Thioester-containing Proteins in the Drosophila melanogaster Immune Response against the Pathogen Photorhabdus

Sgabd-2 plays specific role in immune response against biopesticide Metarhizium anisopliae in Aphis citricola

Metarhizium anisopliae is an effective biopesticide for controlling Aphis citricola, which has developed resistance to many chemical pesticides. However, the powerful immune system of A. citricola has limited the insecticidal efficacy of M. anisopliae. The co-evolution between insects and entomogenous fungi has led to emergence of new antifungal immune genes, which remain incompletely understood. In this study, an important immune gene Sgabd-2 was identified from A. citricola through transcriptome analysis. Sgabd-2 gene showed high expression in the 4th instar nymph and adult stages, and was mainly distributed in the abdominal region of A. citricola. The recombinant protein (rSgabd-2) exhibited no antifungal activity but demonstrated clear agglutination activity towards the conidia of M. anisopliae. RNA interference of Sgabd-2 by dsRNA feeding resulted in decreased phenoloxidase (PO) activity and weakened defense for A. citricola against M. anisopliae. Simultaneous silence of GNBP-1 and Sgabd-2 effectively reduced the immunity of A. citricola against M. anisopliae more than the individual RNAi of GNBP-1 or Sgabd-2. Furthermore, a genetically engineered M. anisopliae expressing double-stranded RNA (dsSgabd-2) targeting Sgabd-2 in A. citricola successfully suppressed the expression of Sgabd-2 and demonstrated increased virulence against A. citricola. Our findings elucidated Sgabd-2 as a critical new antifungal immune gene and proposed a genetic engineering strategy to enhance the insecticidal virulence of entomogenous fungi through RNAi-mediated inhibition of pest immune genes.

Common carp intelectin 3 (cITLN3) plays a role in the innate immune response

Intelectin is a lectin with the capacity to recognize and bind to carbohydrates. In this study, we successfully cloned cITLN3 from common carp, which consists of a signal peptide domain, a FReD domain, and an intelectin domain. The expression levels of cITLN3 were detected in various organs of common carp, including the liver, head kidney, spleen, foregut, midgut, and hindgut, with the highest expression observed in the liver. Following infection with Staphylococcus aureus (S. aureus) or Aeromonas hydrophila (A. hydrophila), the expression level of cITLN3 was significantly upregulated in all organs of common carp. Subsequently, we expressed and purified the recombinant cITLN3 protein using an E. coli expression system. The cITLN3 could aggregate both gram-positive and gram-negative bacteria in the presence of Ca2+, with a stronger affinity for gram-positive bacteria. Moreover, our study demonstrated that cITLN3 displayed a higher binding affinity towards PGN compared to LPS. Furthermore, we observed that cITLN3 had the potential to inhibit bacterial proliferation in common carp and safeguard intestinal integrity during bacterial stimulation. And the results also indicated that cITLN3 might played a role in the Toll-like receptors (TLRs) signaling pathway activation.

Functional role of thioester-containing proteins in the Drosophila anti-pathogen immune response

Thioester-containing proteins (TEPs) are present in many animal species ranging from deuterostomes to protostomes, which emphasizes their evolutionary conservation and importance in animal physiology. Phylogenetically, insect TEPs share sequence similarity with mammalian α2-macroglobulin. Drosophila melanogaster is specifically considered a superb model for teasing apart innate immune processes. Here we review recent discoveries on the involvement of Drosophila TEPs in the immune response against bacterial pathogens, nematode parasites, and parasitoid wasps. This information generates novel insights into the role of TEPs as regulators of homeostasis in Drosophila and supports the complexity of immune recognition and specificity in insects and more generally in invertebrates. These developments together with recent advances in gene editing and multi-omics will enable the fly immunity community to appreciate the molecular and mechanistic contributions of TEPs to the modulation of the host defense against infectious disease and possibly to translate this information into tangible therapeutic benefits.

Regulators and signalling in insect antimicrobial innate immunity: Functional molecules and cellular pathways

Insects possess an immune system that protects them from attacks by various pathogenic microorganisms that would otherwise threaten their survival. Immune mechanisms may deal directly with the pathogens by eliminating them from the host organism or disarm them by suppressing the synthesis of toxins and virulence factors that promote the invasion and destructive action of the intruder within the host. Insects have been established as outstanding models for studying immune system regulation because innate immunity can be explored as an integrated system at the level of the whole organism. Innate immunity in insects consists of basal immunity that controls the constitutive synthesis of effector molecules such as antimicrobial peptides, and inducible immunity that is activated after detection of a microbe or its product(s). Activation and coordination of innate immune defenses in insects involve evolutionary conserved immune factors. Previous research in insects has led to the identification and characterization of distinct immune signalling pathways that modulate the response to microbial infections. This work has not only advanced the field of insect immunology, but it has also rekindled interest in the innate immune system of mammals. Here we review the current knowledge on key molecular components of insect immunity and discuss the opportunities they present for confronting infectious diseases in humans.

Special Issue: Insects, Nematodes, and Their Symbiotic Bacteria

This special issue contains articles that add to the ever-expanding toolbox of insect pathogenic nematodes (entomopathogenic nematodes; EPNs) as well articles that provide new insights into the mutualistic interaction between EPNs and their hosts. The study of natural infection models such as EPNs allows detailed insight into micro- and macro-evolutionary dynamics of innate immune reactions, including known but also emerging branches of innate immunity. Additional new insights into the kinetics of EPN infections are gained by increased spatiotemporal resolution of advanced transcriptome studies and live imaging.