Chemokine-like MDL proteins modulate flowering time and innate immunity in plants.

Human macrophage migration inhibitory factor (MIF) is an atypical chemokine implicated in intercellular signaling and innate immunity. MIF orthologs (MIF/D-DT-like proteins, MDLs) are present throughout the plant kingdom, but remain experimentally unexplored in these organisms. Here, we provide an in planta characterization and functional analysis of the three-member gene/protein MDL family in Arabidopsis thaliana. Subcellular localization experiments indicated a nucleo-cytoplasmic distribution of MDL1 and MDL2, while MDL3 is localized to peroxisomes. Protein-protein interaction assays revealed the in vivo formation of MDL1, MDL2, and MDL3 homo-oligomers, as well as the formation of MDL1-MDL2 hetero-oligomers. Functionally, Arabidopsismdl mutants exhibited a delayed transition from vegetative to reproductive growth (flowering) under long-day conditions, but not in a short-day environment. In addition, mdl mutants were more resistant to colonization by the bacterial pathogen Pseudomonas syringae pv. maculicola. The latter phenotype was compromised by the additional mutation of SALICYLIC ACID INDUCTION DEFICIENT 2 (SID2), a gene implicated in the defense-induced biosynthesis of the key signaling molecule salicylic acid. However, the enhanced antibacterial immunity was not associated with any constitutive or pathogen-induced alterations in the levels of characteristic phytohormones or defense-associated metabolites. Interestingly, bacterial infection triggered relocalization and accumulation of MDL1 and MDL2 at the peripheral lobes of leaf epidermal cells. Collectively, our data indicate redundant functionality and a complex interplay between the three chemokine-like Arabidopsis MDL proteins in the regulation of both developmental and immune-related processes. These insights expand the comparative cross-kingdom analysis of MIF/MDL signaling in human and plant systems.

Deciphering the molecular mechanisms of mother-to-egg immune protection in the mealworm beetle Tenebrio molitor.

In a number of species, individuals exposed to pathogens can mount an immune response and transmit this immunological experience to their offspring, thereby protecting them against persistent threats. Such vertical transfer of immunity, named trans-generational immune priming (TGIP), has been described in both vertebrates and invertebrates. Although increasingly studied during the last decade, the mechanisms underlying TGIP in invertebrates are still elusive, especially those protecting the earliest offspring life stage, i.e. the embryo developing in the egg. In the present study, we combined different proteomic and transcriptomic approaches to determine whether mothers transfer a "signal" (such as fragments of infecting bacteria), mRNA and/or protein/peptide effectors to protect their eggs against two natural bacterial pathogens, namely the Gram-positive Bacillus thuringiensis and the Gram-negative Serratia entomophila. By taking the mealworm beetle Tenebrio molitor as a biological model, our results suggest that eggs are mainly protected by an active direct transfer of a restricted number of immune proteins and of antimicrobial peptides. In contrast, the present data do not support the involvement of mRNA transfer while the transmission of a "signal", if it happens, is marginal and only occurs within 24h after maternal exposure to bacteria. This work exemplifies how combining global approaches helps to disentangle the different scenarios of a complex trait, providing a comprehensive characterization of TGIP mechanisms in T. molitor. It also paves the way for future alike studies focusing on TGIP in a wide range of invertebrates and vertebrates to identify additional candidates that could be specific to TGIP and to investigate whether the TGIP mechanisms found herein are specific or common to all insect species.

Parental transfer of the antimicrobial protein LBP/BPI protects Biomphalaria glabrata eggs against oomycete infections.

Vertebrate females transfer antibodies via the placenta, colostrum and milk or via the egg yolk to protect their immunologically immature offspring against pathogens. This evolutionarily important transfer of immunity is poorly documented in invertebrates and basic questions remain regarding the nature and extent of parental protection of offspring. In this study, we show that a lipopolysaccharide binding protein/bactericidal permeability increasing protein family member from the invertebrate Biomphalaria glabrata (BgLBP/BPI1) is massively loaded into the eggs of this freshwater snail. Native and recombinant proteins displayed conserved LPS-binding, antibacterial and membrane permeabilizing activities. A broad screening of various pathogens revealed a previously unknown biocidal activity of the protein against pathogenic water molds (oomycetes), which is conserved in human BPI. RNAi-dependent silencing of LBP/BPI in the parent snails resulted in a significant reduction of reproductive success and extensive death of eggs through oomycete infections. This work provides the first functional evidence that a LBP/BPI is involved in the parental immune protection of invertebrate offspring and reveals a novel and conserved biocidal activity for LBP/BPI family members.

Diversification of MIF immune regulators in aphids: link with agonistic and antagonistic interactions.

BACKGROUND: The widespread use of genome sequencing provided evidences for the high degree of conservation in innate immunity signalling pathways across animal phyla. However, the functioning and evolutionary history of immune-related genes remains unknown for most invertebrate species. A striking observation coming from the analysis of the pea aphid Acyrthosiphon pisum genome is the absence of important conserved genes known to be involved in the antimicrobial responses of other insects. This reduction in antibacterial immune defences is thought to be related to their long-term association with beneficial symbiotic bacteria and to facilitate symbiont maintenance. An additional possibility to avoid elimination of mutualistic symbionts is a fine-tuning of the host immune response. To explore this hypothesis we investigated the existence and potential involvement of immune regulators in aphid agonistic and antagonistic interactions. RESULTS: In contrast to the limited antibacterial arsenal, we showed that the pea aphid Acyrthosiphon pisum expresses 5 members of Macrophage Migration Inhibitory Factors (ApMIF), known to be key regulators of the innate immune response. In silico searches for MIF members in insect genomes followed by phylogenetic reconstruction suggest that evolution of MIF genes in hemipteran species has been shaped both by differential losses and serial duplications, raising the question of the functional importance of these genes in aphid immune responses. Expression analyses of ApMIFs revealed reduced expression levels in the presence, or during the establishment of secondary symbionts. By contrast, ApMIFs expression levels significantly increased upon challenge with a parasitoid or a Gram-negative bacteria. This increased expression in the presence of a pathogen/parasitoid was reduced or missing, in the presence of facultative symbiotic bacteria. CONCLUSIONS: This work provides evidence that while aphid's antibacterial arsenal is reduced, other immune genes widely absent from insect genomes are present, diversified and differentially regulated during antagonistic or agonistic interactions.

Insecticidal efficacy and possibility of Combretum trifoliatum Vent. (Myrtales: Combretaceae) extracts in controlling Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae).

BACKGROUND: The fall armyworm Spodoptera frugiperda (J.E. Smith), is an important pest of agronomical crops. It is interesting to discover secondary metabolites in plants that are environmentally safer than synthetic pesticides. For this purpose, Combretum trifoliatum crude extract and its isolated compounds were investigated for their insecticidal activities against S. frugiperda. RESULTS: The median lethal dose (LD50 ) was evaluated in the second-instar larvae using the topical application method. The isolated compounds, apigenin and camphor, demonstrated a highly toxic effect on larvae at a lower LD50 dose than crude extract. Moreover, when the larvae were exposed to crude extract concentrations, the development to pupa and adult stages was reduced by more than 50%. The ovicidal toxicity was examined using a hand sprayer. The extract concentration 5, 10, and 20 µg/egg significantly decreased the egg hatchability. In addition, crude extract showed a significant difference in inhibiting acetylcholinesterase (AChE) activity while crude extract and camphor showed significant inhibitory effects on carboxylesterase (CE) and glutathione-S-transferase (GST) activities. CONCLUSION: The crude ethanol extract of Combretum trifoliatum was toxic to S. frugiperda in terms of larval mortality, negatively affecting biological parameters, and decreasing egg hatchability. Additionally, the activities of cholinergic and detoxifying enzymes were affected by crude extract and its isolated compounds. These results highlight that Combretum trifoliatum might be efficient as a bioinsecticide to control S. frugiperda. © 2023 Society of Chemical Industry.

The Molecular Resistance Mechanisms of European Earwigs from Apple Orchards Subjected to Different Management Strategies.

To date, apple orchards are among the most treated crops in Europe with up to 35 chemical treatments per year. Combining control methods that reduce the number of pesticide treatments is essential for agriculture and more respectful of the environment, and the use of predatory insects such as earwigs may be valuable to achieve this goal. European earwigs, Forficula auricularia (Dermaptera: Forficulidae) are considered beneficial insects in apple orchards where they can feed on many pests like aphids. The aim of this study was to investigate the potential impact of orchards' insecticide treatments on resistance-associated molecular processes in natural populations of earwigs. Because very few molecular data are presently available on earwigs, our first goal was to identify earwig resistance-associated genes and potential mutations. Using earwigs from organic, integrated pest management or conventional orchards, we identified mutations in acetylcholinesterase 2, α1 and ß2 nicotinic acetylcholine receptors. In addition, the expression level of these targets and of some essential detoxification genes were monitored using RT-qPCR. Unexpectedly, earwigs collected in organic orchards showed the highest expression for acetylcholinesterase 2. Four cytochromes P450, one esterase and one glutathione S-transferases were over-expressed in earwigs exposed to various management strategies in orchards. This first study on resistance-associated genes in Forficula auricularia paves the way for future experimental studies aimed at better understanding the potential competition between natural enemies in apple orchards in order to optimize the efficiency of biocontrol.

MIF-like domain containing protein orchestrates cellular differentiation and virulence in the fungal pathogen Magnaporthe oryzae.

Macrophage migration inhibitory factor (MIF) is a pleiotropic protein with chemotactic, pro-inflammatory, and growth-promoting activities first discovered in mammals. In parasites, MIF homologs are involved in immune evasion and pathogenesis. Here, we present the first comprehensive analysis of an MIF protein from the devastating plant pathogen Magnaporthe oryzae (Mo). The fungal genome encodes a single MIF protein (MoMIF1) that, unlike the human homolog, harbors multiple low-complexity regions (LCRs) and is unique to Ascomycota. Following infection, MoMIF1 is expressed in the biotrophic phase of the fungus, and is strongly down-regulated during subsequent necrotrophic growth in leaves and roots. We show that MoMIF1 is secreted during plant infection, affects the production of the mycotoxin tenuazonic acid and inhibits plant cell death. Our results suggest that MoMIF1 is a novel key regulator of fungal virulence that maintains the balance between biotrophy and necrotrophy during the different phases of fungal infection.

Involvement of the cytokine MIF in the snail host immune response to the parasite Schistosoma mansoni.

We have identified and characterized a Macrophage Migration Inhibitory Factor (MIF) family member in the Lophotrochozoan invertebrate, Biomphalaria glabrata, the snail intermediate host of the human blood fluke Schistosoma mansoni. In mammals, MIF is a widely expressed pleiotropic cytokine with potent pro-inflammatory properties that controls cell functions such as gene expression, proliferation or apoptosis. Here we show that the MIF protein from B. glabrata (BgMIF) is expressed in circulating immune defense cells (hemocytes) of the snail as well as in the B. glabrata embryonic (Bge) cell line that has hemocyte-like features. Recombinant BgMIF (rBgMIF) induced cell proliferation and inhibited NO-dependent p53-mediated apoptosis in Bge cells. Moreover, knock-down of BgMIF expression in Bge cells interfered with the in vitro encapsulation of S. mansoni sporocysts. Furthermore, the in vivo knock-down of BgMIF prevented the changes in circulating hemocyte populations that occur in response to an infection by S. mansoni miracidia and led to a significant increase in the parasite burden of the snails. These results provide the first functional evidence that a MIF ortholog is involved in an invertebrate immune response towards a parasitic infection and highlight the importance of cytokines in invertebrate-parasite interactions.

RNA-based technologies for insect control in plant production.

RNA interference (RNAi) is a biological process in which small RNA (sRNA) molecules sequence-specifically silence gene expression at the transcriptional or post-transcriptional level, either by directing inhibitory chromatin modifications or by decreasing the stability or translation potential of the targeted mRNA. The trigger for gene silencing is double-stranded RNA (dsRNA) generated from an endogenous genomic locus or a foreign source, such as a transgene or virus. The process of gene silencing can be exploited in agriculture to control plant diseases and pests. Of the pests that impact crop yield (including nematodes, arthropods, rodents, snails, slugs and birds), insects constitute the largest and most diverse group. Here, we review the "pros" and "cons" of using RNAi technology mediated by dsRNA-expressing transgenic plants (host-induced gene silencing, HIGS) or direct application of chemically synthesized dsRNA to control plant-damaging insects. Rapid progress in elucidating RNAi mechanisms has led to the first commercial products on the market. Given the high potential of RNAi strategies, their use in agriculture, horticulture, and forestry will likely be extensive in the future. However, further studies are needed to improve the efficacy of RNAi-based plant protection strategies and to assess their associated safety risks.

Atypical Membrane-Anchored Cytokine MIF in a Marine Dinoflagellate.

Macrophage Migration Inhibitory Factors (MIF) are pivotal cytokines/chemokines for vertebrate immune systems. MIFs are typically soluble single-domain proteins that are conserved across plant, fungal, protist, and metazoan kingdoms, but their functions have not been determined in most phylogenetic groups. Here, we describe an atypical multidomain MIF protein. The marine dinoflagellate Lingulodinium polyedra produces a transmembrane protein with an extra-cytoplasmic MIF domain, which localizes to cell-wall-associated membranes and vesicular bodies. This protein is also present in the membranes of extracellular vesicles accumulating at the secretory pores of the cells. Upon exposure to biotic stress, L. polyedra exhibits reduced expression of the MIF gene and reduced abundance of the surface-associated protein. The presence of LpMIF in the membranes of secreted extracellular vesicles evokes the fascinating possibility that LpMIF may participate in intercellular communication and/or interactions between free-living organisms in multispecies planktonic communities.

[Immunity in parasite-vector snails]. / Arche de Noé immunologique : Immunité des mollusques vecteurs de parasites humains.

Aquatic snails play a key role in the transmission of parasites such as the human blood or liver flukes (Schistosomes and Fasciola sp.). During the last decade, particular efforts have been made by a small number of scientists to progress in our understanding of the molecular mechanisms underlying snail immune responses and/or host parasite interactions. Complementary approaches using the gastropod snail Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, have yielded a number of unexpected results such as the existence of highly diversified pathogen-binding proteins (FREPs), or potential immune regulators similar to mammalian cytokines. Although molecular immune processes largely remain to be elucidated, accumulating data support the idea that snail innate immunity is much more complex than originally thought.

Cross-Kingdom Analysis of Diversity, Evolutionary History, and Site Selection within the Eukaryotic Macrophage Migration Inhibitory Factor Superfamily.

Macrophage migration inhibitory factors (MIF) are multifunctional proteins regulating major processes in mammals, including activation of innate immune responses. MIF proteins also play a role in innate immunity of invertebrate organisms or serve as virulence factors in parasitic organisms, raising the question of their evolutionary history. We performed a broad survey of MIF presence or absence and evolutionary relationships across 803 species of plants, fungi, protists, and animals, and explored a potential relation with the taxonomic status, the ecology, and the lifestyle of individual species. We show that MIF evolutionary history in eukaryotes is complex, involving probable ancestral duplications, multiple gene losses and recent clade-specific re-duplications. Intriguingly, MIFs seem to be essential and highly conserved with many sites under purifying selection in some kingdoms (e.g., plants), while in other kingdoms they appear more dispensable (e.g., in fungi) or present in several diverged variants (e.g., insects, nematodes), suggesting potential neofunctionalizations within the protein superfamily.

Excretory-secretory products of larval Fasciola hepatica investigated using a two-dimensional proteomic approach.

So far, very few secreted proteins from trematodes have been characterized, although their role in the mechanisms that allow the parasite to escape host's immune response have been largely documented. Here we performed a proteomic analysis of excretory-secretory proteins from the intra-molluscan larval stages of Fasciola hepatica. We identified two antioxidative enzymes: a Cu/Zn-superoxide dismutase (Cu/Zn SOD) and a thioredoxin (TRX) previously characterized in ES products from adult stages. These results support the importance of parasite detoxication of reactive oxygen species in invertebrate hosts, and raise the question of the possible conservation of major immune evasion effectors across trematode developmental life-stages.

Excretory-secretory proteome of larval Schistosoma mansoni and Echinostoma caproni, two parasites of Biomphalaria glabrata.

Schistosoma mansoni and Echinostoma caproni are two trematode species that use different strategies (mimicry and immunosuppression, respectively) to interfere with the snail innate immune system. Parasites excretory-secretory (ES) products have been shown to play a key role in these host-parasite immune interactions. However, they remain largely uncharacterized in larval trematodes. We developed a global proteomic approach to characterize the ES proteome of S. mansoni and E. caproni primary sporocysts. In ES products of both parasites, we found proteins involved in reactive oxygen species scavenging, glycolysis, signalling or calcium binding (superoxide dismutase Cu/Zn; glutathione S-transferase; aldo-keto-reductase; triose-phosphate isomerase; glyceraldehyde-3-phosphate dehydrogenase; aldolase, enolase, MICAL-like, calreticulin). According to their predicted functions, we propose a model in which these proteins (i) are involved in antioxidant activity, (ii) prevent hemocyte encapsulation process or (iii) favor invasion and migration of sporocysts in host tissues. These results suggest that S. mansoni and E. caproni sporocysts develope a strong immune protection during the first hours of infection giving them enough time to build up a long lasting immune evasion strategy relying on molecular mimicry or immunosuppression, respectively.

Identification and expression of gene transcripts generated during an anti-parasitic response in Biomphalaria glabrata.

In order to gain further insights into the molecular basis of gastropod anti-parasite immune responses, we investigated transcripts of Biomphalaria glabrata regulated during hemocytic encapsulation. Using a snail strain that is resistant to the parasite Echinostoma caproni, we performed suppression subtractive hybridization (SSH) to construct cDNA libraries of transcripts more abundantly expressed in unexposed or parasite-exposed snails. After sequence analysis and quantitative PCR analysis of expression, we identified 10 candidates of particular interest. They belonged to various functional groups such as detoxification enzymes (GST, SOD), antimicrobial proteins (LBI/BPI), protease inhibitors (cystatins), calcium-binding proteins, or C-type lectins. In situ hybridization (ISH) analysis revealed that one overexpressed cystatin-like candidate is specifically expressed in hemocytes participating in parasite encapsulation or aggregating at the site of infection. Two other candidates (C-type lectin and a LBP/BPI) were expressed in the albumen gland, further supporting the role of this organ in immunity and/or host-parasite interaction.

Whole genome analysis of a schistosomiasis-transmitting freshwater snail.

Biomphalaria snails are instrumental in transmission of the human blood fluke Schistosoma mansoni. With the World Health Organization's goal to eliminate schistosomiasis as a global health problem by 2025, there is now renewed emphasis on snail control. Here, we characterize the genome of Biomphalaria glabrata, a lophotrochozoan protostome, and provide timely and important information on snail biology. We describe aspects of phero-perception, stress responses, immune function and regulation of gene expression that support the persistence of B. glabrata in the field and may define this species as a suitable snail host for S. mansoni. We identify several potential targets for developing novel control measures aimed at reducing snail-mediated transmission of schistosomiasis.

Corrigendum: Whole genome analysis of a schistosomiasis-transmitting freshwater snail.

This corrects the article DOI: 10.1038/ncomms15451.

Glyceroneogenesis: an unexpected metabolic pathway for glutamine in Schistosoma mansoni sporocysts.

To date, glyceroneogenesis has only been described in mammals but we demonstrate in this paper that it could exist in the invertebrate Schistosoma mansoni, the parasitic helminth transmitted by fresh water molluscs and responsible for the major human endemic disease, schistosomiasis. Glyceroneogenesis is a phosphoenolpyruvate carboxykinase (PEPCK)-dependent process by which glycerol can be produced from precursors like glutamine and therefore represents a truncated gluconeogenic pathway. We have previously demonstrated the possible central role of glutamine in mollusc-schistosome interactions. In this work, we show that glutamine effectively promotes in vitro survival and protein synthesis in sporocysts, the intramolluscan larval stages of S. mansoni, possibly through its role as an energy source. However, the demonstration that PEPCK is massively expressed in these larval forms as compared to adult parasites, together with the observation that 3-mercaptopicolinate, a specific inhibitor of PEPCK, significantly reduces the effect of glutamine on sporocyst growth, suggest that glutamine could also be used for glucose or glycerol production. Results of [14C] glutamine incorporation confirmed that neosynthesis of glucose and mainly of glycerol occurred in sporocysts and was dependent on PEPCK activity. Therefore, our results strongly indicate that glyceroneogenesis could exist in schistosomes. Several hypotheses can be proposed concerning the importance of glycerol for the adaptation of this helminth to its host osmotic and energetic environment.

A Novel Mechanism of Immune Memory Unveiled at the Invertebrate-Parasite Interface.

Pinaud et al. recently provided the first global investigation of the molecular processes underlying innate immune memory in an invertebrate species. They showed that the memory response of the snail Biomphalaria glabrata to Schistosoma mansoni infection is associated with a shift from cellular to humoral mechanisms.

The LBP/BPI multigenic family in invertebrates: Evolutionary history and evidences of specialization in mollusks.

LBPs (lipopolysaccharide binding proteins) and BPIs (bactericidal permeability increasing proteins) are important proteins involved in defense against bacterial pathogens. We recently discovered a novel biocidal activity of a LBP/BPI from the gastropod Biomphalaria glabrata and demonstrated its role in parental immune protection of eggs, highlighting the importance of LBP/BPIs in invertebrate immunity. Here we characterize four additional LBP/BPI from B. glabrata, presenting conserved sequence architecture and exon-intron structure. Searches of invertebrate genomes revealed that existence of LBP/BPIs is not a conserved feature since they are absent from phyla such as arthropods and platyhelminths. Analyses of LBP/BPI transcripts from selected mollusk species showed recent parallel duplications in some species, including B. glabrata. In this snail species, LBP/BPI members vary in their expression tissue localization as well as their change in expression levels after immune challenges (Gram-negative bacterium; Gram-positive bacterium or yeast). These results, together with the predicted protein features provide evidences of functional specialization of LBP/BPI family members in molluscs.