Cell lines from diamondback moth exhibiting differential susceptibility to baculovirus infection and expressing midgut genes

Exploring the role of the ovary-serine protease gene in the female fertility of the diamondback moth using CRISPR/Cas9

BACKGROUND

Oogenesis is a complex pathway necessary for proper female reproduction in insects. Ovary-serine protease (Osp) is a homologous gene of serine protease Nudel (SpNudel) and plays an essential role in the oogenesis and ovary development of Drosophila melanogaster. However, the function of Osp is not determined in Plutella xylostella, a highly destructive pest of cruciferous crops.

RESULTS

The PxOsp gene comprises a 5883-bp open-reading frame that encodes a protein consisting of 1994 amino acids, which contain four conserved domains. PxOsp exhibited a high relative expression in adult females with a specific expression in the ovary. Through the utilization of CRISPR/Cas9 technology, homozygous mutants of PxOsp were generated. These homozygous mutant females produced fewer eggs (average of 56 eggs/female) than wild-type (WT) females (average of 97 eggs/female) when crossed with WT males, and these eggs failed to hatch. Conversely, mutant males produced normal progeny when crossed with WT females. The ovarioles in homozygous mutant females were significantly shorter (5.02 mm in length) and contained fewer eggs (average of 3 eggs/ovariole) than WT ovarioles (8.09 mm in length with an average of 8 eggs/ovariole). Moreover, eggs laid by homozygous mutant females were fragile, with irregular shapes, and were unable to maintain structural integrity due to eggshell ruptures. However, no significant differences were observed between WT and mutant individuals regarding developmental duration, pupal weight, and mating behavior.

CONCLUSION

Our study suggesteds that PxOsp plays a vital role in female reproduction, particularly in ovary and egg development. Disrupting PxOsp results in recessive female sterility while leaving the male reproductive capability unaffected. This report represents the first study of a haplosufficient gene responsible for female fertility in lepidopteran insects. Additionally, these findings emphasize PxOsp as a potential target for genetically-based pest management of P. xylostella. © 2024 Society of Chemical Industry.

Hsp70 and Hsp90 Elaborately Regulate RNAi Efficiency in Plutella xylostella

Heat-shock proteins (HSPs) serve as molecular chaperones in the RNA interference (RNAi) pathway of eukaryotic organisms. In model organisms, Hsp70 and Hsp90 facilitate the folding and remodeling of the client protein Argonaute (Ago). However, the specific function of HSPs in the RNAi pathway of Plutella xylostella (L.) (Lepidoptera: Plutellidae) remains unknown. In this study, we identified and analyzed the coding sequences of PxHsc70-4 and PxHsp83 (also known as PxHsp90). Both PxHsc70-4 and PxHsp83 exhibited three conserved domains that covered a massive portion of their respective regions. The knockdown or inhibition of PxHsc70-4 and PxHsp83 in vitro resulted in a significant increase in the gene expression of the dsRNA-silenced reporter gene PxmRPS18, leading to a decrease in its RNAi efficiency. Interestingly, the overexpression of PxHsc70-4 and PxHsp83 in DBM, Sf9, and S2 cells resulted in an increase in the bioluminescent activity of dsRNA-silenced luciferase, indicating a decrease in its RNAi efficiency via the overexpression of Hsp70/Hsp90. Furthermore, the inhibition of PxHsc70-4 and PxHsp83 in vivo resulted in a significant increase in the gene expression of PxmRPS18. These findings demonstrated the essential involvement of a specific quantity of Hsc70-4 and Hsp83 in the siRNA pathway in P. xylostella. Our study offers novel insights into the roles played by HSPs in the siRNA pathway in lepidopteran insects.

An LW-Opsin Mutation Changes the Gene Expression of the Phototransduction Pathway: A Cryptochrome1 Mutation Enhances the Phototaxis of Male Plutella xylostella (Lepidoptera: Plutellidae)

Plutella xylostella is a typical phototactic pest. LW-opsin contributes to the phototaxis of P. xylostella, but the expression changes of other genes in the phototransduction pathway caused by the mutation of LW-opsin remain unknown. In the study, the head transcriptomes of male G88 and LW-opsin mutants were compared. A GO-function annotation showed that DEGs mainly belonged to the categories of molecular functions, biological processes, and cell composition. Additionally, a KEGG-pathway analysis suggested that DEGs were significantly enriched in some classical pathways, such as the phototransduction-fly and vitamin digestion and absorption pathways. The mRNA expressions of genes in the phototransduction-fly pathway, such as Gq, ninaC, and rdgC were significantly up-regulated, and trp, trpl, inaD, cry1, ninaA and arr1 were significantly down-regulated. The expression trends of nine DEGs in the phototransduction pathway confirmed by a RT-qPCR were consistent with transcriptomic data. In addition, the influence of a cry1 mutation on the phototaxis of P. xylostella was examined, and the results showed that the male cry1 mutant exhibited higher phototactic rates to UV and blue lights than the male G88. Our results indicated that the LW-opsin mutation changed the expression of genes in the phototransduction pathway, and the mutation of cry1 enhanced the phototaxis of a P. xylostella male, providing a basis for further investigation on the phototransduction pathway in P. xylostella.

Optimization and Application of CRISPR/Cas9 Genome Editing in a Cosmopolitan Pest, Diamondback Moth

The CRISPR/Cas9 system is an efficient tool for reverse genetics validation, and the application of this system in the cell lines provides a new perspective on target gene analysis for the development of biotechnology tools. However, in the cell lines of diamondback moth, Plutella xylostella, the integrity of the CRISPR/Cas9 system and the utilization of this cell lines still need to be improved to ensure the application of the system. Here, we stabilize the transfection efficiency of the P. xylostella cell lines at different passages at about 60% by trying different transfection reagents and adjusting the transfection method. For Cas9 expression in the CRIPSPR/Cas9 system, we identified a strong endogenous promoter: the 217–2 promoter. The dual-luciferase and EGFP reporter assay demonstrated that it has a driving efficiency close to that of the IE1 promoter. We constructed pB-Cas9-Neo plasmid and pU6-sgRNA plasmid for CRISPR/Cas9 system and subsequent cell screening. The feasibility of the CRISPR/Cas9 system in P. xylostella cell lines was verified by knocking out endogenous and exogenous genes. Finally, we generated a transgenic Cas9 cell line of P. xylostella that would benefit future exploitation, such as knock-in and multi-threaded editing. Our works provides the validity of the CRISPR/Cas9 system in the P. xylostella cell lines and lays the foundation for further genetic and molecular studies on insects, particularly favoring gene function analysis.

Genome-Wide Identification, Expression Profiling, and Characterization of Cyclin-like Genes Reveal Their Role in the Fertility of the Diamondback Moth

Simple Summary

Cyclin genes are known as cell cycle regulators and play a significant role in the fertility of different organisms, including mice and insects. Until now, no study has been performed on the complete identification of the cyclin genes in insects. Here, we identified 21 cyclin genes in the diamondback moth (DBM) genome through a comprehensive genome-wide analysis and evaluated the gene structure, genomic location, and evolutionary relationship. Cis-regulatory elements and potential miRNA targeting the cyclin genes were also assessed. By analyzing the transcriptomic and RT-qPCR based expression profiling at different stages and tissues, we found that the majority of the cyclin genes were significantly expressed in the reproductive tissues. Moreover, RNAi-mediated characterization of PxCyc B1 showed its role in female fertility. The current study provides a basis for further evaluation of the cyclin genes, which may be used as a potential target for pest management programs.

Abstract

Cyclin-like genes are primarily considered as cell cycle regulators and have shown to be crucial for insect growth, development, reproduction, and fertility. However, no research has been performed on the cyclin-like genes in the diamondback moth (Plutella xylostella). Here, we identified the 21 cyclin genes in the genome of P. xylostella and clustered them into four groups. Most cyclin genes showed a well-maintained gene structure and motif distribution within the same group. The putative promoter regions of cyclin genes contained several transcription binding factors related to reproduction, along with growth and development. Furthermore, 16 miRNAs were identified targeting the 13 cyclin genes. Transcriptome and quantitative real-time PCR (qRT-PCR)-based expression profiling of cyclin-like genes at different stages and tissues were evaluated, revealing that 16 out of 21 cyclin genes were highly expressed in reproductive tissues of adult females and males. The Cyclin B1 gene (PxCyc B1) was only expressed in the ovary of the adult female and selected for the subsequent analysis. RNAi-mediated suppression of PxCyc B1 interrupted the external genitalia and length of the ovariole of female adults. Furthermore, the egg-laying capacity and hatching rate were also significantly decreased by suppressing the PxCyc B1, indicating the importance of cyclin genes in the reproduction and fertility of P. xylostella. The current study explained the detailed genome-wide analysis of cyclin-like genes in P. xylostella, which provided a basis for subsequent research to assess the roles of cyclin genes in reproduction, and the cyclin gene may be considered an effective target site to control this pest.

Biological, morphological, and molecular characterization of the baculovirus PlxyMNPV_LBIV-11, and its virulence towards Plutella xylostella, Trichoplusia ni, and Spodoptera frugiperda larvae

PlxyMNPV_LBIV-11 is an alphabaculovirus strain, isolated from Plutella xylostella larvae. This work characterized this strain at a biological, morphological, and molecular level to evaluate its similarity with other baculoviruses. Its ultrastructure showed a multiple arrangement of nucleocapsids within enveloped virions, all occluded within large cubical polyhedra. PlxyMNPV_LBIV-11 showed infectivity on the Hi5 and Sf9 cell lines, despite these being from heterologous origin. This in vitro infectivity was observed using either BVs or by transfection with genomic DNA. Restriction fragment patterns of PlxyMNPV_LBIV-11, using the enzymes EcoRI, BamHI and HindIII, showed a high relationship with those patterns shown by AcMNPV, except for one or two differential bands with each enzyme. Sequences of core genes lef-8 and lef-9 and the conserved polh gene showed identities ranging from 98 to 100% when compared with those of AcMNPV. Somewhat lower was the sequence identity of the gp64 gene (94%) as compared with those of AcMNPV and PlxyMNPV_CL3, which might be related to the difference in virulence. Besides, the presence of this gene in PlxyMNPV_LBIV-11 indicates that it belongs to group 1 of alphabaculoviruses. A phylogram was estimated with the core and conserved gene sequences, corroborating its high relationship with AcMNPV and PlxyMNPV_CL3. Bioassays were performed with P. xylostella larvae reared on a meridic diet, whose LC₅₀ values indicated lower virulence than AcMNPV when tested against P. xylostella, Spodoptera frugiperda, and Trichoplusia ni larvae. Its virulence against S. frugiperda was only seven times lower than AcMNPV. Its potential as a biological control agent is discussed.

Utilization of Recombinant Baculovirus Expression System to Produce the RBD Domain of SARS-CoV-2 Spike Protein

Continuous outbreaks of viral diseases in humans facilitates a need for the rapid development of viral test kits and vaccines. These require expression systems to produce a pure and high yield of target viral proteins. We utilized a baculovirus–silkworm expression system to produce the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. First, we had to develop a strategy for constructing a recombinant baculovirus for RBD expression. For this, the coding region of the Bombyx mori cypovirus (BmCPV) polyhedron was assembled with the Bombyx mori nuclear polyhedrosis virus (BmNPV) promoter. We demonstrated that the recombinant baculovirus has the ability to form polyhedrons within host silkworm cells. In addition, the encapsulated BVs are able to infect silkworms by ingestion and induce foreign protein expression. In this way, we utilized this novel system to obtain a high yield of the target foreign protein, the RBD of the SARS-CoV-2 S protein. However, the viral infection rate of our recombinant BV needs to be improved. Our study shed light on developing a highly efficient expression system for the production of antigens and subsequent immunoassays and vaccines.

Virulence and genetic characterization of six baculovirus strains isolated from different populations of Spodoptera frugiperda (Lepidoptera: Noctuidae)

Fall armyworm (FAW), Spodoptera frugiperda (Smith, 1797), is a polyphagous, voracious, and economically important agricultural pest. Biological control of FAW is a strategy that must be further explored. This study evaluated six baculovirus strains isolated from infected FAW larvae from Mexico, Argentina, Honduras, and the United States. Five alphabaculoviruses (SfNPV-An₂, SfNPV-Arg, SfNPV-Fx, SfNPV-Ho, and SfNPV-Sin) and one betabaculovirus (SfGV-RV) were tested against FAW larvae, showing a wide diversity of virulence levels among strains when their estimated LC₅₀s were compared, being SfNPV-Arg, SfNPV-Ho and SfNPV-Fx more virulent than SfNPV-An₂, SfNPV-Sin, and SfGV-RV. To determine any virulence difference in vitro studies of these isolates, Sf9 cell cultures were used. Interestingly, only ODVs from four of the test SfNPV strains showed infectivity on Sf9 cell cultures, and some differences in virulence were observed. Genomic restriction analyses and partial sequences of lef-8, lef-9, and polh/granulin genes showed little variability among alphabaculoviruses, both, among them and with previously reported sequences. However, sequences from SfGV-RV were closer to previously reported sequences from the SfGV-VG008 strain than the SfGV-Arg and SfGV-VG014 strains. The great difference in the in vivo virulence was not correlated with great similarity among the isolates. The characterization of these six baculovirus isolates offers the basis for exploring their potential as biological control agents against S. frugiperda, as well the initial studies on their specific infection mechanisms, evolution, and ecology.

Large-scale genome-wide study reveals climate adaptive variability in a cosmopolitan pest

Understanding the genetic basis of climatic adaptation is essential for predicting species' responses to climate change. However, intraspecific variation of these responses arising from local adaptation remains ambiguous for most species. Here, we analyze genomic data from diamondback moth (Plutella xylostella) collected from 75 sites spanning six continents to reveal that climate-associated adaptive variation exhibits a roughly latitudinal pattern. By developing an eco-genetic index that combines genetic variation and physiological responses, we predict that most P. xylostella populations have high tolerance to projected future climates. Using genome editing, a key gene, PxCad, emerged from our analysis as functionally temperature responsive. Our results demonstrate that P. xylostella is largely capable of tolerating future climates in most of the world and will remain a global pest beyond 2050. This work improves our understanding of adaptive variation along environmental gradients, and advances pest forecasting by highlighting the genetic basis for local climate adaptation.

CRISPR/Cas9-mediated knockout of LW-opsin reduces the efficiency of phototaxis in the diamondback moth Plutella xylostella

BACKGROUND

Opsins are crucial for animal vision. The identity and function of opsins in Plutella xylostella remain unknown. The aim of the research is to confirm which opsin gene(s) contribute to phototaxis of P. xylostella.

RESULTS

LW-opsin, BL-opsin and UV-opsin, were identified in the P. xylostella genome. LW-opsin was more highly expressed than the other two opsin genes, and all three genes were specifically expressed in the head. Three P. xylostella strains, LW-13 with a 13-bp deletion in LW-opsin, BL + 2 with a 2-bp insertion in BL-opsin, and UV-29 with a 5-bp insertion and a 34-bp deletion in UV-opsin, were established from the strain G88 using the CRISPR/Cas9 system. Among the three opsin-knockout strains, only male and female LW-13 exhibited weaker phototaxis to lights of different wavelengths and white light than G88 at 2.5 lx due to defective locomotion, and LW-13 was defective to sense white, green and infrared lights. The locomotion of LW-13 was reduced compared with G88 at 2.5, 10, 20, 60, 80, 100, and 200 lx under the green light, but the locomotion of LW-13 female was recovered at 80, 100 and 200 lx. The defective phototaxis to the green light of male LW-13 was not affected by light intensity, while the defective phototaxis to the green light of female LW-13 was recovered at 10, 20, 60, 80, 100, and 200 lx.

CONCLUSION

LW-opsin is involved in light sensing and locomotion of P. xylostella, providing a potential target gene for controlling the pest. © 2021 Society of Chemical Industry.

Identification and characterization of the vasa gene in the diamondback moth, Plutella xylostella

Vasa is an ATP-dependent RNA helicase, participating in multiple biological processes. It has been widely used as a germ cell marker and its promoter has become a key component of several genetic pest control systems. Here we present the vasa gene structure and its promoter activity in Plutella xylostella, one of the most destructive pests of cruciferous crops. Full length Pxvasa cDNA sequences were obtained, revealing 14 exons and at least 30 alternatively spliced transcripts. Inferred amino acid sequences showed nine conserved DEAD-box family protein motifs with partial exclusion from some isoforms. Real-time quantitative PCR indicated the up-regulation of Pxvasa in both female and male adults compared with other developmental stages, and the expression levels of Pxvasa were found to be much higher in adult gonads, especially ovaries, than in other tissues. The putative promoter region of Pxvasa was sequenced and several ecdysone-induced transcription factor (TF) binding sites were predicted in silico. To further analyze the promoter region, two upstream regulatory fragments of different lengths were tested as putative promoters in transient cell and embryo expression assays, one of which was subsequently utilized to drive Cas9 expression in vivo. A transgenic line was recovered and the expression patterns of Cas9 and native Pxvasa were profiled in adult tissues and eggs with RT-PCR. This work provides the foundation for further studies on the gene functions of Pxvasa as well as the potential application of its promoter in genetic manipulation of P. xylostella.

Functional characterization of the cis-regulatory region for the vitellogenin gene in Plutella xylostella

The vitellogenin gene promoter (VgP) is an essential cis-regulatory element that plays a significant role in transcription of the vitellogenin (Vg) gene, leading to the production of yolk protein in insects, including lepidopterans. However, the function of VgP is still not clear in Plutella xylostella. Here, we cloned a 5.1 kb DNA fragment of the cis-regulatory region adjacent to the 5' end of the Vg gene of P. xylostella (PxVg). We identified two promoter sites in that 5' upstream sequence of PxVg and performed in vitro analysis of two promoter sequences (PxVgP1, 4.9 kb, and PxVgP2, 2.9 kb) in the embryonic cell line of P. xylostella. PxVgP2 exhibited higher enhanced green fluorescent protein (EGFP) expression, so PxVgP2 was used for in vivo analysis. Strong EGFP fluorescence was observed in adult females and the fat body of females, with low expression in embryos. Our results suggest that PxVgP is an important stage-, tissue- and sex-specific endogenous cis-regulatory element in P. xylostella.

Molecular Characterization and the Function of Argonaute3 in RNAi Pathway of Plutella xylostella

Argonaute (Ago) protein family plays a key role in the RNA interference (RNAi) process in different insects including Lepidopteran. However, the role of Ago proteins in the RNAi pathway of Plutella xylostella is still unknown. We cloned an Argonaute3 gene in P. xylostella (PxAgo3) with the complete coding sequence of 2832 bp. The encoded protein had 935 amino acids with an expected molecular weight of 108.9 kDa and an isoelectric point of 9.29. It contained a PAZ (PIWI/Argonaute/Zwile) domain and PIWI (P-element-induced whimpy testes) domain. PxAgo3 was classified into the Piwi subfamily of Ago proteins with a high similarity of 93.0% with Bombyx mori Ago3 (BmAgo3). The suppression of PxAgo3 by dsPxAgo3 was observed 3 h after treatment and was maintained until 24 h. Knockdown of PxAgo3 decreased the suppression level of PxActin by dsPxActin in P. xylostella cells, while overexpression of PxAgo3 increased the RNAi efficiency. Our results suggest that PxAgo3 play a key role in the double stranded RNA (dsRNA)-regulated RNAi pathway in P. xylostella.