cDNA cloning and characterization of two trehalases from Spodoptera litura (Lepidoptera; Noctuidade)

Host trehalose metabolism disruption by validamycin A results in reduced fitness of parasitoid offspring

The general cutworm, Spodoptera litura (Lepidoptera: Noctuidae) is a worldwide destructive omnivorous pest and the endoparasitoid wasp Meteorus pulchricornis (Hymenoptera: Braconidae) is the dominant endoparasitoid of S. litura larvae. Trehalase is a key enzyme in insect trehalose metabolism and plays an important role in the growth and development of insects. However, the specific function of trehalase in parasitoid and host associations has been less reported. In this study, we obtained two trehalase genes (SlTre1 and SlTre2) from our previously constructed S. litura transcriptome database; they were highly expressed in 3rd instar larvae. SlTre1 was mainly expressed in the midgut, and SlTre2 was expressed highest in the head. SlTre1 and SlTre2 were highly expressed 5 days after parasitization by M. pulchricornis. Treatment with the trehalase inhibitor validamycin A significantly inhibited the expression levels of SlTre1 and SlTre2, and the trehalase activity. Besides, the content of trehalose was increased but the content of glucose was decreased 24 h after validamycin A treatment in parasitized S. litura larvae. In addition, the immune-related genes in phenoloxidase (PO) pathway and fatty acid synthesis-related genes in lipid metabolism were upregulated in parasitized host larvae after validamycin A treatment. Importantly, the emergence rate, proportion of normal adults, and body size of parasitoid offspring was decreased in parasitized S. litura larvae after validamycin A treatment, indicating that validamycin A disrupts the trehalose metabolism of parasitized host and thus reduces the fitness of parasitoid offspring. The present study provides a novel perspective for coordinating the application of biocontrol and antibiotics in agroecosystem.

Knockdown of Two Trehalase Genes by RNA Interference Is Lethal to the White-Backed Planthopper Sogatella furcifera (Horváth) (Hemiptera:Delphacidae)

Trehalase (Tre) is a crucial enzyme involved in trehalose metabolism, and it plays pivotal roles in insect development and metamorphosis. However, the biological function of Tre genes in Sogatella furcifera remains unclear. In the present study, two Tre genes—SfTre1 and SfTre2—were cloned and identified based on the S. furcifera transcriptome data. Bioinformatic analysis revealed that the full-length complementary DNA of SfTre1 and SfTre2 genes were 3700 and 2757 bp long, with 1728- and 1902-bp open reading frame encoding 575 and 633 amino acid residues, respectively. Expression analysis indicated that SfTre1 and SfTre2 were expressed at all developmental stages, with the highest expression in day two adults. Furthermore, the highest expression levels of SfTre1 and SfTre2 were observed in the ovary; enriched expression was also noted in head tissues. The knockdown of SfTre1 and SfTre2 via injecting double-stranded RNAs decreased the transcription levels of the corresponding mRNAs and led to various malformed phenotypes and high lethality rates. The results of our present study indicate that SfTre1 and SfTre2 play crucial roles in S. furcifera growth and development, which can provide referable information for Tre genes as a potential target for planthopper control.

Purification and Functional Characterization of a Soluble Trehalase in Lissorhoptrus oryzophilus (Coleoptera: Curculionidae)

Trehalase is the only enzyme known for the irreversible splitting of trehalose and plays a major role in insect growth and development. In this report, we describe a basic study of the trehalase gene fragment encoding a soluble trehalase from Lissorhoptrus oryzophilus (LoTRE1). Sequence alignment and phylogenetic analysis suggested that LoTRE1 was similar to some known insect trehalases and belongs to the Coleoptera trehalase group. Additionally, LoTRE1 was expressed mainly in the fat body. Purified protein was obtained using heterologous expression of LoTRE1 in Escherichia coli, and the recombinant protein exhibited the ability to decompose trehalose. Enzyme-substrate docking indicated the potential involvement of other residues in the catalytic activity, in addition to Asp 333. Moreover, feeding of adults on LoTRE1 dsRNA silenced the transcription of LoTRE1 and thereby reduced the activity of trehalase and increased the trehalose content; it also led to a 12% death rate. This study reveals essential molecular features of trehalase and offers insights into the structural aspects of this enzyme, which might be related to its function. Taken together, the findings demonstrate that LoTRE1 is indispensable for adults of this pest and provide a new target for the control of L. oryzophilus.

Parasitoid Wasps Can Manipulate Host Trehalase to the Benefit of Their Offspring

Trehalase is an essential hydrolase of trehalose in insects. However, whether and how trehalase performs in the association of parasitoid wasps and their hosts still remains unknown. Here, the exact function of trehalase of the general cutworm Spodoptera litura after it was parasitized by its predominant endoparasitoid Meterous pulchricornis was elucidated. Two trehalase genes (SlTre1, SlTre2) were identified, and they were highly expressed five days after parasitization by M. pulchricornis. Then, we successfully silenced SlTre1 and SlTre2 in parasitized third instar S. litura larvae. The content of glucose, which is the hydrolysate of trehalose, was significantly decreased after silencing SlTres in parasitized S. litura larvae, and the activities of trehalase were also notably reduced. In addition, the cocoon weight, the emergence rate, proportion of normal adults, and the body size of parasitoid offsprings were significantly decreased in SlTre1- or SlTre2-silenced groups compared to the controls. These results implied that parasitization by parasitoids regulated the trehalase of host larvae to create a suitable nutritional environment for the parasitoid offspring. The present study broadens the knowledge of trehalase in the interaction between parasitoids and their hosts and is of benefit to biological control of S. litura acting by parasitoid wasps.

Characterization and Functional Analysis of trehalase Related to Chitin Metabolism in Glyphodes pyloalis Walker (Lepidoptera: Pyralidae)

Simple Summary

Sericulture has always been threatened by Glyphodes pyloalis Walker (G. pyloalis). Trehalase is an essential enzyme in chitin metabolism and energy supply. In this study, two trehalase genes in G. pyloalis (GpTre1 and GpTre2) were identified and functionally analyzed. Knockdown of the two genes led to the significant downregulation of chitin metabolism pathway-related genes, the difficulty in molting of larvae, and the deformation of adult wings. Moreover, the trehalase inhibitor, Validamycin A, treatment increased GpTre1 and GpTre2 expression and affected the expressions of chitin metabolism pathway-related genes. The inhibitor also caused a significantly increased cumulative mortality of larvae. The results suggested that GpTre1 and GpTre2 played a vital role on G. pyloalis development, which could be useful for providing information for insect pest control in the future.

Abstract

Glyphodes pyloalis Walker (G. pyloalis) is a serious pest on mulberry. Due to the increasing pesticide resistance, the development of new and effective environmental methods to control G. pyloalis is needed. Trehalase is an essential enzyme in trehalose hydrolysis and energy supply, and it has been considered a promising target for insect pest control. However, the specific function of trehalase in G. pyloalis has not been reported. In this study, two trehalase genes (GpTre1 and GpTre2) were identified from our previous transcriptome database. The functions of the trehalase in chitin metabolism were studied by injecting larvae with dsRNAs and trehalase inhibitor, Validamycin A. The open reading frames (ORFs) of GpTre1 and GpTre2 were 1,704 bp and 1,869 bp, which encoded 567 and 622 amino acid residues, respectively. Both of GpTre1 and GpTre2 were mainly expressed in the head and midgut. The highest expression levels of them were in 5th instar during different development stages. Moreover, knockdown both of GpTre1 and GpTre2 by the dsRNAs led to significantly decreased expression of chitin metabolism pathway-related genes, including GpCHSA, GpCDA1, GpCDA2, GpCHT3a, GpCHT7, GpCHSB, GpCHT-h, GpCHT3b, GpPAGM, and GpUAP, and abnormal phenotypes. Furthermore, the trehalase inhibitor, Validamycin A, treatment increased the expressions of GpTre1 and GpTre2, increased content of trehalose, and decreased the levels of glycogen and glucose. Additionally, the inhibitor caused a significantly increased cumulative mortality of G. pyloalis larvae on the 2nd (16%) to 6th (41.3%) day, and decreased the rate of cumulative pupation (72.3%) compared with the control group (95.6%). After the activities of trehalase were suppressed, the expressions of 6 integument chitin metabolism-related genes decreased significantly at 24 h and increased at 48 h. The expressions of GpCHSB and GpCHT-h, involved in chitin metabolism pathway of peritrophic membrane in the midgut, increased at 24 h and 48 h, and there were no changes to GpCHT3b and GpPAGM. These results reveal that GpTre1 and GpTre2 play an essential role in the growth of G. pyloalis by affecting chitin metabolism, and this provides useful information for insect pest control in the future.

Evaluation of the Expression and Function of the TRE2-like and TRE2 Genes in Ecdysis of Harmonia axyridis

Harmonia axyridis is an important predatory insect and widely used in biological control of agricultural and forestry pests. Trehalose is directly involved in the energy storage of the H. axyridis and in the oxidative function of various physiological activities thereby providing an energy source for its growth and development. The aim of this study was to explore the potential function of membrane-bound-like trehalase (TRE2-like) and membrane-bound trehalase (TRE2) genes in H. axyridis by RNAi. In addition, the activity of soluble and membrane-bound trehalase and the expression of genes related to trehalose and glycogen metabolism were determined in the larvae injected with dsTRE2-like or dsTRE2. The results showed that wing abnormality and mortality appeared in adults, as well as the activity of soluble trehalase and glycogen contents increased when interfering with TRE2-like gene. However, the activity of membrane-bound trehalase, trehalose and glucose contents in the larvae decreased. The expression of glycogen synthase (GS) and glycogen phosphorylase (GP) genes were decreased after RNAi in the ecdysis stage. The expression of chitin synthase gene A (CHSA), chitin synthase gene B (CHSB), and trehalose-6-phosphate synthase genes (TPS) were decreased significantly after RNAi, especially in the ecdysis stage. These results indicated that RNA interference is capable of knocking down gene expression of TRE2-like and TRE2, thereby disrupting trehalose metabolism which affects the chitin synthesis pathway in turn and also leads to developmental defects, such as wing deformities. This study could provide some theoretical guidance for the function of TRE2 gene in other insects.

Gene Cloning, Prokaryotic Expression, and Biochemical Characterization of a Soluble Trehalase in Helicoverpa armigera Hübner (Lepidoptera: Noctuidae)

Trehalase is an indispensable component of insect hemolymph that plays important role in energy metabolism and stress resistance. In this study, we cloned and expressed the gene encoding soluble trehalase (HaTreh-1) of Helicoverpa armigera (cotton bollworm) and characterized the enzyme. HaTreh-1 had a full-length open reading frame encoding a protein of 571 amino acids. Sequence comparison indicated that HaTreh-1 was similar to some known insect trehalases. Two essential active sites (D321 and E519) and three essential residues (R168, R221, and R286) were conserved in HaTreh-1. The recombinant trehalase was expressed in Escherichia coli and purified by nickel exchange chromatography. Molecular weight of the recombinant protein was about 71 kDa, and the optimum HaTreh-1 enzyme activity is at 55°C with pH 6.0. Enzymatic assays showed a Km value of 72.8 mmol/liter and a Vmax value of 0.608 mmol/(liter·min). Inhibition assays in vitro indicated that castanospermine, a polyhydroxylated alkaloid, was an effective competitive inhibitor of trehalase with a Ki value of 6.7 μmol/liter. The inhibitor action of castanospermine was linked to its modification effect on trehalase structure. The circular dichroism spectrum showed that the percentage of α-helix increased under the presence of castanospermine. Results of our study will aid in developing effective trehalase inhibitors for controlling H. armigera in the future.