Differential induction of heat shock protein genes to the combined treatments of heat with diatomaceous earth,phosphine or carbon dioxide on Plodia interpunctella

Heating is one of the many disinfestation methods commonly used in facilities that store and process agricultural products. In this study, we have investigated whether the combination of heat treatment with diatomaceous earth (DE), phosphine (PH₃) or CO₂ affects the mortality of the wandering larvae of Plodia interpunctella, which is a major pest found in most stored agricultural products. The mortality rate was 35.0% at day 1 after heat treatment at 40°C for 6 h; however, mortality rates increased after combined treatments of heat and 1 ppm DE or 10 ppm PH₃, while 10% CO₂ had no significant effect. Quantitative real‐time PCR analysis showed that combined treatments involving 1 h of heat treatment with either DE, PH₃ or CO₂ increased the mRNA levels of four heat shock protein (hsp) genes (hsp25, hsp70, grp78 and hsp90) in wandering larvae, 1 h post‐treatment, although those rates were slightly differentiated in each heat shock protein. Our results demonstrate that combinations of heat and DE or PH₃ show increased lethality, although insects produce stress responses at the molecular level.     

Sex‐biased gene expression during the adult stage of the Indian meal moth Plodia interpunctella

Sexual dimorphisms are primary regulated by sex‐biased gene expression. In the present study, using real‐time polymerase chain reaction, we determined the expression profiles of nine genes associated with development, metabolism, stress, and defense throughout adulthood of the Indian meal moth Plodia interpunctella, a global pest of stored food products. Most genes were differentially expressed in a sex‐biased manner during the adult lifespan of the moth. Expression of the heat shock protein genes hsp25 and hsp90 and the antioxidant gene thioredoxin peroxidase (Tpx) was highly female biased, whereas the expression of a gene related to host development (ecdysone receptor [EcR]) and two genes associated with immunity (β‐glycan recognition protein [βgrp] and prophenoloxidase [ProPO]) was male biased. In contrast, the expression of hsp70, glucose‐regulated protein 78 (grp78) and ultraspiracle (USP) was not sex biased. The results of the present study provide important insights into the role of sex‐biased genes in the physiology and behavior of P. interpunctella.     

Three heat shock proteins are essential for rotifer thermotolerance

Heat shock proteins (HSPs) are important molecules in the stress response of organisms from prokaryotes to mammals, and thus may be useful biomarkers for environmental stress. Here we characterize the functional roles of genes belonging to four distinct families of HSPs (hsp40, hsp60, hsp70, and hsp90) in the monogonont rotifer Brachionus manjavacas. Because B. manjavacas inhabits ponds of varying thermal regimes, including ephemeral ponds that may experience temperature fluctuations, HSP-mediated thermotolerance likely is important to its survival and adaptation. Using interference RNA (RNAi), we provide the first conclusive evidence that HSPs are required for rotifer survival following heat stress. Effective RNAi-mediated suppression of all hsp genes except hsp90 was verified via quantitative PCR. Hsp40, hsp60, and hsp70 are required for rotifer thermotolerance (P < 0.05); however, our data do not indicate hsp90 is essential. Quantitative PCR further revealed immediate up-regulation of hsp40 mRNA following heat stress. Additionally, we demonstrated expression of hsp40 mRNA in multiple tissues using fluorescent in situ hybridization. Our characterization of mRNA expression and functional roles for four distinct hsp genes provides a baseline for molecular-level comparisons of the stress response of rotifers with other taxonomic groups, and the technique for in-depth studies of the role of specific genes in rotifer stress responses. Considering the potential for ambient temperatures to impact species survival, competitive interactions, and body size of individuals, thermotolerance may be an important influence on zooplankton community structure.     

Evaluation of stress-inducible hsp90 gene expression as a potential molecular biomarker in Xenopus laevis

In this study we have evaluated stress-inducible hsp90 mRNA accumulation as a potential molecular biomarker in Xenopus laevis. In order to obtain a probe for Northern blot analysis we employed a PCR-based approach using degenerate primers for the amplification and cloning of an hsp90 gene sequence from Xenopus laevis. The deduced amino acid sequence is 102 amino acids in length and exhibited the highest degree of identity with zebrafish and human hsp90 β genes. Futhermore, the putative intron and exon boundaries of this fragment are the same as hsp90 β in chicken, mouse and human, indicating that the fragment represents a Xenopus hsp90 β-like gene. Northern blot analyses revealed that this gene was constitutively expressed in cultured A6 cells. While heat shock and sodium arsenite exposure resulted in the increased accumulation of hsp90 mRNA in A6 cells, treatment with cadmium chloride and zinc chloride did not. Also, exposure of A6 cells to concurrent heat shock and sodium arsenite produced a mild synergistic response with respects to hsp90 mRNA levels in contrast to hsp70 mRNA levels which displayed a strong synergistic effect. Finally, hsp90 mRNA was detected consitutively throughout early embrogenesis but was heat-inducible only in late blastula and later stages of development. Given the normal abundance and limited stress-induced accumulation of hsp90 mRNA, it may not have a great deal of potential as a molecular biomarker compared to hsp70 and hsp30 mRNA. However, it may be useful in conjunction with other stress protein mRNAs to establish a set of biomarker profiles to characterize the cellular response to a stressful or toxic agent.     

Changes in the expression of four heat shock proteins during the aging process in Brachionus calyciflorus (rotifera)

Heat shock proteins (HSPs) are molecular chaperones and have an important role in the refolding and degradation of misfolded proteins, and these functions are related to aging. Rotifer is a useful model organism in aging research, owing to small body size (0.1–1 mm), short lifespan (6–14 days), and senescence phenotypes that can be measured relatively easily. Therefore, we used rotifer as a model to determine the role of four typical hsp genes on the aging process in order to provide a better understanding of rotifer aging. We cloned cDNA encoding hsp genes (hsp40, hsp60, hsp70, and hsp90) from the rotifer Brachionus calyciflorus Pallas, analyzed their molecular characteristics, determined its modulatory response under different temperatures and H₂O₂ concentrations and investigated the changes in expression of these genes during the aging process. We found that Bchsp70 mRNA expression significantly decreased with aging. In addition, we also studied the effects of dietary restriction (DR) and vitamin E on rotifer lifespan and reproduction and analyzed the changes in expression of these four Bchsp genes in rotifers treated with DR and vitamin E. The results showed that DR extended the lifespan of rotifers and reduced their fecundity, whereas vitamin E had no significant effect on rotifer lifespan or reproduction. Real-time PCR indicated that DR increased the expression of these four Bchsps. However, vitamin E only improved the expression of Bchsp60, and reduced the expression of Bchsp40, Bchsp70, and Bchsp90. DR pretreatment also increased rotifer survival rate under paraquat-induced oxidative stress. These results indicated that hsp genes had an important role in the anti-aging process.     

Host behaviour and its influence on foraging and acceptance by the solitary parasitoid wasp,Venturia canescens (Hym: Ichneumonidae)

Behavioural interactions between the solitary koinobiont parasitoid,Venturia canescens, and two of its hosts,Plodia interpunctella andCorcyra cephalonica, were investigated. The response of both hosts to simulated antennation using a two-haired brush was examined over instars 3 (L3) to 5 (L5). YoungP. interpunctella larvae predominantly adopted escape tactics (writhe, trash) whereas L5P. interpunctella usually froze after the stimulus was applied. L3C. cephalonica larvae were more aggressive (headrear, flick) thanP. interpunctella in response to the application of the stimulus, but olderC. cephalonica responded less aggressively than in earlier instars. AlthoughV. canescens readily jabbed its ovipositor at both hosts after antennation,P. interpunctella was considerably more susceptible to parasitoid attack thanC. cephalonica, irrespective of size in the final (L5) instar.C. cephalonica, the larger, more aggressive host, actively resisted parasitism whereasP. interpunctella responded much more passively after parasitoid contact. Parasitoids examined and jabbed their ovipositors at dead hosts, but this behaviour was not sustained, implying that host movement stimulates parasitoid attack. On patches containingV. canescens, L5C. cephalonica andP. interpunctella, mostP. interpunctella larvae responded by freezing after parasitoid contact.P. interpunctella that froze usually avoided parasitism, whereas larvae that attempted to escape by crawling were pursued with vigour byV. canescens and usually parasitized. Irrespective of behaviour after parasitoid contact,C. cephalonia displayed more aggressive behaviour and had much greater success in warding off parasitoid attack. Host acceptance byV. canescens is clearly affected by the size and species of the host it attacks. The influence of host defensive behaviour is discussed in relation to the evolution of parasitoid counter-defences and oviposition strategies.