RNA editing and DYW-type PPR proteins in the moss Physcomitrella patens

已知与RNA结合的PPR(五肽重复)蛋白参与细胞器RNA的成熟事件。它们广泛地扩展到被子植物中有400多个成员的大基因家族，并频繁地定位于线粒体和叶绿体，这引发了人们对它们作为特异性因子参与这两个植物细胞器中丰富的RNA编辑活动的猜测。这一点最近得到了拟南芥功能遗传分析的大力支持。探索一个独特的羧基末端延伸，它在植物特有的PPR蛋白亚类-dyw结构域中高度保守，我们最近发现，植物特有的dyw蛋白也存在于菊科植物中，但不存在于马鞭草属植物中。这与观察到的RNA编辑现象完全一致，前者存在RNA编辑，而后者不存在。我们还发现，在分离的基础苔属Haplomitrium中，既有频繁的RNA编辑，也有dyw型PPR蛋白多样性。我们现在已经在实验上服从的模式苔藓Physcomitrella patens的转录组中探索了线粒体RNA编辑的多样性。与上述观察结果一致，我们在Physcomitrella(11)中发现了非常有限的RNA编辑位点，这也与现在从完整的苔藓基因组序列中推断出的dyw-蛋白质(10)的低多样性一致。我们建议利用Physcomitrella作为模型系统，采用新颖的RNA免疫共沉淀(RIP-CHIP)方法，从功能上研究dyw蛋白和RNA编辑。

The RNA-binding PPR (Pentatricopeptide Repeat) proteins are known to be involved in organellar RNA maturation events. Their wide expansion into large gene families with more than 400 members in angiosperms and their frequent targeting into mitochondria and chloroplasts had raised speculations on their involvement, as specificity factors, also in the abundant RNA editing events in the two plant organelles. This has recently received strong support from functional genetic analyses in Ambidopsis. Exploring a unique carboxyterminal extension, which is highly conserved in a plant-specific sub-clade of PPR proteins, the DYW domain, we have recently found that the plant-specific DYW proteins are also present in jungermanniid, but not in marchantiid liverworts. This is fully congruent with observations that RNA editing is present in the former but not in the latter liverwort class. We also found both, frequent RNA editing and DYW-type PPR protein diversity, in the isolated, basal liverwort genus Haplomitrium. We have now explored mitochondrial RNA editing diversity in the transcriptome of the experimentally amenable model moss Physcomitrella patens. In line with the above observations, we find a very limited number of RNA editing sites in Physcomitrella (11), again in congruence with a low diversity of DYW-proteins (10) now deducible from the completed moss genomic sequence. We here suggest to make use of Physcomitrella as a model system to functionally investigate DYW proteins and RNA editing, employing the novel RNA immuno co-precipitation (RIP-CHIP) methodology.