Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX, USA.
Facultad de Ciencias, Instituto de Ciencias Ambientales Y Evolutivas, Universidad Austral de Chile, Valdivia, Chile.
Plant Cell Rep. 2020 Dec;39(12):1669-1685. doi: 10.1007/s00299-020-02594-0. Epub 2020 Sep 21.
tRNA Adenosine Deaminase 3 helps to sustain telomere tracts in a telomerase-independent fashion, likely through regulating cellular metabolism. Telomere length maintenance is influenced by a complex web of chromatin and metabolism-related factors. We previously reported that a lncRNA termed AtTER2 regulates telomerase activity in Arabidopsis thaliana in response to DNA damage. AtTER2 was initially shown to partially overlap with the 5' UTR of the tRNA ADENOSINE DEAMINASE 3 (TAD3) gene. However, updated genome annotation showed that AtTER2 was completely embedded in TAD3, raising the possibility that phenotypes ascribed to AtTER2 could be derived from TAD3. Here we show through strand-specific RNA-Seq, strand-specific qRT-PCR and bioinformatic analyses that AtTER2 does not encode a stable lncRNA. Further examination of the original tad3 (ter2-1/tad3-1) mutant revealed expression of an antisense transcript driven by a cryptic promoter in the T-DNA. Hence, a new hypomorphic allele of TAD3 (tad3-2) was examined. tad3-2 mutants showed hypersensitivity to DNA damage, but no deregulation of telomerase, suggesting that the telomerase phenotype of tad3-1 mutants reflects an off-target effect. Unexpectedly, however, tad3-2 plants displayed progressive loss of telomeric DNA over successive generations that was not accompanied by alteration of terminal architecture or end protection. The phenotype was exacerbated in plants lacking the telomerase processivity factor POT1a, indicating that TAD3 promotes telomere maintenance through a non-canonical, telomerase-independent pathway. The transcriptome of tad3-2 mutants revealed significant dysregulation of genes involved in auxin signaling and glucosinolate biosynthesis, pathways that intersect the stress response, cell cycle regulation and DNA metabolism. These findings indicate that the TAD3 locus indirectly contributes to telomere length homeostasis by altering the metabolic profile in Arabidopsis.
tRNA 腺苷脱氨酶 3 以端粒酶非依赖的方式帮助维持端粒片段，可能通过调节细胞代谢。端粒长度的维持受到染色质和代谢相关因素的复杂网络的影响。我们之前报道称，一种称为 AtTER2 的长非编码 RNA 可调节拟南芥中的端粒酶活性，以响应 DNA 损伤。AtTER2 最初被显示与 tRNA ADENOSINE DEAMINASE 3（TAD3）基因的 5'UTR 部分重叠。然而，更新的基因组注释显示 AtTER2 完全嵌入 TAD3 中，这使得归因于 AtTER2 的表型可能源自 TAD3。在这里，我们通过特异性 RNA-Seq、特异性 qRT-PCR 和生物信息学分析表明，AtTER2 不编码稳定的长非编码 RNA。对原始 tad3（ter2-1/tad3-1）突变体的进一步研究揭示了由 T-DNA 中的隐蔽启动子驱动的反义转录本的表达。因此，研究了 TAD3 的一个新的弱等位基因（tad3-2）。tad3-2 突变体对 DNA 损伤敏感，但端粒酶没有失调，这表明 tad3-1 突变体的端粒酶表型反映了一个脱靶效应。然而，出乎意料的是，tad3-2 植物在连续几代中表现出端粒 DNA 的逐渐丢失，而末端结构或末端保护没有改变。在缺乏端粒酶持续因子 POT1a 的植物中，该表型加剧，表明 TAD3 通过非典型的端粒酶非依赖途径促进端粒维持。tad3-2 突变体的转录组显示，参与生长素信号转导和硫代葡萄糖苷生物合成的基因显著失调，这些途径与应激反应、细胞周期调控和 DNA 代谢相交。这些发现表明，TAD3 通过改变拟南芥的代谢特征，间接地促进端粒长度的动态平衡。
