Evidence for Positive Selection within the PgiC1 Locus in the Grass Festuca ovina.

Yuan Li,Tomas Johansson,Anders Tunlid,Björn Canbäck,Honor C Prentice,Diego F Gomez-Casati

doi:10.1371/journal.pone.0125831

Abstract

The dimeric metabolic enzyme phosphoglucose isomerase (PGI, EC 5.3.1.9) plays an essential role in energy production. In the grass Festuca ovina, field surveys of enzyme variation suggest that genetic variation at cytosolic PGI (PGIC) may be adaptively important. In the present study, we investigated the molecular basis of the potential adaptive significance of PGIC in F. ovina by analyzing cDNA sequence variation within the PgiC1 gene. Two, complementary, types of selection test both identified PGIC1 codon (amino acid) sites 200 and 173 as candidate targets of positive selection. Both candidate sites involve charge-changing amino acid polymorphisms. On the homology-modeled F. ovina PGIC1 3-D protein structure, the two candidate sites are located on the edge of either the inter-monomer boundary or the inter-domain cleft; examination of the homology-modeled PGIC1 structure suggests that the amino acid changes at the two candidate sites are likely to influence the inter-monomer interaction or the domain-domain packing. Biochemical studies in humans have shown that mutations at several amino acid sites that are located close to the candidate sites in F. ovina, at the inter-monomer boundary or the inter-domain cleft, can significantly change the stability and/or kinetic properties of the PGI enzyme. Molecular evolutionary studies in a wide range of other organisms suggest that PGI amino acid sites with similar locations to those of the candidate sites in F. ovina may be the targets of positive/balancing selection. Candidate sites 200 and 173 are the only sites that appear to discriminate between the two most common PGIC enzyme electromorphs in F. ovina: earlier studies suggest that these electromorphs are implicated in local adaptation to different grassland microhabitats. Our results suggest that PGIC1 sites 200 and 173 are under positive selection in F. ovina.

Highlights

The identification of the key genes and the key mutations that underlie fitness variation is one of the central tasks in evolutionary biology [1]
The present study of PgiC1 cDNA sequences in F. ovina used two, complementary, types of approach to test for positive selection on PGIC1
On the homology-modeled PGIC1 protein structure, the two candidate sites are located on the edge of either the inter-monomer boundary or the inter-domain cleft

Summary

Introduction

The identification of the key genes and the key mutations that underlie fitness variation is one of the central tasks in evolutionary biology [1]. Candidate genes that may be involved in fitness differences in natural populations of non-model species can often be proposed on the basis of information from earlier studies on model organisms [1]. One such candidate is the gene that codes for the dimeric enzyme phosphoglucose isomerase (PGI) (EC 5.3.1.9) [1]. Variation in PGI activity is expected to affect the activity of the glycolytic pathway, which plays a central role in the production of energy and is likely to be implicated in organisms’ adaptive responses to their environment

Methods

Results

Conclusion