title: Evolution of land plant genes encoding L-Ala-D/L-Glu epimerases (AEEs) via horizontal gene transfer and positive selection.
abstract: BACKGROUND
  The L-Ala-D/L-Glu epimerases (AEEs), a subgroup of the enolase superfamily, catalyze the epimerization of L-Ala-D/L-Glu and other dipeptides in bacteria and contribute to the metabolism of the murein peptide of peptidoglycan. Although lacking in peptidoglycan, land plants possess AEE genes that show high similarity to those in bacteria.
  
  
  RESULTS
  Similarity searches revealed that the AEE gene is ubiquitous in land plants, from bryophytas to angiosperms. However, other eukaryotes, including green and red algae, do not contain genes encoding proteins with an L-Ala-D/L-Glu_epimerase domain. Homologs of land plant AEE genes were found to only be present in prokaryotes, especially in bacteria. Phylogenetic analysis revealed that the land plant AEE genes formed a monophyletic group with some bacterial homologs. In addition, land plant AEE proteins showed the highest similarity with these bacterial homologs and shared motifs only conserved in land plant and these bacterial AEEs. Integrated information on the taxonomic distribution, phylogenetic relationships and sequence similarity of the AEE proteins revealed that the land plant AEE genes were acquired from bacteria through an ancient horizontal gene transfer (HGT) event. Further evidence revealed that land plant AEE genes had undergone positive selection and formed the main characteristics of exon/intron structures through gaining some introns during the initially evolutionary period in the ancestor of land plants.
  
  
  CONCLUSIONS
  The results of this study clearly demonstrated that the ancestor of land plants acquired an AEE gene from bacteria via an ancient HGT event. Other findings illustrated that adaptive evolution through positive selection has contributed to the functional adaptation and fixation of this gene in land plants.
authors: Jiangsu Provincial Key Laboratory of Crop Genetics and Physiology, College of Agriculture, Yangzhou University, Yangzhou, 225009, China.
authors: Zefeng
authors: Z
authors: Yang
authors: Yifan
authors: Y
authors: Wang
authors: Yong
authors: Y
authors: Zhou
authors: Qingsong
authors: Q
authors: Gao
authors: Enying
authors: E
authors: Zhang
authors: Lei
authors: L
authors: Zhu
authors: Yunyun
authors: Y
authors: Hu
authors: Chenwu
authors: C
authors: Xu
mesh_terms: D044002:Bryophyta / Q000235:genetics; D019143:Evolution, Molecular; D005091:Exons / Q000235:genetics; D022761:Gene Transfer, Horizontal / Q000235:genetics*; D007438:Introns / Q000235:genetics; D019684:Magnoliopsida / Q000235:genetics; D010802:Phylogeny; D019998:Racemases and Epimerases / Q000235:genetics*
chemical_list: D019998:Racemases and Epimerases