School of Life Sciences, University of Sussex, Brighton, UK.
Department of Ecology and Evolutionary Biology, UC Irvine, Irvine, CA 92697, USA.
Curr Opin Plant Biol. 2016 Apr;30:123-33. doi: 10.1016/j.pbi.2016.02.009. Epub 2016 Mar 4.
Transposable elements (TEs) constitute the majority of plant genomes, but most are epigenetically inactivated by their host. Research over the last decade has elucidated many of the molecular components that are required for TE silencing. In contrast, the evolutionary dynamics between TEs and silencing pathways are less clear. Here, we discuss current information about these dynamics from both mechanistic and evolutionary perspectives. We highlight new evidence that palindromic sequences within TEs may act as signals for host recognition and that cis-regulatory regions of TEs may be sites of ongoing arms races with host defenses. We also discuss patterns of TE aging after they are silenced; while there is not yet a consensus, it appears that TEs are removed more rapidly near genes, such that older TE insertions tend to be farther from genes. We conclude by discussing the energetic costs for maintaining silencing pathways, which appear to be substantive. The maintenance of silencing pathways across many species suggests that epigenetic emergencies are frequent.
转座元件 (TEs) 构成了植物基因组的大部分，但大多数通过其宿主被表观遗传失活。过去十年的研究阐明了许多用于 TE 沉默的分子组成部分。相比之下，TE 和沉默途径之间的进化动态不太清楚。在这里，我们从机制和进化的角度讨论这些动态的当前信息。我们强调了新的证据表明 TE 中的回文序列可能作为宿主识别的信号，并且 TE 的顺式调控区域可能是与宿主防御持续军备竞赛的地点。我们还讨论了沉默后 TE 衰老的模式；虽然还没有共识，但似乎在基因附近更快地去除 TE，因此较旧的 TE 插入往往离基因更远。最后，我们讨论了维持沉默途径的能量成本，这似乎是实质性的。沉默途径在许多物种中的维持表明表观遗传紧急情况很频繁。
