Gene duplication in the major insecticide target site,Rdl, inDrosophila melanogaster

Abstract

The Resistance to Dieldrin gene, Rdl, encodes a GABA-gated chloride channel subunit that is targeted by cyclodiene and phenylpyrazole insecticides. The gene was first characterized in Drosophila melanogaster by genetic mapping of resistance to the cyclodiene dieldrin. The 4,000-fold resistance observed was due to a single amino acid replacement, Ala 301 to Ser. The equivalent change was subsequently identified in Rdl orthologs of a large range of resistant insect species. Here, we report identification of a duplication at the Rdl locus in D. melanogaster. The 113-kb duplication contains one WT copy of Rdl and a second copy with two point mutations: an Ala 301 to Ser resistance mutation and Met 360 to Ile replacement. Individuals with this duplication exhibit intermediate dieldrin resistance compared with single copy Ser 301 homozygotes, reduced temperature sensitivity, and altered RNA editing associated with the resistant allele. Ectopic recombination between Roo transposable elements is involved in generating this genomic rearrangement. The duplication phenotypes were confirmed by construction of a transgenic, artificial duplication integrating the 55.7-kb Rdl locus with a Ser 301 change into an Ala 301 background. Gene duplications can contribute significantly to the evolution of insecticide resistance, most commonly by increasing the amount of gene product produced. Here however, duplication of the Rdl target site creates permanent heterozygosity, providing unique potential for adaptive mutations to accrue in one copy, without abolishing the endogenous role of an essential gene.T he single point mutation in the Resistance to dieldrin (Rdl) gene represents one of the most significant cases of target site resistance to an insecticide yet observed. Cyclodiene resistance was reported in 62% of insecticide resistant species in the 1980s, following widespread use of cyclodiene insecticides, including dieldrin, which started in the 1950s (1). The nature of the genetic target, Rdl, was discovered after dieldrin was discontinued because of the widespread evolution of resistance in many species. Rdl was first discovered in Drosophila melanogaster using a positional cloning approach. High homology to human GABA receptors confirmed it was the first insect ligand-gated chloride channel subunit identified (2-4). A point mutation in the chloride channel pore-lining domain, replacing alanine 301 with serine, was present in all resistant D. melanogaster strains (5). This mutation provided 4,000-fold resistance when homozygous and lower levels of resistance in heterozygotes (2, 6). The homologous mutation was subsequently found in a large number of cyclodiene-resistant species from many insect orders (7-9), as well as a glycine replacement at the homologous site in some resistant strains of Drosophila simulans and other species (5, 10, 11).Characterization of deficiency lines and inversions in D. melanogaster showed that Rdl is an essential gene (3). Thus, the Ala 301 to Ser or Gly mutation in Rdl exhibits unique properties, p...

Impact of transposable elements on insect genomes and biology

“…Indeed, similar or identical TE sequences possess the potential to induce non-allelic homologous recombination (i.e., ectopic recombination) resulting in chromosomal rearrangements such as inversions, deletions and duplications [43,44]. Several studies have provided evidence of the role of TEs as inductors of segmental duplication and inversions in D. melanogaster and A. gambiae [45][46][47].…”

Adaptive deletion in resistance gene duplications in the malaria vector Anopheles gambiae

“…The chromosomal segment concerned by the duplication can indeed far exceed the gene of interest so that the resulting amplicons contain several other genes, as shown for example in Saccharomyces cerevisiae (Koszul, Caburet, Dujon, & Fischer, 2004), D. melanogaster (Remnant et al., 2013), and An. gambiae (Assogba et al., 2016).…”

“…On the contrary, heterogeneous duplications seem to be selected because the two alleles they carry can perform two different functions, by fixing the heterozygote advantage without segregation cost (Haldane, 1932; Milesi, Weill et al., 2017; Spofford, 1969). Such duplications have been documented in a few cases of insecticide resistance, the Rdl gene in Drosophila melanogaster (Remnant et al., 2013), or the ace‐1 gene in Anopheles gambiae and Culex pipiens (Assogba et al., 2016; Labbé, Berthomieu et al., 2007; Milesi, Assogba et al., 2017), where they associate one resistance and one susceptible copy of the gene. While still providing some resistance, this association partially alleviates the deleterious pleiotropic effects (or fitness cost) associated with the resistance allele (Assogba et al., 2015; Labbé et al., 2014; Milesi, Weill et al., 2017).…”

The ace-1 Locus Is Amplified in All Resistant Anopheles gambiae Mosquitoes: Fitness Consequences of Homogeneous and Heterogeneous Duplications

“…However, empirical evidence of heterogeneous duplications remains scarce, and the role of such duplications in adaptive processes is poorly documented. The few examples described to date concern genes targeted by insecticides: rdl in Drosophila melanogaster [16] and the parallel evolution of the ace-1 locus in the West Nile mosquito C . pipiens and the malaria mosquito An .…”