MBE Advance Access published online on March 23, 2009
Molecular Biology and Evolution, doi:10.1093/molbev/msp057
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Research Article |
Molecular Evolution and Functional Diversification of Fatty Acid Desaturases after Recurrent Gene Duplication in Drosophila
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* Biodiversity Research Center, Academia Sinica, Taipei, Taiwan 115, ROC
Department of Life Science, & Institute of Ecology and Evolutionary Biology, National Taiwan University, Taipei, Taiwan 106, ROC
Institute of Zoology, National Taiwan University, Taipei, Taiwan 106, ROC
Corresponding author: Shun-Chern Tsaur, E-mail: sctsaur{at}sinica.edu.tw, Phone: +886 2789 9523, Fax: +886 2785 8059
Received for publication December 5, 2008. Revision received February 19, 2009. Accepted for publication February 25, 2009.
Frequent gene duplications in the genome incessantly supply new genetic materials for functional innovation presumably driven by positive Darwinian selection. This mechanism in the desaturase gene family has been proposed to be important in triggering the pheromonal diversification in insects. With the recent completion of a dozen Drosophila genomes, a genome-wide perspective is possible. In this study, we first identified homologs of desaturase genes in 12 Drosophila species and noted that while gene duplication events are relatively frequent, gene losses are not scarce, especially in the desat1-desat2-desatF clade. By reconciling the gene tree with species phylogeny and the chromosomal synteny of the sequenced Drosophila genomes, at least 1 gene loss in desat2 and a minimum of 6 gene gains (resulting in 7 desatF homologs, 
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), 3 gene losses and 1 relocation in desatF were inferred. Upon branching off the ancestral desat1 lineage, both desat2 and desatF gained novel functions through accelerating protein evolution. The amino acid residues under positive selection located near the catalytic sites and the C-terminal region might be responsible for altered substrate selectivity between closely related species. The association between the expression pattern of desatF- and the chemical composition of cuticular hydrocarbons implies that the ancestral function of desatF- is the second desaturation at the 4 carbons after the first double bond in diene synthesis, and the shift from bisexual to female-specific expression in desatF- occurred in the ancestral lineage of D. melanogaster subgroup. A relationship between the number of expressed desatF homologs and the diene diversification has also been observed. These results suggest that the molecular diversification of fatty acid desaturases after recurrent gene duplication plays an important role in pheromonal diversity in Drosophila.
Key Words: cuticular hydrocarbon • fatty acid desaturase • gene duplication • pheromonal diversity • positive selection
1 These authors contributed equally to this work
2 Current address: Department of Life Science, Fu Jen Catholic University, Taipei County, Taiwan 242, ROC