Dataset Information

Developmental control of a lepidopteran pest Spodoptera exigua by ingestion of bacteria expressing dsRNA of a non-midgut gene.

ABSTRACT: BACKGROUND: RNA interference (RNAi) induced through double stranded RNA (dsRNA) has been used widely to study gene function in insects. Recently, it has been reported that gene knockdown in several insects can be induced successfully through feeding with dsRNA. However, it is still unknown whether phenotypic silencing of genes not expressed in the midgut occurs after ingestion of insect dsRNA. PRINCIPAL FINDINGS: Using chitin synthase gene A (SeCHSA) as the target gene, which is expressed in the cuticle and tracheae of the lepidopteran pest Spodoptera exigua, we showed that the growth and development of S. exigua larvae fed Escherichia coli expressing dsRNA of SeCHSA was disturbed, resulting in lethality. In the 4th and 5th larval instars, prepupae, and pupae, the mean survival rates of insects fed the dsRNA-containing diet were 88.64%, 74.24%, 68.43% and 62.63% respectively. The survival rates in the 5th instar larvae, prepupae and pupae stages were significantly lower than those of all controls, and significant lethality differences were also found between dsSeCHSA treatment and dsControl or ddH(2)O control in the 4th instar larvae. The effects of ingesting bacterially expressed dsRNA on transcription of the target gene, tissue structure, and survival rates of insects were dose-dependent. CONCLUSIONS: Our results suggest that SeCHSA dsRNA may be useful as a means of insect pest control.

SUBMITTER: Tian H

PROVIDER: S-EPMC2704864 | biostudies-literature | 2009

REPOSITORIES: biostudies-literature

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Developmental control of a lepidopteran pest Spodoptera exigua by ingestion of bacteria expressing dsRNA of a non-midgut gene.

Tian Honggang H Peng Han H Yao Qiong Q Chen Hongxin H Xie Qi Q Tang Bin B Zhang Wenqing W

PloS one 20090713 7

<h4>Background</h4>RNA interference (RNAi) induced through double stranded RNA (dsRNA) has been used widely to study gene function in insects. Recently, it has been reported that gene knockdown in several insects can be induced successfully through feeding with dsRNA. However, it is still unknown whether phenotypic silencing of genes not expressed in the midgut occurs after ingestion of insect dsRNA.<h4>Principal findings</h4>Using chitin synthase gene A (SeCHSA) as the target gene, which is exp ...[more]

PMID: 19593438

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Project description:Epoxyoctadecamonoenoic acids (EpOMEs) are epoxide derivatives of linoleic acid (9,12-octadecadienoic acid) and include 9,10-EpOME and 12,13-EpOME. They are synthesized by cytochrome P450 monooxygenases (CYPs) and degraded by soluble epoxide hydrolase (sEH). Although EpOMEs are well known to play crucial roles in mediating various physiological processes in mammals, their role is not well understood in insects. This study chemically identified their presence in insect tissues: 941.8 pg/g of 9,10-EpOME and 2,198.3 pg/g of 12,13-EpOME in fat body of a lepidopteran insect, Spodoptera exigua. Injection of 9,10-EpOME or 12,13-EpOME into larvae suppressed the cellular immune responses induced by bacterial challenge. EpOME treatment also suppressed the expression of antimicrobial peptide (AMP) genes. Among 139 S. exigua CYPs, an ortholog (SE51385) to human EpOME synthase was predicted and its expression was highly inducible upon bacterial challenge. RNA interference (RNAi) of SE51385 prevented down-regulation of immune responses at a late stage (> 24 h) following bacterial challenge. A soluble epoxide hydrolase (Se-sEH) of S. exigua was predicted and showed specific expression in all development stages and in different larval tissues. Furthermore, its expression levels were highly enhanced by bacterial challenge in different tissues. RNAi reduction of Se-sEH interfered with hemocyte-spreading behavior, nodule formation, and AMP expression. To support the immune association of EpOMEs, urea-based sEH inhibitors were screened to assess their inhibitory activities against cellular and humoral immune responses of S. exigua. 12-(3-adamantan-1-yl-ureido) dodecanoic acid (AUDA) was highly potent in suppressing the immune responses. The addition of AUDA to a pathogenic bacterium significantly increased bacterial pathogenicity by suppressing host immune defense. In sum, this study demonstrated that EpOMEs play a crucial role in facilitating anti-inflammatory responses in S. exigua.

Project description:Lepidoptera comprise some of the most devastating herbivorous pest insects worldwide. One of the most promising novel pest control strategies is exploiting the RNA interference (RNAi) mechanism to target essential genes for knockdown and incite toxic effects in the target species without harming other organisms in the ecosystem. However, many insects are refractory to oral RNAi, often due to rapid degradation of ingested dsRNA in their digestive system. This is the case for many lepidopteran insects, including the beet armyworm Spodoptera exigua, which is characterized by a very alkaline gut environment (pH > 9.0) and a strong intestinal nucleolytic activity. In this research, guanidine-containing polymers were developed to protect dsRNA against nucleolytic degradation, specifically in high pH environments. First, their ability to protect dsRNA against nucleolytic degradation in gut juice of the beet armyworm S. exigua was investigated ex vivo. Polymers with high guanidine content provided a strong protection against nucleolytic degradation at pH 11, protecting the dsRNA for up to 30 h. Next, cellular uptake of the dsRNA and the polyplexes in lepidopteran CF203 midgut cells was investigated by confocal microscopy, showing that the polymer also enhanced cellular uptake of the dsRNA. Finally, in vivo feeding RNAi bioassays demonstrated that using these guanidine-containing polymer nanoparticles led to an increased RNAi efficiency in S. exigua. Targeting the essential gene chitin synthase B, we observed that the mortality increased to 53% in the polymer-protected dsRNA treatment compared to only 16% with the naked dsRNA and found that polymer-protected dsRNA completely halted the development of the caterpillars. These results show that using guanylated polymers as a formulation strategy can prevent degradation of dsRNA in the alkaline and strongly nucleolytic gut of lepidopteran insects. Furthermore, the polymer also enhances cellular uptake in lepidopteran midgut cells. This new delivery strategy could be of great use in further fundamental research in lepidopterans, using RNAi as a research tool, and could lead to future applications for RNAi-based pest control of lepidopteran insects.

Dataset Information

Developmental control of a lepidopteran pest Spodoptera exigua by ingestion of bacteria expressing dsRNA of a non-midgut gene.

Publications

Developmental control of a lepidopteran pest Spodoptera exigua by ingestion of bacteria expressing dsRNA of a non-midgut gene.

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