A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, 119992 Moscow, Russia.
Konstantinov St.-Petersburg Nuclear Physics Institute, National Research Center «Kurchatov Institute», 188300 Gatchina, Russia.
Int J Mol Sci. 2022 Nov 11;23(22):13890. doi: 10.3390/ijms232213890.
Retrozymes are nonautonomous retrotransposons with hammerhead ribozymes in their long terminal repeats (LTRs). Retrozyme transcripts can be self-cleaved by the LTR ribozyme, circularized, and can undergo RNA-to-RNA replication. Here, we demonstrate that the genome contains hundreds of retrozyme loci, of which nine represent full-length retrozymes. The LTR contains a promoter directing retrozyme transcription. Although retrozyme RNA is easily detected in plants, the LTR region is heavily methylated, pointing to its transcriptional silencing, which can be mediated by 24 nucleotide-long retrozyme-specific RNAs identified in . A transcriptome analysis revealed that half of the retrozyme-specific RNAs in plant leaves have no exact matches to genomic retrozyme loci, containing up to 13% mismatches with the closest genomic sequences, and could arise as a result of many rounds of RNA-to-RNA replication leading to error accumulation. Using a cloned retrozyme copy, we show that retrozyme RNA is capable of replication and systemic transport in plants. The presented data suggest that retrozyme loci in the genome are transcriptionally inactive, and that circular retrozyme RNA can persist in cells due to its RNA-to-RNA replication and be transported systemically, emphasizing functional and, possibly, evolutionary links of retrozymes to viroids-noncoding circular RNAs that infect plants.
反转录酶是具有锤头核酶的非自主反转录转座子，其长末端重复序列（LTR）中含有核酶。反转录酶转录本可以通过 LTR 核酶自我切割、环化，并进行 RNA 到 RNA 的复制。在这里，我们证明基因组中含有数百个反转录酶基因座，其中 9 个代表全长反转录酶。LTR 包含一个指导反转录酶转录的启动子。尽管植物中很容易检测到反转录酶 RNA，但 LTR 区域高度甲基化，表明其转录沉默，这可以通过在 中鉴定的 24 个核苷酸长的反转录酶特异性 RNA 来介导。转录组分析显示，植物叶片中一半的反转录酶特异性 RNA 与基因组反转录酶基因座没有完全匹配，与最近的基因组序列最多有 13%的不匹配，可能是由于多次 RNA 到 RNA 复制导致错误积累而产生的。使用克隆的反转录酶副本，我们表明反转录酶 RNA 能够在植物中进行复制和系统运输。所提供的数据表明， 基因组中的反转录酶基因座转录失活，并且由于其 RNA 到 RNA 的复制，环状反转录酶 RNA 可以在细胞中持续存在，并进行系统运输，强调了反转录酶与类病毒（感染植物的非编码环状 RNA）之间的功能和可能的进化联系。
