The Maize Methylome

DNA methylation is a chromatin modification that has generally been associated with gene silencing or heterochromatin. Plants have mechanisms to allow for the stable inheritance of DNA methylation through mitosis or meiosis. This creates the potential for DNA methylation to provide epigenetic inheritance for traits in maize and other crops. Epigenetics refers to heritable transmission of information that is not solely attributable to DNA sequence. Several examples of epigenetic inheritance were first described in maize including paramutation, imprinting, and transposable element inactivation. There is evidence that DNA methylation is associated with each of these epigenetic phenomena. In addition, natural variation for epigenetic states may contribute substantially to variation among maize inbreds and could be an important source of variation for crop improvement. Advances in our understanding of the molecular mechanisms controlling DNA methylation in Arabidopsis have provided clues to the genes and pathways likely to be important in maize. Recent technological developments have provided the opportunity to characterize the genome-wide distribution of DNA methylation in the maize genome. This has provided insights into the patterns of DNA methylation in plant species with large, complex genomes and has led to the identification of potential cryptic genomic information that is silenced by DNA methylation. We will summarize current understanding of the mechanisms that regulate methylation and factors that influence variation and stability of the maize methylome