Abstract

BackgroundThere have been many claims of adaptive molecular evolution, but what role does positive selection play in functional divergence? The aim of this study was to test the relationship between evolutionary and functional shifts with special emphasis on the role of the environment. For this purpose, we studied the fungal lipase/feruloyl esterase A family, whose functional diversification makes it a very promising candidate.ResultsThe results suggested functional shift following a duplication event where neofunctionalisation of feruloyl esterase A had occurred with conservation of the ancestral lipase function. Evolutionary shift was detected using the branch-site model for testing positive selection on individual codons along specific lineages. Positively selected amino acids were detected. Furthermore, biological data obtained from site-directed mutagenesis experiments clearly demonstrated that certain amino acids under positive selection were involved in the functional shift. We reassessed evolutionary history in terms of environmental response, and hypothesized that environmental changes such as colonisation by terrestrial plants might have driven adaptation by functional diversification in Euascomycetes (Aspergilli), thus conferring a selective advantage on this group.ConclusionThe results reported here illustrate a rare example of connection between fundamental events in molecular evolution. We demonstrated an unequivocal connection between evolutionary and functional shifts, which led us to conclude that these events were probably linked to environmental change.

Highlights

  • There have been many claims of adaptive molecular evolution, but what role does positive selection play in functional divergence? The aim of this study was to test the relationship between evolutionary and functional shifts with special emphasis on the role of the environment

  • Thereafter, the step is to identify the impact of environment context in these events and establish whether the functional novelty responds to the environmental change and confers a selective advantage for the species

  • Evolutionary analysis of the homologous proteins from the lipase/feruloyl esterase A family All homologous proteins of the type-A feruloyl esterase (FAEA) from A. niger were included in a phylogenetic analysis, and the corresponding phylogenetic tree was constructed (Fig. 1)

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Summary

Introduction

There have been many claims of adaptive molecular evolution, but what role does positive selection play in functional divergence? The aim of this study was to test the relationship between evolutionary and functional shifts with special emphasis on the role of the environment. Fundamental criteria for studying molecular adaptation during protein evolution would consist in i) detecting evolutionary and functional shifts, ii) linking the sites under positive selection to the functional changes, iii) reassessing these evolutionary events in terms of response to environmental context, iv) studying whether the novelty confers a selective environmental advantage, and v) studying whether functional convergence occurred under the same environmental changes. The case of RNaseI from ruminants offers a strong example, with the novel biochemical function (i.e. the ability to digest single-stranded RNA at low pH) attributed to positively-selected sites [7] This functional shift probably occurred in response to the acquisition of herbivory which conferred an advantage for ruminants eating grass. There are other examples where positively-selected sites are involved in the functional shift but without there being a clear link with the environmental shift [9,10,11,12]

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