A digestive tract expressing α-amylase influences the adult lifespan of Pteromalus puparum revealed through RNAi and rescue analyses

Insect α-Amylases and Their Application in Pest Management

Amylase is an indispensable hydrolase in insect growth and development. Its varied enzymatic parameters cause insects to have strong stress resistance. Amylase gene replication is a very common phenomenon in insects, and different copies of amylase genes enable changes in its location and function. In addition, the classification, structure, and interaction between insect amylase inhibitors and amylases have also invoked the attention of researchers. Some plant-derived amylase inhibitors have inhibitory activities against insect amylases and even mammalian amylases. In recent years, an increasing number of studies have clarified the effects of pesticides on the amylase activity of target and non-target pests, which provides a theoretical basis for exploring safe and efficient pesticides, while the exact lethal mechanisms and safety in field applications remain unclear. Here, we summarize the most recent advances in insect amylase studies, including its sequence and characteristics and the regulation of amylase inhibitors (α-AIs). Importantly, the application of amylases as the nanocide trigger, RNAi, or other kinds of pesticide targets will be discussed. A comprehensive foundation will be provided for applying insect amylases to the development of new-generation insect management tools and improving the specificity, stability, and safety of pesticides.

RNA meets toxicology: efficacy indicators from the experimental design of RNAi studies for insect pest management

RNA interference (RNAi) selectively targets genes and silences their expression in vivo, causing developmental defects, mortality and altered behavior. Consequently, RNAi has emerged as a promising research area for insect pest management. However, it is not yet a viable alternative over conventional pesticides despite several theoretical advantages in safety and specificity. As a first step toward a more standardized approach, a machine learning algorithm was used to identify factors that predict trial efficacy. Current research on RNAi for pest management is highly variable and relatively unstandardized. The applied random forest model was able to reliably predict mortality ranges based on bioassay parameters with 72.6% accuracy. Response time and target gene were the most important variables in the model, followed by applied dose, double-stranded RNA (dsRNA) construct size and target species, further supported by generalized linear mixed effect modeling. Our results identified informative trends, supporting the idea that basic principles of toxicology apply to RNAi bioassays and provide initial guidelines standardizing future research similar to studies of traditional insecticides. We advocate for training that integrates genetic, organismal, and toxicological approaches to accelerate the development of RNAi as an effective tool for pest management. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A chromosome-level genome assembly of the parasitoid wasp Pteromalus puparum

Parasitoid wasps represent a large proportion of hymenopteran species. They have complex evolutionary histories and are important biocontrol agents. To advance parasitoid research, a combination of Illumina short-read, PacBio long-read and Hi-C scaffolding technologies was used to develop a high-quality chromosome-level genome assembly for Pteromalus puparum, which is an important pupal endoparasitoid of caterpillar pests. The chromosome-level assembly has aided in studies of venom and detoxification genes. The assembled genome size is 338 Mb with a contig N50 of 38.7 kb and a scaffold N50 of 1.16 Mb. Hi-C analysis assembled scaffolds onto five chromosomes and raised the scaffold N50 to 65.8 Mb, with more than 96% of assembled bases located on chromosomes. Gene annotation was assisted by RNA sequencing for the two sexes and four different life stages. Analysis detected 98% of the BUSCO (Benchmarking Universal Single-Copy Orthologs) gene set, supporting a high-quality assembly and annotation. In total, 40.1% (135.6 Mb) of the assembly is composed of repetitive sequences, and 14,946 protein-coding genes were identified. Although venom genes play important roles in parasitoid biology, their spatial distribution on chromosomes was poorly understood. Mapping has revealed venom gene tandem arrays for serine proteases, pancreatic lipase-related proteins and kynurenine-oxoglutarate transaminases, which have amplified in the P. puparum lineage after divergence from its common ancestor with Nasonia vitripennis. In addition, there is a large expansion of P450 genes in P. puparum. These examples illustrate how chromosome-level genome assembly can provide a valuable resource for molecular, evolutionary and biocontrol studies of parasitoid wasps.

Venom α-amylase of the endoparasitic wasp Pteromalus puparum influences host metabolism

BACKGROUND

Pteromalus puparum (Hymenoptera: Pteromalidae) is an endoparasitoid wasp that parasitizes many butterfly species, including a Brassicaceae pest, Pieris rapae (Lepidoptera: Pieridae), the small white cabbage butterfly. P. puparum females inject venom along with their eggs into hosts to ensure successful parasitism. The venom regulates host development and behavior, suppresses host immunity, and influences host metabolism. It has been shown that the venom contains α-amylases, a group of hydrolytic enzymes that act in insect sugar metabolism. So far, three α-amylases have been identified in P. puparum (Pteromalus puparum α-amylases, PpAmys) and the function of PpAmy1 has been reported. However, the functions of PpAmy2 and PpAmy3 remain unknown.

RESULTS

We studied the functions of an α-amylase highly expressed in muscle-rich tissues (PpAmy2) and an α-amylase highly expressed in venom apparatus (PpAmy3) using RNAi and GC-TOF-MS techniques. Knockdown of PpAmy3 by RNAi reduced the body length and weight of 1-day old larval offspring while there was no significant effect when PpAmy2 was knocked down. Compared to the control injected with siGFP, many metabolites in P. puparum changed when PpAmy2 was knocked down, while the injection of PpAmy3 recombinant protein into host induced metabolite changes in the P. rapae hemolymph.

CONCLUSION

Our study demonstrated that PpAmy2 acts in metabolism in the muscles of the parasitoid while PpAmy3 could influence the host metabolism and may support the development of parasitic wasp offspring. © 2020 Society of Chemical Industry.

Identification and Comparative Analysis of Venom Proteins in a Pupal Ectoparasitoid, Pachycrepoideus vindemmiae

Parasitoid wasps inject venom containing complex bioactive compounds to regulate the immune response and development of host arthropods and sometime paralyze host arthropods. Although extensive studies have been conducted on the identification of venom proteins in larval parasitoids, relatively few studies have examined the pupal parasitoids. In our current study, a combination of transcriptomic and proteomic methods was used to identify 64 putative venom proteins from Pachycrepoideus vindemmiae, an ectoparasitoid of Drosophila. Expression analysis revealed that 20 tested venom proteins have 419-fold higher mean expression in the venom apparatus than in other wasp tissues, indicating their specialization to venom. Comparisons of venom proteins from P. vindemmiae and other five species spanning three parasitoid families detected a core set of "ancient" orthologs in Pteromalidae. Thirty-five venom proteins of P. vindemmiae were assigned to the orthologous groups by reciprocal best matches with venoms of other pteromalids, while the remaining 29 were not. Of the 35 categories, twenty-seven have orthologous relationships with Nasonia vitripennis venom proteins and 25 with venoms of Pteromalus puparum. More distant relationships detected that five and two venom proteins of P. vindemmiae are orthologous with venoms of two Figitidae parasitoids and a Braconidae representative, respectively. Moreover, twenty-two venoms unique to P. vindemmiae were also detected, indicating considerable interspecific variation of venom proteins in parasitoids. Phylogenetic reconstruction based on a set of single-copy genes clustered P. vindemmiae with P. puparum, N. vitripennis, and other members of the family Pteromalidae. These findings provide strong evidence that P. vindemmiae venom proteins are well positioned for future functional and evolutionary studies.

Functional Characterization of a Venom Protein Calreticulin in the Ectoparasitoid Pachycrepoideus vindemiae

Venom proteins act in the immunological interactions between parasitoids and their host insects. The effect of venom proteins on host immunity is not fully understood in pupal parasitoids. We identified the functions of a venom protein, calreticulin (PvCRT), in the pupal ectoparasitoid Pachycrepoideus vindemiae. Here, we report that PvCRT features a signal peptide and two conserved "calreticulin" domains. Multiple sequence alignments show that PvCRT shares 83.54% amino acid identity with CRT from both Pteromalus puparum and Nasonia vitripennis, which infers a close relationship among these three species. Using qPCR analysis, we found a lower expression level of PvCRT (0.27-fold) in the venom apparatus compared to the corresponding carcass. Immunohistochemical localization revealed that PvCRT was ubiquitously expressed in venom gland. The expression of the PvCRT gene in Drosophila transgenic lines via the UAS/Gal4 binary expression system reduced the self-encapsulation phenotype of tu(1)Sz1 mutants. Additionally, studies on humoral immunity indicate that PvCRT does not affect the antimicrobial immune responses of the host. This work on an ectoparasitoid will increase our understanding of venom-mediated host-parasitoid interactions.