The phylogenetic and evolutionary analyses of detoxification gene families in Aphidinae species

A pooled-sample draft genome assembly provides insights into host plant-specific transcriptional responses of a Solanaceae-specializing pest, Tupiocoris notatus (Hemiptera: Miridae)

The assembly of genomes from pooled samples of genetically heterogenous samples of conspecifics remains challenging. In this study, we show that high-quality genome assemblies can be produced from samples of multiple wild-caught individuals. We sequenced DNA extracted from a pooled sample of conspecific herbivorous insects (Hemiptera: Miridae: Tupiocoris notatus) acquired from a greenhouse infestation in Tucson, Arizona (in the range of 30-100 individuals; 0.5 mL tissue by volume) using PacBio highly accurate long reads (HiFi). The initial assembly contained multiple haplotigs (>85% BUSCOs duplicated), but duplicate contigs could be easily purged to reveal a highly complete assembly (95.6% BUSCO, 4.4% duplicated) that is highly contiguous by short-read assembly standards (N 50 = 675 kb; Largest contig = 4.3 Mb). We then used our assembly as the basis for a genome-guided differential expression study of host plant-specific transcriptional responses. We found thousands of genes (N = 4982) to be differentially expressed between our new data from individuals feeding on Datura wrightii (Solanaceae) and existing RNA-seq data from Nicotiana attenuata (Solanaceae)-fed individuals. We identified many of these genes as previously documented detoxification genes such as glutathione-S-transferases, cytochrome P450s, and UDP-glucosyltransferases. Together our results show that long-read sequencing of pooled samples can provide a cost-effective genome assembly option for small insects and can provide insights into the genetic mechanisms underlying interactions between plants and herbivorous pests.

Characterization of the physiological, histopathological, and gene expression alterations in Spodoptera frugiperda larval midguts affected by toosendanin exposure

The fall armyworm, Spodoptera frugiperda, is a polyphagous pest worldwide and feeds on many grain and cash crops, which threatens the safety of agriculture and forestry production. Toosendanin (TSN) is a commercial insecticidal active ingredient used to manage various pests in the field and showed adverse effects against S. frugiperda, while the effects of TSN on the larval midguts are not yet known. In this study, the effects of 10 and 20 mg/kg TSN exposures on the larval midguts were analyzed. The structural changes of the larval midgut induced by TSN treatments were also determined by hematoxylin-eosin staining. Besides, TSN treatments also changed the enzyme activities of three digestive enzymes (α-amylase, lipase, and trypsin) and two detoxification enzymes (CarE and GST). A total of 2868 differentially expressed genes (DEGs) were identified by RNA-Seq in the larval midguts with 20 mg/kg TSN treatment, and the DEGs responsible for food digestion and detoxification were further examined. Our findings revealed the preliminary modes of action of TSN on the larval midguts of S. frugiperda, which provide a preliminary rationale for controlling S. frugiperda with TSN in the field.

Genome-wide identification and characterization of the chemosensory relative protein genes in Rhus gall aphid Schlechtendalia chinensis

BACKGROUND

The Rhus gall aphid Schlechtendalia chinensis specially uses the only species Rhus chinensis and certain moss species (Mniaceae) as its primary host plant and secondary host plants, respectively. Rhus galls are formed on the primary host by the sucking of aphids, and used in traditional medicine as well as other various areas due to their high tannin contents. Chemoreception is critical for insect behaviors such as host searching, location and identification of mates and reproductive behavior. The process of chemoreception is mediated by a series of protein gene families, including odorant-binding proteins (OBPs), chemosensory proteins (CSPs), olfactory receptors (ORs), gustatory receptors (GRs), ionotropic receptors (IRs), and sensory neuron membrane proteins (SNMPs). However, there have been no reports on the analysis of molecular components related to the chemoreception system of S. chinensis at the genome level.

RESULTS

We examined the genes of eight OBPs, nine CSPs, 24 ORs, 16 GRs, 22 IRs, and five SNMPs in the S. chinensis genome using homological searches, and these chemosensory genes appeared mostly on chromosome 1. Phylogenetic and gene number analysis revealed that the gene families, e.g., ORs, GRs, CSPs and SNMPs in S. chinensis, have experienced major contractions by comparing to Myzus persicae, while the two gene families OBPs and IRs had slight expansion. The current results might be related to the broader host range of M. persicae versus the specialization of S. chinensis on only a host plant. There were 28 gene pairs between genomes of S. chinensis and Acyrthosiphon pisum in the chemoreceptor gene families by collinear comparison. Ka/Ks ratios (< 1) indicated that the genes of S. chinensis were mainly affected by purification selection during evolution. We also found the lower number and expression level of chemoreception genes in S. chinensis than in other 11 aphid species, such as ORs, GRs and IRs, which play an important role in host search.

CONCLUSION

Our study firstly identified the genes of the different chemosensory protein gene families in the S. chinensis genome, and analyzed their general features and expression profile, demonstrating the importance of chemoreception in the aphid and providing new information for further functional research.

Metabolization and sequestration of plant specialized metabolites in insect herbivores: Current and emerging approaches

Herbivorous insects encounter diverse plant specialized metabolites (PSMs) in their diet, that have deterrent, anti-nutritional, or toxic properties. Understanding how they cope with PSMs is crucial to understand their biology, population dynamics, and evolution. This review summarizes current and emerging cutting-edge methods that can be used to characterize the metabolic fate of PSMs, from ingestion to excretion or sequestration. It further emphasizes a workflow that enables not only to study PSM metabolism at different scales, but also to tackle and validate the genetic and biochemical mechanisms involved in PSM resistance by herbivores. This review thus aims at facilitating research on PSM-mediated plant-herbivore interactions.

Detoxification Gene Families at the Genome-Wide Level of Rhus Gall Aphid Schlechtendalia chinensis

The Rhus gall aphid Schlechtendalia chinensis uses the species Rhus chinensis as its primary host plant, on which galls are produced. The galls have medicinal properties and can be used in various situations due to their high tannin content. Detoxification enzymes play significant roles in the insect lifecycle. In this study, we focused on five detoxification gene families, i.e., glutathione-S-transferase (GST), ABC transporter (ABC), Carboxylesterase (CCE), cyto-chrome P450 (CYP), and UDP-glycosyltransferase (UDP), and manually annotated 144 detoxification genes of S. chinensis using genome-wide techniques. The detoxification genes appeared mostly on chromosome 1, where a total of two pair genes were identified to show tandem duplications. There were 38 gene pairs between genomes of S. chinensis and Acyrthosiphon pisum in the detoxification gene families by collinear comparison. Ka/Ks ratios showed that detoxification genes of S. chinensis were mainly affected by purification selection during evolution. The gene expression numbers of P450s and ABCs by transcriptome sequencing data were greater, while gene expression of CCEs was the highest, suggesting they might be important in the detoxification process. Our study has firstly identified the genes of the different detoxification gene families in the S. chinensis genome, and then analyzed their general features and expression, demonstrating the importance of the detoxification genes in the aphid and providing new information for further research.