Abstract
BackgroundBemisia tabaci is one of the most damaging agricultural pests world-wide. Although its control is based on insecticides, B. tabaci has developed resistance against almost all classes of insecticides, including neonicotinoids.ResultsWe employed an RNA-seq approach to generate genome wide expression data and identify genes associated with neonicotinoid resistance in Mediterranean (MED) B. tabaci (Q1 biotype). Twelve libraries from insecticide resistant and susceptible whitefly populations were sequenced on an Illumina Next-generation sequencing platform, and genomic sequence information of approximately 73 Gbp was generated.A reference transcriptome was built by de novo assembly and functionally annotated. A total of 146 P450s, 18 GSTs and 23 CCEs enzymes (unigenes) potentially involved in the detoxification of xenobiotics were identified, along with 78 contigs encoding putative target proteins of six different insecticide classes. Ten unigenes encoding nicotinic Acetylcholine Receptors (nAChR), the target of neoinicotinoids, were identified and phylogenetically classified. No nAChR polymorphism potentially related with the resistant phenotypes, was observed among the studied strains.DE analysis revealed that among the 550 differentially (logFC > 1) over-transcribed unigenes, 52 detoxification enzymes were over expressed including unigenes with orthologues in P450s, GSTs, CCE and UDP-glucuronosyltransferases.Eight P450 unigenes belonging to clades CYP2, CYP3 and CYP4 were highly up-regulated (logFC > 2) including CYP6CM1, a gene already known to confer imidacloprid resistance in B. tabaci. Using quantitative qPCRs, a larger screening of field MED B. tabaci from Crete with known neonicotinoid phenotype was performed to associate expression levels of P450s with resistance levels. Expression levels of five P450s, including CYP6CM1, were found associated with neonicotinoid resistance. However, a significant correlation was found only in CYP303 and CYP6CX3, with imidacloprid and acetamiprid respectively.ConclusionOur work has generated new toxicological data and genomic resources which will significantly enrich the available dataset and substantially facilitate the molecular studies in MED B. tabaci. No evidence of target site neonicotinoid resistance has been found. Eight P450 unigenes, including CYP6CM1, were found significantly over-expressed in resistant B. tabaci. This study suggests at least two novel P450s (CYP303 and CYP6CX3) as candidates for their functional characterization as detoxification mechanisms of neonicotinoid resistance in B. tabaci.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-2161-5) contains supplementary material, which is available to authorized users.
Highlights
Bemisia tabaci is one of the most damaging agricultural pests world-wide
This study suggests at least two novel P450 monooxygenases (P450s) (CYP303 and CYP6CX3) as candidates for their functional characterization as detoxification mechanisms of neonicotinoid resistance in B. tabaci
Three field derived strains originally collected from eggplants maintained in the laboratory on cotton plants under Imidacloprid (GR0-IS, GR9-IS) or Acetamiprid Selection (GR4-AS) for few generations were used in this study, along with their Parental ‘relaxed’ strains (GR0-IP, GR9-IP and GR4-AP), namely the respective original strains maintained in the absence of any insecticide contact
Summary
Bemisia tabaci is one of the most damaging agricultural pests world-wide. Its control is based on insecticides, B. tabaci has developed resistance against almost all classes of insecticides, including neonicotinoids. B. tabaci is a complex of 31 putative morphocryptic species [1] and one of the most damaging pests of protected, field crops and ornamentals worldwide [2]. The control of B. tabaci relies on insecticides Their extensive and chronic use has imposed strong selection pressures for resistance to many insecticide classes in B. tabaci, including neonicotinoids, which are the world market leaders of insecticides [3,4,5,6,7]. Imidacloprid was the first neonicotinoid introduced in the market in 1991 followed by acetamiprid, thiamethoxam, thiacloprid and clothianidin [8]
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