METHYLATION STATE IN MEDICAGO SATIVA POLYPLOIDIZED PLANTS

Polyploidization is a widespread mechanism in eukaryotes and is predominant in flowering plants. Polyploids are very common among plants and are produced by multiplication of a genome derived from a single species (autopolyploids) or combination of two or more divergent genomes from different species (allopolyploids). Alteration in DNA methylation could regulate gene expression or other important epigenetic processes including dosage compensation, genomic imprinting, nucleolar dominance, de-repression of dormant transposable elements and alterations in chromatin structure among others. Polyploidization is known to involve altered DNA methylation in plants and recent studies provided evidence for changes in newly formed allopolyploids. Several genes responsible for the DNA methylation status have been studied so far. We investigated some members of the three major DNA methyltransferase family genes (MET) and their expression pattern in tetraploid plant of alfalfa (Medicago sativa L. 2n=4x=32) obtained by crossing diploid parents producing 2n gametes (bilaterla sexual polyploidization). Gene expression changes induced by polyploidization have been investigated using qRT-PCR and expression data have been validated to identify genes whose expression is affected by ploidy changes. We also carried out an evolutionary analysis on a collection of methyltransferase homologous genes identified by database searching using as a query M. sativa genes. A comprehensive overview of the distribution of conserved domains was obtained as well as phylogenetic relationships between members of the MET family. Previous observations indicate that the genome methylation status is affected by polyploidization in alfalfa. This expression study may contribute to answer the question of how this occurs, and provide useful information for crop improvement.