Two Mosquito LRR Proteins Function as Complement Control Factors in the TEP1-Mediated Killing of Plasmodium

SummaryPlasmodium development within Anopheles mosquitoes is a vulnerable step in the parasite transmission cycle, and targeting this step represents a promising strategy for malaria control. The thioester-containing complement-like protein TEP1 and two leucine-rich repeat (LRR) proteins, LRIM1 and APL1, have been identified as major mosquito factors that regulate parasite loads. Here, we show that LRIM1 and APL1 are required for binding of TEP1 to parasites. RNAi silencing of the LRR-encoding genes results in deposition of TEP1 on Anopheles tissues, thereby depleting TEP1 from circulation in the hemolymph and impeding its binding to Plasmodium. LRIM1 and APL1 not only stabilize circulating TEP1, they also stabilize each other prior to their interaction with TEP1. Our results indicate that three major antiparasitic factors in mosquitoes jointly function as a complement-like system in parasite killing, and they reveal a role for LRR proteins as complement control factors

Functionally Redundant RXLR Effectors from <em>Phytophthora infestans</em> Act at Different Steps to Suppress Early flg22-Triggered Immunity

Genome sequences of several economically important phytopathogenic oomycetes have revealed the presence of large families of so-called RXLR effectors. Functional screens have identified RXLR effector repertoires that either compromise or induce plant defense responses. However, limited information is available about the molecular mechanisms underlying the modes of action of these effectors in planta. The perception of highly conserved pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs), such as flg22, triggers converging signaling pathways recruiting MAP kinase cascades and inducing transcriptional re-programming, yielding a generic anti-microbial response. We used a highly synchronizable, pathogen-free protoplast-based assay to identify a set of RXLR effectors from Phytophthora infestans (PiRXLRs), the causal agent of potato and tomato light blight that manipulate early stages of flg22-triggered signaling. Of thirty-three tested PiRXLR effector candidates, eight, called Suppressor of early Flg22-induced Immune response (SFI), significantly suppressed flg22-dependent activation of a reporter gene under control of a typical MAMP-inducible promoter (pFRK1-Luc) in tomato protoplasts. We extended our analysis to Arabidopsis thaliana, a non-host plant species of P. infestans. From the aforementioned eight SFI effectors, three appeared to share similar functions in both Arabidopsis and tomato by suppressing transcriptional activation of flg22-induced marker genes downstream of post-translational MAP kinase activation. A further three effectors interfere with MAMP signaling at, or upstream of, the MAP kinase cascade in tomato, but not in Arabidopsis. Transient expression of the SFI effectors in Nicotiana benthamiana enhances susceptibility to P. infestans and, for the most potent effector, SFI1, nuclear localization is required for both suppression of MAMP signaling and virulence function. The present study provides a framework to decipher the molecular mechanisms underlying the manipulation of host MAMP-triggered immunity (MTI) by P. infestans and to understand the basis of host versus non-host resistance in plants towards P. infestans

Molecular mechanisms of TEP1-dependent killing of Plasmodium in the mosquito Anopheles gambiae

Avec plus de deux milliards de personnes exposées et un million de morts infantiles par an, le paludisme est une maladie dévastatrice. L'agent infectieux Plasmodium est transmis par la piqûre d'un moustique. Lors du développement dans le vecteur principal Anopheles gambiae, le parasite, ingéré avec le repas sanguin, traverse l'épithélium intestinal pour rejoindre le côté basal. À ce stade, il subit une perte drastique en nombre causée par l'immunité du moustique. Les bases moléculaires de cette défense restent peu comprises. La protéine à thioester TEP1, similaire au complément, est un facteur immunitaire important, induisant la mort d'une vaste majorité de parasites. Elle est sécrétée dans l'hemolymphe (sang), où elle se lie aux parasites, provoquant ainsi leur lyse. Dans ce travail, nous avons intégré de nouveaux acteurs dans le mécanisme d'élimination TEP1-dépendant des parasites. Deux protéines à LRR (répétitions riches en leucine) ont été caractérisées en tant que facteurs de contrôle du complément, stabilisant TEP1 en circulation et empêchant sa fixation sur les tissus du soi avant qu elle ait pu se lier aux parasites envahissants. De plus, nous avons identifié la protéine nucléaire conservée IMAF, qui module la capacité de liaison de TEP1 et joue ainsi un rôle capital dans le contrôle de la charge parasitaire. L'invalidation d'IMAF par ARNi sera utilisée à présent comme outil pour disséquer la régulation de l'efficacité de liaison de TEP1. Pour la première fois, nous avons pu montrer que des protéines immunes essentielles agissent dans une voie unique pour assurer conjointement l'élimination des parasites en interagissant de façon directe ou indirecte avec TEP1.With more than two billion people at risk and one million child deaths per year, malaria is a devastating infectious disease. The causative agent Plasmodium is transmitted through a mosquito bite. During the development in its major vector Anopheles gambiae, the parasite, ingested with the blood meal, crosses the midgut epithelium to reach the basal side. Here, it undergoes dramatic losses caused by mosquito immunity. The molecular basis of this defence remains poorly understood. The complement-like thioester-containing protein TEP1 is an important immune factor, which induces killing of a vast majority of rodent P. berghei parasites. It is secreted into the haemolymph (blood), where it binds to parasites, promoting their lysis. In this work, we integrated novel players within the TEP1-dependent killing mechanism. Two antiparasitic LRR (leucine-rich repeat) proteins were characterised as complement-control factors stabilising TEP1 in circulation and preventing its uncontrolled deposition on self-tissues before it could bind to invading parasites. Moreover, we identified a novel highly conserved nuclear protein, IMAF (intracellular mosquito anti-Plasmodium factor), which modulates the TEP1-binding capacity and therefore plays an essential role in controlling parasite loads. Silencing of IMAF by RNAi will at present be used as a tool to dissect the regulation of TEP1-binding efficiency. For the first time, we could show that key immune proteins act in a single pathway to jointly promote parasite killing by either directly or indirectly interacting with TEP1

Molecular mechanisms of TEP1-dependent killing of Plasmodium in the mosquito Anopheles gambiae

Avec plus de deux milliards de personnes exposées et un million de morts infantiles par an, le paludisme est une maladie dévastatrice. L'agent infectieux Plasmodium est transmis par la piqûre d'un moustique. Lors du développement dans le vecteur principalWith more than two billion people at risk and one million child deaths per year, malaria is a devastating infectious disease. The causative agent Plasmodium is transmitted through a mosquito bite. During the development in its major vector Anopheles gamb

Killing two birds with one stone: trans-kingdom suppression of PAMP/MAMP-induced immunity by T3E from enteropathogenic bacteria

Within the past decade, remarkable similarities between the molecular organization of animal and plant systems for non-self discrimination were revealed. Obvious parallels exist between the molecular structures of the receptors mediating the recognition of pathogen- or microbe-associated molecular patterns (PAMPs/MAMPs) with plant pattern recognition receptors (PRRs) strikingly resembling mammalian Toll-like receptors. Mitogen-activated protein (MAP) kinase cascades, leading to the transcriptional activation of immunity-associated genes, illustrate the conservation of whole molecular building blocks of PAMP/MAMP-induced signaling. Enteropathogenic Salmonella and Escherichia coli use a type three secretion system (T3SS) to inject effector proteins into the mammalian host cell to subvert defense mechanisms and promote gut infection. Lately, disease occurrence was increasingly associated with bacteria-contaminated fruits and vegetables and common themes have emerged with regard to whether and how effectors target innate immune responses in a trans-kingdom manner. We propose that numerous Salmonella or E. coli effectors may be active in planta and tend to target central components (hubs) of immune signaling pathways

Genetic clonality of Plasmodium falciparum affects the outcome of infection in Anopheles gambiae

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AP-1/Fos-TGase2 axis mediates wounding-induced Plasmodium falciparum killing in Anopheles gambiae

Anopheline mosquitoes are the only vectors of human malaria worldwide. It is now widely accepted that mosquito immune responses play a crucial role in restricting Plasmodium development within the vector; therefore, further dissection of the molecular mechanisms underlying these processes should inform new vector control strategies urgently needed to roll back the disease. Here, using genome-wide transcriptional profiling, bioinformatics, and functional gene analysis, we identify a new axis of mosquito resistance to monoclonal Plasmodium falciparum infections that includes the AP-1 transcription factor Fos and the transglutaminase 2 (TGase2), a cross-linking enzyme with known roles in wound responses. We demonstrate that Fos regulates induction of TGase2 expression after wounding but does not affect expression of the components of the well characterized complement-like system. Silencing of Fos or of TGase2 aborts the wounding-induced mosquito killing of P. falciparum. These results reveal multiple signaling pathways that are required for efficient Plasmodium killing in Anopheles gambiae

Trans-kingdom competence of <em>Salmonella</em> effector proteins revealed by SpvC, a phosphothreonine lyase functional in plant cell

National audienceSalmonella is one of the most prominent causes of food poisoning and increasing evidence indicates that contaminated fruits and vegetables are an increasing concern for human health. Successful infection demands the suppression of the host immune system, which is often achieved via injection of bacterial effector proteins into host cells. In this report we present for the first time a function of Salmonella effector protein in plant cell, supporting the new concept of trans-kingdom competency of this bacteria. We identified several Salmonella Typhimurium effector proteins with a function in plants. Among these, the phosphothreonine lyase SpvC was found to attenuate the induction of resistance relevant genes when expressed in plant cells. Using in vitro and in vivo systems we show that this effector protein actively interacts with and dephosphorylates activated Arabidopsis mitogen-activated protein kinase 6 (MPK6), thereby inhibiting defense signaling. The requirement of Salmonella SpvC for full virulence toward plants was demonstrated by the decreased pathogenicity of the L1spvC mutant. These results suggest that some Salmonella effector proteins have conserved role during animal and plant infection. The fact that Salmonella and other Enterobacteriaceae can actively use plants as hosts strongly suggests that plants might represent a much larger reservoir of animal pathogens than so far estimated