Laboratoire de Microbiologie Fondamentale et Pathogénicité UMR5234, Centre National de la Recherche Scientifique and Université Bordeaux Segalen, 146 rue Léo Saignat, 33076, Bordeaux Cedex, France.
Curr Genet. 2011 Oct;57(5):317-25. doi: 10.1007/s00294-011-0349-z. Epub 2011 Jun 24.
In the leptosporangiate fern Osmunda regalis, cox1 gene is disrupted by a 1071-nucleotide-long group I intron that is homologous to the Marchantia polymorpha cox1 intron 4 (cox1i395g1). This intron, which shares 89% sequence identity with its bryophyte counterpart, lost the capacity to encode for a maturase due to insertion/deletion mutations. The cox1 coding region is interrupted by a stop codon in both exons. The cox1 transcript undergoes 58 C-to-U and 13 U-to-C conversions, including the suppression of two stop codons that result in the recovery of a functional cox1 ORF. Interestingly, 4 C-to-U conversions found in mRNA precursors showed that the O. regalis cox1i395g1 intron is efficiently edited. These modifications improved the sequence identity with the Marchantia cox1i395 intron. In particular, the RNA editing events affect regions involved in secondary and tertiary structures of the intron, restoring three base pairing in the structural P5a and P9 helices, and correcting a highly conserved U in the P7 helix that contributes to the catalytic core. Moreover, cox1 intron orthologous from three different fern species were found to be edited by both C-to-U and U-to-C conversions in P7 and P9. Thus, RNA editing helps to correct the conserved domains of group I introns in "true ferns", suggesting a possible link between editing and splicing. We present here the first experimental evidence of RNA editing concerning a group I intron in plant organelles.
在小型叶木贼科植物金毛狗（Osmunda regalis）中，cox1 基因被一个 1071 个核苷酸长的 I 型内含子所破坏，该内含子与卷柏科植物 cox1 内含子 4（cox1i395g1）同源。这个内含子与苔藓植物同源序列的同源性高达 89%，由于插入/缺失突变而失去了编码成熟酶的能力。cox1 编码区在两个外显子中都被一个终止密码子所打断。cox1 转录本经历了 58 次 C 到 U 和 13 次 U 到 C 的转换，包括两个终止密码子的抑制，从而恢复了功能正常的 cox1 ORF。有趣的是，在 mRNA 前体中发现的 4 次 C 到 U 的转换表明，O. regalis cox1i395g1 内含子的编辑效率很高。这些修饰提高了与卷柏 cox1i395 内含子的序列一致性。特别是，RNA 编辑事件影响了内含子的二级和三级结构区域，恢复了结构 P5a 和 P9 螺旋中的三个碱基配对，并纠正了 P7 螺旋中高度保守的 U，该 U 有助于催化核心。此外，在三个不同的蕨类植物物种中发现的 cox1 内含子在 P7 和 P9 都经历了 C 到 U 和 U 到 C 的转换编辑。因此，RNA 编辑有助于纠正“真蕨类植物”中 I 型内含子的保守结构域，这表明编辑和剪接之间可能存在联系。我们在这里首次提供了有关植物细胞器中 I 型内含子的 RNA 编辑的实验证据。
