Genomic imprinting in plants: observations and evolutionary implications

The epigenetic phenomenon of genomic imprinting occurs among both plants an d animals. In species where imprinting is observed, there are parent-of-ori gin effects on the expression of imprinted genes in offspring. This review focuses on imprinting in plants with examples from maize, where gene imprin ting was first described, and Arabidopsis. Our current understanding of imp rinting in plants is presented in the context of cytosine methylation and i mprinting in mammals, where developmentally essential genes are imprinted. Important considerations include the structure and organization of imprinte d genes and the role of regional, differential methylation. Imprinting in p lants may be related to other epigenetic phenomena including paramutation a nd transgene silencing. Finally, we discuss the role of gene structure and evolutionary implications of imprinting in plants.