Epigenetic Control of Gene Expression in Maize.

Epigenetic gene regulation is important for proper development and gene expression in eukaryotes. Maize has a large and complex genome that includes abundant repetitive sequences which are frequently silenced by epigenetic mechanisms, making it an ideal organism to study epigenetic gene regulation. Epigenetic modifications are chromosome-bound, heritable changes to the genome that do not affect the DNA sequence, and can include DNA methylation, histone modification, and RNA processing. Our appreciation and understanding of epigenetic regulation has grown with the field since its inception ∼65 years ago. Early examples of epigenetic regulation were often associated with transposable elements, starting with McClintock's early work in the 1950s. The observation of other intriguing phenotypes segregating in non-Mendelian ratios in the 1950s provided material for genetic screens that allowed for mechanistic studies of epigenetic regulation that have come to fruition within the past 20 years. The relationship between epigenetic mechanisms and genome organization has become clear with the application of new technologies to characterize maize epigenomes. Our understanding of epigenetic control of gene expression now encompasses the context of genes relative to DNA methylation, chromatin structure, and transposable element content.