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 P450s 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-Feyereisen1" target="_blank">[19]</a> and this study.</p

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

<p><i>B. oleae</i> CCEs clustered within clades <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone.0066533-Claudianos1" target="_blank">[36]</a>. A: hymenopteran radiation with related group containing odorant degrading esterases, B: dipteran mitochondrial, cytosolic and secreted esterases, C: dipteran microsomal, α-esterases, D: integument esterases, E: β-esterases and pheromone esterases, F: dipteran juvenile hormone esterases, G: lepidopteran juvenile hormone esterases, H: glutactin and glutactin-like enzymes, I: uncharacterized group, J: acetylcholinesterases, K: gliotactins, L: neuroligins, M: neurotactins. Aaeg: <i>Aedes aegypti</i>, Acal: <i>Anisopteromalus calandrae</i>, Agam: <i>Anopheles gambiae</i>, Agos: <i>Aphis gossypii</i>, Amel: <i>Apis mellifera</i>, Apol: <i>Antheraea polyphemus</i>, Bdor: <i>Bactrocera dorsalis</i>, Bmor: <i>Bombyx mori</i>, Bole: <i>Bactrocera oleae</i>, Cfum: <i>Choristoneura fumiferana</i>, Cpip: <i>Culex pipiens</i>, Ctar: <i>Culex tarsalis</i>, Ctri: <i>Culex tritaeniorhynchus</i>, Dmel: <i>Drosophila melanogaster</i>, Hirr: <i>Haematobia irritans</i>, Hvir: <i>Heliothis virescens</i>, Lcup: <i>Lucilia cuprina</i>, Ldec: <i>Leptinotarsa decemlineata</i>, Mdom: <i>Musca domestica</i>, Mper: <i>Myzus persicae,</i> Nlug: <i>Nilaparvata lugens</i>, Sgra: <i>Schizaphis graminum</i>, Tcas: <i>Tribolium castaneum,</i> Tmol: <i>Tenebrio molitor</i>.</p

Phylogenetic analysis of <b><i>B. oleae</i></b>putative P450s.

<p><i>B. oleae</i> P450s clustered within the 4 major insect CYP clades. Aech: <i>Acromyrmex echinatior,</i> Agam: <i>Anopheles gambiae</i>, Amel: <i>Apis mellifera,</i> Bdor: <i>Bactrocera dorsalis</i> (“JF” sequences were obtained from Shen <i>et al</i>., 2011), Bger: <i>Blatella germanica,</i> Bmor: <i>Bombyx mor</i>i, Btab: <i>Bemisia tabaci</i>, Dmel: <i>Drosophila melanogaster,</i> Dpas: <i>Depressaria pastinacella</i>, Dpun<i>: Diploptera punctata</i>, Harm: <i>Helicoverpa armigera</i>, Hsap<i>: Homo sapiens</i>, Hzea: <i>Helicoverpa zea</i>, Mdom: <i>Musca domestica</i>, Ppol: <i>Papilio polyxenes</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

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

Comparison of CCEs 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>**<p>for full CCE clade names, see legend of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066533#pone-0066533-g006" target="_blank">Figure 6</a>.</p

Summary of run statistics and assembly.

*<p>size above which 50% of the assembled sequences can be found.</p