Trehalose and glucose levels regulate feeding behavior of the phloem-feeding insect, the pea aphid Acyrthosiphon pisum Harris

Trehalose serves multifarious roles in growth and development of insects. In this study, we demonstrated that the high trehalose diet increased the glucose content, and high glucose diet increased the glucose content but decreased the trehalose content of Acyrthosiphon pisum. RNA interference (RNAi) of trehalose-6-phosphate synthase gene (ApTPS) decreased while RNAi of trehalase gene (ApTRE) increased the trehalose and glucose contents. In the electrical penetration graph experiment, RNAi of ApTPS increased the percentage of E2 waveform and decreased the percentage of F and G waveforms. The high trehalose and glucose diets increased the percentage of E2 waveform of A. pisum red biotype. The correlation between feeding behavior and sugar contents indicated that the percentage of E1 and E2 waveforms were increased but np, C, F and G waveforms were decreased in low trehalose and glucose contents. The percentage of np, E1 and E2 waveforms were reduced but C, F and G waveforms were elevated in high trehalose and glucose contents. The results suggest that the A. pisum with high trehalose and glucose contents spent less feeding time during non-probing phase and phloem feeding phase, but had an increased feeding time during probing phase, stylet work phase and xylem feeding phase.

Characteristics and Expression Analyses of Trehalose-6-Phosphate Synthase Family in Prunus mume Reveal Genes Involved in Trehalose Biosynthesis and Drought Response

Trehalose and its key synthase (trehalose-6-phosphate synthase, TPS) can improve the drought tolerance of plants. However, little is known about the roles of trehalose and the TPS family in Prunus mume response to drought. In our study, we discovered that the trehalose content in leaf, root, and stem tissues significantly increased in P. mume in response to drought. Therefore, the characteristics and functions of the TPS family are worth investigating in P. mume. We identified nine TPS family members in P. mume, which were divided into two sub-families and characterized by gene structure, promoter elements, protein conserved domains, and protein motifs. We found that the Hydrolase_3 domain and several motifs were highly conserved in Group II instead of Group I. The distinctions between the two groups may result from selective constraints, which we estimated by the dN/dS (ω) ratio. The ω values of all the PmTPS family gene pairs were evaluated as less than 1, indicating that purity selection facilitated their divergence. A phylogenetic tree was constructed using 92 TPSs from 10 Rosaceae species, which were further divided into five clusters. Based on evolutionary analyses, the five clusters of TPS family proteins mainly underwent varied purity selection. The expression patterns of PmTPSs under drought suggested that the TPS family played an important role in the drought tolerance of P. mume. Combining the expression patterns of PmTPSs and the trehalose content changes in leaf, stem, and root tissues under normal conditions and drought stress, we found that the PmTPS2 and PmTPS6 mainly function in the trehalose biosynthesis in P. mume. Our findings not only provide valuable information about the functions of trehalose and TPSs in the drought response of P. mume, but they also contribute to the future drought breeding of P. mume.

Knockdown of the Trehalose-6-Phosphate Synthase Gene Using RNA Interference Inhibits Synthesis of Trehalose and Increases Lethality Rate in Asian Citrus Psyllid, Diaphorina citri (Hemiptera: Psyllidae)

Diaphorina citri Kuwayama is the vector of citrus “huanglongbing”, a citrus disease which poses a significant threat to the global citrus industry. Trehalose-6-phosphate synthase (TPS) plays an important role in the regulation of trehalose levels of insects, while its functions in D. citri are unclear. In this study, full-length cDNA sequences of the TPS gene from D. citri (DcTPS) were cloned and its expression patterns at various developmental stages were investigated. The results indicated that DcTPS mRNA was expressed at each developmental stage and the highest DcTPS expression was found in the fifth-instar nymphs of D. citri. Additionally, mortality and deformity of D. citri were observed after 24 and 48 h by feeding with three different dsRNA concentrations (20, 100 and 500 ng/μL). The results indicated that DcTPS expression was declined, and mortality and malformation in nymphs were increased via feeding with dsDcTPS. Moreover, the enzyme and trehalose content were decreased, while the content of glucose was significantly higher than that of untreated (control) individuals. This suggests that DcTPS might be vital for the growth and development of D. citri and further studies of the genes should be related to molting and metabolism for controlling D. citri.

Exploring Trehalose on the Release of Levonorgestrel from Implantable PLGA Microneedles

Hydrophobic drugs wrapped in poly (lactic-co-glycolic acid) (PLGA)-based microneedles (MNs) require a long time to release completely. To obtain the desired duration, it is still necessary to modulate the release of hydrophobic drugs from MNs, while the PLGA composition is unchangeable. In this work, implantable PLGA microneedles (IPMNs) composed of PLGA arrowheads encapsulating levonorgestrel (LNG) and a water-soluble supporting array were designed. We explored trehalose used as a porogen on the release of hydrophobic LNG from PLGA-based MNs. Varying the trehalose content in PLGA arrowheads could induce different rates of drug release. The highest cumulative release of LNG was 76.2 ± 3.9% for IPMNs with 33.3% trehalose during 21 days in vitro, while the cumulative release of LNG was 60.4 ± 3.5% for IPMNs without trehalose. Pharmacokinetic results in rats showed that plasma levels of LNG were sustained for 13 days for IPMNs with 33.3% trehalose and 16 days for IPMNs without trehalose. Furthermore, the PLGA arrowheads with trehalose degraded more rapidly than those without trehalose over 21 days in rats. Consequently, using trehalose as a porogen was a feasible approach to modulate the release of a hydrophobic drug from PLGA-based MNs.

Glucose Utilization in the Regulation of Chitin Synthesis in Brown Planthopper

Glucose-6-phosphatase (G6Pase) and hexokinase (HK) are two key enzymes in the glycolysis and gluconeogenesis pathways, which catalyze the synthesis and degradation of glucose in insects, respectively. G6Pase and HK play an important role in insect growth by regulating the metabolism of glucose, leading to the efficient metabolism of other macromolecules. However, it is unclear whether these genes could be investigated for pest control through their actions on chitin metabolism. We studied the potential functions of G6Pase and HK genes in the regulation of chitin metabolism pathways by RNAi technology. Interference with G6Pase expression did not affect trehalose and chitin metabolism pathways in brown planthopper, Nilaparvata lugens (Stål). However, knockdown of the HK gene resulted in a significant decrease of expression of genes associated with the trehalose metabolic pathway but had no significant effect on trehalase activity, trehalose content, or glucogen content. Additionally, HK knockdown resulting in downregulation of the genes involved in chitin metabolism in the brown planthopper. These insects also showed wing deformities and difficulty in molting to varying degrees. We suggest that the silencing of HK expression directly inhibited the decomposition of glucose, leading to impaired chitin synthesis.