A Comparative Analysis of DNA Methylation in Diploid and Tetraploid Apple (Malus x domestica Borkh.).

DNA methylation is one of the major epigenetic modifications. It is very important to the regulation of gene expression. Methylation-sensitive amplification polymorphism (MSAP) profiling was applied to a diploid apple cultivar and its derived autotetraploid in order to characterize the level and pattern of DNA methylation at the two different ploidies. The frequency of methylated restriction sites was very similar between the two types (28.0% vs 27.3%), implying that polyploidization had a low effect on the global level of DNA methylation. However, with respect to the pattern of methylation, the frequency of hemi-methylated sites was higher in the tetraploid. When the transcription level of three genes encoding DNA methyltransferase was investigated in various tissues, it was established that MET1 transcript abundance was the lowest of the three genes throughout the plant, while that of DRM2 was high in the leaf, flower and fruit, as was that of CTM3 in the fruit. Polyploidization had no discernible effect on the transcription level of any of the three genes. [ABSTRACT FROM AUTHOR]