BACKGROUND AND AIMS Dioecious species with well-established sex chromosomes are rare in the plant kingdom. Most sex chromosomes increase in size but no comprehensive analysis of the kind of sequences which drive this expansion has been presented. Here, we analyse sex chromosome structure in common sorrel (Rumex acetosa), a dioecious plant with XY1Y2 sex determination, and we provide the first chromosome specific repeatome analysis for a plant species possessing sex chromosomes. METHODS We flow-sorted and separately sequenced sex chromosomes and autosomes in R. acetosa using the two-dimensional Fluorescence In Situ Hybridization in Suspension (FISHIS) method and Illumina sequencing. We identified and quantified individual repeats using RepeatExplorer, Tandem Repeat Finder and the Tandem Repeats Analysis Program. We employed Fluorescence In Situ Hybridization (FISH) to analyse chromosome localisation of satellites and transposons. KEY RESULTS We identified a number of novel satellites, which have, in a fashion similar to previously known satellites, significantly expanded on the Y chromosome but not as much on the X nor on autosomes. Additionally, the size increase of Y chromosomes is caused by non-LTR and LTR retrotransposons, while only the latter ones contribute to the enlargement of the X chromosome. However, the X chromosome is populated by different LTR retrotransposon lineages than Y chromosomes. CONCLUSIONS The X and Y chromosomes significantly diverged in terms of repeat composition. The lack of recombination probably contributed to the expansion of diverse satellites and microsatellites and faster fixation of newly inserted transposable elements (TEs) on the Y chromosomes. In addition, X and Y chromosomes, despite similar total counts of TEs, significantly differ in the representation of individual TE lineages, which indicates that transposons proliferate preferentially either in the paternal or maternal lineage.

中文翻译：

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马齿苋性染色体重复元件组成的根本不同

背景和目的 具有完善性染色体的雌雄异株物种在植物界很少见。大多数性染色体的大小都会增加，但没有对驱动这种扩展的序列类型进行全面分析。在这里，我们分析了具有 XY1Y2 性别决定的雌雄同株酢浆草 (Rumex acetosa) 的性染色体结构，并为具有性染色体的植物物种提供了第一个染色体特异性重复组分析。方法 我们使用悬浮液中二维荧光原位杂交 (FISHIS) 方法和 Illumina 测序对 R. acetosa 中的性染色体和常染色体进行流式分选和单独测序。我们使用RepeatExplorer、Tandem Repeat Finder 和Tandem Repeats Analysis Program 识别和量化单个重复。我们采用荧光原位杂交 (FISH) 来分析卫星和转座子的染色体定位。主要结果 我们鉴定了许多新的卫星，它们以类似于以前已知的卫星的方式在 Y 染色体上显着扩增，但在 X 和常染色体上没有那么多。此外，Y 染色体的大小增加是由非 LTR 和 LTR 逆转录转座子引起的，而只有后者有助于 X 染色体的增大。然而，X 染色体由与 Y 染色体不同的 LTR 逆转录转座子谱系填充。结论 X 和 Y 染色体在重复组成方面存在显着差异。重组的缺乏可能导致不同卫星和微卫星的扩展以及新插入的转座因子 (TE) 更快地固定在 Y 染色体上。此外，尽管 TE 的总计数相似，但 X 和 Y 染色体在个体 TE 谱系的表示方面存在显着差异，这表明转座子优先在父系或母系中增殖。