Project description: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
Project description:The whitefly Bemisia tabaci is a notorious pest of worldwide agriculture. It is believed to secrete saliva to counter plant defenses, but the underlying mechanism remains to be elucidated. Here, we characterize the gene/protein repertoires of B. tabaci salivary glands and secreted saliva by transcriptomic and LC–MS/MS analysis. A total of 698 salivary gland-higher expressed unigenes, as well as 172 saliva proteins are identified. Comparative analysis of the saliva composition in different arthropod species illustrates that proteins associated with binding, hydrolysis and oxidation-reduction are widely distributed in herbivorous saliva. There are 74 saliva proteins exclusively identified in B. tabaci, with 34 of them being B. tabaci-specific. In addition, eleven B. tabaci-specific saliva proteins plastically regulated in response to different diets, which might be associated with wide host range of this pest. Our results gain insight into whitefly–plant interactions, and provide a good resource for functional characterization of effectors
Project description:Begomoviruses, the largest, most damaging and emerging group of plant viruses in the world, infect hundreds of plant species and new virus species of the group are discovered each year. They are transmitted by species of the whitefly Bemisia tabaci. Tomato yellow leaf curl virus (TYLCV) is one of the most devastating begomoviruses worldwide and causes major losses in tomato crops as well as in many more agriculturally important plant species. Different B. tabaci populations vary in their virus transmission abilities; the causes for these differences are attributed among others to genetic diversity of vector populations, as well as to differences in the bacterial symbiont flora of the insects. Here, we performed discovery proteomic analyses in nine whiteflies populations from both B (MEAM1) and Q (MED) species with different TYLCV transmission abilities. The results provide the first comprehensive list of candidate insect and bacterial symbiont (mainly Rickettsia) proteins associated with virus transmission. Efficient vector populations from two different B. tabaci species over-expressed or downregulated expression of proteins belonging to two different molecular pathways.
Project description:The whitefly, Bemisia tabaci MEAM1 is a devastating vector capable of transmitting hundreds of plant viruses, including Tomato yellow leaf curl virus (TYLCV), to important food and fiber crops. Here we performed genome-wide profiling of micro RNAs (miRNAs) and piwi-interacting RNAs (piRNAs) in whiteflies after feeding on TYLCV-infected tomato or uninfected tomato for 24, 48 and 72 h. Overall, 160 miRNAs were discovered, 68 of which were conserved and 92 were B. tabaci-specific miRNAs. Majority of the genes that were predicted to be targeted by miRNAs had gene ontologies related to metabolic processes. We identified two miRNAs that were differentially expressed in whiteflies when fed on TYLCV-infected tomato compared to whiteflies that fed on uninfected tomato. The identified piRNAs were expressed as clusters throughout the whitefly genome. A total of 53 piRNA clusters were expressed across all time points and treatments, while 5 piRNA clusters were exclusively expressed in whiteflies that fed on TYLCV-infected tomato, and 24 clusters were exclusively expressed in whiteflies that fed on uninfected tomato. Approximately 62% of all identified piRNAs were derived from non-coding sequences that included intergenic regions, introns, and UTRs with unknown functions. The remaining 38% of piRNAs were derived from coding sequences (CDS) and repeat elements. Transposable elements targeted by piRNA clusters included both class I retrotransposons such as Gypsy, Copia, and LINEs and class II DNA transposons such as MITE, hAT, and TcMar. Lastly, six protein coding genes were targeted in whiteflies that fed on TYLCV-infected tomato. Information on how TYLCV influences miRNA and piRNA expression in whiteflies provides a greater understanding of regulatory pathways involved in mediating whitefly-virus interactions, and will facilitate the identification of novel targets for RNAi control.
Project description:The whitefly Bemisia tabaci (Gennadius) causes tremendous losses to agriculture by direct feeding on plants and by vectoring several families of plant viruses. The B. tabaci species complex comprises over 10 genetic groups (biotypes) that are well defined by DNA markers and biological characteristics. B and Q are amongst the most dominant and damaging biotypes, differing considerably in fecundity, host range, insecticide resistance, virus vectoriality, and the symbiotic bacteria they harbor. We used a spotted B. tabaci cDNA microarray to compare the expression patterns of 6,000 ESTs of B and Q biotypes under standard 25°C regime and heat stress at 40°C. Overall, the number of genes affected by increasing temperature in the two biotypes was similar. Gene expression under 25ºC normal rearing temperature showed clear differences between the two biotypes: B exhibited higher expression of mitochondrial genes, and lower cytoskeleton, heat-shock and stress-related genes, compared to Q. Exposing B-biotype whiteflies to heat stress was accompanied by rapid alteration of gene expression. For the first time, the results here present differences in gene expression between very closely related and sympatric B. tabaci biotypes, and suggest that these clear-cut differences are due to better adaptation of one biotype over another and might eventually lead to changes in the local and global distribution of both biotypes.
Project description:The whitefly Bemisia tabaci (Gennadius) causes tremendous losses to agriculture by direct feeding on plants and by vectoring several families of plant viruses. The B. tabaci species complex comprises over 10 genetic groups (biotypes) that are well defined by DNA markers and biological characteristics. B and Q are amongst the most dominant and damaging biotypes, differing considerably in fecundity, host range, insecticide resistance, virus vectoriality, and the symbiotic bacteria they harbor. We used a spotted B. tabaci cDNA microarray to compare the expression patterns of 6,000 ESTs of B and Q biotypes under standard 25°C regime and heat stress at 40°C. Overall, the number of genes affected by increasing temperature in the two biotypes was similar. Gene expression under 25ºC normal rearing temperature showed clear differences between the two biotypes: B exhibited higher expression of mitochondrial genes, and lower cytoskeleton, heat-shock and stress-related genes, compared to Q. Exposing B-biotype whiteflies to heat stress was accompanied by rapid alteration of gene expression. For the first time, the results here present differences in gene expression between very closely related and sympatric B. tabaci biotypes, and suggest that these clear-cut differences are due to better adaptation of one biotype over another and might eventually lead to changes in the local and global distribution of both biotypes. 3 replicates comparing Q biotype under 40 degrees celsius (C) with three replicates under 25 C. The same number of replicates comparing B biotype under 40 C and 25 C, and three replicates comparing B and Q biotypes under 25 C.
Project description:The whitefly, Bemisia tabaci, a notorious agricultural pest, has complex relationships with diverse microbes. It recognizes and degrades pathogens, as other insects do, and also relies on endosymbionts for its survival. Both types of interaction have received great attention, because of their potential importance in developing novel whitefly control technologies. The recent developments in RNA-seq technology allows us to perform a comprehensive investigation of a whitefly’s defense responses after it has ingested the pathogen, Pseudomonas aeruginosa. Compared to uninfected whiteflies, 6 and 24 hour post-infected (hpi) whiteflies showed 1,348 and 1,888 differentially expressed genes, respectively. Functional analysis highlighted the involvement of mitogen associated protein kinase (MAPK) pathway in host-defense regulation. Three knottin-like antimicrobial peptide genes and several components of the humoral and cellular immune response were also activated, indicating that key immune elements recognized in other insect species are also important for the host response of B. tabaci. Our data also suggest that intestinal stem cell mediated epithelium renewal might be an important component of the whitefly’s defense against oral bacterial infection. In addition, we also show stress responses to be an essential component of the defense system. We identify for the first time the key immune-response elements utilized by B. tabaci against bacterial infection. This provides a framework for future research into the complex interactions between whiteflies and microbes.
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.