Pyrosequencing the <em>Bemisia tabaci</em> Transcriptome Reveals a Highly Diverse Bacterial Community and a Robust System for Insecticide Resistance

<div><h3>Background</h3><p><em>Bemisia tabaci</em> (Gennadius) is a phloem-feeding insect poised to become one of the major insect pests in open field and greenhouse production systems throughout the world. The high level of resistance to insecticides is a main factor that hinders continued use of insecticides for suppression of <em>B. tabaci</em>. Despite its prevalence, little is known about <em>B. tabaci</em> at the genome level. To fill this gap, an invasive <em>B. tabaci</em> B biotype was subjected to pyrosequencing-based transcriptome analysis to identify genes and gene networks putatively involved in various physiological and toxicological processes.</p> <h3>Methodology and Principal Findings</h3><p>Using Roche 454 pyrosequencing, 857,205 reads containing approximately 340 megabases were obtained from the <em>B. tabaci</em> transcriptome. <em>De novo</em> assembly generated 178,669 unigenes including 30,980 from insects, 17,881 from bacteria, and 129,808 from the nohit. A total of 50,835 (28.45%) unigenes showed similarity to the non-redundant database in GenBank with a cut-off E-value of 10–5. Among them, 40,611 unigenes were assigned to one or more GO terms and 6,917 unigenes were assigned to 288 known pathways. <em>De novo</em> metatranscriptome analysis revealed highly diverse bacterial symbionts in <em>B. tabaci</em>, and demonstrated the host-symbiont cooperation in amino acid production. In-depth transcriptome analysis indentified putative molecular markers, and genes potentially involved in insecticide resistance and nutrient digestion. The utility of this transcriptome was validated by a thiamethoxam resistance study, in which annotated cytochrome P450 genes were significantly overexpressed in the resistant <em>B. tabaci</em> in comparison to its susceptible counterparts.</p> <h3>Conclusions</h3><p>This transcriptome/metatranscriptome analysis sheds light on the molecular understanding of symbiosis and insecticide resistance in an agriculturally important phloem-feeding insect pest, and lays the foundation for future functional genomics research of the <em>B. tabaci</em> complex. Moreover, current pyrosequencing effort greatly enriched the existing whitefly EST database, and makes RNAseq a viable option for future genomic analysis.</p>