Department of Cell Biology and Radiobiology, Institute of Biophysics of the Czech Academy of Sciences, Brno CZ-61265, Czech Republic.
Mendel Centre for Plant Genomics and Proteomics, CEITEC Masaryk University, Brno CZ-62500, Czech Republic.
Nucleic Acids Res. 2021 Jul 21;49(13):7680-7694. doi: 10.1093/nar/gkab545.
The enormous sequence heterogeneity of telomerase RNA (TR) subunits has thus far complicated their characterization in a wider phylogenetic range. Our recent finding that land plant TRs are, similarly to known ciliate TRs, transcribed by RNA polymerase III and under the control of the type-3 promoter, allowed us to design a novel strategy to characterize TRs in early diverging Viridiplantae taxa, as well as in ciliates and other Diaphoretickes lineages. Starting with the characterization of the upstream sequence element of the type 3 promoter that is conserved in a number of small nuclear RNAs, and the expected minimum TR template region as search features, we identified candidate TRs in selected Diaphoretickes genomes. Homologous TRs were then used to build covariance models to identify TRs in more distant species. Transcripts of the identified TRs were confirmed by transcriptomic data, RT-PCR and Northern hybridization. A templating role for one of our candidates was validated in Physcomitrium patens. Analysis of secondary structure demonstrated a deep conservation of motifs (pseudoknot and template boundary element) observed in all published TRs. These results elucidate the evolution of the earliest eukaryotic TRs, linking the common origin of TRs across Diaphoretickes, and underlying evolutionary transitions in telomere repeats.
端粒酶 RNA (TR) 亚基的巨大序列异质性使得在更广泛的系统发育范围内对其进行特征描述变得复杂。我们最近发现，陆地植物 TR 与已知纤毛虫 TR 相似，由 RNA 聚合酶 III 转录，并受 III 型启动子的控制，这使得我们能够设计一种新策略来研究早期分化的绿藻门生物以及纤毛虫和其他有孔虫谱系中的 TR。从鉴定一系列小核 RNA 中保守的 III 型启动子上游序列元件和预期的最小 TR 模板区域开始，我们在选定的有孔虫基因组中鉴定了候选 TR。然后使用同源 TR 构建协方差模型，以鉴定更远缘物种中的 TR。通过转录组数据、RT-PCR 和 Northern 杂交确认了鉴定出的 TR 的转录本。我们的一个候选物的模板作用在 Physcomitrium patens 中得到了验证。二级结构分析表明，所有已发表的 TR 中观察到的基序（假结和模板边界元件）具有深度保守性。这些结果阐明了最早的真核 TR 的进化，将 TR 在有孔虫中的共同起源联系起来，并为端粒重复的进化转变提供了依据。
