Genome Size and the Role of Transposable Elements
Genome Size and the Role of Transposable Elements
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DOI：
10.1007/7397_2015_3
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发表时间：
2015
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影响因子：
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通讯作者：
A. Schulman
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文献类型：
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作者：
A. Schulman
基因组大小和生物体复杂性之间缺乏相关性早期被称为“C 值悖论”；即使考虑基因数量而不是整体有机体复杂性，它仍然成立。现在，大型真核基因组的测序已经彻底解决了这个难题，证明大多数核 DNA 包含各种类型的重复序列，主要是转座元件 (TE)。 TE 的移动和复制能力固有且可变，这解释了基因组大小为何会因它们而发生如此巨大的变化。 I 类 TE 或逆转录转座子具有复制周期，涉及通过逆转录酶将转录的基因组 RNA 复制到 dsDNA 中。由于逆转录转座子的复制生命周期，它们构成了植物中大部分大型基因组。其患病率的差异解释了单倍体水平上基因组大小的大部分变化。然而，逆转录转座子不仅通过上述繁殖生命周期获得，而且还可能通过渐进性小缺失和截短的组合而丢失。 Brachypodium distachyon 的基因组约为 372 Mb，位于开花植物分布的下端。 B．结构的紧凑性尽管二穗基因组包含许多最近插入的转座元件，但其与相对较少数量的逆转录转座子相关。 TheB.尽管反转录转座子在持续繁殖，但二穗基因组似乎通过重组脱落而保持整齐。然而，在逆转录转座子随时间的增加和丢失以及两个超家族（Copia 和 Gypsy）的相对积累方面，染色体之间显示出显着差异。
The lack of correlation between genome size and organismal complexity was early on dubbed the “C-value Paradox;” it holds even when gene number is considered instead of overall organismal complexity. The sequencing of large eukaryotic genomes has now conclusively solved this conundrum with the demonstration that most nuclear DNA comprises various classes of repeats, primarily transposable elements (TEs). The inherent and variable capacity of the TEs for mobility and replication explains how genome size can vary so greatly on their account. The Class I TEs or retrotransposons have a replication cycle involving the copying of a transcribed, genomic RNA into dsDNA by reverse transcriptase. As a result of their replicative life cycle, the retrotransposons comprise most of large genomes among plants; differences in their prevalence explain most of the variation in genome size on the monoploid level. However, retrotransposons are not only gained through the propagative life cycle described above, but they also can be lost through a combination of progressive small deletions and truncations. The genome ofBrachypodium distachyon,at ~372 Mb, is at the lower end of the distribution for flowering plants. The compactness of theB. distachyongenome is correlated with a relatively low number of retrotransposons, although it contains many recently inserted transposable elements. TheB. distachyongenome appears to stay trim through recombinational shedding of retrotransposons, despite their continuing propagation. Nevertheless, the chromosomes show remarkable differences among them regarding the gain and loss of retrotransposons over time and the relative accumulation of the two superfamilies,CopiaandGypsy.