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Multiple mutations in the nicotinic acetylcholine receptor Cc?6 gene associated with resistance to spinosad in medfly.

ABSTRACT: Spinosad is an insecticide widely used for the control of insect pest species, including Mediterranean fruit fly, Ceratitis capitata. Its target site is the ?6 subunit of the nicotinic acetylcholine receptors, and different mutations in this subunit confer resistance to spinosad in diverse insect species. The insect ?6 gene contains 12 exons, with mutually exclusive versions of exons 3 (3a, 3b) and 8 (8a, 8b, 8c). We report here the selection of a medfly strain highly resistant to spinosad, JW-100?s, and we identify three recessive Cc?6 mutant alleles in the JW-100?s population: (i) Cc?63aQ68* containing a point mutation that generates a premature stop codon on exon 3a (3aQ68*); (ii) Cc?63aAG>AT containing a point mutation in the 5' splicing site of exon 3a (3aAG?>?AT); and (iii) Cc?63aQ68*-K352* that contains the mutation 3aQ68* and another point mutation on exon 10 (K352*). Though our analysis of the susceptibility to spinosad in field populations indicates that resistance has not yet evolved, a better understanding of the mechanism of action of spinosad is essential to implement sustainable management practices to avoid the development of resistance in field populations.

SUBMITTER: Urena E

PROVIDER: S-EPMC6393475 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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Multiple mutations in the nicotinic acetylcholine receptor Ccα6 gene associated with resistance to spinosad in medfly.

Ureña Enric E Guillem-Amat Ana A Couso-Ferrer Francisco F Beroiz Beatriz B Perera Nathalia N López-Errasquín Elena E Castañera Pedro P Ortego Félix F Hernández-Crespo Pedro P

Scientific reports 20190227 1

Spinosad is an insecticide widely used for the control of insect pest species, including Mediterranean fruit fly, Ceratitis capitata. Its target site is the α6 subunit of the nicotinic acetylcholine receptors, and different mutations in this subunit confer resistance to spinosad in diverse insect species. The insect α6 gene contains 12 exons, with mutually exclusive versions of exons 3 (3a, 3b) and 8 (8a, 8b, 8c). We report here the selection of a medfly strain highly resistant to spinosad, JW-1 ...[more]

PMID: 30814521

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Project description:Spinosad, a widely used and economically important insecticide, targets the nicotinic acetylcholine receptor (nAChRs) of the insect nervous system. Several studies have associated loss of function mutations in the insect nAChR α6 subunit with resistance to spinosad, and in the process identified this particular subunit as the specific target site. More recently a single non-synonymous point mutation, that does not result in loss of function, was identified in spinosad resistant strains of three insect species that results in an amino acid substitution (G275E) of the nAChR α6 subunit. The causal role of this mutation has been called into question as, to date, functional evidence proving its involvement in resistance has been limited to the study of vertebrate receptors. Here we use the CRISPR/Cas9 gene editing platform to introduce the G275E mutation into the nAChR α6 subunit of Drosophila melanogaster. Reverse transcriptase-PCR and sequencing confirmed the presence of the mutation in Dα6 transcripts of mutant flies and verified that it does not disrupt the normal splicing of the two exons in close vicinity to the mutation site. A marked decrease in sensitivity to spinosad (66-fold) was observed in flies with the mutation compared to flies of the same genetic background minus the mutation, clearly demonstrating the functional role of this amino acid substitution in resistance to spinosad. Although the resistance levels observed are 4.7-fold lower than exhibited by a fly strain with a null mutation of Dα6, they are nevertheless predicated to be sufficient to result in resistance to spinosad at recommended field rates. Reciprocal crossings with susceptible fly strains followed by spinosad bioassays revealed G275E is inherited as an incompletely recessive trait, thus resembling the mode of inheritance described for this mutation in the western flower thrips, Frankliniella occidentalis. This study both resolves a debate on the functional significance of a target-site mutation and provides an example of how recent advances in genome editing can be harnessed to study insecticide resistance.

Project description:BackgroundNicotinic acetylcholine receptors (nAChRs) mediate fast synaptic cholinergic transmission in the insect central nervous system. The insect nAChR is the molecular target of a class of insecticides, neonicotinoids. Like mammalian nAChRs, insect nAChRs are considered to be made up of five subunits, coded by homologous genes belonging to the same family. The nAChR subunit genes of Drosophila melanogaster, Apis mellifera and Anopheles gambiae have been cloned previously based on their genome sequences. The silkworm Bombyx mori is a model insect of Lepidoptera, among which are many agricultural pests. Identification and characterization of B. mori nAChR genes could provide valuable basic information for this important family of receptor genes and for the study of the molecular mechanisms of neonicotinoid action and resistance.ResultsWe searched the genome sequence database of B. mori with the fruit fly and honeybee nAChRs by tBlastn and cloned all putative silkworm nAChR cDNAs by reverse transcriptase-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods. B. mori appears to have the largest known insect nAChR gene family to date, including nine alpha-type subunits and three beta-type subunits. The silkworm possesses three genes having low identity with others, including one alpha and two beta subunits, alpha 9, beta2 and beta 3. Like the fruit fly and honeybee counterparts, silkworm nAChR gene alpha 6 has RNA-editing sites, and alpha 4, alpha 6 and alpha 8 undergo alternative splicing. In particular, alternative exon 7 of Bm alpha 8 may have arisen from a recent duplication event. Truncated transcripts were found for Bm alpha 4 and Bm alpha 5.ConclusionB. mori possesses a largest known insect nAChR gene family characterized to date, including nine alpha-type subunits and three beta-type subunits. RNA-editing, alternative splicing and truncated transcripts were found in several subunit genes, which might enhance the diversity of the gene family.

Dataset Information

Multiple mutations in the nicotinic acetylcholine receptor Cc?6 gene associated with resistance to spinosad in medfly.

Publications

Multiple mutations in the nicotinic acetylcholine receptor Ccα6 gene associated with resistance to spinosad in medfly.

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