Abstract

A previous study describing the genome of Zostera marina, the most widespread seagrass in the Northern hemisphere, revealed some genomic signatures of adaptation to the aquatic environment such as the loss of stomatal genes, while other functions such as an algal-like cell wall composition were acquired. Beyond these, the genome structure and organization were comparable with those of the majority of plant genomes sequenced, except for one striking feature that went unnoticed at that time: the presence of human-like instead of the expected plant-type telomeric sequences. By using different experimental approaches including fluorescence in situ hybridization (FISH), genome skimming by next-generation sequencing (NGS), and analysis of non-coding transcriptome, we have confirmed its telomeric location in the chromosomes of Z. marina. We have also identified its telomerase RNA (TR) subunit, confirming the presence of the human-type telomeric sequence in the template region. Remarkably, this region was found to be very variable even in clades with a highly conserved telomeric sequence across their species. Based on this observation, we propose that alternative annealing preferences in the template borders can explain the transition between the plant and human telomeric sequences. The further identification of paralogues of TR in several plant genomes led us to the hypothesis that plants may retain an increased ability to change their telomeric sequence. We discuss the implications of this occurrence in the evolution of telomeres while introducing a mechanistic model for the transition from the plant to the human telomeric sequences.

中文翻译：

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Zostera滨海区的类人端粒显示出从植物到人端粒序列的过渡模式。

摘要

先前的一项研究描述了北半球最普遍的海草藻（Zostera marina）的基因组，揭示了一些适应水生环境的基因组特征，例如气孔基因的丧失，而其他功能（如藻类细胞壁的组成）获得。除此以外，基因组的结构和组织与大多数已测序植物基因组的结构和组织具有可比性，只是当时没有注意到的一个引人注目的特征是：存在人样而不是预期的植物型端粒序列。通过使用不同的实验方法，包括原位荧光杂交（FISH），通过下一代测序（NGS）进行基因组略读以及非编码转录组的分析，我们已经证实了其端粒位于滨海梭菌的染色体中。我们还确定了其端粒酶RNA（TR）亚基，确认了模板区域中人型端粒序列的存在。值得注意的是，即使在进化枝中其物种中端粒序列高度保守的进化枝中，该区域也变化很大。基于此观察，我们建议模板边界中的替代退火偏好可以解释植物和人类端粒序列之间的过渡。在几种植物基因组中TR旁系同源物的进一步鉴定使我们得出这样的假设，即植物可能保留增加的改变其端粒序列的能力。我们讨论了端粒进化中这种现象的含义，同时介绍了一种从植物到人类端粒序列过渡的机制模型。