Role of alternative polyadenylation in epigenetic silencing and antisilencing

Abstract

Epigenetic marks such as DNA methylation and histone modifications are widely involved in regulating different aspects of developmental and environmental responses (1). Meanwhile, DNA methylation and histone modification are also used constitutively to silence transposable elements and repeat elements (TREs) (2). Such TRE-mediated silencing should necessarily be limited to the intended targets only and not spread to adjacent genes and their regulatory elements. Higher eukaryotic organisms have evolved antisilencing mechanisms to keep the balance between silencing and antisilencing that is required for precise gene expression regulation. Earlier work revealed that repressor of silencing 1 (ROS1) is one such antisilencing gene (3). Recently, a group of unique antisilencing genes has been discovered, including enhanced downy mildew 2 (EDM2) reported both by Lei et al. in PNAS (4) and earlier by Tsuchiya and Eulgem (5), anti-silencing 1 (ASI1) by Wang et al. (6), and increase in bonsai methylation 1 (IBM1) by Saze et al. (7). What distinguishes the latter group of genes from ROS1 is that they seem to be involved in posttranscriptional regulation through alternative polyadenylation (APA).