Quantitative genetic analysis of attractiveness of yeast products to Drosophila

The interaction between two model organisms, the fruit fly Drosophila melanogaster, and the budding yeast Saccharomyces cerevisiae, is widely perceived as mutually beneficial. The bridge of this biological connection is the volatile compounds from yeast fermentation, which can be attractive to the flies. The generation of volatile molecules derives from complex metabolism and different yeast will generate different combinations of volatiles. The attractiveness to fruit flies can therefore be considered a complex trait. In this study, six strains from SGRP were selected for fermenting commercial grape juice. The attractiveness of these ferments to a wild fruit fly line was then tested. Flies prefer the ferments of the Wine European (WE) strain over the North America (NA) strain. The preference assay was then applied to ferments of genotyped F1 progeny of WE crossed to NA for QTL mapping of genetic variation in attractiveness. GC-MS profiling of all ferments demonstrated that NA could be easily distinguished from other strains. 15 compounds were further quantified and the concentrations in F1 progeny ferments were correlated with genotypes using our r/QTL pipeline. Candidate genes from QTL mapping were tested by reciprocal hemizygosity analysis, validating the impact of two genes, PTC6 and YFL040W. The alleles of these validated genes from NA has better effect on the preference assay than the allele from WE, which is can be considered as antagonistic QTLs. The identification variation in these two genes underpinning metabolic differences, demonstrates how WE and NA have different attraction to one wild fruit fly line.