Transposable elements (TEs) are DNA sequences that can mobilize and proliferate throughout eukaryotic genomes. Previous studies have shown that in plant genomes, TEs can influence gene expression in various ways such as inserting in introns or exons to alter transcript structure and content, and providing novel promoters and regulatory elements to generate new regulatory patterns. Furthermore, TEs can also regulate gene expression at the epigenetic level by modifying chromatin structure, changing DNA methylation status and generating small RNAs. In this study, we demonstrated that Ac/fAc transposable elements are able to induce ectopic gene expression by duplicating and shuffling enhancer elements. Ac/fAc elements belong to the hAT family of Class II TEs. They can undergo standard transposition events, which involve the two termini of a single transposon, or alternative transposition events which involve the termini of two different, nearby elements. Our previous studies have shown that alternative transposition can generate various genome rearrangements such as deletions, duplications, inversions, translocations and Composite Insertions (CIs). We identified over 50 independent cases of CIs generated by Ac/fAc alternative transposition and analyzed 10 of them in detail. We show that these CIs induced ectopic expression of the maize pericarp color 2(p2) gene, which encodes a Myb-related protein. All the CIs analyzed contain sequences including a transcriptional enhancer derived from the nearby p1 gene, suggesting that the CI-induced activation of p2 is effected by mobilization of the p1 enhancer. This is further supported by analysis of a mutant in which the CI is excised and p2 expression is lost. These results show that alternative transposition events are not only able to induce genome rearrangements, but also generate Composite Insertions that can control gene expression.

中文翻译：

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玉米基因的异位表达是由选择性转座产生的复合插入诱导的。

转座元件 (TE) 是可以在整个真核基因组中动员和增殖的 DNA 序列。先前的研究表明，在植物基因组中，TE可以通过多种方式影响基因表达，例如插入内含子或外显子以改变转录本结构和内容，以及提供新的启动子和调控元件以产生新的调控模式。此外，TE还可以通过修饰染色质结构、改变DNA甲基化状态和生成小RNA来在表观遗传水平上调节基因表达。在这项研究中，我们证明了Ac/fAc转座元件能够通过复制和改组增强子元件来诱导异位基因表达。Ac/fAc元件属于II 类 TE 的hAT家族。它们可以经历标准转座事件（涉及单个转座子的两个末端）或替代转座事件（涉及两个不同的邻近元件的末端）。我们之前的研究表明，选择性转座可以产生各种基因组重排，例如删除、重复、倒位、易位和复合插入（CI）。我们识别了 50 多个由Ac/fAc替代转座产生的 CI 独立案例，并详细分析了其中 10 个。我们发现这些 CI 诱导玉米果皮颜色 2 (p2)基因的异位表达，该基因编码 Myb 相关蛋白。所有分析的 CI 都含有来自附近p1基因的转录增强子序列，表明 CI 诱导的p2激活是通过p1增强子的动员来实现的。对 CI 被切除且p2表达丢失的突变体的分析进一步支持了这一点。这些结果表明，替代转座事件不仅能够诱导基因组重排，还能产生可以控制基因表达的复合插入。