Emanuel Carola, Weihe Andreas, Graner Andreas, Hess Wolfgang R, Börner Thomas
Humboldt-University, Department of Biology/Genetics, Chausseestr. 117, D-10115 Berlin, Germany.
Plant J. 2004 May;38(3):460-72. doi: 10.1111/j.0960-7412.2004.02060.x.
We have identified the barley gene and cDNA encoding the plastid phage-type RNA polymerase (RNAP), nuclear-encoded plastid RNAP (RpoTp), and the nearly full-length cDNA of the mitochondrial RNAP, nuclear-encoded mitochondrial RNAP (RpoTm). RpoTp spans more than 9000 nt, consists of 19 exons and 18 introns, gives rise to a 3632-nt mRNA and is localized to the long arm of chromosome 1 (7H). The length of the deduced polypeptide is 948 residues. The mRNA levels of RpoTp and RpoTm were determined in roots and primary leaf sections of 7-day-old barley seedlings of the albostrians mutant, which were either phenotypically normal and exhibited a gradient of chloroplast development, or contained ribosome-deficient undifferentiated plastids. Transcript levels of RpoTp and RpoTm in almost all sections reached higher concentrations in plastid ribosome-deficient leaves than in the wild-type material, except in the most basal part of the leaf. These data indicate a role of plastid-to-nucleus signalling in the expression of the two RpoT genes. The mRNA levels of the plastid genes, beta-subunit of plastid-encoded RNAP (rpoB), proteolytic subunit of the Clp protease (clpP) and ribosomal protein Rpl2 (rpl2), all known to be transcribed by the nuclear-encoded RNAP (NEP), followed closely the pattern of RpoTp mRNA accumulation, strongly suggesting that RpoTp and NEP are identical. Transcripts of RpoTm and RpoTm-transcribed mitochondrial genes cytochrome oxidase subunit 2 (coxII) and ATPase subunit 9 (atp9) accumulated to the highest levels in the most basal parts of the leaf and declined considerably towards the leaf tip with a pronounced reduction in green versus white leaves. Our data revealed a marked influence of the developmental stage of the plastid on the expression and activity of organellar phage-type RNAPs and their target genes. Thus, interorganellar cross-talk in the regulated expression of nuclear-encoded plastid and mitochondrial RNAP genes might be a key element governing the concerted expression of genes located within plastids, mitochondria and the nucleus of the plant cell.
我们已经鉴定出了编码质体噬菌体型RNA聚合酶（RNAP）、核编码质体RNAP（RpoTp）以及线粒体RNAP的近全长cDNA（核编码线粒体RNAP，RpoTm）的大麦基因。RpoTp跨度超过9000 nt，由19个外显子和18个内含子组成，产生一个3632 nt的mRNA，定位于1号染色体（7H）的长臂上。推导的多肽长度为948个残基。在白化突变体7天大麦幼苗的根和初生叶切片中测定了RpoTp和RpoTm的mRNA水平，这些幼苗要么表型正常且呈现叶绿体发育梯度，要么含有核糖体缺陷的未分化质体。除了叶片最基部外，几乎所有切片中RpoTp和RpoTm的转录水平在质体核糖体缺陷叶片中都比野生型材料中更高。这些数据表明质体到细胞核的信号传导在两个RpoT基因的表达中起作用。质体基因质体编码RNAP的β亚基（rpoB）、Clp蛋白酶的蛋白水解亚基（clpP）和核糖体蛋白Rpl2（rpl2）的mRNA水平，已知这些基因均由核编码RNAP（NEP）转录，其积累模式与RpoTp mRNA密切相关，强烈表明RpoTp和NEP是相同的。RpoTm以及由RpoTm转录的线粒体基因细胞色素氧化酶亚基2（coxII）和ATP酶亚基9（atp9）的转录本在叶片最基部积累到最高水平，并朝着叶尖显著下降，绿叶与白叶相比下降更为明显。我们的数据揭示了质体发育阶段对细胞器噬菌体型RNAP及其靶基因的表达和活性有显著影响。因此，核编码质体和线粒体RNAP基因调控表达中的细胞器间相互作用可能是控制植物细胞内质体、线粒体和细胞核中基因协同表达的关键因素。
