Université Paris-Saclay, INRAE, AgroParisTech, Institut Jean-Pierre Bourgin (IJPB), 78000 Versailles, France.
Nucleic Acids Res. 2023 Aug 11;51(14):7619-7630. doi: 10.1093/nar/gkad493.
Initiation and termination of plant mitochondrial transcription are poorly controlled steps. Precursor transcripts are thus often longer than necessary, and 3'-end processing as well as control of RNA stability are essential to produce mature mRNAs in plant mitochondria. Plant mitochondrial 3' ends are determined by 3'-to-5' exonucleolytic trimming until the progression of mitochondrial exonucleases along transcripts is stopped by stable RNA structures or RNA binding proteins. In this analysis, we investigated the function of the endonucleolytic mitochondrial stability factor 1 (EMS1) pentatricopeptide repeat (PPR) protein and showed that it is essential for the production and the stabilization of the mature form of the nad2 exons 1-2 precursor transcript, whose 3' end corresponds to the 5' half of the nad2 trans-intron 2. The accumulation of an extended rather than a truncated form of this transcript in ems1 mutant plants suggests that the role of EMS1 in 3' end formation is not strictly limited to blocking the passage of 3'-5' exonucleolytic activity, but that 3' end formation of the nad2 exons 1-2 transcript involves an EMS1-dependent endonucleolytic cleavage. This study demonstrates that the formation of the 3' end of mitochondrial transcripts may involve an interplay of endonucleolytic and exonucleolytic processing mediated by PPR proteins.
植物线粒体转录的起始和终止是控制较差的步骤。因此，前体转录本通常比必要的长，并且 3'-末端加工以及 RNA 稳定性的控制对于植物线粒体中产生成熟的 mRNA 是至关重要的。植物线粒体的 3' 末端由 3'-5' 外切核酸酶修剪决定，直到线粒体外切核酸酶沿着转录本的前进被稳定的 RNA 结构或 RNA 结合蛋白所阻止。在这项分析中，我们研究了内切核酸酶线粒体稳定因子 1（EMS1）五肽重复（PPR）蛋白的功能，并表明它对于 nad2 外显子 1-2 前体转录本的成熟形式的产生和稳定是必需的，其 3' 端对应于 nad2 反内含子 2 的 5' 半部分。在 ems1 突变体植物中积累的是扩展形式而不是截断形式的这种转录本，这表明 EMS1 在 3' 末端形成中的作用不仅限于阻止 3'-5' 外切核酸酶活性的传递，而且 nad2 外显子 1-2 转录本的 3' 末端形成涉及 EMS1 依赖性内切核酸酶切割。本研究表明，线粒体转录本 3' 末端的形成可能涉及由 PPR 蛋白介导的内切核酸酶和外切核酸酶加工的相互作用。
