Abstract
Insect odorant-binding proteins function in the sensing of odors, tastes, and pheromones. Genes encoding two odorant-binding proteins, Obp57d and Obp57e, were identified to be involved in the behavioral adaptation of Drosophila sechellia to its host plant. The two genes are expressed in cells associated with taste sensilla on the legs, and the expression pattern in the legs is conserved among closely related species. To identify the cis-regulatory elements necessary for the expression in the leg sensilla, the promoter sequences of Obp57d and Obp57e were compared among species. Two types of conserved sequence-motifs were found as candidate cis-regulatory elements. Functions of these conserved elements in the promoters of D. melanogaster Obp57d and Obp57e were examined by using a newly constructed vector that combines the advantages of φC31 integrase-based transformation and gypsy transposable-element-derived insulators. By GFP-reporter assay using the new vector, it was confirmed that these conserved elements are necessary for the expression in the legs, working synergistically with each other to affect the expression level. Single-nucleotide substitutions in these elements dramatically changed the promoter activity. These results provide insight into the molecular mechanism for evolution of adaptive behavior via modulation of OBP expression levels.
Highlights
The evolution of gene expression is an important mechanism generating variation in phenotypes
A GFP-reporter assay showed that a small, 4-bp insertion found in the promoter of D. sechellia Obp57e results in the loss of expression in the D. melanogaster background, suggesting that the evolution of host-plant preference was caused by changes in the regulatory mechanisms of OBP expression (Matsuo et al, 2007)
Conserved motifs in the promoter sequences of Obp57d and Obp57e In our previous study, GFPreporter constructs using the promoters from several species in the melanogaster species group reproduced the expression pattern of Obp57d and Obp57e in the legs of D. melanogaster, suggesting that these promoters maintain conserved cis-regulatory elements
Summary
The evolution of gene expression is an important mechanism generating variation in phenotypes. Genes encoding two odorant-binding proteins, Obp57d and Obp57e, were identified to be involved in the evolution of hostplant preference in Drosophila sechellia (Matsuo et al, 2007; Matsuo, 2008a). A GFP-reporter assay showed that a small, 4-bp insertion found in the promoter of D. sechellia Obp57e results in the loss of expression in the D. melanogaster background, suggesting that the evolution of host-plant preference was caused by changes in the regulatory mechanisms of OBP expression (Matsuo et al, 2007). To find cis-regulatory elements in the promoters of Obp57d and Obp57e, conserved sequence motifs were searched for in the promoter sequences. Two types of cis-regulatory elements that are necessary for expression in the legs were identified
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