ABSTRACT

Circular RNAs (circRNAs) are regulatory molecules involved in the modulation of gene expression. Although originally assumed as non-coding RNAs, recent studies have evidenced that animal circRNAs can act as translatable transcripts. The study of plant-circRNAs is incipient, and no autonomous coding plant-circRNA has been described yet. Viroids are the smallest plant-pathogenic circRNAs known to date. Since their discovery 50 years ago, viroids have been considered valuable systems for the study of the structure-function relationships in RNA, essentially because they have not been shown to have coding capacity. We used two pathogenic circRNAs (Hop stunt viroid and Eggplant latent viroid) as experimental tools to explore the coding potential of plant-circRNAs. Our work supports that the analysed viroids contain putative ORFs able to encode peptides carrying subcellular localization signals coincident with the corresponding replication-specific organelle. Bioassays in well-established hosts revealed that mutations in these ORFs diminish their biological efficiency. Interestingly, circular forms of HSVd and ELVd were found to co-sediment with polysomes, revealing their physical interaction with the translational machinery of the plant cell. Based on this evidence we hypothesize about the possibility that plant circRNAs in general, and viroids in particular, can act, under certain cellular conditions, as non-canonical translatable transcripts.

 抽象的

环状 RNA (circRNA) 是参与基因表达调节的调节分子。尽管最初被认为是非编码 RNA，但最近的研究证明动物 circRNA 可以充当可翻译的转录本。植物 circRNA 的研究刚刚起步，尚未描述自主编码植物 circRNA。类病毒是迄今为止已知的最小的植物病原性circRNA。自 50 年前发现以来，类病毒一直被认为是研究 RNA 结构与功能关系的有价值的系统，主要是因为它们尚未被证明具有编码能力。我们使用两种致病性circRNA（啤酒花矮化类病毒和茄子潜伏类病毒）作为实验工具来探索植物circRNA的编码潜力。我们的工作支持，分析的类病毒含有假定的ORF，能够编码携带与相应的复制特异性细胞器一致的亚细胞定位信号的肽。在成熟宿主中进行的生物测定表明，这些 ORF 中的突变会降低其生物效率。有趣的是，HSVd 和 ELVd 的圆形被发现与多核糖体共同沉积，揭示了它们与植物细胞翻译机制的物理相互作用。基于这一证据，我们假设植物 circRNA，特别是类病毒，在某些细胞条件下可以作为非规范可翻译转录本发挥作用。