Genome-wide identification of candidate chemosensory receptors in the bean bug Riptortus pedestris (Hemiptera: Alydidae) and the functional verification of its odorant receptor co-receptor (Orco) in recognizing aggregation pheromone

Abstract

A sophisticated and sensitive olfactory system plays a vital role in the survival and reproduction of insects. Chemosensory receptors are indispensable for the molecular recognition and discrimination of semiochemicals. Riptortus pedestris is a notorious pest of legume plants, resulting in yield losses and quality decreases in soybeans. It is well accepted that R. pedestris highly relies on its olfactory system in detecting aggregation pheromones, host volatiles, and pesticides; however, little research focused on its chemosensory receptors. In the present study, we identified 237 odorant receptors (ORs), 42 gustatory receptors (GRs), and 31 ionotropic receptors (IRs) from the reported genome of R. pedestris, and analyzed their phylogenetic relationship with other hemipteran species. Through the results of RNA-seq and real-time quantitative PCR (qRT-PCR), we found that RpedORs displayed different expression levels in the antennae of R. pedestris at different development stages. To further verify the function of odorant receptor co-receptor (Orco), an obligate and unique insect OR, we silenced RpedOrco by RNA interference (RNAi) method. The results showed that silencing RpedOrco could significantly impair the response to aggregation pheromone in R. pedestris, indicating that RpedOrco plays an essential role in odorant detection. Our results can provide the theoretical foundations for revealing the olfactory recognition mechanism of R. pedestris and help explore and develop novel olfactory-based agents against this pest.

Evaluation of Reference Genes for Quantitative Real-Time PCR Analysis in the Bean Bug, Riptortus pedestris (Hemiptera: Alydidae)

“…The genomic and transcriptomic data of R. pedestris have been published to study its development, chemosensory genes, and insecticide resistance [20,[23][24][25]41,42]. Previous qRT-PCR studies on R. pedestris commonly employed universal reference genes for insect species [23][24][25][26]. Nevertheless, the use of inappropriate ones may result in misinterpretation of data.…”

“…Fu et al identified numerous differentially expressed genes implicated in wing formation through a comparative analysis of the transcriptomes of R. pedestris eggs, first-, second-, third-, fourth-, and fifth-instar nymphs, as well as adults [23]. Moreover, Liu et al [24] and Li et al [25] conducted a transcriptional analysis of gene expression in the antennae of R. pedestris and identified several genes potentially involved in olfactory and taste transduction. The quantitative assessment of gene expression not only enhances the comprehension of the molecular mechanisms associated with insect development, stress response, and behavioral regulation in R. pedestris but also holds the potential to reveal novel targets for effective pest control.…”

“…Actin, EF1, and GAPDH have been employed as reference genes to normalize the expression of target genes implicated in the development, odor perception, odor discrimination, and behaviors (such as feeding and mating) of R. pedestris [23][24][25][26]. Nevertheless, the aforementioned studies did not assess the appropriateness of these genes in experimental conditions.…”