The ABCs of Eye Color in Tribolium castaneum: Orthologs of the Drosophila white, scarlet, and brown Genes

In Drosophila melanogaster , each of the three paralogous ABC transporters, White, Scarlet and Brown, is required for normal pigmentation of the compound eye. We have cloned the three orthologous genes from the beetle Tribolium castaneum . Conceptual translations of Tribolium white ( Tcw ), scarlet ( Tcst ) and brown ( Tcbw ), are 51%, 48% and 32% identical to their respective Drosophila counterparts. We have identified loss-of-eye-pigment strains that bear mutations in Tcw and Tcst : the Tcw gene in the ivory ( i ) strain carries a single-base transversion, which leads to an E→D amino-acid substitution in the highly conserved Walker B motif, while the Tcst gene in the pearl ( p ) strain has a deletion resulting in incorporation of a premature stop codon. In light of these findings the mutant strains i and p are herein renamed white ivory ( w i ) and scarlet pearl ( st p ), respectively. In addition, RNA inhibition of Tcw and Tcst recapitulates the mutant phenotypes, confirming the roles of these genes in normal eye pigmentation, while RNAi of Tcbw provides further evidence that it has no role in eye pigmentation in Tribolium . We also consider the evolutionary implications of our findings.