Insecticide resistance by a host-symbiont reciprocal detoxification

Insecticide resistance is one of the most serious problems in contemporary agriculture and public health. Although recent studies revealed that insect gut symbionts contribute to resistance, the symbiont-mediated detoxification process remains unclear. Here we report the in vivo detoxification process of an organophosphorus insecticide, fenitrothion, in the bean bug Riptortus pedestris. Using transcriptomics and reverse genetics, we reveal that gut symbiotic bacteria degrade this insecticide through a horizontally acquired insecticide-degrading enzyme into the non-insecticidal but bactericidal compound 3-methyl-4-nitrophenol, which is subsequently excreted by the host insect. This integrated “host-symbiont reciprocal detoxification relay” enables the simultaneous maintenance of symbiosis and efficient insecticide degradation. We also find that the symbiont-mediated detoxification process is analogous to the insect genome-encoded fenitrothion detoxification system present in other insects. Our findings highlight the capacity of symbiosis, combined with horizontal gene transfer in the environment, as a powerful strategy for an insect to instantly eliminate a toxic chemical compound, which could play a critical role in the human-pest arms race.

Screening Candidate Effectors of the Bean Bug Riptortus pedestris by Proteomic and Transcriptomic Analyses

The damage of Riptortus pedestris is exceptional by leading soybean plants to keep green in late autumn. Identification of the salivary proteins is essential to understand how the pest-plant interaction occurs. Here, we have tried to identify them by a combination of proteomic and transcriptomic analyses. The transcriptomes of salivary glands from R. pedestris males, females and nymphs showed about 28,000 unigenes, in which about 40% had open reading frames (ORFs). Therefore, the predicted proteins in the transcriptomes with secretion signals were obtained. Many of the top 1,000 expressed transcripts were involved in protein biosynthesis and transport, suggesting that the salivary glands produce a rich repertoire of proteins. In addition, saliva of R. pedestris males, females and nymphs was collected and proteins inside were identified. In total, 155, 20, and 11 proteins were, respectively, found in their saliva. We have tested the tissue-specific expression of 68 genes that are likely to be effectors, either because they are homologs of reported effectors of other sap-feeding arthropods, or because they are within the top 1,000 expressed genes or found in the salivary proteomes. Their potential functions in regulating plant defenses were discussed. The datasets reported here represent the first step in identifying effectors of R. pedestris.

Oviposition-promoting pars intercerebralis neurons show period-dependent photoperiodic changes in their firing activity in the bean bug

Animals show photoperiodic responses in physiology and behavior to adapt to seasonal changes. Recent genetic analyses have demonstrated the significance of circadian clock genes in these responses. However, the importance of clock genes in photoperiodic responses at the cellular level and the physiological roles of the cellular responses are poorly understood. The bean bug Riptortus pedestris shows a clear photoperiodic response in its reproduction. In the bug, the pars intercerebralis (PI) is an important brain region for promoting oviposition. Here, we analyzed the role of the photoperiodic neuronal response and its relationship with clock genes, focusing on PI neurons. Large PI neurons exhibited photoperiodic firing changes, and high firing activities were primarily found under photoperiodic conditions suitable for oviposition. RNA interference-mediated knockdown of the clock gene period abolished the photoperiodic response in PI neurons, as well as the response in ovarian development. To clarify whether the photoperiodic response in the PI was dependent on ovarian development, we performed an ovariectomy experiment. Ovariectomy did not have significant effects on the firing activity of PI neurons. Finally, we identified the output molecules of the PI neurons and analyzed the relevance of the output signals in oviposition. PI neurons express multiple neuropeptides—insulin-like peptides and diuretic hormone 44—and RNA interference of these neuropeptides reduced oviposition. Our results suggest that oviposition-promoting peptidergic neurons in the PI exhibit a circadian clock-dependent photoperiodic firing response, which contributes to the photoperiodic promotion of oviposition.

Chromosome-level genome assembly of the bean bug Riptortus pedestris

The bean bug (Riptortus pedestris) causes great economic losses of soybeans by piercing and sucking pods and seeds. Although R. pedestris has become the focus of numerous studies associated with insect–microbe interactions, plant–insect interactions, and pesticide resistance, a lack of genomic resources has limited deeper insights. In this study, we report the first R. pedestris genome at the chromosomal level using PacBio, Illumina, and Hi-C technologies. The assembled genome was 1.193 Gb in size with a contig N50 of 13.97 Mb. More than 95.7% of the total genome bases were successfully anchored to 6 unique chromosomes, with the scaffold N50 reaching 181.34 Mb. Genome resequencing of male and female individuals and chromosomic staining demonstrated that the sex chromosome system of R. pedestris is XO, and the shortest chromosome is the X chromosome. In total, 21,562 protein-coding genes were predicted, 21,320 of which were validated as being expressed in different tissues or different developmental stages. Evolutionary analysis demonstrated that R. pedestris and Oncopeltus fasciatus formed a sister group and split ∼35 million years ago. Additionally, a 5.04 Mb complete genome of symbiotic Serratia marcescens Rip1 was assembled, and the virulence factors that account for successful colonization in the host midgut were identified. The high-quality R. pedestris genome provides a valuable resource for further research, as well as for the pest management of bug pests.