Molecular Evolution and Functional Diversification of Fatty Acid Desaturases after Recurrent Gene Duplications in Drosophila
author: Dr. Shu Fang zofang@sinica.edu.tw [Fang, Shu, zofang@gate.sinica.edu.tw merged with this user on 19-Feb-2008 by Raffaele, Elizabeth] Academia Sinica Biodiversity Research Center Taipei Taiwan, Provinc; Dr. Chau-Ti Ting ctting@ntu.edu.tw [Jan 20 2003 - Added using 'Add Reviewer on the fly' by Prof. Pierre Capy Ting, Chau-Ti, ctting@life.nthu.edu.tw [Last in: 11-Mar-2007 12:32] merged with this user o; Mr. Cheng-Ruei Lee qqsmallfrog@yahoo.com.tw Academia Sinica Biodiversity Research Center Taipei Taiwan, Province of China; Mr. Kuang-Hsi Chu wester830007@yahoo.com.tw National Taiwan University Institute of Zoology Taipei Taiwan, Province of China; Dr. Shun-Chern Tsaur sctsaur@sinica.edu.tw Academia Sinica Biodiversity Research Center Taipei Taiwan, Province of China; Dr. Chuan-Chan Wang gwennywang@ntu.edu.tw Academia Sinica Biodiversity Research Center Taipei Taiwan, Province of China
language: en

Abstract

Frequent gene duplications in the genome incessantly supply new genetic materials for functional innovation presumably driven by positive Darwinian selection. This mechanism in desaturase gene family has been proposed to be important in triggering the pheromonal diversification in insects. With the recent completion of a dozen <i>Drosophila</i> genomes, it provides a genome-wide perspective on the evolutionary patterns of desaturase genes. In this study, we first identified homologs of desaturase genes in 12 <i>Drosophila</i> species and noted that while gene duplication events are relatively frequent, gene losses are not scarce, especially in the <i>desat1-desat2-desatF</i> clade. By reconciling the gene tree with species phylogeny and the chromosomal synteny of the sequenced <i>Drosophila</i> genomes, at least 1 gene loss in <i>desat2</i> and a minimum of 6 gene gains (resulting in 7 <i>desatF</i> homologs, <i>α-η</i>), 3 gene losses plus 1 relocation in <i>desatF</i> were inferred. Upon branching off the ancestral <i>desat1</i> lineage, both <i>desat2</i> and <i>desatF</i> gained novel functions through accelerating protein evolution. The amino acid residues under positive selection located nearby the catalytic sites and the C-terminal region might be responsible for altered substrate selectivity between closely related species. Moreover, the association between the expression pattern of <i>desatF-α</i> and the chemical composition of cuticular hydrocarbons implies that the ancestral function of <i>desatF-α</i> 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 <i>desatF-α</i> occurred in the ancestral lineage of <i>D. melanogaster</i> subgroup. A relationship between the number of expressed <i>desatF</i> homologs and the diene diversification has also been observed. These results suggest that the molecular diversification of fatty acid desaturases after recurrent gene duplications plays an important role in pheromonal diversity.