Thanatin

Penicillium digitatum is the most damaging pathogen provoking green mold in citrus fruit during storage, and there is an urgent need for novel antifungal agents with high efficiency. The aim of this study was to investigate the antifungal effects of peptide thanatin against P. digitatum and the molecular mechanisms. Results showed that peptide thanatin had a prominent inhibitory effect on P. digitatum by in vitro and in vivo test. A total of 938 genes, including 556 downregulated and 382 upregulated genes, were differentially expressed, as revealed by RNA-seq of whole P. digitatum genomes analysis with or without thanatin treatment. The downregulated genes mainly encoded RNA polymerase, ribosome biogenesis, amino acid metabolism, and major facilitator superfamily. The genes associated with heat shock proteins and antioxidative systems were widely expressed in thanatin-treated group. DNA, RNA, and the protein content of P. digitatum were significantly decreased after thanatin treatment. In conclusion, thanatin could inhibit the growth of P. digitatum, and the underlying mechanism might be the genetic information processing and stress response were affected. The research will provide more precise and directional clues to explore the inhibitory mechanism of thanatin on growth of P. digitatum.

Antimicrobial peptides (AMPs) possess great potential for combating drug-resistant bacteria. Thanatin is a pathogen-inducible single-disulfide-bond-containing β-hairpin AMP which was first isolated from the insect Podisus maculiventris. The 21-residue-long thanatin displays broad-spectrum activity against both Gram-negative and Gram-positive bacteria as well as against various species of fungi. Remarkably, thanatin was found to be highly potent in inhibiting the growth of bacteria and fungi at considerably low concentrations. Although thanatin was isolated around 25 years ago, only recently has there been a pronounced interest in understanding its mode of action and activity against drug-resistant bacteria. In this review, multiple modes of action of thanatin in killing bacteria and in vivo activity, therapeutic potential are discussed. This promising AMP requires further research for the development of novel molecules for the treatment of infections caused by drug resistant pathogens.

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.