Department of Agronomy, Purdue University, West Lafayette, IN 47907, USA.
Protein Cell. 2013 Jul;4(7):493-501. doi: 10.1007/s13238-013-3037-6. Epub 2013 Jun 23.
Transposable elements (TEs), particularly, long terminal repeat retrotransposons (LTR-RTs), are the most abundant DNA components in all plant species that have been investigated, and are largely responsible for plant genome size variation. Although plant genomes have experienced periodic proliferation and/or recent burst of LTR-retrotransposons, the majority of LTR-RTs are inactivated by DNA methylation and small RNA-mediated silencing mechanisms, and/or were deleted/truncated by unequal homologous recombination and illegitimate recombination, as suppression mechanisms that counteract genome expansion caused by LTR-RT amplification. LTR-RT DNA is generally enriched in pericentromeric regions of the host genomes, which appears to be the outcomes of preferential insertions of LTR-RTs in these regions and low effectiveness of selection that purges LTR-RT DNA from these regions relative to chromosomal arms. Potential functions of various TEs in their host genomes remain blurry; nevertheless, LTR-RTs have been recognized to play important roles in maintaining chromatin structures and centromere functions and regulation of gene expressions in their host genomes.
转座元件（TEs），特别是长末端重复逆转录转座子（LTR-RTs），是所有已研究过的植物物种中最丰富的 DNA 成分，它们在很大程度上导致了植物基因组大小的变异。尽管植物基因组经历了周期性的增殖和/或 LTR-逆转录转座子的近期爆发，但大多数 LTR-RTs 被 DNA 甲基化和小 RNA 介导的沉默机制失活，和/或通过非同源重组和非规范重组而缺失/截断，作为抵消 LTR-RT 扩增引起的基因组扩张的抑制机制。LTR-RT DNA 通常在宿主基因组的着丝粒区域富集，这似乎是 LTR-RT 优先在这些区域插入的结果，以及相对于染色体臂，选择从这些区域清除 LTR-RT DNA 的效率较低的结果。各种 TEs 在其宿主基因组中的潜在功能仍然模糊不清；然而，已经认识到 LTR-RTs 在维持宿主基因组中的染色质结构和着丝粒功能以及调节基因表达方面发挥着重要作用。
