Is the alpha-amylase paralogue Amyrel dispensable in Drosophila melanogaster?

Divergent duplicated gene copies are considered to get new or variant function or regulation through sub- or neofunctionalization. In Drosophila and other flies (Muscomorpha), the alpha-amylase paralogue Amyrel is known to have peculiar enzymological properties compared with the classical enzyme Amy. Yet, its real function in fly biology is unclear. Here, we show that Amyrel and Amy share similar regulation patterns such as sugar downregulation and midgut-specific expression in Drosophila melanogaster. Most regulatory information lies within 500 bp of the upstream sequence, as enhanced green fluorescent protein expression under the Amyrel promoter mimics Amyrel expression quite well. To get an insight into Amyrel function, we knocked out the gene using CRISPR-Cas9. Setting a competition experiment between wild-type (wt) and null alleles over 40 generations, we estimated the selective advantage of the wt to be 2%. However, Amyrel-null mutant lines exhibited no clear defect in several life history traits. Interestingly, while Amyrel had very low expression in young adults, it was significantly upregulated in females aged two months; however, lifespan was not affected. Overall, we were able to document substantial functional and regulatory differences between the Amyrel copy and the regular amylase, and we showed that carrying an Amyrel gene conferred a competitive fitness advantage.