Structural features and expression analysis of a linear mitochondrial plasmid in rapeseed (Brassica napus L.)
Structural features and expression analysis of a linear mitochondrial plasmid in rapeseed (Brassica napus L.)
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DOI：
10.1007/s00438-002-0711-4
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发表时间：
2002-08-01
影响因子：
3.1
通讯作者：
Sato, H
中科院分区：
文献类型：
--
作者：
Handa, H;Itani, K;Sato, H
油菜（Brassica napes L.）某些品种的线粒体中存在一个长约11 kb的线性质粒分子。这种质粒可以通过花粉从父本遗传，也可以通过通常的母系途径遗传，尽管油菜籽中主要的线粒体基因组是母系遗传的。我们确定了该质粒DNA的完整核苷酸序列，并阐明了其遗传结构。线性质粒的长度为11，640 bp。在质粒分子的末端是327 bp的反向重复序列。质粒DNA的GC含量为30.9%;因此，与高等植物中的主要线粒体基因组相比，质粒相当富含AT。该质粒有6个ORF，其中两个分别编码噬菌体型DNA聚合酶和噬菌体型RNA聚合酶。RT-PCR分析表明，所有六个ORF的转录，和所有四个ORF的负链可能是共转录从一个单一的启动子位于末端反向重复。我们还表明，在这里，至少有三个的六个ORF被翻译成蛋白质在油菜籽线粒体，并在花中表达相对较高的水平，如Western分析所示。这些结果表明，这种线性DNA分子能够作为自主复制子进行复制，并在油菜籽线粒体中表达其携带的基因。
A linear plasmid molecule about 11 kb in length is present in the mitochondria of some varieties of rapeseed (Brassica napes L.). This plasmid can be inherited from the male parent, through the pollen, as well as by the usual maternal route, although the main mitochondrial genome is maternally inherited in rapeseed. We determined the complete nucleotide sequence of this plasmid DNA and clarified its genetic organization. The length of the linear plasmid is 11,640 bp. At the termini of the plasmid molecule are inverted repeats of 327 bp. The GC content of the plasmid DNA is 30.9%; thus, the plasmid is quite AT-rich compared to the main mitochondrial genome in higher plants. The plasmid has six ORFs, two of which encode a phage-type DNA polymerase and a phage-type RNA polymerase, respectively. RT-PCR analyses revealed that all six ORFs are transcribed, and all four ORFs on the minus strand are probably cotranscribed from a single promoter located in the terminal inverted repeat. We also show here that at least three of the six ORFs are translated into proteins in rapeseed mitochondria, and expressed at relatively high levels in flowers, as shown by Western analysis. These results suggest that this linear DNA molecule is able to replicate as an autonomous replicon and to express the genes it carries in rapeseed mitochondria.