Origin and evolution of the Amyrel gene in the alpha-amylase multigene family of Diptera.

Alpha-amylase genes often form multigene families in living organisms. In Diptera, a remote paralog, Amyrel, had been discovered in Drosophila, where this gene is currently used as a population and phylogenetic marker. The putative encoded protein has about 40% divergence with the classical amylases. We have searched the presence of the paralog in other families of Diptera to track its origin and understand its evolution. Amyrel was detected in a number of families of Muscomorpha (Brachycera-Cyclorrapha), suggesting an origin much older than previously thought. It has not been found elsewhere to date, and it is absent from the Anopheles gambiae genome. The intron-exon structures of the genes found so far suggest that the ancestral gene (before the duplication which gave rise to Amyrel) had two introns, and that subsequent, repeated and independent loss of one or both introns occurred in some Muscomorpha families. It seems that the Amyrel protein has experienced specific amino acid substitutions in regions generally well conserved in amylases, raising the possibility of peculiar, functional adaptations of this protein.