Analysis of the olive fruit fly Bactrocera oleae transcriptome and phylogenetic classification of the major detoxification gene families

he olive fruit fly Bactrocera oleae has a unique ability to cope with olive flesh, and is the most destructive pest of olives worldwide. Its control has been largely based on the use of chemical insecticides, however, the selection of insecticide resistance against several insecticides has evolved. The study of detoxification mechanisms, which allow the olive fruit fly to defend against insecticides, and/or phytotoxins possibly present in the mesocarp, has been hampered by the lack of genomic information in this species. In the NCBI database less than 1,000 nucleotide sequences have been deposited, with less than 10 detoxification gene homologues in total. We used 454 pyrosequencing to produce, for the first time, a large transcriptome dataset for B. oleae. A total of 482,790 reads were assembled into 14,204 contigs. More than 60% of those contigs (8,630) were larger than 500 base pairs, and almost half of them matched with genes of the order of the Diptera. Analysis of the Gene Ontology (GO) distribution of unique contigs, suggests that, compared to other insects, the assembly is broadly representative for the B. oleae transcriptome. Furthermore, the transcriptome was found to contain 55 P450, 43 GST-, 15 CCE- and 18 ABC transporter-genes. Several of those detoxification genes, may putatively be involved in the ability of the olive fruit fly to deal with xenobiotics, such as plant phytotoxins and insecticides. In summary, our study has generated new data and genomic resources, which will substantially facilitate molecular studies in B. oleae, including elucidation of detoxification mechanisms of xenobiotic, as well as other important aspects of olive fruit fly biology

Comparison of cytosolic GSTs in different insect species.^*

*<p>numbers were derived from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Hsu2" target="_blank">[14]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Karatolos1" target="_blank">[15]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Hayes1" target="_blank">[40]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Oakeshott2" target="_blank">[41]</a> and this study.</p

GO terms (level 2) distribution of <i>B.</i><i>oleae</i> transcriptome.

<p>(A) molecular function, (B) biological process, (C) cellular component.</p

Summary of KEGG pathway mapping of <i>B. oleae</i> contigs.

<p>Summary of KEGG pathway mapping of <i>B. oleae</i> contigs.</p

Phylogenetic analysis of <i>B. oleae putative GSTs</i>.

<p><i>B. oleae</i> sequences, corresponding to cytosolic GSTs, clustered within classes. δ: delta class, ε: epsilon class, ζ: zeta class, θ: theta class, σ: sigma class, ω: omega class. Agam: <i>Anopheles gambiae</i>, Amel: <i>Apis mellifera</i>, Bdor: <i>Bactrocera dorsalis </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Shen1" target="_blank">[12]</a>, Bpap: <i>Bactrocera papaya</i>.</p

Comparison of ABC genes in different insect species.^*

*<p>numbers were derived from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Sturm1" target="_blank">[42]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Liu2" target="_blank">[43]</a> and this study.</p

Analysis of the distribution of the 8,129 top blast hits obtained by blast against the nr database (NCBI).

<p>Percentage distribution within different taxonomic groups.</p

Enzyme Classification (EC) analysis of the transcriptome of <b><i>B. oleae.</i></b>

<p>(A) Distribution of EC number in general EC terms, (B) percentage of EC number distribution of <i>B. oleae</i> compared to that from transcriptome sequencing of <i>B. dorsali</i>s <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Hsu2" target="_blank">[14]</a>, <i>M. domestica </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Liu1" target="_blank">[16]</a> and <i>T. vaporariorum </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Karatolos1" target="_blank">[15]</a>.</p