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Open Access Highly Accessed Research article

Complete sequence of heterogenous-composition mitochondrial genome (Brassica napus) and its exogenous source

Juan Wang1, Jinjin Jiang1, Xiaoming Li1, Aimin Li2, Yongtai Zhang2, Rongzhan Guan3 and Youping Wang1*

Author affiliations

1 Jiangsu Provincial Key Laboratory of Crop Genetics and Physiology, Yangzhou University, Yangzhou, 225009, China

2 Jiangsu Institute of Agricultural Science in the Lixiahe District, Yangzhou, 225009, China

3 State Key Laboratory of Crop Genetics and Germplasm Enhancement, Nanjing Agricultural University, Nanjing, 210095, China

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Citation and License

BMC Genomics 2012, 13:675  doi:10.1186/1471-2164-13-675

Published: 28 November 2012

Abstract

Background

Unlike maternal inheritance of mitochondria in sexual reproduction, somatic hybrids follow no obvious pattern. The introgressed segment orf138 from the mitochondrial genome of radish (Raphanus sativus) to its counterpart in rapeseed (Brassica napus) demonstrates that this inheritance mode derives from the cytoplasm of both parents. Sequencing of the complete mitochondrial genome of five species from Brassica family allowed the prediction of other extraneous sources of the cybrids from the radish parent, and the determination of their mitochondrial rearrangement.

Results

We obtained the complete mitochondrial genome of Ogura-cms-cybrid (oguC) rapeseed. To date, this is the first time that a heterogeneously composed mitochondrial genome was sequenced. The 258,473 bp master circle constituted of 33 protein-coding genes, 3 rRNA sequences, and 23 tRNA sequences. This mitotype noticeably holds two copies of atp9 and is devoid of cox2-2. Relative to nap mitochondrial genome, 40 point mutations were scattered in the 23 protein-coding genes. atp6 even has an abnormal start locus whereas tatC has an abnormal end locus. The rearrangement of the 22 syntenic regions that comprised 80.11% of the genome was influenced by short repeats. A pair of large repeats (9731 bp) was responsible for the multipartite structure. Nine unique regions were detected when compared with other published Brassica mitochondrial genome sequences. We also found six homologous chloroplast segments (Brassica napus).

Conclusions

The mitochondrial genome of oguC is quite divergent from nap and pol, which are more similar with each other. We analyzed the unique regions of every genome of the Brassica family, and found that very few segments were specific for these six mitotypes, especially cam, jun, and ole, which have no specific segments at all. Therefore, we conclude that the most specific regions of oguC possibly came from radish. Compared with the chloroplast genome, six identical regions were found in the seven mitochondrial genomes, which show that the Brassica family has a stable chloroplast-derived source.