Characterization of two alcohol dehydrogenase (Adh) loci from the olive fruit fly, Bactrocera (Dacus) oleae and implications for Adh duplication in dipteran insects

We report the cloning and structural characterization of two Adh loci of th e olive fruit fly, Bactrocera oleae, Each of the two genes, named Adh1 and Adh2, consists of three exons and two introns for a total length of 1981 an d 988 nucleotides, respectively. Their deduced amino acid sequences of 257 and 258 residues exhibit a 77% identity and display the characteristics of the insect ADH enzymes, which belong to the short-chain dehydrogenases/redu ctases family. The Adh genes of B. oleae are compared to the two genes of t he Mediterranean fly, Ceratitis capitata, the only other species of the Tep hritidae family in which the Adh genes have been studied. On the basis of a mino acid divergence the four genes form two clusters each containing one g ene from each species, as expected if there was one duplication event befor e speciation. On the basis of nucleotide sequence the four sequences form t wo clusters each containing the two sequences from the same species, as exp ected if there was a separate duplication event in each species, To help de cide between the two alternatives, we compared at both the amino acid and D NA level the Adh genes of five Drosophila species that are known to carry t wo such genes and observed that, with only one exception at the amino acid level, conspecific loci cluster together. We conclude that the information we have at present does not allow a firm choice between the hypothesis of a single duplication event that occurred before the split of Bactrocera and Ceratitis from their common ancestor and the hypothesis of two independent duplication events, one in each of the two genera.