Insight into hypoxia tolerance in cowpea bruchid: metabolic repression and heat shock protein regulation via hypoxia-inducible factor 1

The Role of TcCYP6K1 and TcCYP9F2 Influences Trehalose Metabolism under High-CO2 Stress in Tribolium castaneum (Coleoptera)

Cytochrome P450 monooxygenases (CYP), crucial detoxification enzymes in insects, are involved in the metabolism of endogenous substances as well as the activation and degradation of exogenous compounds. In this study, T. castaneum was utilized to investigate the roles of TcCYP6K1 and TcCYP9F2 genes influencing in the trehalose metabolism pathway under high-CO2 stress. By predicting the functional sequences of TcCYP6K1 and TcCYP9F2 genes and analyzing their spatiotemporal expression patterns, it was discovered that both genes belong to the CYP3 group and exhibit high expression levels during the larval stage, decreasing during the pupal stage, while showing high expression in the fatty body, intestine, and malpighian tubules. Furthermore, following the knockdown of TcCYP6K1 and TcCYP9F2 genes in combination with treating larvae with 75% CO2, it was observed that larval mortality increased, and glycogen content significantly decreased, while trehalose content increased significantly. Additionally, membrane-bound trehalase enzyme activity declined, TPS gene expression was significantly upregulated, GS gene expression was significantly downregulated, and ATP content showed a marked decrease. In conclusion, CYP genes are critical responsive genes of T. castaneum to high CO2 levels, potentially impacting the insect's resistance to carbon dioxide through their involvement in the synthesis or breakdown of the carbohydrate metabolism pathway. These findings could serve as a theoretical basis for the utilization of novel pesticides in low-oxygen grain storage techniques and offer new insights for environmentally friendly pest control strategies in grain storage.

Surviving in a multistressor world: Gene expression changes in earthworms exposed to heat, desiccation, and chemicals

An investigation of the effects of anthropogenic stress on terrestrial ecosystems is urgently needed. In this work, we explored how exposure to heat, desiccation, and chemical stress alters the expression of genes that encode heat shock proteins (HSPs), an enzyme that responds to oxidative stress (CAT), hypoxia-related proteins (HIF1 and HYOU), and a DNA repair-related protein (PARP1) in the earthworm Eisenia fetida. Exposure to heat (31°C) for 24 h upregulated HSPs and hypoxia-related genes, suggesting possible acquired thermotolerance. Desiccation showed a similar expression profile; however, the HSP response was activated to a lesser extent. Heat and desiccation activated the small HSP at 24 h, suggesting that they may play a role in adaptation. Simultaneous exposure to endosulfan and temperature for 7 h upregulated all of the evaluated genes, implicating a coordinated response involving multiple biological processes to ensure survival and acclimation. These results highlight the relevance of multistress analysis in terrestrial invertebrates.

In silico promoter analysis and functional validation identify CmZFH, the co-regulator of hypoxia-responsive genes CmScylla and CmLPCAT

Oxygen (O₂) plays an essential role in aerobic organisms including terrestrial insects. Under hypoxic stress, the cowpea bruchid (Callosobruchus maculatus) ceases feeding and growth. However, larvae, particularly 4th instar larvae exhibit very high tolerance to hypoxia and can recover normal growth once brought to normoxia. To better understand the molecular mechanism that enables insects to cope with low O₂ stress, we performed RNA-seq to distinguish hypoxia-responsive genes in midguts and subsequently identified potential common cis-elements in promoters of hypoxia-induced and -repressed genes, respectively. Selected elements were subjected to gel-shift and transient transfection assays to confirm their cis-regulatory function. Of these putative common cis-elements, AREB6 appeared to regulate the expression of CmLPCAT and CmScylla, two hypoxia-induced genes. CmZFH, the putative AREB6-binding protein, was hypoxia-inducible. Transient expression of CmZFH in Drosophila S2 cells activated CmLPCAT and CmScylla, and their induction was likely through interaction of CmZFH with AREB6. Binding to AREB6 was further confirmed by bacterially expressed CmZFH recombinant protein. Deletion analyses indicated that the N-terminal zinc-finger cluster of CmZFH was the key AREB6-binding domain. Through in silico and experimental exploration, we discovered novel transcriptional regulatory components associated with gene expression dynamics under hypoxia that facilitated insect survival.

Insights into Temperature and Hypoxia Tolerance in Cowpea Weevil via HIF-1

Cowpea weevil (Callosobruchus maculatus) is a major pest that leads to severe damage of the stored leguminous grains. Several management approaches, including physical barriers, biological or chemical methods, are used for controlling bruchid in cowpea. These methods usually target the metabolically active state of weevil. However, it becomes less effective at early stages as egg, larva, or pupa under low temperature and oxygen conditions. Since hypoxia-inducible factor-1 (HIF-1) is known to coordinate multiple gene responses to low oxygen or low temperature signals, we examined the HIF-1α gene expression under low temperature and hypoxic treatments. At −20 °C, it took 4 h to reduce the survival rate for eggs, larvae, and pupae down to 10%, while at 4 °C and 15 °C, the survival rate remained higher than 50% even after 128 h as HIF-1α gene expression peaked at 15 °C. Moreover, HIF-1 protein offers a valuable target for early stage pest control complementary to traditional methods. In particular, HIF-1 inhibitor camptothecin (CPT), one of the five HIF-1 inhibitors examined, achieved a very significant reduction of 96.2% and 95.5% relative to the control in weevil survival rate into adult at 4 °C and 30 °C, respectively. Our study can be used as one model system for drug development in virus infections and human cancer.

Parental hypoxic exposure influences performance of offspring in Callosobruchus maculatus

BACKGROUND

Modified atmosphere based on lack of O₂ can protect stored grains from insect pest damage. Although population expansion of cowpea bruchid (Callosobruchus maculatus (Fabricius)) could be temporarily arrested when exposed to 2% O₂ , this insect could survive extended periods of hypoxia and continue its normal development if normoxic conditions resumed. It is not clear whether parental hypoxic treatment has any effects on offspring performance and response to hypoxia.

RESULTS

Hypoxia postponed development of treated parental bruchids at all stages. Its negative effects on oviposition and hatch rate of these eggs were significant only when hypoxia was administered at the parental fourth instar larval stage or later. When the F1 generation was exposed to hypoxia at the fourth instar larval stage, they exhibited comparable developmental delay and reduction in adult emergence and fecundity whether the parents experienced hypoxia or not. Interestingly, eggs laid by hypoxia-treated F1s had increased hatch rates if their parents had also been exposed to hypoxia. Stronger suppression of the digestive protease gene CatL and elevated basal expression of the stress responsive gene Hsp27 were observed in F1 larvae with parental hypoxic experience.

CONCLUSION

Parental hypoxic experience appeared to better prepare the F1 progenies for further hypoxic challenge. © 2019 Society of Chemical Industry.

Genome-wide association studies for heat stress response in Bos taurus × Bos indicus crossbred cattle

Heat stress is an important issue in the global dairy industry. In tropical areas, an alternative to overcome heat stress is the use of crossbred animals or synthetic breeds, such as the Girolando. In this study, we performed a genome-wide association study (GWAS) and post-GWAS analyses for heat stress in an experimental Gir × Holstein F₂ population. Rectal temperature (RT) was measured in heat-stressed F₂ animals, and the variation between 2 consecutive RT measurements (ΔRT) was used as the dependent variable. Illumina BovineSNP50v1 BeadChip (Illumina Inc., San Diego, CA) and single-SNP approach were used for GWAS. Post-GWAS analyses were performed by gene ontology terms enrichment and gene-transcription factor (TF) networks, generated from enriched TF. The breed origin of marker alleles in the F₂ population was assigned using the breed of origin of alleles (BOA) approach. Heritability and repeatability estimates (± standard error) for ΔRT were 0.13 ± 0.08 and 0.29 ± 0.06, respectively. Association analysis revealed 6 SNP significantly associated with ΔRT. Genes involved with biological processes in response to heat stress effects (LIF, OSM, TXNRD2, and DGCR8) were identified as putative candidate genes. After performing the BOA approach, the 10% of F₂ animals with the lowest breeding values for ΔRT were classified as low-ΔRT, and the 10% with the highest breeding values for ΔRT were classified as high-ΔRT. On average, 49.4% of low-ΔRT animals had 2 alleles from the Holstein breed (HH), and 39% had both alleles from the Gir breed (GG). In high-ΔRT animals, the average proportion of animals for HH and GG were 1.4 and 50.2%, respectively. This study allowed the identification of candidate genes for ΔRT in Gir × Holstein crossbred animals. According to the BOA approach, Holstein breed alleles could be associated with better response to heat stress effects, which could be explained by the fact that Holstein animals are more affected by heat stress than Gir animals and thus require a genetic architecture to defend the body from the deleterious effects of heat stress. Future studies can provide further knowledge to uncover the genetic architecture underlying heat stress in crossbred cattle.

Comparative transcriptome analyses of adzuki bean weevil (Callosobruchus chinensis) response to hypoxia and hypoxia/hypercapnia

Stored product insects show high adaption to hypoxia and hypercapnia, but the underlying mechanism is still unclear. Herein, a comparative transcriptome on 4th adzuki bean weevil (Callosobruchus chinensis) instar larvae was studied to clarify the response mechanisms to hypoxia (HA) and hypoxia/hypercapnia (HHA) using NextSeq500 RNA-Seq. Transcript profiling showed a significant difference in HA or HHA exposure both quantitatively and qualitatively. Compared with control, 631 and 253 genes were significantly changed in HHA and HA, respectively. Comparing HHA with HA, 1135 differentially expressed genes (DEGs) were identified. The addition of hypercapnia made a complex alteration on the hypoxia response of bean weevil transcriptome, carbohydrate, energy, lipid and amino acid metabolism were the most highly enriched pathways for genes significantly changed. In addition, some biological processes that were not significantly enriched but important were also discussed, such as immune system and signal transduction. Most of the DEGs related to metabolism both in HHA and HA were up-regulated, while the DEGs related to the immune system, stress response or signal transduction were significantly down-regulated or suppressed. This research reveals a comparatively full-scale result in adzuki bean weevil hypoxia and hypoxia/hypercapnia tolerance mechanism at transcription level, which might provide new insights into the genomic research of this species.

Hypoxic environment protects cowpea bruchid (Callosobruchus maculatus) from electron beam irradiation damage

BACKGROUND

Electron beam (eBeam) irradiation and hermetic storage are safe and effective technologies to protect stored products. Although hypoxic environment improves performance of some irradiated insects, whether hypoxia affects irradiation of storage insects and impacts pest control efficacy remains to be investigated.

RESULTS

Using cowpea bruchid (Callosobruchus maculatus) larvae, we showed that, relative to eBeam irradiation under normoxia, the adult emergence rate increased substantially if they were exposed to hypoxia prior to and during eBeam treatment. Conversely, exposure to hypoxia only after eBeam irradiation did not have this protective effect. eBeam irradiation caused an increase in reactive oxygen species (ROS) in normoxic larvae but not in hypoxic larvae. The activity of citrate synthase, a pace-making enzyme in the citric acid cycle, was suppressed under hypoxia but resumed normal function within hours of reoxygenation, suggesting that reduced mitochondrial activity, and thus less ROS production under hypoxia increased insect tolerance to irradiation. Furthermore, reoxygenation accelerated eBeam-induced glutathione-S-transferase activation and potentiated eBeam-enhanced catalase activities. Faster and stronger detoxification capacity in eBeam-irradiated, hypoxic larvae may have protected them from oxidative damage.

CONCLUSION

Hypoxic environment enhanced radiotolerance of bruchid larvae, presumably due to limited ROS production and elevated antioxidant enzymatic activities after reoxygenation. © 2018 Society of Chemical Industry.

Comparative Efficacy of Four Hermetic Bag Brands Against Prostephanus truncatus (Coleoptera: Bostrichidae) in Stored Maize Grain

Hermetic storage technology using plastic liners is threatened by the boring action of Prostephanus truncatus Horn. (Coleoptera: Bostrichidae), a major insect pest of stored maize in sub-Saharan Africa. We investigated the performance of four brands of hermetic storage bags against adult P. truncatus in maize stored for 90 d under simulated resident and incoming infestation. Five treatments were used: four hermetic bag brands; SuperGrain Bag (SGB) IV-R, SGB Farm, Purdue Improved Crop Storage (PICS) bag, and Kuraray bag; and an ordinary plastic bag; each containing 50 kg of shelled maize. Two modes of insect infestation were used whereby 50 adult insects were introduced inside and outside the hermetic bags to simulate resident and incoming insect infestations, respectively. Parameters measured included carbon dioxide-oxygen levels, live adult P. truncatus numbers, grain moisture content, grain damage and weight loss, germination, and number of insect-induced perforations on plastic liners. Externally infested bags had no insect activity; all the introduced insects died of starvation. Internally infested bags were all perforated. The ordinary plastic liner was severely perforated with 151 insect-induced holes compared to hermetic plastic liners (<40 holes). There was no live adult insect infestation in grain samples collected using double-tube multi-slotted sampling probes inserted vertically several times. However, live adult insects were present in the bottom grain layer (0.05 m) of all plastic liners. There were no significant differences between hermetic bags regardless of mode of infestation for all parameters assessed. The results show that the tested hermetic bags are equally susceptible to perforations by resident P. truncatus.

Effects of anoxia on survival and gene expression in Bactrocera dorsalis

The oriental fruit fly (Bactrocera dorsalis) larvae may commonly experience a hypoxia microenvironment and have evolved the ability to survive in the low oxygen condition with some physiological and biochemical mechanisms. However, little is known about the response of B. dorsalis to hypoxia or anoxia. In this study, the effect of anoxia on the survival of B. dorsalis was investigated. The results showed that the B. dorsalis larvae were quite tolerant to anoxia conditions and can tolerate up to 24 h of anoxia exposure without a significant reduction in survival, 100% mortality was reached after 84 h of anoxia exposure. The cDNA of hypoxia inducible factor (HIF) 1α and HIF-1β is 2912 and 3618 bp in length, encoding 766 and 648 amino acid residues, respectively. Both HIF-1α and HIF-1β contain conserved basic helix-loop-helix (bHLH) domain and Per-Arnt-Sim (PAS) domain. HIF-1α can be induced by hypoxia, whereas HIF-1β expression was not significantly changed with the oxygen concentration. Three major heat shock proteins (Hsps) expression increased significantly during anoxia and recovery and Hsp70 was the most responsive to anoxia. Four superoxide dismutase (SOD) genes expression were also up-regulated during anoxia exposure. These data suggest that B. dorsalis has a strategy to induce HIF-1α and HIF-1-responsive genes to survive in the low oxygen condition.

The effect of within-instar development on tracheal diameter and hypoxia-inducible factors α and β in the tobacco hornworm, Manduca sexta

As insects grow within an instar, body mass increases, often more than doubling. The increase in mass causes an increase in metabolic rate and hence oxygen demand. However, the insect tracheal system is hypothesized to increase only after molting and may be compressed as tissues grow within an instar. The increase in oxygen demand in the face of a potentially fixed or decreasing supply could result in hypoxia as insects near the end of an instar. To test these hypotheses, we first used synchrotron X-ray imaging to determine how diameters of large tracheae change within an instar and after molting to the next instar in the tobacco hornworm, Manduca sexta. Large tracheae did not increase in diameter within the first, second, third, and fourth instars, but increased upon molting. To determine if insects are hypoxic at the end of instars, we used the presence of hypoxia-inducible factors (HIFs) as an index. HIF-α and HIF-β dimerize in hypoxia and act as a transcription factor that turns on genes that will increase oxygen delivery. We sequenced both of these genes and measured their mRNA levels at the beginning and end of each larval instar. Finally, we obtained an antibody to HIF-α and measured protein expression during the same time. Both mRNA and protein levels of HIFs were increased at the end of most instars. These data support the hypothesis that some insects may experience hypoxia at the end of an instar, which could be a signal for molting.

SUMMARY STATEMENT

As caterpillars grow within an instar, major tracheae do not increase in size, while metabolic demand increases. At the same life stages, caterpillars increased expression of hypoxia inducible factors, suggesting that they become hypoxic near the end of an instar.

Blowfly puparia in a hermetic container: survival under decreasing oxygen conditions

Despite widely accepted standards for sampling and preservation of insect evidence, unrepresentative samples or improperly preserved evidence are encountered frequently in forensic investigations. Here, we report the results of laboratory studies on the survival of Lucilia sericata and Calliphora vomitoria (Diptera: Calliphoridae) intra-puparial forms in hermetic containers, which were stimulated by a recent case. It is demonstrated that the survival of blowfly intra-puparial forms inside airtight containers is dependent on container volume, number of puparia inside, and their age. The survival in both species was found to increase with an increase in the volume of air per 1 mg of puparium per day of development in a hermetic container. Below 0.05 ml of air, no insect survived, and above 0.2 ml of air per 1 mg of puparium per day, survival reached its maximum. These results suggest that blowflies reveal a single, general pattern of survival under decreasing oxygen conditions and that this pattern is a product of number of developing insects, their age and the initial amount of available air. Implications for forensic entomology are discussed.

De novo transcriptome characterization of the ghost moth, Thitarodes pui, and elevation-based differences in the gene expression of its larvae

Thitarodes pui larvae are the hosts of a medicinal fungus, Ophiocordyceps sinensis, and are naturally distributed at an altitude of 4100-4650 m on Segrila Mountain of the Tibetan Plateau. Here, we conducted transcriptome profiling of T. pui larvae based on the Illumina high-throughput sequencing platform. Subsequently, we explored elevation-based differences of T. pui by comparing gene expression profiles between larvae at high-altitude (natural conditions) and larvae exposed to short-term (2months) low-altitude conditions. A total of 105,935,208 clean reads were assembled into 70,048 unigenes with a mean length of 639 bp. All unigenes were searched against public databases, with 51.26% unigenes being successfully annotated in the NR, SWISS-PROT, EuKaryotic Orthologous Groups (KOG), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genome (KEGG) databases. A total of 11,846 unigenes were functionally classified into 239 KEGG pathways. Metabolism was the most represented pathway, with 4271 unigenes (36.05%). Using the transcriptome data as a reference, 629 (311 up-regulated/318 down-regulated) genes were differentially expressed by low-altitude larvae when compared with those of high-altitude larvae. The most significantly differentially expressed genes were annotated in the processes of carbohydrate metabolism, lipid metabolism, and respiration. This report provides valuable information about the T. pui transcriptome for future genomic studies, including how gene expression is altered in larvae reared at different elevations.

Insecticides and Bio-insecticides Modulate the Glutathione-related Antioxidant Defense System of Cowpea Storage Bruchid (Callosobruchus maculatus)

The possible cellular involvements of cowpea storage bruchid (Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae]) glutathione and its related enzymes system in the cellular defense against insecticides (Cypermethrin and λ-cyhalothrin) and bio-insecticides (ethanolic extract of Tithonia diversifolia, Cyperus rotundus, Hyptis suavolens leaves, and Jatropha curcas seed) were investigated. The results showed that the effect of insecticides and bio-insecticides on the C. maculatus is a function of oxidative and nitrosative stresses generated in vivo. A significant (p < 0.05) increase in carbonyl protein (CP) and lipid peroxidation (LPO) contents in bio-insecticides and insecticides exposed groups compared to the control indicates the extent of vital organs damage. These stresses caused similar and significant increase of glutathione peroxidase and glutathione synthetase in response to insecticides and bio-insecticide exposure in a dose-dependent manner. There was no post-translational modification of glutathione transferases expression induced. The alterations of the insect glutathione-dependent antioxidant enzyme activities reflect the presence of a functional defense mechanism against the oxidative and nitrosative stress and are related firmly to the glutathione demands and metabolism but appear inadequate by the significant reduction in glutathione reductase (GR) activity to prevent the damages. Exogenous application of reduced glutathione (GSH), to complement the in vivo demand, could not protect against the onslaught.

Insecticides and Bio-insecticides Modulate the Glutathione-related Antioxidant Defense System of Cowpea Storage Bruchid (Callosobruchus maculatus)

The possible cellular involvements of cowpea storage bruchid (Callosobruchus maculatus (Fab.) [Coleoptera: Chrysomelidae]) glutathione and its related enzymes system in the cellular defense against insecticides (Cypermethrin and λ-cyhalothrin) and bio-insecticides (ethanolic extract of Tithonia diversifolia, Cyperus rotundus, Hyptis suavolens leaves, and Jatropha curcas seed) were investigated. The results showed that the effect of insecticides and bio-insecticides on the C. maculatus is a function of oxidative and nitrosative stresses generated in vivo. A significant (p < 0.05) increase in carbonyl protein (CP) and lipid peroxidation (LPO) contents in bio-insecticides and insecticides exposed groups compared to the control indicates the extent of vital organs damage. These stresses caused similar and significant increase of glutathione peroxidase and glutathione synthetase in response to insecticides and bio-insecticide exposure in a dose-dependent manner. There was no post-translational modification of glutathione transferases expression induced. The alterations of the insect glutathione-dependent antioxidant enzyme activities reflect the presence of a functional defense mechanism against the oxidative and nitrosative stress and are related firmly to the glutathione demands and metabolism but appear inadequate by the significant reduction in glutathione reductase (GR) activity to prevent the damages. Exogenous application of reduced glutathione (GSH), to complement the in vivo demand, could not protect against the onslaught.

CO2 enhances effects of hypoxia on mortality, development, and gene expression in cowpea bruchid, Callosobruchus maculatus

Modified atmosphere based on lack of O2 offers a safe, residue-free alternative to chemical fumigants for pest control in stored grains. In this study, we intended to determine whether elevated CO2 (at a biologically achievable level) has an enhanced suppressive effect over low O2 atmosphere alone on the cowpea bruchid (Callosobruchus maculatus), a storage pest of cowpea and other legumes. Experiments were performed under two modified atmospheric conditions, (1) 2% O2+18% CO2+80% N2 and (2) 2% O2+98% N2. Both hypoxic environments significantly affected the development and survival of all insect developmental stages. Eggs were most vulnerable to hypoxia, particularly at the early stage (4-6h old), surviving only up to a maximum of 2 days in both treatments. These were followed by adults, pupae and larvae, in order of decreasing susceptibility. The 3rd and 4th instar larvae were most resilient to hypoxia and could survive up to 20 days of low O2. The presence of 18% CO2 significantly increased the mortality of adults, the later stage of eggs, as well as 1st and 4th instar larvae caused by hypoxia. However, the surviving insects exhibited faster development, evidenced by their earlier emergence from cowpea seeds compared to those without CO2. One interesting observation was the frequent, premature opening of the emergence windows in the 4th instar larvae when CO2 was involved. This phenomenon was not observed at all in insects stressed by low O2 alone. Differential expression profiling of metabolic genes and proteolytic activity of midgut digestive enzymes suggested that the rate of metabolic activity could contribute in part to the difference in insect development and survival under hypoxia in the presence and absence of CO2.