Molecular characterization and enzyme inhibition studies of NADP+- farnesol dehydrogenase from diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Identification and functional characterization of chemosensory genes in olfactory and taste organs of Spodoptera litura (Lepidoptera: Noctuidae)

The tobacco cutworm Spodoptera litura is one of the most destructive polyphagous crop pests. Olfaction and taste play a crucial role in its host plant selection and sexual communication, but the expression profile of chemosensory genes remains unclear. In this study, we identified 185 chemosensory genes from 7 organs in S. litura by transcriptome sequencing, of which 72 genes were published for the first time, including 27 odorant receptors (ORs), 26 gustatory receptors (GRs), 1 ionotropic receptor (IR), 16 odorant-binding proteins (OBPs), and 2 chemosensory proteins (CSPs). Phylogenetic analyses revealed that ORs, IRs, OBPs, and sensory neuron membrane proteins (SNMPs) were mainly expressed in antennae and sequence-conserved among Noctuidae species. The most differentially expressed genes (DEGs) between sexes were ORs and OBPs, and no DEGs were found in GRs. GR transcripts were enriched in proboscis, and the expression of sugar receptors was the highest. Carbon dioxide receptors, sugar receptor-SliuGR6, and bitter GRs-SlituGR43 and SlituGR66 had higher sequence identities between Noctuidae species. CSPs were broadly expressed in various organs, and SlituCSP13 was a DEG in adult antennae. The functional analysis in the Drosophila OR67d expression system found that SlituOR50, a receptor highly expressed in female antennae, is selectively tuned to farnesyl acetate. The results provide a solid foundation for understanding the molecular mechanisms by which chemosensory genes operate to elicit behavioral responses in polyphagous insects.

Transcriptome analysis reveals mechanisms of metabolic detoxification and immune responses following farnesyl acetate treatment in Metisa plana

Metisa plana is a widespread insect pest infesting oil palm plantations in Malaysia. Farnesyl acetate (FA), a juvenile hormone analogue, has been reported to exert in vitro and in vivo insecticidal activity against other insect pests. However, the insecticidal mechanism of FA on M. plana remains unclear. Therefore, this study aims to elucidate responsive genes in M. plana in response to FA treatment. The RNA-sequencing reads of FA-treated M. plana were de novo-assembled with existing raw reads from non-treated third instar larvae, and 55,807 transcripts were functionally annotated to multiple protein databases. Several insecticide detoxification-related genes were differentially regulated among the 321 differentially expressed transcripts. Cytochrome P450 monooxygenase, carboxylesterase, and ATP-binding cassette protein were upregulated, while peptidoglycan recognition protein was downregulated. Innate immune response genes, such as glutathione S-transferases, acetylcholinesterase, and heat shock protein, were also identified in the transcriptome. The findings signify that changes occurred in the insect's receptor and signaling, metabolic detoxification of insecticides, and immune responses upon FA treatment on M. plana. This valuable information on FA toxicity may be used to formulate more effective biorational insecticides for better M. plana pest management strategies in oil palm plantations.

Characterization and transcriptomic analyses of the toxicity induced by toosendanin in Spodoptera frugipreda

The fall armyworm, Spodoptera frugiperda, is a destructive agricultural pest that seriously threatens global food security. Insecticide resistance of this pest has gradually formed in recent years due to improper usage, and alternative methods are badly needed. Toosendanin (TSN) is a botanical compound with broad-spectrum insecticidal activities against many pests. However, the effects of TSN on S. frugiperda are still unclear. In this study, the growth inhibition phenomenon, including weight loss and prolonged developmental duration, in the larvae with TSN exposure was clearly observed. Compared to the control group, a total of 450 and 3314 differentially expressed genes (DEGs) were identified by RNA-Seq in the larvae groups treated with 10 and 20 mg/kg TSN, respectively. Furthermore, the DEGs involved in the juvenile hormone and ecdysone signal pathways and downstream processes, including detoxifying enzyme genes, chitin synthesis and metabolism genes, and cuticular protein genes, were found. Our findings suggest that TSN regulates the expression of key genes in juvenile hormone and ecdysone signal pathways and a series of downstream processes to alter the hormone balance and cuticle formation and eventually inhibit larval growth, which laid the foundation for the molecular toxicological mechanism research of TSN on S. frugiperda larvae.

Isolation, purification and biochemical characterization of Conopomorpha cramerella farnesol dehydrogenase

In Southeast Asia, Conopomorpha cramerella (Snellen) which is commonly known as the cocoa pod borer (CPB) moth has been identified as the most detrimental pest of Theobroma cacao L. Apart from the various side effects on human health and non-target organisms, heavily relying on synthetic pyrethroid insecticides to control CPB infestations also increases the environmental contamination risks. Thus, developing biorational insecticides that minimally affect the non-target organism and environment by targeting the insect growth regulation process is needed to manage the pest population. In insects, juvenile hormones (JH) regulate critical biological events, especially metamorphosis, development and reproduction. Since the physiological roles of JH III vary among different organisms, the biochemical properties, especially substrate specificity and analogue inhibition, may also be different. Therefore, studies on the JH III biosynthetic pathway enzymes in both plants and insects are beneficial to discover more effective analogues. Bioinformatic analysis and biochemical characterization of a NADP⁺ -dependent farnesol dehydrogenase, an intermediate enzyme of the JH III pathway, from C. cramerella (CcFolDH), were described in this study. In addition, the farnesol analogues that may act as a potent analogue inhibitor for CcFolDH ware determined using in vitro enzymatic study. The phylogenetic analysis indicated that CcFolDH shared a close phylogenetic relationship to the honeybee's short-chain dehydrogenase/reductase. The 27 kDa CcFolDH has an NADP(H) binding domain with a typical Rossmann fold and is likely a homotetrameric protein in the solution. The enzyme had a greater preference for substrate trans, trans-farnesol and coenzyme NADP⁺ . In terms of analogue inhibitor inhibition, hexahydroxyfarnesyl acetone showed the highest inhibition (the lowest K_i ) compared to other farnesol analogues. Thus, hexahydroxyfarnesyl acetone would serve as the most potent active ingredient for future biorational pesticide management for C. cramerella infestation. Based on the bioinformatic analyses and biochemical characterizations conducted in this research, we proposed that rCcFolDH differs slightly from other reported farnesol dehydrogenases in terms of molecular weight, substrate preference, coenzymes utilization and analogue inhibitors selection.

Ensemble-based, high-throughput virtual screening of potential inhibitor targeting putative farnesol dehydrogenase of Metisa plana (Lepidoptera: Psychidae)

Metisa plana (Lepidoptera: Psychidae) bagworm is a leaf-eater caterpillar ubiquitously found as a damaging pest in oil palm plantations, specifically in Malaysia. Various strategies have been implemented, including the usage of chemical insecticides. However, the main challenges include the development of insecticide resistance and its detrimental effects on the environment and non-target organisms. Therefore, a biorational insecticide is introduced by targeting the juvenile hormone (JH) biosynthetic pathway, which is mainly present in the insect and vital for the insect's growth, diapause, metamorphosis, and adult reproduction. This study aimed to investigate the potential inhibitor for the rate-limiting enzyme involved in the JH pathway known as farnesol dehydrogenase. A 255 amino acids sequence encoded for the putative M. plana farnesol dehydrogenase (MpFolDH) open reading frame had been identified and isolated. The three-dimensional structure of MpFolDH was predicted to have seven β- sheets with α-helices at both sides, showing typical characteristics for classical short-chain dehydrogenase and associated with oxidoreductase activity. Then, the ensemble-based virtual screening was conducted based on the ZINC20 database, in which 43 768 compounds that fulfilled pesticide-likeness criteria were screened by site-specific molecular docking. After a short molecular dynamics simulation (5 ns) was conducted towards 102 compounds, only the top 10 compounds based on their most favourable binding energy were selected for a more extended simulation (100 ns). Based on the protein-ligand stability, protein compactness, residues rigidity, binding interaction, binding energy throughout the 100 ns simulation, and physicochemical analysis, ZINC000408743205 was selected as a potential inhibitor for this enzyme. Amino acids decomposition analysis indicates Ile18, Ala95, Val198 and Val202 were the critical contributor residues for MpFolDH-inhibitors(s) complex.

Biosynthesis of geranate via isopentenol utilization pathway in Escherichia coli

Isoprenoids are a large family of natural products with diverse structures, which allow them to play diverse and important roles in the physiology of plants and animals. They also have important commercial uses as pharmaceuticals, flavoring agents, fragrances, and nutritional supplements. Recently, metabolic engineering has been intensively investigated and emerged as the technology of choice for the production of isoprenoids through microbial fermentation. Isoprenoid biosynthesis typically originates in plants from acetyl-coA in central carbon metabolism, however, a recent study reported an alternative pathway, the isopentenol utilization pathway (IUP), that can provide the building blocks of isoprenoid biosynthesis from affordable C5 substrates. In this study, we expressed the IUP in Escherichia coli to efficiently convert isopentenols into geranate, a valuable isoprenoid compound. We first established a geraniol-producing strain in E. coli that uses the IUP. Then, we extended the geraniol synthesis pathway to produce geranate through two oxidation reactions catalyzed by two alcohol/aldehyde dehydrogenases from Castellaniella defragrans. The geranate titer was further increased by optimizing the expression of the two dehydrogenases and also parameters of the fermentation process. The best strain produced 764 mg/L geranate in 24 h from 2 g/L isopentenols (a mixture of isoprenol and prenol). We also investigated if the dehydrogenases could accept other isoprenoid alcohols as substrates.

Crystal structure and molecular characterization of NADP+-farnesol dehydrogenase from cotton bollworm, Helicoverpaarmigera

Farnesol dehydrogenase (FDL) orchestrates the oxidation reaction catalyzing farnesol to farnesal, a key step in the juvenile hormone (JH) biosynthesis pathway of insects and hence, represents a lucrative target for developing insect growth regulators (IGRs). However, information on the structural and functional characterization of JH-specific farnesol dehydrogenase in insects remains elusive. Herein, we identified a transcript that encodes farnesol dehydrogenase (HaFDL) from Helicoverpa armigera, a major pest of cotton. The investigations of molecular assembly, biochemical analysis and spatio-temporal expression profiling showed that HaFDL exists as a soluble homo-tetrameric form, exhibits a broad substrate affinity and is involved in the JH-specific farnesol oxidation in H. armigera. Additionally, the study presents the first crystal structure of the HaFDL-NADP enzyme complex determined at 1.6 Å resolution. Structural analysis revealed that HaFDL belongs to the NADP-specific cP2 subfamily of the classical short-chain dehydrogenase/reductase (SDR) family and exhibits typical structural features of those enzymes including the conserved nucleotide-binding Rossman-fold. The isothermal titration calorimetry (ITC) showed a high binding affinity (dissociation constant, Kd, 3.43 μM) of NADP to the enzyme. Comparative structural analysis showed a distinct substrate-binding pocket (SBP) loop with a spacious and hydrophobic substrate-binding pocket in HaFDL, consistent with the biochemically observed promiscuous substrate specificity. Finally, based on the crystal structure, substrate modeling and structural comparison with homologs, a two-step reaction mechanism is proposed. Overall, the findings significantly impact and contribute to our understanding of farnesol dehydrogenase functional properties in JH biosynthesis in H. armigera.

Anti-mosquito properties of Pelargonium roseum (Geraniaceae) and Juniperus virginiana (Cupressaceae) essential oils against dominant malaria vectors in Africa

BACKGROUND

More than 90% of malaria cases occur in Africa where the disease is transmitted by Anopheles gambiae and Anopheles arabiensis. This study evaluated the anti-mosquito properties of Juniperus virginiana (JVO) and Pelargonium roseum (PRO) essential oils (EOs) against larvae and adults of An. gambiae sensu lato (s.l.) from East Africa in laboratory and semi-field conditions.

METHODS

EOs was extracted from the aerial green parts of Asian herbs by hydrodistillation. Their constituents were characterized by gas chromatography-mass spectrometry (GC-MS). Larvicidal activities of JVO, PRO, and PRO components [citronellol (CO), linalool (LO), and geraniol (GO)] were investigated against An. gambiae sensu stricto (s.s.). The percentage of knockdown effects and mortality rates of all oils were also evaluated in the adults of susceptible An. gambiae s.s. and permethrin-resistant An. arabiensis.

RESULTS

GC-MS analyses identified major constituents of JVO (sabinene, dl-limonene, β-myrcene, bornyl acetate, and terpinen-4-ol) and PRO (citronellol, citronellyl formate, L-menthone, linalool, and geraniol). Oils showed higher larvicidal activity in the laboratory than semi-field trials. The LC50 values for JVO/PRO were computed as 10.82-2.89/7.13-0.9 ppm and 10.75-9.06/13.63-8.98 ppm in laboratory and semi-field environments, respectively at exposure time of 24-72 h. The percentage of knockdown effects of the oils were also greater in An. gambiae s.s. than in An. arabiensis. Filter papers impregnated with JVO (100 ppm) and PRO (25 ppm) displayed 100% mortality rates for An. gambiae s.s. and 3.75% and 90% mortality rates, for An. arabiensis populations, respectively. Each component of CO, LO, and GO exhibited 98.13%, 97.81%, and 87.5%, respectively, and a mixture of the PRO components indicated 94.69% adult mortality to permethrin-resistant An. arabiensis.

CONCLUSIONS

The findings of this study show that PRO and its main constituents, compared to JVO, have higher anti-mosquito properties in terms of larvicidal, knockdown, and mortality when applied against susceptible laboratory and resistant wild populations of An. gambiae s.l. Consequently, these oils have the potential for the development of new, efficient, safe, and affordable agents for mosquito control.

Interspecies Isobaric Labeling-Based Quantitative Proteomics Reveals Protein Changes in the Ovary of Aedes aegypti Coinfected With ZIKV and Wolbachia

Zika is a vector-borne disease caused by an arbovirus (ZIKV) and overwhelmingly transmitted by Ae. aegypti. This disease is linked to adverse fetal outcomes, mostly microcephaly in newborns, and other clinical aspects such as acute febrile illness and neurologic complications, for example, Guillain-Barré syndrome. One of the most promising strategies to mitigate arbovirus transmission involves releasing Ae. aegypti mosquitoes carrying the maternally inherited endosymbiont bacteria Wolbachia pipientis. The presence of Wolbachia is associated with a reduced susceptibility to arboviruses and a fitness cost in mosquito life-history traits such as fecundity and fertility. However, the mechanisms by which Wolbachia influences metabolic pathways leading to differences in egg production remains poorly known. To investigate the impact of coinfections on the reproductive tract of the mosquito, we applied an isobaric labeling-based quantitative proteomic strategy to investigate the influence of Wolbachia wMel and ZIKV infection in Ae. aegypti ovaries. To the best of our knowledge, this is the most complete proteome of Ae. aegypti ovaries reported so far, with a total of 3913 proteins identified, were also able to quantify 1044 Wolbachia proteins in complex sample tissue of Ae. aegypti ovary. Furthermore, from a total of 480 mosquito proteins modulated in our study, we discuss proteins and pathways altered in Ae. aegypti during ZIKV infections, Wolbachia infections, coinfection Wolbachia/ZIKV, and compared with no infection, focusing on immune and reproductive aspects of Ae. aegypti. The modified aspects mainly were related to the immune priming enhancement by Wolbachia presence and the modulation of the Juvenile Hormone pathway caused by both microorganism’s infection.

Identification of neuropeptides and neuropeptide receptor genes in Phauda flammans (Walker)

Neuropeptides and neuropeptide receptors are crucial regulators to insect physiological processes. The 21.0 Gb bases were obtained from Illumina sequencing of two libraries representing the female and male heads of Phauda flammans (Walker) (Lepidoptera: Phaudidae), which is a diurnal defoliator of ficus plants and usually outbreaks in the south and south-east Asia, to identify differentially expressed genes, neuropeptides and neuropeptide receptor whose tissue expressions were also evaluated. In total, 99,386 unigenes were obtained, in which 156 up-regulated and 61 down-regulated genes were detected. Fifteen neuropeptides (i.e., F1b, Ast, NP1, IMF, Y, BbA1, CAP2b, NPLP1, SIF, CCH2, NP28, NP3, PDP3, ARF2 and SNPF) and 66 neuropeptide receptor genes (e.g., A2-1, FRL2, A32-1, A32-2, FRL3, etc.) were identified and well-clustered with other lepidopteron. This is the first sequencing, identification neuropeptides and neuropeptide receptor genes from P. flammans which provides valuable information regarding the molecular basis of P. flammans.