DNA methylation is the most common epigenetic phenomenon that controls gene regulation. In animals, it has been implicated in a number of biological phenomena, including genomic imprinting, X- chromosome inactivation, tissue specific gene expression, silencing transposable elements and regulation of gene expression. In plants the function of DNA methylation is well known in silencing of transgenes, transposons and pseudogenes. DNA methylation has also been characterized by self-incompatibility and maternal inheritance. Alteration in DNA methylation is associated with various human diseases. DNA methylation plays fundamental roles in the regulation of gene expression and is essential for plant and animal development. In animals, Dnmt1, Dnmt3a and Dnmt3b maintain the methylation whereas plants have three classes of DNA methyltransferases that maintain the methylation pattern. In this review, we discuss the role of mammalian and plant DNA methyltransferases, focusing on their structural and functional features as well as their roles in gene regulation.
