Abstract
Spätzle family proteins activate the Toll pathway and induce antimicrobial peptide (AMP) production against microbial infections. However, the functional importance of Tmspätzle4 (TmSpz4) in the immune response of Tenebrio molitor has not been reported. Therefore, here, we have identified and functionally characterized the role of TmSpz4 against bacterial and fungal infections. We showed that TmSpz4 expression was significantly induced in hemocytes at 6 h post-injection with Escherichia coli, Staphylococcus aureus, and Candida albicans. TmSpz4 knock-down significantly reduced larval survival against E. coli and C. albicans. To understand the reason for the survivability difference, the role of TmSpz4 in AMP production was examined in TmSpz4-silenced larvae following microbe injection. The AMPs that are active against Gram-negative bacteria, including TmTenecin-2, TmTenecin-4, TmAttacin-1a, TmDefensin-2, and TmCecropin-2, were significantly downregulated in response to E. coli in TmSpz4-silenced larvae. Similarly, the expression of TmTenecin-1, TmTenecin-3, TmThaumatin-like protein-1 and -2, TmDefensin-1, TmDefensin-2, and TmCecropin-2 were downregulated in response to C. albicans in TmSpz4-silenced larvae. In addition, the transcription factor NF-κB (TmDorX1 and TmDorX2) expression was significantly suppression in TmSpz4-silenced larvae. In conclusion, these results suggest that TmSpz4 plays a key role in regulating immune responses of T. molitor against to E. coli and C. albicans.
Highlights
IntroductionInsects are the largest and most diverse group of animals on Earth, and have highly adaptable defenses against different environmental threats, including microorganisms (bacteria, fungi, and viruses) and parasites
Insects are the largest and most diverse group of animals on Earth, and have highly adaptable defenses against different environmental threats, including microorganisms and parasites
Domain analysis suggested that TmSpz4 contains one cystine-knot domain at the C-terminus, which is a ligand of the Toll receptor; one cleavage site that is predicted to
Summary
Insects are the largest and most diverse group of animals on Earth, and have highly adaptable defenses against different environmental threats, including microorganisms (bacteria, fungi, and viruses) and parasites. Insects have developed a potent defense mechanism, known as innate immunity, which can recognize and eliminate microbes [1]. This well-developed system includes physical defenses, as well as cellular and humoral immunity. The humoral immune system principally relies on antimicrobial peptides (AMPs), lectins, lysozyme, and protease inhibitors [2]. The innate immune system depends on pattern recognition receptors (PRRs) that recognize conserved molecules on pathogens, called pathogen-associated molecular patterns [3]. Recognition of invading pathogens activates signal transduction pathways [Toll or immune deficiency (IMD)], leading to the expression of AMPs that attack the invading pathogens [4,5]
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