Meeting Abstract
Mechanisms driving selection on protein coding genes may be best understood by examining them in a comparative evolutionary context. For loci undergoing purifying selection, non-synonymous SNPs leading to functional amino acid changes are unusual and may signal local adaptation. In montane populations of the leaf beetle Chrysomela aeneicollis, electrophoretic variation at the glycolytic enzyme locus phosphoglucose isomerase (Pgi) is concordant with environmental gradients in temperature and oxygen. Pgi genotypes differ in effects of these stressors on survival, performance and reproductive success. In this study, the complete coding sequence of C. aeneicollis Pgi was obtained using PoolSeq and 10X genomics. These data were combined with homologous insect Pgi sequences located from Genbank using a variety of BLAST options. A multiple sequence alignment of 22 insect Pgi coding sequences was 1,689 bp long. There was 30% variation in nucleotide coding sequence leading to 21% variation in amino acids. Pairwise sequence and individual codon comparisons revealed strong evidence for purifying selection at Pgi. The willow beetle Pgi gene is 1,674 base pairs long and contains 7 exons and 6 introns. The SNP responsible for previously described allozyme variation at Pgi is in exon 2. A 3D structure of Colias eurytheme Pgi monomer was used to posit locations of this and other key SNPs on the protein. This analysis revealed a charge-changing substitution (K426D) near the subunit binding site not observed in other insects. In contrast, the SNP characterizing Pgi variation in Sierra populations (D138N) appears to be on the surface of the protein, suggesting a non-enzymatic (moonlighting) function driving differences in performance and reproductive success among Pgi genotypes.
