Afin de caractériser les mécanismes moléculaires sous-jacents au processus d’adhésion des bactéries commensales, nous avons utilisé Streptococcus salivarius comme modèle. Streptococcus salivarius est une bactérie pionière dans la colonisation des surfaces orales chez le nouveau né, et devient par la suite un composant majoritaire du microbiote oral de l'adulte avec un rôle écologique majeur. Nous avons développé une méthode pour identifier, par des tests de criblage phénotypique, les gènes impliqués dans l’adhésion de S. salivarius aux surfaces bactériennes ou de l’hôte. Notre approche a permis d’identifier un ensemble de gènes codant pour des protéines de surfaces, des glycosyltransférases, des transporteurs qui sont impliqués dans les phénomènes d’auto-agréation et / ou de co-agrégation avec d’autres espèces et / ou l’adhésion aux protéines de l’hôte.En particulier, nous avons montré que le système SecA2Y2, qui comprend des gènes codant pour des protéines dédiées à la glycosylation et l'export de protéines de surface riche en sérine (SRRPs), participe aux processus d’agrégation, de formation de biofilms, à l'adhésion in vitro aux protéines de l’hôte et in vivo à la colonisation du tractus digestif de souris. Alors que toutes les bactéries contenant un système similaire possèdent un substrat unique au système, une SRRP, le locus génétique secA2Y2 comprend trois SRRPs qui présentent des rôles complémentaires dans les phénotypes précédement cités. SrpB est spécifiquement impliquée dans la liaison aux cellules epitheliales, tandis que SrpC participe à l’adhésion aux protéines de la matrice extracellulaire et le mucus. De manière atypique, nous avons démontré que le processus de maturation des SRRPs est supporté par glycosyltransférases extra-cluster. Cette étude est le premier rapport indiquant la présence dans une bactérie de trois SRRPs, qui présentent des rôles complémentaires dans l'interaction bactéries-hôte. Bien que le système SecA2Y2 soit principalement associé à la virulence des bactéries pathogènes, il semble être clairement impliqué dans les caractères de commensalité de S. salivarius, tels que la colonisation de ses niches écologiques orales et intestinales. Ce travail offre de nouvelles perspectives sur les mécanismes de colonisation des bactéries commensales. / To characterize molecular mechanisms underlying adhesion of commensal bacteria, we used Streptococcus salivarius (SSAL) as a model. SSAL is among the most important pioneer colonizers of neonatal oral mucosal surfaces, and later becomes a predominant component of the human adult oral microbiota with pre-eminent ecological role. We developed a method to identified, through phenotypic screening assays, genes involved in SSAL adhesion to host or bacterial surfaces. In particular, we showed that the SecA2Y2 system, which comprises genes devoted to glycosylation and export of surface Serine Rich Repeat Proteins (SRRPs), participates to bacterial aggregation, biofilm formation, in vitro adhesion and colonization of mice. While all bacteria containing a similar system possess only one SRRP, the SSAL secA2Y2 locus comprises three SRRPs with complementary role in line with the previous phenotypes. Interestingly, SrpB is specifically involved in the binding to epithelial cells, while SrpC to the extracellular matrix and mucus proteins. We showed that these interactions require glycosylation of both bacterial SRPs and host surfaces. Surprisingly, we demonstrated that this essential process is shared by glycosyltransferases located in other genomic regions. This work is the first report showing the presence in a bacterium of three SRPs, which display complementary roles in bacterial-host interaction. While the SecA2Y2 system is mostly associated to virulence in pathogenic bacteria, it appears to be involved in the expression of commensal traits in SSAL, such as its colonization and its resilience to oral and intestinal niches. This work may offer new insights into the mechanisms of niche establishment (host, microbial communities) of commensal bacteria.

"April 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 158-181). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Insulin and glucagon are released in pulses from pancreatic β- and α-cells, respectively. Both cell types are electrically excitable, and elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) due to depolarization with voltage-dependent entry of the cation is the main trigger of hormone secretion. Store-operated Ca2+ entry  (SOCE) also contributes to the [Ca2+]i elevation and this process has been suggested to be particularly important for glucagon secretion. cAMP is another important messenger that amplifies Ca2+-triggered secretion of both hormones, but little is known about cAMP dynamics in islet cells. In type-2 diabetes, there is deteriorated β-cell function associated with elevated concentrations of fatty acids, but the underlying mechanisms are largely unknown. To clarify the processes that regulate insulin and glucagon secretion, cAMP signalling and the store-operated pathway were investigated in β- and α-cells, primarily within their natural environment in intact mouse and human islets of Langerhans. Fluorescent biosensors and total internal reflection microscopy were used to investigate signalling specifically at the plasma membrane (PM). Adrenaline increased and decreased the sub-PM cAMP concentration ([cAMP]pm) in immuno-identified α-cells and β-cells, respectively, which facilitated cell identification. Glucagon elicited [cAMP]pm oscillations in α- and β-cells, demonstrating both auto- and paracrine effects of the hormone. Whereas glucagon-like peptide 1 (GLP-1) consistently elevated [cAMP]pm in β-cells, only few α-cells responded, indicating that GLP-1 regulates glucagon secretion without changes of α-cell [cAMP]pm. Both α- and β-cells responded to glucose with pronounced oscillations of [cAMP]pm that were partially Ca2+-dependent and synchronized among islet β-cells. The glucose-induced cAMP formation was mediated by plasma membrane-bound adenylyl cyclases. Several phosphodiesterases (PDEs), including the PDE1, -3, -4, and -8 families, were required for shaping the [cAMP]pm signals and pulsatile insulin secretion. Prolonged exposure of islets to the fatty acid palmitate deteriorated glucose-stimulated insulin secretion with loss of pulsatility. This defect was associated with impaired cAMP generation, while [Ca2+]i signalling was essentially unaffected. Stromal interacting molecule 1 (STIM1) is critical for activation of SOCE by sensing the Ca2+ concentration in the endoplasmic reticulum (ER). ER Ca2+ depletion caused STIM1 aggregation, co-clustering with the PM Ca2+ channel protein Orai1 and SOCE activation. Glucose, which inhibits SOCE by filling the ER with Ca2+, reversed the PM association of STIM1. Consistent with a role of the store-operated pathway in glucagon secretion, this effect was maximal at the low glucose concentrations that inhibit glucagon release, whereas considerably higher concentrations were required in β-cells. Adrenaline induced STIM1 translocation to the PM in α-cells and the reverse process in β-cells, partially reflecting the opposite effects of adrenaline on cAMP in the two cell types. However, cAMP-induced STIM1 aggregates did not co-cluster with Orai1 or activate SOCE, indicating that STIM1 translocation can occur independently of Orai1 clustering and SOCE.

The polyamines spermine and spermidine play important roles in many cellular processes, and unusual levels of these polyamines have been associated with numerous human diseases. Spermidine/spermine N¹-acetyltransferase (SSAT) is an enzyme involved in polyamine regulation, where acetylation of polyamines by SSAT ultimately leads to their degradation or export from the cell. In this dissertation, x-ray crystallography and nuclear magnetic resonance (NMR) are used to provide insights into the structure and function of this important enzyme. X-ray crystallography provided two distinct views of SSAT: one of the enzyme in complex with coenzyme A (CoA), and another of the enzyme in complex with CoA and the polyamine spermine. Together, the two structures reveal structural plasticity in the active site of the enzyme. The complex with spermine provides a direct view of polyamine binding by SSAT, and shows that the enzyme relies heavily on associated water molecules to bind spermine; these water molecules also appear to form a "proton relay" between the primary amine of spermine and the side-chain of a conserved glutamate residue. Guided by the structural results, NMR methods were used to test hypotheses regarding the enzyme mechanism of SSAT. The activity of the enzyme over a range of solution conditions, and towards different polyamine substrates, was determined; the effects of mutating single amino acids in the enzyme were also evaluated. The enzyme appeared to be most active between pH 8.5 and 9.5, and mutation of the aforementioned glutamate significantly altered this behavior. This suggests the glutamate is directly involved in the acetyltransfer reaction, where it likely functions as a catalytic base though the proton relay in the enzyme active site. These studies advance our general understanding of how polyamines are regulated in mammalian cells, and have the potential to assist in developing new therapeutic options for human diseases involving polyamines. / text

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Précédemment, nous avons montré que la surexpression de l'échangeur Na/Ca NCX1), une protéine responsable de la sortie de calcium (Ca2+) des cellules, augmentait la mort cellulaire programmée ou « apoptose » et réduisait la prolifération des cellules β. Afin d’étudier plus en profondeur le rôle de l’échangeur dans les cellules β in vivo, nous avons développé et caractérisé des souris présentant une inactivation de NCX1.<p>Des méthodes biologiques et morphologiques (imagerie du Ca2+, capture de Ca2+, métabolisme du glucose, sécrétion d'insuline et morphométrie par comptage de points) ont été utilisées pour évaluer la fonction de la cellule β in vitro. Les taux de glucose et d'insuline dans le sang ont été mesurés afin de déterminer le métabolisme du glucose et la sensibilité à l’insuline in vivo. Des îlots ont été transplantés sous la capsule rénale pour évaluer leur capacité à corriger le diabète chez les souris rendues diabétiques par l’alloxane.<p>L'inactivation hétérozygote de Ncx1 chez les souris provoque une augmentation de la sécrétion d’insuline induite par le glucose avec un renforcement important à la fois de la première et de la deuxième phase. Ces résultats s’accompagnent d’une augmentation de la masse et de la prolifération des cellules β. La mutation augmente également le contenu en insuline, l’immunomarquage de la proinsuline, la capture de Ca2+ induite par le glucose et la résistance à l'hypoxie des cellules β. En outre, les îlots de souris Ncx1+/- montrent une capacité à compenser le diabète 2 à 4 fois plus élevé que les îlots de souris Ncx1+/+ lorsque transplantés chez des souris diabétiques.<p>En conclusion, l’inactivation de l'échangeur Na/Ca conduit à une augmentation de la fonction de la cellule β, de sa prolifération, de sa masse et de sa résistance au stress physiologique, à savoir à divers changements de fonction des cellules β opposés aux principales anomalies rencontrées dans le diabète de type 2 (Type 2 Diabetes Mellitus,T2DM). Ceci nous procure un modèle unique pour la prévention et le traitement du dysfonctionnement des cellules β dans le T2DM et pour la transplantation d'îlots.<p> / Doctorat en Sciences biomédicales et pharmaceutiques / info:eu-repo/semantics/nonPublished

Le système de sécrétion de type II (T2SS) assure le transport de protéines sous une forme repliée du périplasme dans le milieu extracellulaire. Ce système est largement exploité par les bactéries à Gram négatif pathogènes des plantes, des animaux et de l'homme où il permet la sécrétion de facteurs de virulence (des toxines et des enzymes lytiques). La bactérie phytopathogène Dickeya dadantii utilise le T2SS appelé Out, pour sécréter une douzaine de pectinases qui dégradent les parois des cellules végétales. Les protéines sécrétées par le T2SS n'ont pas de motif de sécrétion apparent et leur sécrétion implique plusieurs interactions transitoires avec les composants du système. La nature moléculaire de ces interactions n'est pas connue. Afin de capter ces interactions transitoires lors du processus de sécrétion, j'ai utilisé le pontage dirigé in vivo. Cette technique repose sur l'incorporation d'un analogue photoréactif d'un acide aminé (le para-benzoyl Lphénylalanine, pBpa) à la place des résidus soupçonnés de faire partie d'un site d'interaction. Le pontage est ensuite activé par une courte exposition des cellules aux UV ce qui permet la formation des complexes protéiques. Tout d'abord, cette technique a été utilisée pour introduire le pBpa dans plusieurs régions exposées à la surface d'une exoprotéine, PelI. Cette stratégie a permis de mettre en évidence qu'un élément structural, la boucle 3 du domaine Fn3 de PelI, est impliquée dans l'interaction avec la sécrétine OutD, le composant du T2SS situé dans la membrane externe, et avec le domaine PDZ d'OutC, un composant de la membrane interne. Ces résultats suggèrent que la boucle 3 fait partie d'un motif de sécrétion. Deux autres régions ont été identifiées au sein de PelI : le linker entre les deux domaines de PelI qui est impliqué dans l'interaction avec OutD et une région exposée du domaine catalytique qui interagit avec la protéine OutC. La même approche a été utilisée pour introduire le pBpa dans les deux composants du T2SS, OutC et OutD. Ces expériences ont suggéré que le domaine PDZ d'OutC interagit avec une autre exoprotéine, PelB. Cette étude, de façon complémentaire à d'autres approches, nous a permis de démontrer certains détails moléculaires essentiels de la sécrétion par le T2SS / The type II secretion system (T2SS) transports folded proteins from the periplasm through the outer membrane into the milieu. In many pathogenic Gram-negative bacteria, the T2SS secretes various virulence factors in host tissue and is directly involved in pathogenesis. The phytopathogen Dickeya dadantii secretes a dozen of pectinases through a T2SS named Out. The secreted proteins are lacking an obvious common signal and secretion is thought to involve multiple transient interactions of folded exoproteins with several T2SS components. Molecular nature of these interactions remains unknown. To address this question we used an in vivo sitespecific photo-crosslinking approach to capture such transient interactions within the functional T2SS of D. dadantii. In this technique, the photo-crosslinker para-benzoyl-L-phenylalanine, pBpa, is introduced in vivo in place of a residue of interest and UV-irradiation of living cells provokes the formation of complexes between the protein of interest and its partners. First, in a systematic approach, pBpa was introduced at several surface-exposed sites of the secreted protein PelI. This strategy permitted us to identify that one structural element, loop 3 of Fn3 domain in PelI, interacts both with the secretin, the outer membrane T2SS component, and with the PDZ domain of OutC, an inner membrane T2SS component. These results suggest that this loop 3 is a part of the secretion motif. The same approach permitted us to identify two other regions of PelI interacting with the T2SS: a linker situated between the two domains of PelI, which interacts with OutD, and an exposed region of the catalytic domain of PelI interacting with OutC. In another approach, pBpa was introduced into the T2SS components, OutC and OutD. These experiments suggested that the PDZ domain of OutC interacts with the secreted protein PelB. This study, in complement with other approaches, allowed us to uncover some important molecular features of the protein secretion by the T2SS

L'élévation de la concentration du calcium (Ca2+) cytosolique est responsable de l’activation plaquettaire. Cette élévation est due à l'entrée du Ca2+ à partir du milieu extérieur (influx) ou sa translocation (mobilisation) dans le cytosol depuis ses réserves internes. Les SERCAs (Sarco/Endoplasmic Reticulum Ca2+ ATPases) pompent le Ca2+ depuis le cytosol vers les réserves internes, maintenant le Ca2+ cytosolique bas (100 nM) et les plaquettes au repos. D'autre part elles assurent une concentration calcique élevée (≥1 mM) dans les réserves calciques permettant sa mobilisation, et enfin modulent l'intensité et la forme du signal calcique lors de l'activation. Mais les rôles respectifs des SERCAs plaquettaires, SERCA2b et SERCA3, sont encore mal définis. D’où l’intérêt de mon projet qui a été de déterminer si SERCA3 avait un rôle fonctionnel précis et spécifique. Nous avons observé sur des souris SERCA3-/- un défaut de l'hémostase et s’accompagne d’une résistance à la thrombose dû à un déficit de sécrétion d'ADP, entrainant un défaut d'agrégation et d'adhérence. SERCA3 semble contrôler une voie de sécrétion initiale d'ADP capable d’agir en synergie avec une faible activation plaquettaire, aboutissant à un renforcement de la sécrétion et de l'agrégation. De plus, l’utilisation des inhibiteurs pharmacologiques spécifiques de SERCA2b (thapsigargine) ou SERCA3 (tBHQ), a montré que la sécrétion initiale d'ADP n'était pas dépendante de la mobilisation des réserves SERCA2b mais dépendait spécifiquement des réserves SERCA3. Nous avons retrouvé la même voie de sécrétion d'ADP dépendante de SERCA3 dans les plaquettes humaines. Nous avons en particulier montré par le suivi d'une cohorte de patientes atteintes d'obésité morbide, un déficit d'agrégation, une faible mobilisation calcique et un taux faible de SERCA3 plaquettaire, revenus à la normale après retour à un poids normal après chirurgie bariatrique. Surtout nous avons retrouvé, dans les plaquettes de ces patientes obèses, un défaut de sécrétion d'ADP associé au défaut de SERCA3. Il s'agit du premier défaut de SERCA3 plaquettaire lié à une pathologie humaine. Nous avons ensuite montré que la sécrétion initiale d'ADP était rapide (5 sec) et entièrement dépendante de SERCA3. A l'aide d'une sonde calcique fluorescente membranaire (FURA2-NearMem-AM), nous avons démontré l’existence d’une mobilisation calcique juxta-membranaire spécifique de SERCA3, indépendante de l'ADP, correspondant donc à une sécrétion primaire. Cette mobilisation SERCA3 s'est avérée indépendante d'IP3, mais dépendante du NAADP, qui mobilise spécifiquement les réserves SERCA3 et non SERCA2b. En conclusion, nous avons mis en évidence une nouvelle voie d'activation plaquettaire, indépendante de l'IP3 mais dépendante du NAADP qui libère le Ca2+ des stocks internes dépendants de SERCA3 et spécifiquement engagés dans la libération précoce d'ADP lors de l'activation plaquettaire. Ces données identifient de nouvelles cibles avec un intérêt thérapeutiques anti-thrombotiques potentiel. / The elevation of cytosolic calcium (Ca2 +) is responsible for platelet activation. This elevation is due to the entry of Ca2 + from the extracellular medium (influx) where its translocation (mobilization) into the cytosol from its Ca2+ stores. SERCAs (Sarco / EndoplasmicReticulumCa2 + ATPases) pump Ca2 + from the cytosol to the Ca2+ stores, maintaining low cytosolic Ca2 + (100 nM) and platelets at resting state. On the other hand, they ensure a high calcium concentration (≥ 1 mM) in the Ca2+ stores allowing its mobilization, and finally modulate the intensity and the shape of the Ca2 signal during the activation. However, the respective roles of SERCA platelets, SERCA2b and SERCA3, are still poorly defined. Hence the interest of my project which was to determine if SERCA3 had a precise and specific functional role. We observed in SERCA3 - / - mice a defect in hemostasis that is accompanied by resistance to thrombosis due to ADP secretion deficiency, resulting in a lack of aggregation and adhesion. SERCA3 seems to control an initial pathway of ADP secretion able to acting in synergy with low platelet activation, resulting in increased secretion and aggregation. In addition, the use of specific pharmacological inhibitors of SERCA2b (thapsigargine) or SERCA3 (tBHQ) showed that the initial secretion of ADP was not dependent on the mobilization of SERCA2b stores, but was specifically dependent on SERCA3 stores. We found the same SERCA3-dependent ADP secretion pathway in human platelets. In particular, we observed a defect of platelet aggregation, low Ca2+ mobilization and low platelet SERCA3 levels in a cohort of patients with morbid obesity compared to control subjects. Platelet functions and SERCA3 levels are restored after weight loss by a surgery bariatric. Above all, we found in the platelets of these obese patients, a defect of secretion of ADP associated with the defect of SERCA3. This is the first defect of platelet SERCA3 related to human pathology. We then showed that the initial secretion of ADP was rapid (5 sec) and entirely dependent on SERCA3. Using a membrane fluorescent Ca2+ probe (FURA2-NearMem-AM), we have demonstrated the existence of a juxta-membrane-specific calcium mobilization specific to SERCA3, independently of ADP, corresponding to primary secretion. This SERCA3 mobilization proved to be independent of IP3, but dependent on the NAADP, which specifically mobilizes the SERCA3 and not SERCA2b reserves. In conclusion, we have demonstrated a new platelet activation pathway, independent of IP3 but dependent on NAADP, which releases Ca2 + from SERCA3 dependent stores and specifically involved in the early release of ADP during platelet activation. These data identify new targets with a potential interest of anti-thrombotic therapy.

Doctor of Philosophy / Genetics Interdepartmental Program, Plant Pathology / Xiaoyan Tang / Pseudomonas syringae bacteria utilize the type III secretion system (T3SS) to deliver effector proteins into host cells. The T3SS and effector genes (together called the T3 genes hereafter) are repressed in nutrient rich medium but are rapidly induced after the bacteria are transferred into minimal medium (MM) or infiltrated into the plant. The induction of the T3 genes is mediated by HrpL, an alternative sigma factor that recognizes the conserved hrp box motif in the T3 gene promoters. The induction of hrpL is mediated by HrpR and HrpS, two homologous proteins that bind the hrpL promoter. To identify additional genes involved in regulation of the T3 genes, P. s. pv. phaseolicola (Psph) NPS3121 transposon insertion mutants were screened for reduced induction of avrPto-luc and hrpL-luc, reporter genes for promoters of effector gene avrPto and hrpL, respectively. Determination of the transposon-insertion sites led to the identification of genes with putative functions in signal transduction and transcriptional regulation, protein synthesis, and basic metabolism. A transcriptional regulator (AefRNPS3121) identified in the screen is homologous to AefR, a regulator of the quorum sensing signal and epiphytic (plant-associated) traits that was not known previously to regulate the T3 genes in P. s. pv. syringae (Psy) B728a. AefRNPS3121 in Psph NPS3121 and AefR in Psy B728a are similar in regulating the quorum sensing signal in liquid medium but different in regulating epiphytic traits such as swarming motility, entry into leaves, and survival on the leaf surface. The two component system RhpRS was identified in Pseudomonas syringae as a regulator of the T3 genes (Xiao et al. 2007). In the rhpS- mutant, the response regulator RhpR represses the induction of the T3 gene regulatory cascade, but induces its own promoter in a phosphorylation-dependent manner. Deletion and mutagenesis analyses revealed an inverted repeat (IR) element GTATC-N6-GATAC in the rhpR promoter that confers the RhpR-dependent induction. Computational search of the P. syringae genomes for the putative IR elements and Northern blot analysis of the genes with a putative IR element in the promoter region uncovered five genes that were upregulated (PSPTO2036, PSPTO2767, PSPTO3477, PSPTO3574, and PSPTO3660) and two genes that were down-regulated (PSPTO0536 and PSPTO0897) in an RhpR-dependent manner. ChIP assays indicated that RhpR binds the promoters containing a putative IR element but not the hrpR and hrpL promoters that do not have an IR element, suggesting that RhpR indirectly regulates the transcriptional cascade of hrpRS, hrpL, and the T3 genes. To identify additional genes involved in the rhpRS pathway, suppressor mutants were screened that restored the induction of the avrPto-luc reporter gene in the rhpS- mutant. Determination of the transposon-insertion sites led to the identification of rhpR, an ATP-dependent Lon protease, a sigma 70 family protein (PSPPH1909), and other metabolic genes. A lon- rhpS- double mutant exhibited phenotypes typical of a lon- mutant, suggesting that rhpS acts with or through lon. The expression of lon was elevated in rhpS- and other T3-deficient mutants, indicating a negative feedback mechanism. Both the lon- rhpS- and the PSPPH1909- rhpS- double mutant displayed enhanced transcription of hrpL in MM than did the rhpS- mutant.

Appressorium-mediated plant infection is a common strategy used by many plant pathogenic fungi. Understanding the underlying genetic network that controls cellular differentiation of appressorium is therefore pivotal to design durable resistance strategies for these devastating pathogens. This thesis describes four published studies, which investigate the role of septin GTPases in infection and the role of secretion during plant tissue invasion by the rice blast pathogen Magnaporthe oryzae. Appressorium development involves a series of morphogenetic changes that are tightly regulated by cell cycle checkpoints. Entry into mitosis allows differentiation of an appressorium, while penetration peg emergence appears to require progression through subsequent cell cycle checkpoints and cytokinesis. The studies presented here show that symmetry-breaking events that occur during appressorium differentiation are mediated by scaffold proteins, named septins. Septin GTPases recruit actomyosin ring components during septation and define the site of cytokinesis. They also recruit a toroidal cortical F-actin network to the appressorium pore that provides cortical rigidity to facilitate plant infection. Septins act as diffusion barriers for proteins that mediate membrane curvature necessary for penetration peg formation. Repolarization of the F-actin cytoskeleton at the appressorium pore is essential for plant penetration and is controlled by cell polarity regulators, such as Cdc42 and Chm1. Septin-mediated plant infection is regulated by NADPH oxidase (Nox) dependent generation of reactive oxygen species (ROS). The Nox2/NoxR complex is essential for septin organization at the appressorium pore. Septins are therefore key determinants of appressorium repolarization. I also report an investigation of fungal secretory processes during tissue invasion and present evidence that distinct pathways are involved in effector secretion by Magnaporthe oryzae. A BrefeldinA-sensitive pathway is necessary for secretion of apoplastic effectors, such as Bas4 and Slp1, while a BrefeldinA-insensitive pathway is necessary for secretion of effectors destined for delivery to rice cells.