Abstract
The increase in availability of whole genome sequences makes it possible to search for evidence of adaptation at an unprecedented scale. Despite recent progress, our understanding of the adaptive process is still very limited due to the difficulties in linking adaptive mutations to their phenotypic effects. In this study, we integrated different levels of biological information to pinpoint the ecologically relevant fitness effects and the underlying molecular and biochemical mechanisms of a putatively adaptive TE insertion in Drosophila melanogaster: the pogo transposon FBti0019627. We showed that other than being incorporated into Kmn1 transcript, FBti0019627 insertion also affects the polyadenylation signal choice of CG11699 gene. Consequently, only the short 3′UTR transcript of CG11699 gene is produced and the expression level of this gene is higher in flies with the insertion. Our results indicated that increased CG11699 expression leads to xenobiotic stress resistance through increased ALDH-III activity: flies with FBti0019627 insertion showed increased survival rate in response to benzaldehyde, a natural xenobiotic, and to carbofuran, a synthetic insecticide. Although differences in survival rate between flies with and without the insertion were not always significant, when they were, they were consistent with FBti0019627 mediating resistance to xenobiotics. Taken together, our results provide a plausible explanation for the increase in frequency of FBti0019627 in natural populations of D. melanogaster and add to the limited number of examples in which a natural genetic mutation has been linked to its ecologically relevant phenotype. Furthermore, the widespread distribution of TEs across the tree of life and conservation of stress response pathways across organisms make our results relevant not only for Drosophila, but for other organisms as well.
Highlights
Understanding the functional consequences of naturally occurring mutations is one of the key challenges in modern biology
While there were no differences in survival rate between flies with and without the insertion in unstressed conditions, we found that flies with the insertion showed increased survival rate compared to flies without the insertion when exposed to high concentrations of benzaldehyde
FBti0019627 insertion mediates resistance to xenobiotics In this study, we showed that FBti0019627 insertion mediates resistance to xenobiotics by increasing CG11699 expression leading to increased ALDH-III activity (Figure 2 and Figure 3)
Summary
Understanding the functional consequences of naturally occurring mutations is one of the key challenges in modern biology. There are some examples in which adaptive mutations have been connected to their phenotypic effects [2,3,4,5], our knowledge of the functional consequences of particular genetic variants is still very limited. Current efforts in genotype-phenotype mapping include projects in several model organisms [8]. Because genes tend to work in evolutionarily conserved pathways, genotype-phenotype insights obtained in D. melanogaster provide valuable information that is relevant for other organisms as well [7]. Most ongoing projects in Drosophila focus on mapping SNP variants to a given set of phenotypic traits such as olfactory behavior or stress resistance [9,10,11,12]. While SNPs certainly contribute to ecologically relevant phenotypes, these efforts ignore other types of mutations, such as those caused by transposable element (TE) insertions
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