Molecular characterization of soluble and membrane-bound trehalases of the whitefly, Bemisia tabaci

Effects of insulin-like peptide 7 in Bemisia tabaci MED on tomato chlorosis virus transmission

BACKGROUND

Tomato chlorosis virus (ToCV) is a semi-persistent plant virus that is primarily transmitted by the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae). It causes a serious disease that lowers tomato yield. Insulin-like peptide (ILP), an insulin homolog, regulates trehalose metabolism in a variety of insects. In a previous study, we discovered that trehalose metabolism is required for whiteflies to transmit ToCV effectively. Furthermore, transcriptome sequencing revealed that the BtILP7 gene was highly expressed in B. tabaci infected with ToCV. Therefore, the whitefly ILP7 gene may facilitate the transmission of ToCV and be an attractive target for the control of whiteflies and subsequently ToCV.

RESULTS

The ToCV content in B. tabaci MED was found to be correlated with BtILP7 gene expression. Subsequent RNA interference (RNAi) of the BtILP7 gene had a significant impact on B. tabaci MED's trehalose metabolism and reproductive capacity, as well as ability to transmit ToCV.

CONCLUSIONS

These results indicate that the BtILP7 gene was closely related to ToCV transmission by regulating trehalose metabolism and reproduction behavior, thus providing a secure and environmentally friendly management strategy for the control of whiteflies and ToCV-caused disease. © 2022 Society of Chemical Industry.

Trehalose-6-phosphate phosphatases are involved in trehalose synthesis and metamorphosis in Bactrocera minax

Trehalose is the principal sugar circulating in the hemolymph of insects, and trehalose synthesis is catalyzed by trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP). Insect TPS is a fused enzyme containing both TPS domain and TPP domain. Thus, many insects do not possess TPP genes as TPSs have replaced the function of TPPs. However, TPPs are widely distributed across the dipteran insects, while the roles they play remain largely unknown. In this study, 3 TPP genes from notorious dipteran pest Bactrocera minax (BmiTPPB, BmiTPPC1, and BmiTPPC2) were identified and characterized. The different temporal-spatial expression patterns of 3 BmiTPPs implied that they exert different functions in B. minax. Recombinant BmiTPPs were heterologously expressed in yeast cells, and all purified proteins exhibited enzymatic activities, despite the remarkable disparity in performance between BmiTPPB and BmiTPPCs. RNA interference revealed that all BmiTPPs were successfully downregulated after double-stranded RNA injection, leading to decreased trehalose content and increased glucose content. Also, suppression of BmiTPPs significantly affected expression of downstream genes and increased the mortality and malformation rate. Collectively, these results indicated that all 3 BmiTPPs in B. minax are involved in trehalose synthesis and metamorphosis. Thus, these genes could be evaluated as insecticidal targets for managing B. minax, and even for other dipteran pests.

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.

Effects of the plant volatile trans‑2-hexenal on the dispersal ability, nutrient metabolism and enzymatic activities of Bursaphelenchus xylophilus

Bursaphelenchus xylophilus causes pine wilt disease (PWD), which severely damages pine species. The plant volatile trans‑2-hexenal has strong activity against nematodes, although the precise mechanism of this inhibitory action remains unclear. In this paper, the fumigant effects of the LC₁₀ and LC₃₀ of trans‑2-hexenal on B. xylophilus were demonstrated. The trans‑2-hexenal treatments significantly inhibited the dispersal ability of nematodes. The results also indicated that trans‑2-hexenal affects the metabolism of nutrients and the activity of digestive enzymes. Among detoxifying enzymes, after treatment with trans‑2-hexenal, glutathione S-transferase activity increased significantly and general esterase activity decreased significantly. Based on these results, trans‑2-hexenal disturbs the normal physiological and biochemical activities of this nematode. These results provide valuable insight into the nematicidal mechanisms of trans‑2-hexenal.

Study on the Effect of Wing Bud Chitin Metabolism and Its Developmental Network Genes in the Brown Planthopper, Nilaparvata lugens, by Knockdown of TRE Gene

The brown planthopper, Nilaparvata lugens is one of the most serious pests of rice, and there is so far no effective way to manage this pest. However, RNA interference not only can be used to study gene function, but also provide potential opportunities for novel pest management. The development of wing plays a key role in insect physiological activities and mainly involves chitin. Hence, the regulating role of trehalase (TRE) genes on wing bud formation has been studied by RNAi. In this paper, the activity levels of TRE and the contents of the two sugars trehalose and glucose were negatively correlated indicating the potential role of TRE in the molting process. In addition, NlTRE1-1 and NlTRE2 were expressed at higher levels in wing bud tissue than in other tissues, and abnormal molting and wing deformity or curling were noted 48 h after the insect was injected with any double-stranded TRE (dsTRE), even though different TREs have compensatory functions. The expression levels of NlCHS1b, NlCht1, NlCht2, NlCht6, NlCht7, NlCht8, NlCht10, NlIDGF, and NlENGase decreased significantly 48 h after the insect was injected with a mixture of three kinds of dsTREs. Similarly, the TRE inhibitor validamycin can inhibit NlCHS1 and NlCht gene expression. However, the wing deformity was the result of the NlIDGF, NlENGase, NlAP, and NlTSH genes being inhibited when a single dsTRE was injected. These results demonstrate that silencing of TRE gene expression can lead to wing deformities due to the down-regulation of the AP and TSH genes involved in wing development and that the TRE inhibitor validamycin can co-regulate chitin metabolism and the expression of wing development-related genes in wing bud tissue. The results provide a new approach for the prevention and management of N. lugens.

Transcriptomic and metabolomic profiles of Chinese citrus fly, Bactrocera minax (Diptera: Tephritidae), along with pupal development provide insight into diapause program

The Chinese citrus fly, Bactrocera minax (Enderlein), is a devastating citrus pest in Asia. This univoltine insect enters obligatory pupal diapause in each generation, while little is known about the course and the molecular mechanisms of diapause. In this study, the course of diapause was determined by measuring the respiratory rate throughout the pupal stage. In addition, the variation of transcriptomic and metabolomic profiles of pupae at five developmental stages (pre-, early-, middle-, late-, and post-diapause) were evaluated by next-generation sequencing technology and ¹H nuclear magnetic resonance spectroscopy (NMR), respectively. A total of 4,808 genes were significantly altered in ten pairwise comparisons, representing major shifts in metabolism and signal transduction as well as endocrine system and digestive system. Gene expression profiles were validated by qRT-PCR analysis. In addition, 48 metabolites were identified and quantified by ¹H NMR. Nine of which significantly contributed to the variation in the metabolomic profiles, especially proline and trehalose. Moreover, the samples collected within diapause maintenance (early-, middle-, and late-diapause) only exhibited marginal transcriptomic and metabolomic variation with each other. These findings greatly improve our understanding of B. minax diapause and lay the foundation for further pertinent studies.

Physiological roles of trehalose in Leptinotarsa larvae revealed by RNA interference of trehalose-6-phosphate synthase and trehalase genes

Trehalose is proposed to serve multiple physiological roles in insects. However, its importance remains largely unconfirmed. In the present paper, we knocked down either a trehalose biosynthesis gene (trehalose-6-phosphate synthase, LdTPS) or each of three degradation genes (soluble trehalases LdTRE1a, LdTRE1b or membrane-bound LdTRE2) in Leptinotarsa decemlineata by RNA interference (RNAi). Knockdown of LdTPS decreased trehalose content and caused larval and pupal lethality. The LdTPS RNAi survivors consumed a greater amount of foliage, obtained a heavier body mass, accumulated more glycogen, lipid and proline, and had a smaller amount of chitin compared with the controls. Ingestion of trehalose but not glucose rescued the food consumption increase and larval mass rise, increased survivorship, and recovered glycogen, lipid and chitin to the normal levels. In contrast, silencing of LdTRE1a increased trehalose content and resulted in larval and pupal lethality. The surviving LdTRE1a RNAi hypomorphs fed a smaller quantity of food, had a lighter body weight, depleted lipid and several glucogenic amino acids, and contained a smaller amount of chitin. Neither trehalose nor glucose ingestion rescued these LdTRE1a RNAi defects. Silencing of LdTRE1b caused little effects. Knockdown of LdTRE2 caused larval death, increased trehalose contents in several tissues and diminished glycogen in the brain-corpora cardiaca-corpora allata complex (BCC). Feeding glucose but not trehalose partially rescued the high mortality rate and recovered glycogen content in the BCC. It seems that trehalose is involved in feeding regulation, sugar absorption, brain energy supply and chitin biosynthesis in L. decemlineata larvae.

Molecular characterization of Tps1 and Treh genes in Drosophila and their role in body water homeostasis

In insects, trehalose serves as the main sugar component of haemolymph. Trehalose is also recognized as a mediator of desiccation survival due to its proposed ability to stabilize membranes and proteins. Although the physiological role of trehalose in insects has been documented for decades, genetic evidence to support the importance of trehalose metabolism remains incomplete. We here show on the basis of genetic and biochemical evidence that the trehalose synthesis enzyme Tps1 is solely responsible for the de novo synthesis of trehalose in Drosophila. Conversely, a lack of the gene for the trehalose hydrolyzing enzyme Treh causes an accumulation of trehalose that is lethal during the pupal period, as is observed with Tps1 mutants. Lack of either Tps1 or Treh results in a significant reduction in circulating glucose, suggesting that the maintenance of glucose levels requires a continuous turnover of trehalose. Furthermore, changes in trehalose levels are positively correlated with the haemolymph water volume. In addition, both Tps1 and Treh mutant larvae exhibit a high lethality after desiccation stress. These results demonstrate that the regulation of trehalose metabolism is essential for normal development, body water homeostasis, and desiccation tolerance in Drosophila.

Transcriptomic and Expression Analysis of the Salivary Glands in White-Backed Planthoppers, Sogatella furcifera

The white-backed planthopper (WBPH), Sogatella furcifera (Horváth), is one of the serious rice pests because of its destructive feeding. The salivary glands of the WBPH play an important role in the feeding behaviour. Currently, however, very little is known about the salivary glands at the molecular level. We sequenced the salivary gland transcriptome (sialotranscripome) of adult WBPHs using the Illumina sequencing. A total of 65,595 transcripts and 51,842 unigenes were obtained from salivary glands. According to annotations against the Nr database, many of the unigenes identified were associated with the most studied enzymes in hemipteran saliva. In the present study, we identified 32 salivary protein genes from the WBPH sialotranscripome, which were categorized as those involved in sugar metabolism, detoxification, suppression of plant defense responses, immunity-related responses, general digestion, and other phytophagy processes. Tissue expression profiles analysis revealed that four of 32 salivary protein genes (multicopper oxidase 4, multicopper oxidase 6, carboxylesterase and uridine phosphorylase 1 isform X2) were primarily expressed in the salivary gland, suggesting that they played putative role in insect-rice interactions. 13 of 32 salivary protein genes were primarily expressed in gut, which might play putative role in digestive and detoxify mechanism. Development expression profiles analysis revealed that the expression level of 26 of 32 salivary protein genes had no significant difference, suggesting that they may play roles in every developmental stages of salivary gland of WBPH. The other six genes have a high expression level in the salivary gland of adult. 31 of 32 genes (except putative acetylcholinesterase 1) have no significant difference in male and female adult, suggesting that their expression level have no difference between sexes. This report analysis of the sialotranscripome for the WBPH, and the transcriptome provides a foundational list of the genes involved in feeding. Our data will be useful to investigate the mechanisms of interaction between the WBPH and the host plant.