Abstract
There is growing experimental evidence from both animals and plants that changes in the environment can have profound effects on the epigenetic state of chromatin in nuclei. The epigenetic state of chromatin and the cell-specific transcription profile of genes are mitotically stable and, sometimes, can be transmitted across generations. Plants often show stable transgenerational inheritance of induced alterations of epigenetic states that are associated with morphologically or physiologically distinctive phenotypes. This pattern of inheritance may be due to the fact that germ cells produced by terminal differentiation and to the absence of appreciable epigenetic reprogramming during the life cycle. Recent advances in mass sequencing technology have accelerated the decoding of the epigenomes of various tissues and cell types and provided new insights into the dynamics of epigenetic changes during the plant life cycle and in response to environmental challenges. As plants have a sessile nature, the epigenetic regulation of genes and transposable elements in response to environmental stresses might be crucial for the generation and inheritance of phenotypic variations in plants in natural populations.
Highlights
The epigenetic regulation of gene expression is mediated by a variety of covalent modifications of the nucleotides and chromatin, such as methylation of cytosine residues in the DNA and post-translational alterations of core histone proteins, and by production of small RNA molecules (Law and Jacobsen, 2010; Saze et al, 2012)
Alteration of DNA methylation patterns at some loci were associated with changes in gene expression levels, whereas other loci did not show a significant alteration in expression in response to the methylation changes, indicating the complexity of the effects of DNA methylation and other epigenetic marks on gene transcription behavior
It is known that 5-methyl cytosine (5mC) has a potentially high rate of mutagenic changes (Turner, 2009)
Summary
The epigenetic regulation of gene expression is mediated by a variety of covalent modifications of the nucleotides and chromatin, such as methylation of cytosine residues in the DNA and post-translational alterations of core histone proteins, and by production of small RNA molecules (Law and Jacobsen, 2010; Saze et al, 2012). Epigenetic modifications can be inherited in both a short-term (mitotic) and long-term (meiotic) manner to achieve an active or silent state in particular genes without changes to the primary DNA sequences. Genomes have methylation of CG sites within actively transcribed genes (Zhang et al, 2006; Zilberman et al, 2007); gene body methylation shows evolutionary conservation in plants and animals (Feng et al, 2010; Zemach et al, 2010). The function of the gene body methylation is still enigmatic, DNA methylation has been shown to be preferentially targeted to the nucleosomes of exons in animals and plants, suggesting that DNA methylation has a role in exon definition (Chodavarapu et al, 2010). In addition to epigenetic silencing mechanisms that primarily target TEs and repeat sequences, plants have evolved pathways that prevent accumulation of heterochromatic epigenetic modifications (Fig. 1). I review the evidence on the heritability of epigenetic changes, which has a potential impact on longterm phenotypic variation in plant populations
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