Duplication of the Rdl GABA receptor subunit gene in an insecticide-resistant aphid, Myzus persicae

Mol Gen Genet. 1998 Nov;260(2-3):165-75. doi: 10.1007/s004380050882.


Resistance to cyclodiene insecticides is associated with replacements of a single amino acid (alanine 302) in a gamma-aminobutyric acid (GABA) receptor subunit encoded by the single-copy gene Resistance to dieldrin (Rdl). Alanine 302 is predicted to reside within the second membrane-spanning region of the Rdl receptor, a region that is thought to line the integral chloride ion channel pore. In all cyclodiene-resistant insects studied to date, this same alanine residue is replaced either by a serine, or, in some resistant strains of Drosophila simulans, a glycine residue. Therefore, individuals can carry only two different Rdl alleles. In contrast, here we report the presence of up to four different Rdl-like alleles in individual clones of the green peach aphid, Myzus persicae. In addition to the wild-type copy of Rdl gene (encoding A302 or allele A), M. persicae carries three other alleles with the following amino acid replacements: A302-->Glycine (allele G), A302-->SerineTCG (allele S) and A302-->SerineAGT (allele S'). Evidence from direct nucleotide sequencing and Single Stranded Conformational Polymorphism (SSCP) analysis shows that at least three of these different Rdl alleles (i.e. A, G and S) are commonly present in individual aphids or aphid clones. Southern analysis using allele-specific probes and analysis of sequences downstream of the exon containing the resistance-associated mutation confirm the presence of two independent Rdl-like loci in M. persicae. One locus carries the susceptible alanine (A) and/or resistant glycine (G) allele while the other carries the two serine alleles (S or S'). Whereas resistance levels are correlated with the glycine replacement, the S allele was present in all aphid clones, regardless of their resistance status. These results suggest that target site insensitivity is associated with replacements at the first (A/G) but not the second (S/S') locus. Phylogenetic analysis of nucleotide sequences indicates that both putative aphid Rdl loci are monophyletic with respect to other insect Rdl genes and may have arisen through a recent gene duplication event. The implications of this duplication with respect to insecticide resistance and insect GABA receptor subunit diversity are discussed.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alanine
  • Alleles
  • Amino Acid Sequence
  • Animals
  • Aphids / drug effects
  • Aphids / genetics*
  • Base Sequence
  • Blotting, Southern
  • Drosophila Proteins*
  • Endosulfan / pharmacology
  • Gene Duplication
  • Insecticide Resistance / genetics*
  • Introns
  • Molecular Sequence Data
  • Mutation
  • Phylogeny*
  • Receptors, GABA-A / genetics*
  • Sequence Analysis, DNA


  • Drosophila Proteins
  • Rdl protein, Drosophila
  • Receptors, GABA-A
  • Alanine
  • Endosulfan