Transcriptome-wide identification and characterization of Toll pathway genes in Riptortus pedestris (Hemiptera: Alydidae)

The Toll pathway was first identified in Drosophila and plays an essential role in defense against infection by various pathogens. To date, various noncoding RNAs (ncRNAs) have been demonstrated to maintain immune homeostasis by regulating several target genes in the insect Toll pathway. However, the characterization and function of Toll pathway genes involved in the response to environmental changes at the posttranscriptional level associated with gut bacterial changes in Riptortus pedestris, which is a significant pest of soybeans, remain unclear. In this study, we identified and classified six Toll genes into three subtypes with typical Toll domain arrangements, including a Toll/interleukin receptor (TIR) domain, a transmembrane domain, and multiple leucine-rich repeat (LRR) domains; in addition, only one positive selection site was found in hemipteran sPP-Tolls, and a total of five downstream members in the Toll signaling pathway were selected and characterized. The expression patterns revealed that all these genes were widely expressed at all developmental stages of R. pedestris, and they presented variable expression levels among the different feeding treatments in the R. pedestris gut. Our comprehensive prediction analysis revealed that there are sixty miRNA‒mRNA interaction pairs, including fifty-six miRNA and six Toll pathway genes (P‒Toll1, sP‒Toll, Myd88, Pelle, Tube, and Cactus), and a ceRNA network comprising two lncRNA‒miRNA‒Toll pairs was constructed in response to environmental changes. Finally, the expression of some above genes and ncRNAs from the ceRNA network exhibited positive or negative association with the most changes in gut bacterial genera via Pearson correlation analysis. These findings provide valuable insights into how the Toll pathway of R. pedestris is involved in environmental adaptation at the posttranscriptional level and identifies new avenues for developing more effective methods for pest control through integration with gut bacteria.