IZMB - Institut für Zelluläre und Molekulare Botanik, Abteilung Molekulare Evolution, Universität Bonn, Kirschallee 1, 53115, Bonn, Germany.
Plant Mol Biol. 2020 Jan;102(1-2):185-198. doi: 10.1007/s11103-019-00940-9. Epub 2019 Dec 3.
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.
当被子植物中特有的 C-to-U RNA 编辑的双靶标因子失去叶绿体或线粒体靶标时，其剩余靶标对分子适应性的改善证据很少。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本中 C-to-U RNA 编辑的靶标位点。在已经鉴定的 80 多种 PPR 编辑因子中，AEF1（或 MPR25）是一个特殊的例子，因为它同时靶向两个细胞器，并在拟南芥中平行处理一个必需的线粒体（nad5eU1580SL）和一个必需的叶绿体（atpFeU92SL）RNA 编辑位点。在这里，我们探索了 AEF1 及其两个细胞器靶标在被子植物中的广泛保守性。尽管叶绿体编辑位点已通过 C-to-T 转换发生了许多独立的缺失，并且在其他分类群中的线粒体靶标位点至少发生了四次这样的转换，但 AEF1 在 120 多个抽样的被子植物基因组中仍然保持一致的保守性。没有一个案例同时丢失叶绿体和线粒体编辑靶标，也没有发现 AEF1 解体或丢失，这与之前仅靶向一个细胞器的编辑因子的发现形成对比。与大多数 RNA 编辑因子一样，AEF1 的 PPR 阵列根据当前的 PPR-RNA 结合规则，显示出与靶标“概念上更好契合”的潜力。令人惊讶的是，我们仅观察到在 Asterales、Caryophyllales 和 Poales 中叶绿体靶标深度缺失后，对线粒体靶标的适应的证据很少，或者反之，在 Malvales 中线粒体靶标深度缺失后，对剩余叶绿体靶标的适应的证据很少。这些进化观察结果支持这样一种观点，即 PPR-RNA 错配可能对编辑因子的正常功能至关重要。
