title: Evolutionary history of Methyltransferase 1 genes in hexaploid wheat.
abstract: BACKGROUND
  Plant and animal methyltransferases are key enzymes involved in DNA methylation at cytosine residues, required for gene expression control and genome stability. Taking advantage of the new sequence surveys of the wheat genome recently released by the International Wheat Genome Sequencing Consortium, we identified and characterized MET1 genes in the hexaploid wheat Triticum aestivum (TaMET1).
  
  
  RESULTS
  Nine TaMET1 genes were identified and mapped on homoeologous chromosome groups 2A/2B/2D, 5A/5B/5D and 7A/7B/7D. Synteny analysis and evolution rates suggest that the genome organization of TaMET1 genes results from a whole genome duplication shared within the grass family, and a second gene duplication, which occurred specifically in the Triticeae tribe prior to the speciation of diploid wheat. Higher expression levels were observed for TaMET1 homoeologous group 2 genes compared to group 5 and 7, indicating that group 2 homoeologous genes are predominant at the transcriptional level, while group 5 evolved into pseudogenes. We show the connection between low expression levels, elevated evolution rates and unexpected enrichment in CG-dinucleotides (CG-rich isochores) at putative promoter regions of homoeologous group 5 and 7, but not of group 2 TaMET1 genes. Bisulfite sequencing reveals that these CG-rich isochores are highly methylated in a CG context, which is the expected target of TaMET1.
  
  
  CONCLUSIONS
  We retraced the evolutionary history of MET1 genes in wheat, explaining the predominance of group 2 homoeologous genes and suggest CG-DNA methylation as one of the mechanisms involved in wheat genome dynamics.
authors.forename: Mélanie
authors.initials: M
authors.lastname: Thomas
authors.forename: Lise
authors.initials: L
authors.lastname: Pingault
authors.forename: Axel
authors.initials: A
authors.lastname: Poulet
authors.forename: Jorge
authors.initials: J
authors.lastname: Duarte
authors.forename: Mickaël
authors.initials: M
authors.lastname: Throude
authors.forename: Sébastien
authors.initials: S
authors.lastname: Faure
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Pichon
authors.forename: Etienne
authors.initials: E
authors.lastname: Paux
authors.forename: Aline Valeska
authors.initials: AV
authors.lastname: Probst
authors.affiliation: UMR CNRS 6293 INSERM U 1103 Clermont Université, Genetics Reproduction and Development (GReD), 24 avenue des Landais, BP80026, 63171 Aubière Cedex, France. christophe.tatout@univ-bpclermont.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Tatout
mesh_terms: D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics*; D019175:DNA Methylation; D019143:Evolution, Molecular; D020440:Gene Duplication; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics*; D011123:Polyploidy; D014908:Triticum / Q000201:enzymology* / Q000235:genetics
chemical_list: D010940:Plant Proteins; D004248:DNA (Cytosine-5-)-Methyltransferases