Antibacterial peptides from Monochamus alternatus induced oxidative stress and reproductive defects in pine wood nematode through the ERK/MAPK signaling pathway

Molecular characterization and immunological functions of the antimicrobial peptide theromacin from razor clam Sinonovacula constricta

Antimicrobial peptides are natural immune effector molecules that protect the host from pathogenic microorganisms and play crucial roles in the innate immune system. Herein, the functions of theromacin from the razor clam Sinonovacula constricta (ScTM) were identified. Multiple sequence alignment revealed that the structure of ScTM was similar to that of a theromacin homolog with a signal peptide and conserved Macin domain. Tissue distribution analysis indicated that ScTM mRNA was expressed in all tested tissues. Moreover, ScTM transcripts were upregulated in hemocytes and hepatopancreas after challenge with Vibrio parahaemolyticus. Importantly, interfering with ScTM expression through siRNA transfection reduced hemocyte clearance ability and razor clam survival rates. Further functional analysis indicated that recombinant ScTM protein possessed considerable binding abilities to pathogens and PAMPs, showing the strongest binding ability to LPS. Minimum inhibitory concentration assays revealed that rScTm exerted stronger antimicrobial activities against Gram-negative bacteria than against Gram-positive bacteria. Moreover, rScTM exhibited antimicrobial activity against V. parahaemolyticus by increasing extracellular membrane permeability, impairing inner membrane integrity, and binding to genomic DNA, leading to cytoplasmic efflux and bacterial death. All of the results of this work provide a new perspective for the development of an effective strategy to control razor clam bacterial infection.

Nematicidal activity of pyrazine compounds against Meloidogyne incongnita, Burshaphelenchus xylophilus, and Aphelenchoides besseyi

The increase of plant parasitic nematode resistance poses a great threat to agricultural and forestry production. To search for nematicides with novel mechanism of action, nematicidal activity of the 29 pyrazine compounds were tested. Compound C2 showed excellent nematicidal activity against Bursaphelenchus xylophilus, Meloidogyne incongnita, and Aphelenchoides besseyi, with LC50 values were 2.3, 3.3, and 10.6 mg/L, respectively, and the pot experiment showed that C2 reduced the number of tomato roots knots to a certain extent. In addition, C2 significantly inhibited egg hatching, locomotion and reproductive ability of B. xylophilus, and also reduced the levels of protein and antioxidant enzyme activity to some extent, and the indexes related to oxidative stress showed an increasing trend after treatment. The novel chemical structure of compound D was designed and synthesized based on the lead compound C2 by the scaffold hopping strategy. Interestingly, compound D also has excellent nematicidal activity. Compound D can be used as an excellent scaffold in the discovery of novel nematicides and we will continue to work on the optimization and modification of this scaffold structure in the future.

Discovery of Novel Amide Derivatives Containing an Oxazole/Isoxazole Moiety as Potential SDH Inhibitors: Design, Synthesis, and Nematicidal Activity

To develop new nematicides, amide derivatives with oxazole/isoxazole were synthesized via scaffold-hopping as succinate dehydrogenase (SDH) inhibitors. The nematicidal activities of these target compounds were tested against Bursaphelenchus xylophilus, Aphelenchoides besseyi, and Ditylenchus destructor. Some of the compounds showed excellent nematicidal activities. Compound B21 had LC50 values of 3.2 mg/L for B. xylophilus, 11.5 mg/L for A. besseyi, and 10.5 mg/L for D. destructor. Compound B21 exerted a pronounced inhibitory effect on feeding, reproduction, and embryonic development capabilities of B. xylophilus, while concurrently triggering deleterious oxidative stress responses within the nematodes. These reactions led to intestinal damage and eventually death of the nematodes. Compound B21 exhibited strong hydrophobic interactions with the residues Arg-76, Val-103, Pro-193, and Ile-242 of SDH. Additionally, B21 significantly inhibited the SDH of B. xylophilus, with an IC50 value of 6.5 μmol/L.

Identification of pine wood nematode (Bursaphelenchus xylophilus) loading response genes in Japanese pine sawyer (Monochamus alternatus) through comparative genomics and transcriptomics

BACKGROUND

Pine wood nematode (PWN; Bursaphelenchus xylophilus) is the causative agent of pine wilt disease (PWD), which is considered the most dangerous biohazard to conifer trees globally. The transmission of PWN relies on insect vectors, particularly the Japanese pine sawyer (JPS; Monochamus alternatus). However, the molecular mechanism underlying PWN-JPS assembly remains largely unknown.

RESULTS

Here, we found that both geographical and gender could significantly affect the PCA (PWN carrying amount) of JPS; thus, JPS transcriptomes from diverse locations and genders were explored regard to PWN loading. Due to the shortage of genomes, we developed a full-length reference transcriptome for analyzing next-generation sequencing data. A comparative genomic study was performed, and 11 248 potential PWN-carrying associate genes (β) were nominated in JPS by using the reported genomes of PWN and non-PWN carrier insect species. Then, 151 differentially expressed transcripts (DETs), 28 of them overlapped with β, correlated with the PCA of JPS were nominated by RNA-Seq, and found that fatty acid β-oxidation might be the key factor that affected the PCA of JPS. Furthermore, JPS fatty acid β-oxidation rates were experimentally decreased using the inhibitor Etomoxir, leading to an increased PCA of JPS. Meanwhile, silencing MaCPT1 in JPS by RNA interference led to a decreased fatty acid β-oxidation rate and increased PCA of JPS.

CONCLUSIONS

In conclusion, MaCPT1 was able to decrease the PWN-JPS assembly formation through the fatty acid β-oxidation of JPS. These results provide new insights for exploring the impact of PWN invasion on JPS. © 2024 Society of Chemical Industry.

Calcium stress reduces the reproductive capacity and pathogenicity of the pine wood nematode (Bursaphelenchus xylophilus) by inhibiting oxidative phosphorylation reaction

The continuous use of chemical pesticides to control nematodes could result in the developing of pesticide-resistant nematodes. Novel nucleic acid pesticides are becoming the focus of pesticide research due to their strong specificity, high efficiency, and environmental friendliness. However, the limited known biochemical targets restrict the development of target pesticides for nematodes. The calcium stress experiments on pine wood nematodes (PWN) showed that 100 mmol/L Ca2+ resulted in longitudinal depression on the PWN body wall, reduced oviposition, and increased corrected mortality. To enrich the biological targets of nematode pesticides, we further investigated the response mechanism of PWN to calcium stress at the molecular level. Differentially expressed gene analysis showed that genes involved in the oxidative phosphorylation (OXPHOS) pathway were significantly enriched. RNA interference results of 6 key genes belonging to four mitochondrial complex I (BXNDUFA2), III (BXQCR8), IV (BXCOX17), V (BXV-ATPaseB, BXV-ATPaseE, BXV-ATPaseε) in non-stressed nematodes showed reduction in PWN oviposition, population size, feeding ability, and pathogenicity. The BXNDUFA2 gene interference had the highest inhibitory impact by decreasing the oviposition from 31.00 eggs to 6.75 eggs and PWN population size from 8.27 × 103 nematodes to 1.64 × 103 nematodes, respectively. Interestingly, RNA interference of these 6 key genes in calcium-stressed nematodes also led to increased mortality and decreased oviposition of PWN. In summary, calcium stress inhibited the reproductive capacity of PWN by down-regulating key genes BXNDUFA2, BXQCR8, BXV-ATPaseB, BXV-ATPaseE, BXV-ATPaseε, and BXCOX17, thereby reducing the pathogenicity. The current results enrich the RNAi targets in PWN and provide a scientific basis for developing novel nucleic nematicides.

Identification and characteristic analysis of an extracellular signal-regulated kinase from Ostrinia furnacalis Guenée

The extracellular signal-regulated kinase (ERK) pathway, a critical genetic determinant, controls diverse physiological functions, including innate immunity, development, and stress response. In the current study, a full-length cDNA (1592bp) encoding the ERK gene (OfERK) was cloned from Ostrinia furnacalis Guenée (GenBank accession number: MF797866). The open reading frame of the OfERK gene encoded 364 amino acids and shared 96.43%-98.08% amino acid identities with other insect mitogen-activated protein kinases. For spatiotemporal analysis of the expression pattern, OfERK exhibited a significant peak expression on the 3rd day of the pupa stage and showed the highest expression in hemocytes specifically. Indirect immunofluorescence assays and immuno-electron microscopy revealed a wide distribution of the OfERK protein in hemocytes and epidermis. Moreover, the results demonstrated that the Bt Cry1Ab-activated toxin significantly induces the expression of OfERK. Other genes related to immune response, development, and stress response exhibited dynamic changes in expression after Cry1Ab oral treatment. The expression of OfERK was downregulated through RNA interference, and the correlation of its expression with other related genes was verified using quantitative real-time polymerase chain reaction. Our study provides valuable insights into the regulatory mechanism of ERK in insects for future studies.