Emanuel Carola, von Groll Uritza, Müller Margarete, Börner Thomas, Weihe Andreas
Institute of Biology, Genetics, Humboldt University Berlin, Unter den Linden 6, 10099 Berlin, Germany.
Planta. 2006 Apr;223(5):998-1009. doi: 10.1007/s00425-005-0159-y. Epub 2005 Nov 24.
Arabidopsis thaliana possesses three RpoT genes which encode three different phage-type RNA polymerases with yet unknown function in organelle transcription: RpoTm and RpoTp, imported into mitochondria and plastids, respectively, and RpoTmp, co-targeted into both organelles. Expression of the RpoT genes was analyzed by quantitative RT-PCR, histochemical beta-glucuronidase (GUS) assays and in situ hybridization. Transcripts of all three RpoT genes accumulated to very low amounts in all organs. Surprisingly, RT-PCR revealed their highest levels in flower tissues. RpoTm transcripts were the most abundant in all organs, except mature leaves, in which RpoTp transcripts showed the highest accumulation. In the developing seedling, RpoTm::GUS and RpoTmp::GUS expression precedes that of RpoTp::GUS, the latter showing up only 7 days after germination. The RpoTm and RpoTmp promoters expressed GUS mainly in meristematic and mitochondria-rich cells such as the distal part of the root and companion cells flanking the phloem, whereas RpoTp::GUS activity was found in green tissues as the parenchyme cells of young leaves, the primary cortex of the stem, and sepals of buds and young flowers. Sites of GUS expression coincided spatially with those of in situ hybridization. Our data demonstrate an overlapping expression pattern of RpoTm and RpoTmp, and a completely differing pattern of RpoTp expression. The results suggest that RpoTm and RpoTmp recognize different types of mitochondrial promoters. The plastid polymerase RpoTp might play a major role in green tissue, i.e. in chloroplast transcription, whilst the dual-targeted RpoTmp in plastids should function mainly in the transcription of genes in non-green types.
拟南芥拥有三个RpoT基因，它们编码三种不同的噬菌体类型的RNA聚合酶，其在细胞器转录中的功能尚不清楚：RpoTm和RpoTp分别导入线粒体和质体，而RpoTmp则共同靶向这两个细胞器。通过定量RT-PCR、组织化学β-葡萄糖醛酸酶（GUS）测定和原位杂交分析了RpoT基因的表达。所有三个RpoT基因的转录本在所有器官中的积累量都非常低。令人惊讶的是，RT-PCR显示它们在花组织中的水平最高。RpoTm转录本在所有器官中最丰富，但成熟叶除外，在成熟叶中RpoTp转录本积累量最高。在发育中的幼苗中，RpoTm::GUS和RpoTmp::GUS的表达先于RpoTp::GUS，后者在发芽后7天才出现。RpoTm和RpoTmp启动子主要在分生组织和富含线粒体的细胞中表达GUS，如根的远端和韧皮部两侧的伴细胞，而RpoTp::GUS活性则在绿色组织中发现，如幼叶的薄壁细胞、茎的初生皮层以及芽和幼花的萼片。GUS表达位点在空间上与原位杂交位点一致。我们的数据表明RpoTm和RpoTmp的表达模式重叠，而RpoTp的表达模式则完全不同。结果表明，RpoTm和RpoTmp识别不同类型的线粒体启动子。质体聚合酶RpoTp可能在绿色组织中，即在叶绿体转录中起主要作用，而质体中双靶向的RpoTmp应主要在非绿色类型的基因转录中发挥作用。
