Stop codon readthrough (SCR) is the process of continuation of translation beyond the stop codon, generating protein isoforms with C-terminal extensions. SCR has been observed in viruses, fungi, and multicellular organisms, including mammals. However, SCR is largely unexplored in plants. In this study, we have analyzed ribosome profiling datasets to identify mRNAs that exhibit SCR in Arabidopsis thaliana. Analyses of the ribosome density, ribosome coverage, and three-nucleotide periodicity of the ribosome profiling reads in the mRNA region downstream of the stop codon provided strong evidence for SCR in mRNAs of 144 genes. We show that SCR generated putative evolutionarily conserved nuclear localization signals, transmembrane helices, and intrinsically disordered regions in the C-terminal extensions of several of these proteins. Furthermore, gene ontology functional enrichment analysis revealed that these 144 genes belong to three major functional groups—translation, photosynthesis, and abiotic stress tolerance. Using a luminescence-based readthrough assay, we experimentally demonstrated SCR in representative mRNAs belonging to each of these functional classes. Finally, using microscopy, we show that the SCR product of one gene that contains a nuclear localization signal at the C-terminal extension, CURT1B, localizes to the nucleus as predicted. Based on these observations, we propose that SCR plays an important role in plant physiology by regulating protein localization and function.

终止密码子通读 (SCR) 是在终止密码子之外继续翻译的过程，产生具有 C 末端延伸的蛋白质同种型。已在病毒、真菌和多细胞生物（包括哺乳动物）中观察到 SCR。然而，SCR 在植物中很大程度上尚未开发。在这项研究中，我们分析了核糖体分析数据集，以识别在拟南芥中表现出 SCR 的 mRNA. 对终止密码子下游 mRNA 区域中核糖体分析读数的核糖体密度、核糖体覆盖率和三核苷酸周期性的分析为 144 个基因的 mRNA 中的 SCR 提供了强有力的证据。我们表明，SCR 在其中几种蛋白质的 C 末端延伸中产生推定的进化上保守的核定位信号、跨膜螺旋和本质上无序的区域。此外，基因本体功能富集分析表明，这 144 个基因属于三个主要功能组——翻译、光合作用和非生物胁迫耐受性。使用基于发光的通读分析，我们通过实验证明了属于这些功能类别中的每一个的代表性 mRNA 中的 SCR。最后，使用显微镜，CURT1B，如预测的那样定位于细胞核。基于这些观察，我们提出 SCR 通过调节蛋白质定位和功能在植物生理中发挥重要作用。