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Parasitization of Bemisia tabaci by Eretmocerus mundus

ABSTRACT: The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), and the viruses it transmits, are a major constraint to vegetable crops, worldwide. Although the whitefly is usually controlled using chemical pesticides, biological control agents constitute an important component in integrated pest management programs. One of these agents is the wasp Eretmocerus mundus (Mercet) (Hymenoptera: Aphelinidae). E. mundus lays its egg on the leaf underneath the pupa of B. tabaci. First instars of the wasp hatch and penetrate the whitefly larvae. Initiation of parasitization induces the host to form a cellular capsule around the parasitoid. Around this capsule, epidermal cells multiply and thick layers of cuticle are deposited. The physiological and molecular processes underlying B. tabaci-E. mundus interactions have not been investigated so far. We have used a cDNA microarray containing 6,000 expressed sequence tags (ESTs) from the whitefly genome to study the parasitoid-whitefly interaction. We compared RNA samples collected across two time points of the parasitization process: when the parasitoid first instar started the penetration process and once it had fully penetrated the host. The results clearly indicated that genes known to be part of the defense pathways described in other insects are also involved in the response of B. tabaci to parasitization by E. mundus. Some of the responses observed included the repression of a serine protease inhibitor (serpin) and the induction of a melanization cascade. A second set of genes that strongly responded to parasitization included bacterial genes encoded by whitefly symbionts. Quantitative real-time PCR and FISH analyses showed that proliferation of Rickettsia, a facultative secondary symbiont, was strongly induced following the initiation of the parasitization process, a result that supported previous reports suggesting that endosymbionts may be involved in the insect host resistance to various environmental stresses. This is the first study examining the transcriptional response of a hemipteran insect to the attack of a biological control agent (Hymenopterous parasitoid), using a new genomic approach developed for this insect pest. The defense response in B. tabaci seems to resemble that of model organisms such as Drosophila melanogaster. Moreover, endosymbionts of B. tabaci seem to play a role in the response to parasitization, and this is supported by previously published results from aphids. Keywords: time course

ORGANISM(S): Bemisia tabaci

PROVIDER: GSE11410 | GEO | 2008/05/13

SECONDARY ACCESSION(S): PRJNA106423

REPOSITORIES: GEO

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Project description:Background: The whitefly Bemisia tabaci is a major generalist agricultural pest of field and horticultural crops world-wide. Despite its importance, the molecular bases of defense mechanisms in B. tabaci against major plant secondary defense compounds, such as the phenylpropanoids, remain unknown. Results: Our experimental system utilized transgenic Nicotiana tabacum plants constitutively expressing the PAP1 ⁄ AtMYB75 transcription factor which activates specifically the phenylpropanoid / flavonoids biosynthetic pathway. Our study used suppression subtractive hybridization (SSH) and cDNA microarray approaches to compare gene expression between B. tabaci adults subjected to wild-type or transgenic plants for six hours. A total of 2880 clones from the SSH libraries were sequenced. Both the SSH and cDNA microarray analyses indicated a complex interaction between B. tabaci and secondary defense metabolites produced by the phenylproapnoids / flavonoids pathway, involving enhanced expression of detoxification, immunity, oxidative stress and general stress related genes as well as general metabolism and ribosomal genes. Quantitative PCR revealed significant changes in the expression of several of these genes in response to feeding on artificial diet containing the flavonol quercetin. The elevated transcriptional activity was not accompanied by reduced reproductive performance, indicating high adaptability of B. tabaci to this large group of plant secondary defense metabolites. Conclusion: Results of this study allows first insight into the molecular mechanisms underlining polyphagy in B. tabaci. Our analyses revealed many candidate genes related to the insect's various defense systems capable of neutralizing a broad range of plant toxins. Future technological developments allowing silencing or over-expression of selected target genes in B. tabaci, will enable determining a specific linkage between gene expression and host related performance in this species.

Project description:Background: The whitefly Bemisia tabaci is a major generalist agricultural pest of field and horticultural crops world-wide. Despite its importance, the molecular bases of defense mechanisms in B. tabaci against major plant secondary defense compounds, such as the phenylpropanoids, remain unknown. Results: Our experimental system utilized transgenic Nicotiana tabacum plants constitutively expressing the PAP1 M-bM-^AM-^D AtMYB75 transcription factor which activates specifically the phenylpropanoid / flavonoids biosynthetic pathway. Our study used suppression subtractive hybridization (SSH) and cDNA microarray approaches to compare gene expression between B. tabaci adults subjected to wild-type or transgenic plants for six hours. A total of 2880 clones from the SSH libraries were sequenced. Both the SSH and cDNA microarray analyses indicated a complex interaction between B. tabaci and secondary defense metabolites produced by the phenylproapnoids / flavonoids pathway, involving enhanced expression of detoxification, immunity, oxidative stress and general stress related genes as well as general metabolism and ribosomal genes. Quantitative PCR revealed significant changes in the expression of several of these genes in response to feeding on artificial diet containing the flavonol quercetin. The elevated transcriptional activity was not accompanied by reduced reproductive performance, indicating high adaptability of B. tabaci to this large group of plant secondary defense metabolites. Conclusion: Results of this study allows first insight into the molecular mechanisms underlining polyphagy in B. tabaci. Our analyses revealed many candidate genes related to the insect's various defense systems capable of neutralizing a broad range of plant toxins. Future technological developments allowing silencing or over-expression of selected target genes in B. tabaci, will enable determining a specific linkage between gene expression and host related performance in this species. 3 hybridizations were performed for RNA extracted from Bemisia tabaci adults that fed on PAP Purple transgenic tobacco plants for 6hr, labeled with Cy5 and directly hybridized against 3 samples from B. tabaci adults that fed on wild type plants as a control and labeled with Cy3. Another 3 swap dye hybridizations were performed in which adults that fed on wild type plants for 6hr were coupled with the Cy5 and adults that fed on PAP Purple transgenic plants were coupled with Cy3.

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Parasitization of Bemisia tabaci by Eretmocerus mundus

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