Identification, expression analysis and functional verification of two genes encoding small heat shock proteins in the western flower thrips, Frankliniella occidentalis (Pergande)

Integrated transcriptomic and proteomic analyses reveal the molecular mechanism underlying the thermotolerant response of Spodoptera frugiperda

Spodoptera frugiperda (Lepidoptera: Noctuidae) is a highly destructive invasive pest with remarkable adaptability to extreme climatic conditions, posing a substantial global threat. Although the effects of temperature stress on the biological and ecological properties of S. frugiperda have been elucidated, the molecular mechanisms underlying its responses remain unclear. Herein, we combined transcriptomic and proteomic analyses to explore the key genes and proteins involved in thermotolerance regulation in S. frugiperda larvae at 42 °C. Overall, 1528 differentially expressed genes (DEGs) and 154 differentially expressed proteins (DEPs) were identified in S. frugiperda larvae under heat stress, including antioxidant enzymes, heat shock proteins (Hsps), cytochrome P450s, starch and sucrose metabolism genes, and insulin signaling pathway genes, indicating their involvement in heat tolerance regulation. Correlation analysis of DEGs and DEPs revealed that seven and eight had the same and opposite expression profiles, respectively. After nanocarrier-mediated RNA interference knockdown of SfHsp29, SfHsp20.4, SfCAT, and SfGST, the body weight and mortality of S. frugiperda larvae significantly decreased and increased under heat stress, respectively. This indicates that SfHsp29, SfHsp20.4, SfCAT, and SfGST play a crucial role in the thermotolerance of S. frugiperda larvae. These results provide insight into the mechanism of heat tolerance in S. frugiperda.

The small heat shock protein Hsp20.8 imparts tolerance to high temperatures in the leafminer fly, Liriomyza trifolii (Diptera: Agtomyzidae)

As an environmental factor, temperature impacts the distribution of species and influences interspecific competition. The molecular chaperones encoded by small heat shock proteins (sHsps) are essential for rapid, appropriate responses to environmental stress. This study focuses on Hsp20.8, which encodes a temperature-responsive sHsp in Liriomyza trifolii, an insect pest that infests both agricultural and ornamental crops. Hsp20.8 expression was highest at 39℃ in L. trifolii pupae and adults, and expression levels were greater in pupae than in adults. Recombinant Hsp20.8 was expressed in Escherichia coli and conferred a higher survival rate than the empty vector to bacterial cells exposed to heat stress. RNA interference experiments were conducted using L. trifolii adults and prepupae and the knockdown of Hsp20.8 expression increased mortality in L. trifolii during heat stress. The results expand our understanding of sHsp function in Liriomyza spp. and the ongoing adaptation of this pest to climate change. In addition, this study is also important for predicting the distribution of invasive species and proposing new prevention and control strategies based on temperature adaptation.

Identification, expression analysis, and functional verification of three opsin genes related to the phototactic behaviour of Ostrinia furnacalis

Ostrinia furnacalis is a disreputable herbivorous pest that poses a serious threat to corn crops. Phototaxis in nocturnal moths plays a crucial role in pest prediction and control. Insect opsins are the main component of insect visual system. However, the inherent molecular relationship between phototactic behaviour and vision of insects remains a mystery. Herein, three opsin genes were identified and cloned from O. furnacalis (OfLW, OfBL, and OfUV). Bioinformatics analysis revealed that all opsin genes had visual pigment (opsin) retinal binding sites and seven transmembrane domains. Opsin genes were distributed across different developmental stages and tissues, with the highest expression in adults and compound eyes. The photoperiod-induced assay elucidated that the expression of three opsin genes in females were higher during daytime, while their expression in males tended to increase at night. Under the sustained darkness, the expression of opsin genes increased circularly, although the increasing amplitude in males was lower when compared with females. Furthermore, the expression of OfLW, OfBL, and OfUV was upregulated under green, blue, and ultraviolet light, respectively. The results of RNA interference showed that the knockout of opsin genes decreased the phototaxis efficiency of female and male moths to green, blue, and ultraviolet light. Our results reveal that opsin genes are involved in the phototactic behaviour of moths, providing a potential target gene for pest control and a basis for further investigation on the phototactic behaviour of Lepidoptera insects.

Characterization of genes encoding heat shock proteins reveals a differential response to temperature in two geographic populations of Liriomyza trifolii (Diptera: Agromyzidae)

Liriomyza trifolii is a significant, invasive pest that damages horticultural crops and vegetables. The distribution of L. trifolii is influenced by temperature, and prior research has demonstrated that variations in thermal adaptability differ among geographic populations of the insect. Heat shock proteins (Hsps) are involved in adaptation to temperatures; however, the underlying molecular mechanism for thermal adaption in different L. trifolii populations remains unclear. This study examines the temperature adaptability of two L. trifolii populations from Hainan (HN) and Jiangsu (JS) provinces. The results indicate that the HN population has a higher survival rate and a higher critical thermal maximum (CTmax) than the JS population under high temperature stress. Transcriptome data at 42 °C revealed that the JS population has more differentially expressed genes (DEGs) than the HN population, while the HN population has more upregulated DEGs. The two populations were similar in functional annotation of DEGs, and a large number of Hsps were upregulated. However, the HN population had larger numbers and higher expression levels of Hsps during heat stress as compared to the JS population. Additionally, the expression patterns of differentially expressed Hsps varied between the HN and JS populations in response to different elevated temperatures. Notably, the transcription levels of Hsp70s were higher in the HN population as compared to the JS population, while the expression level of genes encoding small heat shock proteins was higher in the JS population. These findings have significant scientific value in understanding the underlying mechanism of temperature adaption in L. trifolii and provide a fresh perspective on the distribution of this invasive pest.

Comparative Transcriptome Analysis of Galeruca daurica Reveals Cold Tolerance Mechanisms

Galeruca daurica (Joannis) is a pest species with serious outbreaks in the Inner Mongolian grasslands in recent years, and its larvae and eggs are extremely cold-tolerant. To gain a deeper understanding of the molecular mechanism of its cold-tolerant stress response, we performed de novo transcriptome assembly of G. daurica via RNA-Seq and compared the differentially expressed genes (DEGs) of first- and second-instar larvae grown and developed indoors and outdoors, respectively. The results show that cold tolerance in G. daurica is associated with changes in gene expression mainly involved in the glycolysis/gluconeogenesis pathway, the fatty acid biosynthesis pathway and the production of heat shock proteins (HSPs). Compared with the control group (indoor), the genes associated with gluconeogenesis, fatty acid biosynthesis and HSP production were up-regulated in the larvae grown and developed outdoors. While the changes in these genes were related to the physiological metabolism and growth of insects, it was hypothesized that the proteins encoded by these genes play an important role in cold tolerance in insects. In addition, we also investigated the expression of genes related to the metabolic pathway of HSPs, and the results show that the HSP-related genes were significantly up-regulated in the larvae of G. daurica grown and developed outdoors compared with the indoor control group. Finally, we chose to induce significant expression differences in the Hsp70 gene (Hsp70A1, Hsp70-2 and Hsp70-3) via RNAi to further illustrate the role of heat stress proteins in cold tolerance on G. daurica larvae. The results show that separate and mixed injections of dsHSP70A1, dsHsp70-2 and dsHsp70-3 significantly reduced expression levels of the target genes in G. daurica larvae. The super-cooling point (SCP) and the body fluid freezing point (FP) of the test larvae were determined after RNAi using the thermocouple method, and it was found that silencing the Hsp70 genes significantly increased the SCP and FP of G. daurica larvae, which validated the role of heat shock proteins in the cold resistance of G. daurica larvae. Our findings provide an important theoretical basis for further excavating the key genes and proteins in response to extremely cold environments and analyzing the molecular mechanism of cold adaptation in insects in harsh environments.

Effect of silencing Thrips palmi Btk29A and COL3A1 on fitness and virus acquisition

Thrips palmi (Thysanoptera: Thripidae) is a major agricultural pest infesting over 200 plant species. Along with direct injury caused by feeding, T. palmi spreads several orthotospoviruses. Groundnut bud necrosis orthotospovirus (GBNV, family Tospoviridae, genus Orthotospovirus) is the predominant orthotospovirus in Asia, vectored by T. palmi. It is responsible for almost 89 million USD losses in Asia annually. Several transcripts of T. palmi related to innate immune response, receptor binding, cell signaling, cellular trafficking, viral replication, and apoptosis are responsive to the infection of orthotospoviruses in thrips. Expression of T. palmi tyrosine kinase Btk29A isoform X1 (Btk29A) and collagen alpha-1(III) chain-like (COL3A1) are significantly regulated post-GBNV and capsicum chlorosis orthotospovirus infection. In the present study, T. palmi Btk29A and COL3A1 were silenced and the effect on virus titer and fitness was assessed. The expression of Btk29A and COL3A1 was significantly reduced by 3.62 and 3.15-fold, respectively, 24 h post-dsRNA exposure. Oral administration of Btk29A and COL3A1 dsRNAs induced 60 and 50.9% mortality in T. palmi. The GBNV concentration in T. palmi significantly dropped post-silencing Btk29A. In contrast, the silencing of COL3A1 led to an increase in GBNV concentration in T. palmi compared to the untreated control. To the best of our knowledge, this is the first report on the effect of silencing Btk29A and COL3A1 on the fitness and GBNV titer in T. palmi.

Spatiotemporal Patterns of Five Small Heat Shock Protein Genes in Hyphantria cunea in Response to Thermal Stress

Hyphantria cunea (Drury), a destructive polyphagous pest, has been spreading southward after invading northern China, which indicates that this insect species is facing a huge thermal challenge. Small heat shock proteins (sHSPs) function as ATP-independent molecular chaperones that protect insects from heat stress damage. In order to explore the role of sHSPs in the thermotolerance of H. cunea, five novel sHSP genes of H. cunea were cloned, including an orthologous gene (HcHSP21.4) and four species-specific sHSP genes (HcHSP18.9, HcHSP20.1, HcHSP21.5, and HcHSP29.8). Bioinformatics analysis showed that the proteins encoded by these five HcHSPs contained typical α-crystallin domains. Quantitative real-time PCR analysis revealed the ubiquitous expression of all HcHSPs across all developmental stages of H. cunea, with the highest expression levels in pupae and adults. Four species-specific HcHSPs were sensitive to high temperatures. The expression levels of HcHSPs were significantly up-regulated under heat stress and increased with increasing temperature. The expression levels of HcHSPs in eggs exhibited an initial up-regulation in response to a temperature of 40 °C. In other developmental stages, the transcription of HcHSPs was immediately up-regulated at 30 °C or 35 °C. HcHSPs transcripts were abundant in the cuticle before and after heat shock. The expression of HcHSP21.4 showed weak responses to heat stress and constitutive expression in the tissues tested. These results suggest that most of the HcHSPs are involved in high-temperature response and may also have functions in the normal development and reproduction of H. cunea.

Protective effects of small heat shock proteins in Daphnia magna against heavy metal exposure

Daphnia magna is one of the most commonly used model organisms to assess toxicity of heavy metal and other xenobiotics. However, the lack of knowledge about important stress-resistant molecules limits our understanding of the alteration of phenotypic and physiological traits of D. magna upon stress exposures. In this study, we focused on a chaperone family of small heat shock protein (sHSP) that has been found in archaea, bacteria and eukaryotes and plays an important role in stress tolerance. A total of eleven sHSP genes (termed DmsHSP1 - DmsHSP11) were identified from the D. magna genome, whose expression profiles during exposure to heavy metal (Cd²⁺, Cu²⁺ and Zn²⁺) and a few other potential pollutants were evaluated via qRT-PCR and RNA-Seq analysis. The results highlighted the predominant role of DmsHSP1 with the highest basal expression level in adults and robust upregulation upon exposure to heavy metals (Cu²⁺ > Cd²⁺ > Zn²⁺). In vivo, recombinant protein rDmsHSP1-21 and rDmsHSP11-12.8 could not only prevent model substrates agglutination induced by heavy metals or reducer dithiotreitol (DTT), but also protect tissue proteins and enzymes from denaturation and inactivation caused by heavy metals or high temperature. Ectopically expression of DmsHSP1-21 or DmsHSP11-12.8 in E. coli conferred host enhanced resistance against various abiotic stresses including Cd²⁺, Cu²⁺ and phenazine methosulfate (PMS). Knockdown of DmsHSP1-21 by RNAi, but not for DmsHSP11-12.8, significantly increased the vulnerability of D. magna to heavy metal exposure. Our work provides systematic information on the evolution and function of sHSPs in D. magna and leads to important insights into the mechanisms by which D. magna survive in adverse environments.