Taste sensitivity to trehalose and its alteration by gene dosage in Drosophila melanogaster

The taste sensitivity to the disaccharide trehalose of Drosophila melanogaster is under the genetic control by the Tre gene on the X chromosome. The gene is genetically dimorphic for high and low sensitivity and is likely to be functioning in the primary step of chemoreception. We have determined the cytological localization of the Tre gene to be between 5A10 and 5B1-3 by analyzing the sensitivity to trehalose in flies which are segmentally aneuploid bearing either deficiencies or duplicated fragments of T(X;Y) translocations. We also constructed flies which are aneuploidy and thus carry different dosage of Tre and/or Tre(+) alleles in order to examine the gene dosage effect on trehalose sensitivity and to deduce the nature of the gene's action. Trehalose sensitivity decreased in females carrying half the normal dosage of a given Tre allele, but a proportional increase in sensitivity was not observed in flies bearing a duplication of the Tre alleles. The changes in sensitivity in various aneuploid flies suggest that there is an upper limit to the number of molecules that can be incorporated into the receptor membrane. Genetic evidence strongly suggests that Tre is the structural gene for the trehalose receptor. We present a model to account for the mechanism of genetical control on the sensitivity to trehalose.