gene trap mutagenesis approach. GT heterozygote mice were crossed with heterozygote mice for BRG1 Knockout (BRG mice) and with heterozygote mice that overexpressed a dominant negative form of BAF57 (BAFΔN, BAF mice), so as to investigate whether there is a genetic interaction between Geminin and the two members of the SWI/SNF chromatin remodeling complex that have significant roles during development and differentiation of the immune system. Upon conditional inactivation of Geminin’s gene in the immune system, using floxedTKneo and CD2-Cre mouse lines, that allowed the deletion of the gene from the DN stage and on, we were surprised to see that in the Geminin conditional knockout mice, thymic development was largely unaffected. On the contrary, spleenic cellularity from Geminin conditional knockout mice was fairly reduced, when compared to WT control littermates. Mitogenic stimulation with ConA of spleenic whole cell extract from Geminin conditional KO (FlTKneo/KO;CD2) and WT mice demonstrated that the mutant T cells were unable to divide. Finally, we tried to overexpress human Geminin tagged with Green Fluorescent Protein (GFP) specifically in the immune system. This particular system would ensure high expression of the transgene mainly in T cells. We obtained founders for all of the cloned constructs, both with low and high copy transgene integration, but we were unable to detect GFP expression by FACS analysis. Our results show that Geminin has a pivotal role during early mouse embryonic development, whereas tissue specific inactivation in the immune system leaves thymic development largely unaffected, whereas mature CD4 and CD8 T cells in the spleen are drastically reduced. Finally, Geminin seems to operate with SWI.SNF complex for the regulation of thymic CD4 and spleenic CD8.

Submitted by Livia Mello (liviacmello@yahoo.com.br) on 2016-09-22T12:11:52Z No. of bitstreams: 1 DissAVA.pdf: 2653238 bytes, checksum: 6ed4edf2962eb1273324c54a2e900fa6 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-10T14:38:43Z (GMT) No. of bitstreams: 1 DissAVA.pdf: 2653238 bytes, checksum: 6ed4edf2962eb1273324c54a2e900fa6 (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-10T14:38:51Z (GMT) No. of bitstreams: 1 DissAVA.pdf: 2653238 bytes, checksum: 6ed4edf2962eb1273324c54a2e900fa6 (MD5) / Made available in DSpace on 2016-10-10T14:38:59Z (GMT). No. of bitstreams: 1 DissAVA.pdf: 2653238 bytes, checksum: 6ed4edf2962eb1273324c54a2e900fa6 (MD5) Previous issue date: 2015-03-03 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Citrus canker imposes damages to citriculture by causing drop in productivity and fruit quality and the absence of effective control and cure. Thus, the economic potential of citrus is limited in part by this disease mainly caused by the bacterium Xanthomonas citri subsp. citri (XAC) that presents the greatest virulence and broad spectrum of citrus hosts, compared to bacteria Xanthomonas fuscans subsp. aurantifolii types B (XauB) and C (XauC). In a proteomic analysis previously performed by our research group, periplasmic trehalase was identified as a protein which expression differed between XAC e XauC in an in vitro induction of pathogenicity. Trehalase is an enzyme that catalyzes hydrolysis reaction of trehalose, a disaccharide composed of two glucose units, which role in the plant-pathogen interaction is poorly understood. One of the objectives of the study was to obtain this enzyme in purified form using an IPTG-inducible heterologous expression system in E. coli, for purposes of partial characterization of its structure and activity. The recombinant XAC periplasmic trehalase is a monomer bearing wide pH stability and showed Michaelian kinetics. The Michaelis-Menten constant (Km) for trehalose was 0,124 ± 0,015 mM and Vmax 17,319 ± 0,035 μMol glucose.min-1.mg protein-1 . Circular dichroism spectroscopy indicated the following composition of secondary structures: 42.7% α-helices and 13% β-sheets. A gene knockout method based on double homologous recombination between the genomic DNA and suicide vector pNPTS138 has made possible to obtain a strain deleted in the gene encoding the periplasmic trehalase (XACΔ0604), which enabled to evaluate the relationship between this gene and the XAC pathogenicity in Citrus aurantifolia. Infiltrated leaves with XACΔ0604 showed drenching and necrosis of plant tissue and intense brownish pustules compared with wild XAC, suggesting greater virulence of the mutant strain. The periplasmic trehalase activity was compared in XAC and XauC cell extracts from two culture mediums, non-pathogenicity-inducing (CN) and pathogenicity-inducing (XAM-M). Interestingly, XauC has showed higher enzyme activity compared to XAC in XAM-M. Thus, the noticeable higher XACΔ0604 pathogenicity and the greater activity of XauC periplasmic trehalase compared to XAC are indicatives that trehalose may promote pathogenicity. / O cancro cítrico impõe prejuízos ao setor citricultor por ocasionar queda na produtividade e qualidade dos frutos e pela ausência de medidas eficazes de controle e cura. Assim, o potencial econômico dos citros é limitado, em parte, por essa doença causada principalmente pela bactéria Xanthomonas citri subsp. citri (XAC), que apresenta maior virulência e largo espectro de hospedeiros cítricos, comparativamente às bactérias Xanthomonas fuscans subsp. aurantifolii tipos B (XauB) e C (XauC). Em um trabalho de análise proteômica anteriormente realizado por nosso grupo de pesquisa, a trealase periplasmática foi identificada como uma proteína cuja expressão foi diferencial entre XAC e XauC, em condição de indução da patogenicidade in vitro. A trealase é uma enzima que catalisa a reação de hidrólise da trealose, um dissacarídeo formado por duas unidades de glicose, cujo papel na interação planta-patógeno é ainda pouco compreendido. Um dos objetivos do trabalho foi obter esta enzima purificada, utilizando um sistema de expressão heteróloga induzível por IPTG (isopropil-β-D-tiogalactosídeo) em E. coli, para fins de caracterização parcial da sua estrutura e atividade. A trealase periplasmática de XAC de origem heteróloga apresentou-se como um monômero relativamente estável em relação ao pH, e de cinética Michaeliana,. A constante de Michaelis-Menten (Km) da enzima para a trealose foi de 0,124 ± 0,015 mM e a Vmáx 17,319 ± 0,035 μMol de glicose.min-1.mg de proteína-1. Análise de dicroísmo circular resultou na seguinte composição de estruturas secundárias: 42,7 % de α-hélices e 13 % de folhas-β. Uma metodologia de nocaute gênico baseada na dupla recombinação homóloga entre o DNA genômico e o vetor suicida pNPTS138 viabilizou a obtenção de uma linhagem mutante deletada no gene que codifica a trealase periplasmática (XAC∆0604), o que possibilitou avaliar a relação entre tal gene e a patogenicidade de XAC em Citrus aurantifolia. Folhas infiltradas com a suspensão de XAC∆0604 apresentaram maior encharcamento e necrose do tecido vegetal, além de intensas pústulas acastanhadas quando comparadas com as folhas infiltradas com XAC selvagem, sugerindo maior virulência da linhagem mutante. A atividade da trealase periplasmática foi comparada em extratos celulares brutos provenientes de cultivos de XAC e XauC em dois meios de cultura, não-indutor de patogenicidade (CN) e indutor de patogenicidade (XAM- M). A bactéria XauC apresentou maior atividade enzimática de trealase em relação à XAC em XAM-M. Sendo assim, a acentuada patogenicidade de XAC∆0604 em relação à linhagem selvagem XAC e a maior atividade da trealase periplasmática de XauC em relação à XAC reforçam os recentes trabalhos que indicam a trealose como promotora da patogenicidade em fitopatógenos.