The Arabidopsis genome encodes >450 proteins containing the pentatricopeptide repeat (PPR) motif. The PPR proteins are classified into two groups, termed as P and P Long-Short (PLS) classes. Typically, the PLS subclass proteins are mainly involved in the RNA editing of mitochondrial and chloroplast transcripts, whereas most of the analyzed P subclass proteins have been mainly implicated in RNA metabolism, such as 5′ or 3′ transcript stabilization and processing, splicing and translation. Mutations of PPR genes often result in embryogenesis and altered seedling developmental defect phenotypes, but only a limited number of ppr mutants have been characterized in detail. In this report, we show that null mutations in the EMB2794 gene result in embryo arrest, due to altered splicing of nad2 transcripts in the Arabidopsis mitochondria. In angiosperms, nad2 has five exons that are transcribed individually from two mitochondrial DNA regions. Biochemical and in vivo analyses further indicate that recombinant or transgenic EMB2794 proteins bind to the nad2 pre-mRNAs in vitro as well as in vivo, suggesting a role for this protein in trans-splicing of nad2 intron 2 and possibly in the stability of the second pre-mRNA of nad2. Homozygous emb2794 lines, showing embryo-defective phenotypes, can be partially rescued by the addition of sucrose to the growth medium. Mitochondria of rescued homozygous mutant plants contain only traces of respiratory complex I, which lack the NADH-dehydrogenase activity.

中文翻译：

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线粒体五肽重复蛋白EMB2794在拟南芥NADH脱氢酶亚基nad2 mRNA成熟中起关键作用。

拟南芥基因组编码> 450个包含五肽重复序列（PPR）的蛋白质。PPR蛋白分为两类，分别称为P和P长短（PLS）类。通常，PLS亚类蛋白主要参与线粒体和叶绿体转录本的RNA编辑，而大多数分析的P亚类蛋白主要涉及RNA代谢，例如5'或3'转录本的稳定和加工，剪接和翻译。 。PPR基因的突变通常会导致胚胎发生和幼苗发育缺陷表型的改变，但仅对有限数量的ppr突变体进行了详细描述。在本报告中，我们显示EMB2794基因中的无效突变会导致胚胎停滞，这是由于改变了HC1的剪接拟南芥线粒体中的nad2转录本。在被子植物中，nad2具有五个从两个线粒体DNA区域分别转录的外显子。生化和体内分析进一步表明，重组EMB2794蛋白质或转基因EMB2794蛋白质在体外和体内均与nad2 pre-mRNA结合，表明该蛋白质在nad2内含子2反式剪接中可能发挥作用，并可能在第二个内含子的稳定性中起作用。nad2的pre-mRNA 。纯合子emb2794通过向生长培养基中添加蔗糖可以部分挽救显示胚胎缺陷表型的品系。挽救的纯合突变植物的线粒体仅含有痕量的呼吸道复合物I，但缺乏NADH脱氢酶活性。