Differential Change Patterns of Main Antimicrobial Peptide Genes During Infection of Entomopathogenic Nematodes and Their Symbiotic Bacteria

Abstract

The expression of antimicrobial peptides (AMPs) as the main humoral defense reactions of insects during infection by entomopathogenic nematodes (EPNs) and their symbiont is addressed herein. Three AMPs, attacin, cecropin, and spodoptericin, were evaluated in the fifth instar larvae of Spodoptera exigua Hübner (beet armyworm) when challenged with Steinernema carpocapsae or Heterorhabditis bacteriophora. The results indicated that attacin was expressed to a greater extent than either cecropin or spodoptericin. While spodoptericin was expressed to a much lesser extent, this AMP was induced against Gram-positive bacteria, and thus not expressed after penetration of Xenorhabdus nematophila and Photorhabdus luminescens. Attacin and cecropin in the larvae treated with S. carpocapsae at 8 hr post-injection (PI) attained the maximum expression levels and were 138.42-fold and 65.84-fold greater than those of larvae infected with H. bacteriophora, respectively. Generally, the ability of H. bacteriophora to suppress attacin, cecropin, and spodoptericin was greater than that of S. carpocapsae. According to the results, the expression of AMPs by Sp. exigua larvae against S. carpocapsae was determined in the 4 statuses of monoxenic nematode, axenic nematode, live symbiotic bacterium, and dead symbiotic bacterium. The expression of attacin in larvae treated with a monoxenic nematode and live bacterium at 8 and 2 hr PI, respectively, were increased to the maximum amount. Live X. nematophila was the strongest agent for the suppression of attacin. The expression of cecropin against monoxenic nematodes and live symbiotic bacteria at 8 and 4 hr PI, respectively, reached the maximum amount while the expression levels of attacin and cecropin for axenic nematodes were lesser and stable. The results highlighted that the ability of P. luminescens in AMPs suppression was much more than X. nematophila. The results also showed that the effect of symbiotic bacterium in suppressing attacin and cecropin expression was greater than that of a monoxenic nematode; this result provided deep insight into the expression pattern parallels and fluctuations of the main AMPs during nematode infection.

Exploring the Role of Relish on Antimicrobial Peptide Expressions (AMPs) Upon Nematode-Bacteria Complex Challenge in the Nipa Palm Hispid Beetle, Octodonta nipae Maulik (Coleoptera: Chrysomelidae)

“…We therefore joined previous authors to raise a question of how these nematodes and their symbiotic bacteria inhibit the expression of AMP genes? Overall, our data is thus similar to the ones reported in Dipterans particularly in Drosophila , where most AMPs are positively expressed in response to nematodes-bacteria complex infections (Aymeric et al, 2010; Darsouei et al, 2017; Yadav et al, 2017). Therefore, we hold the opinion that the stages of immunity suppressed by these pathogens are absent in Drosophila with regards to cellular and humeral responses in general (Aymeric et al, 2010; Casanova-Torres and Goodrich-Blair, 2013), and as well as with regards to AMPs expressions in O. nipae in particular.…”

“…The expression levels of AMPs, however, vary between the nematodes and their symbiotic bacteria. As reported by Darsouei et al (2017), the mRNA expression levels of attacin, cecropin, and spodoptericin were higher in S. exigua larvae treated with S. carpocapsae than H. bacteriophora . This was supported by Castillo et al (2015).…”

“…However, the pattern of AMP expressions in some insects is irregular and varies with the type of microbial challenge. This is seen in the study of Darsouei et al (2017) where cecropin, attacin and spodoptericin expression levels in H. bacteriophora -treated larvae were less than those of S. carpocapsae -treated ones. This can be linked to the hypothesis that the nematodes and their symbiotic bacteria produce certain toxins to suppress the insect’s immune responses, including the expression of AMPs.…”

Functional Characterization of Outer Membrane Proteins (OMPs) in Xenorhabdus nematophila and Photorhabdus luminescens through Insect Immune Defense Reactions

“…For AMPs expression of the target genes, attacin, cercopin, and spodoptericin, a set of primers were designed and used. Elongation factor 2 (EF2) gene was the reference gene used for normalization [22].…”

Nematobacterial Complexes and Insect Hosts: Different Weapons for the Same War

“…In R. ferrugineus larvae, the down-regulation of antimicrobial activity after the injection of live S. carpocapsae or isolated X. nematophila , has been recently observed; since dead nematodes or their cuticles lack inhibitory properties, the observed effects could be ascribed to X. nematophila [ 178 ]. Besides, in Spodoptera exigua , treatments with both X. nematophila and its culture broth, inhibited the expression of attacin and cecropin genes [ 179 ].…”