Institut Jean-Pierre Bourgin, UMR1318 INRA-AgroParisTech, INRA Centre de Versailles-Grignon, Route de St-Cyr, Versailles Cedex France.
BMC Plant Biol. 2010 Feb 24;10:35. doi: 10.1186/1471-2229-10-35.
Land plant genomes contain multiple members of a eukaryote-specific gene family encoding proteins with pentatricopeptide repeat (PPR) motifs. Some PPR proteins were shown to participate in post-transcriptional events involved in organellar gene expression, and this type of function is now thought to be their main biological role. Among PPR genes, restorers of fertility (Rf) of cytoplasmic male sterility systems constitute a peculiar subgroup that is thought to evolve in response to the presence of mitochondrial sterility-inducing genes. Rf genes encoding PPR proteins are associated with very close relatives on complex loci.
We sequenced a non-restoring allele (L7rfo) of the Rfo radish locus whose restoring allele (D81Rfo) was previously described, and compared the two alleles and their PPR genes. We identified a ca 13 kb long fragment, likely originating from another part of the radish genome, inserted into the L7rfo sequence. The L7rfo allele carries two genes (PPR-1 and PPR-2) closely related to the three previously described PPR genes of the restorer D81Rfo allele (PPR-A, PPR-B, and PPR-C). Our results indicate that alleles of the Rfo locus have experienced complex evolutionary events, including recombination and insertion of extra-locus sequences, since they diverged. Our analyses strongly suggest that present coding sequences of Rfo PPR genes result from intragenic recombination. We found that the 10 C-terminal PPR repeats in Rfo PPR gene encoded proteins result from the tandem duplication of a 5 PPR repeat block.
The Rfo locus appears to experience more complex evolution than its flanking sequences. The Rfo locus and PPR genes therein are likely to evolve as a result of intergenic and intragenic recombination. It is therefore not possible to determine which genes on the two alleles are direct orthologs. Our observations recall some previously reported data on pathogen resistance complex loci.
陆地植物基因组包含多个编码具有五肽重复（PPR）基序的蛋白的真核生物特异性基因家族的成员。一些 PPR 蛋白被证明参与与细胞器基因表达有关的转录后事件，这种类型的功能现在被认为是它们的主要生物学作用。在 PPR 基因中，细胞质雄性不育系统的育性恢复基因（Rf）构成一个特殊的亚群，被认为是为了应对线粒体不育诱导基因的存在而进化的。编码 PPR 蛋白的 Rf 基因与复杂基因座上非常近的亲属相关。
我们对先前描述的育性恢复基因 D81Rfo 的非恢复等位基因（L7rfo）进行了测序，并比较了这两个等位基因及其 PPR 基因。我们鉴定出一个大约 13 kb 长的片段，可能来自萝卜基因组的另一部分，插入到 L7rfo 序列中。L7rfo 等位基因携带两个与先前描述的恢复基因 D81Rfo 等位基因的三个 PPR 基因（PPR-A、PPR-B 和 PPR-C）密切相关的基因（PPR-1 和 PPR-2）。我们的结果表明，自它们分化以来，Rfo 基因座的等位基因经历了复杂的进化事件，包括重组和外显子序列的插入。我们的分析强烈表明，Rfo PPR 基因的现有编码序列是由基因内重组产生的。我们发现，Rfo PPR 基因编码蛋白的 10 个 C 端 PPR 重复是由 5 个 PPR 重复块的串联重复产生的。
Rfo 基因座的进化似乎比其侧翼序列更为复杂。Rfo 基因座及其内部的 PPR 基因可能是由于基因间和基因内重组而进化的。因此，无法确定两个等位基因上的哪些基因是直接的直系同源基因。我们的观察结果让人想起一些先前报道的关于病原体抗性复杂基因座的数据。
