Gene Sequences of Potential Targets of Insecticidal PF2 Lectin Identified from the Larval De Novo Transcriptome of the Mexican Bean Weevil (Zabrotes Subfasciatus; Boheman 1833)

Transcriptome analysis of the endangered dung beetle Copris tripartitus (Coleoptera: Scarabaeidae) and characterization of genes associated to immunity, growth, and reproduction

BACKGROUND

Dung beetles recycle organic matter through the decomposition of feces and support ecological balance. However, these insects are threatened by the indiscriminate use of agrochemicals and habitat destruction. Copris tripartitus Waterhouse (Coleoptera: Scarabaeidae), a dung beetle, is listed as a class-II Korean endangered species. Although the genetic diversity of C. tripartitus populations has been investigated through analysis of mitochondrial genes, genomic resources for this species remain limited. In this study, we analyzed the transcriptome of C. tripartitus to elucidate functions related to growth, immunity and reproduction for the purpose of informed conservation planning.

RESULTS

The transcriptome of C. tripartitus was generated using next-generation Illumina sequencing and assembled de novo using a Trinity-based platform. In total, 98.59% of the raw sequence reads were processed as clean reads. These reads were assembled into 151,177 contigs, 101,352 transcripts, and 25,106 unigenes. A total of 23,450 unigenes (93.40%) were annotated to at least one database. The largest proportion of unigenes (92.76%) were annotated to the locally curated PANM-DB. A maximum of 5,512 unigenes had homologous sequences in Tribolium castaneum. Gene Ontology (GO) analysis revealed a maximum of 5,174 unigenes in the Molecular function category. Further, in Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, a total of 462 enzymes were associated with established biological pathways. Based on sequence homology to known proteins in PANM-DB, representative immunity, growth, and reproduction-related genes were screened. Potential immunity-related genes were categorized into pattern recognition receptors (PRRs), the Toll-like receptor signaling pathway, the MyD88- dependent pathway, endogenous ligands, immune effectors, antimicrobial peptides, apoptosis, and adaptation-related transcripts. Among PRRs, we conducted detailed in silico characterization of TLR-2, CTL, and PGRP_SC2-like. Repetitive elements such as long terminal repeats, short interspersed nuclear elements, long interspersed nuclear elements and DNA elements were enriched in the unigene sequences. A total of 1,493 SSRs were identified among all unigenes of C. tripartitus.

CONCLUSIONS

This study provides a comprehensive resource for analysis of the genomic topography of the beetle C. tripartitus. The data presented here clarify the fitness phenotypes of this species in the wild and provide insight to support informed conservation planning.

Characterization and expression of prohibitin during the mexican bean weevil (Zabrotes subfasciatus, Boheman, 1833) larvae development

Prohibitin (PHB) is a highly conserved eukaryotic protein complex involved in multiple cellular processes. In insects, PHB has been identified as a potential target protein to insecticidal molecules acting as a receptor of PF2 insecticidal lectin in the midgut of Zabrotes subfasciatus larvae (bean pest) and Cry protein of Bacillus thuringiensis in Leptinotarsa decemlineata (Colorado potato beetle). This study aimed to characterize the structural features of Z. subfasciatus prohibitin (ZsPHB) by homology modeling and evaluate its expression and tissue localization at different stages of larval development both at the transcript and protein levels. The samples were collected from eggs and larvae of different developmental stages. The immunodetection of ZsPHB was done with anti-PHB1 and confirmed by LC-MS/MS analysis. Gene expression analysis of ZsPHB1 and ZsPHB2 was performed by RT-qPCR, and immunohistochemistry with FITC-labeled anti-PHB1. Results showed that ZsPHBs exhibit distinctive characteristics of the SPFH protein superfamily. The transcript levels suggest a coordinated expression of ZsPHB1 and ZsPHB2 genes, while ZsPHB1 was detected in soluble protein extracts depending on the stage of development. Histological examination showed ZsPHB1 is present in all larval tissues, with an intense fluorescence signal observed at the gut. These results suggest a physiologically important role of PHB during Z. subfasciatus development and show its regulation occurs at the transcriptional and post-transcriptional levels. This is the first characterization of PHB in Z. subfasciatus.