Upon loss of either its chloroplast or mitochondrial target, a uniquely dual-targeted factor for C-to-U RNA editing in angiosperms reveals low evidence for improved molecular adaptation to its remaining target. RNA-binding pentatricopeptide repeat (PPR) proteins specifically recognize target sites for C-to-U RNA editing in the transcriptomes of plant chloroplasts and mitochondria. Among more than 80 PPR-type editing factors that have meantime been characterized, AEF1 (or MPR25) is a special case given its dual targeting to both organelles and addressing an essential mitochondrial (nad5eU1580SL) and an essential chloroplast (atpFeU92SL) RNA editing site in parallel in Arabidopsis. Here, we explored the angiosperm-wide conservation of AEF1 and its two organelle targets. Despite numerous independent losses of the chloroplast editing site by C-to-T conversion and at least four such conversions at the mitochondrial target site in other taxa, AEF1 remains consistently conserved in more than 120 sampled angiosperm genomes. Not a single case of simultaneous loss of the chloroplast and mitochondrial editing target or of AEF1 disintegration or loss could be identified, contrasting previous findings for editing factors targeted to only one organelle. Like in most RNA editing factors, the PPR array of AEF1 reveals potential for conceptually "improved fits" to its targets according to the current PPR-RNA binding code. Surprisingly, we observe only minor evidence for adaptation to the mitochondrial target also after deep losses of the chloroplast target among Asterales, Caryophyllales and Poales or, vice versa, for the remaining chloroplast target after a deep loss of the mitochondrial target among Malvales. The evolutionary observations support the notion that PPR-RNA mismatches may be essential for proper function of editing factors.

中文翻译：

---

双靶向 RNA 编辑因子 AEF1 在被子植物中普遍保守，并且在其叶绿体或其线粒体靶标丧失时仅显示出微小的适应。

在失去其叶绿体或线粒体靶标后，在被子植物中用于 C-to-U RNA 编辑的独特双靶向因子揭示了改善分子对其剩余靶标的适应性的证据不足。RNA 结合五肽重复 (PPR) 蛋白特异性识别植物叶绿体和线粒体转录组中 C-to-U RNA 编辑的靶位点。在同时表征的 80 多种 PPR 型编辑因子中，AEF1（或 MPR25）是一个特例，因为它既针对细胞器又针对必需的线粒体（nad5eU1580SL）和必需的叶绿体（atpFeU92SL）RNA 编辑位点。与拟南芥平行。在这里，我们探索了 AEF1 及其两个细胞器靶标的被子植物范围内的保护。尽管 C-to-T 转换导致叶绿体编辑位点有许多独立损失，并且在其他分类群的线粒体靶位点至少有四次这样的转换，但 AEF1 在 120 多个采样的被子植物基因组中始终保持保守。没有一例同时丢失叶绿体和线粒体编辑靶标或 AEF1 解体或丢失的病例，这与之前仅针对一个细胞器的编辑因子的发现形成鲜明对比。与大多数 RNA 编辑因子一样，AEF1 的 PPR 阵列揭示了根据当前 PPR-RNA 结合代码在概念上“改进拟合”其目标的潜力。令人惊讶的是，我们仅观察到少量证据表明在 Asterales、Caryophyllales 和 Poales 中叶绿体目标深度丧失后也适应线粒体目标，反之亦然，在 Malvales 线粒体目标深度丢失后剩余的叶绿体目标。进化观察支持这样一种观点，即 PPR-RNA 错配可能对编辑因子的正常功能至关重要。