Multiple Precursor Proteins of Thanatin Isoforms, an Antimicrobial Peptide Associated With the Gut Symbiont of Riptortus pedestris

Abstract

Thanatin is an antimicrobial peptide (AMP) generated by insects for defense against bacterial infections. In the present study, we performed cDNA cloning of thanatin and found the presence of multiple precursor proteins from the bean bug, Riptortus pedestris. The cDNA sequences encoded 38 precursor proteins, generating 13 thanatin isoforms. In the phylogenetic analysis, thanatin isoforms were categorized into two groups based on the presence of the membrane attack complex/perforin (MACPF) domain. In insect-bacterial symbiosis, specific substances are produced by the immune system of the host insect and are known to modulate the symbiont’s population. Therefore, to determine the biological function of thanatin isoforms in symbiosis, the expression levels of three AMP genes were compared between aposymbiotic insects and symbiotic R. pedestris. The expression levels of the thanatin genes were significantly increased in the M4 crypt, a symbiotic organ, of symbiotic insects upon systemic bacterial injection. Further, synthetic thanatin isoforms exhibited antibacterial activity against gut-colonized Burkholderia symbionts rather than in vitro-cultured Burkholderia cells. Interestingly, the suppression of thanatin genes significantly increased the population of Burkholderia gut symbionts in the M4 crypt under systemic Escherichia coli K12 injection. Overgrown Burkholderia gut symbionts were observed in the hemolymph of host insects and exhibited insecticidal activity. Taken together, these results suggest that thanatin of R. pedestris is a host-derived symbiotic factor and an AMP that controls the population of gut-colonized Burkholderia symbionts.

Identification and expression patterns of somatic piRNAs and PIWI genes in Riptortus pedestris (Hemiptera: Alydidae)

“…Antibiotic treatment that disturbs the gut bacterial communities was applied to explore their benefit in the maintenance of host homeostasis at the transcriptional and posttranscriptional levels in insects, such as Bactrocera dorsalis , Altica viridicyanea , A. mellifera , and Plagiodera versicolora (Ma et al, 2021; Ren, Chen, Wang, et al, 2023; Xie et al, 2023; Zhang, Mu, et al, 2022). In previous reports, it is plausible that the available research model of gut bacteria− R. pedestris has been constructed and validated for their roles in host physiology and immunity (Lee & Lee, 2022; Lee, Kim, et al, 2019; Lee et al, 2022). On the basis of these results, we applied the samples of gut bacterial disturbance by antibiotic feeding and two laboratory‐reared to compare the relationships between piRNA expression and gut bacterial shifts, combined the wild samples using WTS technology.…”

Burkholderia gut symbiont induces insect host fecundity by modulating Kr‐h1 gene expression

“…7.1.0.). Phylogenetic trees for the alignment were constructed using the Maximum likelihood method and the Jones–Taylor–Thornton model (Cha & Lee, 2022; Lee et al, 2022).…”

Unraveling the Role of Antimicrobial Peptides in Insects

“…The midgut of R. pedestris is divided into five sections M1, M2, M3, M4B, and M4. In the M4 region, the symbiotic organ contains a specific symbiont Burkholderia insecticola , which is orally acquired from the environment by second-instar nymphs [ 117 ]. Park et al showed that the intestinal immunity of R. pedestris is related to an AMP called rip-thanatin and that the expression of the rip-thanatin gene upon systemic bacterial infection significantly increased in the M4 crypt [ 118 ].…”

“…Indeed, it was shown that rip-thanatin has high activity against E. coli and Staphylococcus aureus bacteria but lower activity against symbiotic Burkholderia. The Burkholderia population has to be controlled in the midgut; when overgrown and present in the hemolymph of host insects, Burkholderia exhibit insecticidal activity [ 117 , 118 , 119 ].…”