Identification of a gene responsible for cytoplasmic male-sterility in onions (Allium cepa L.) using comparative analysis of mitochondrial genome sequences of two recently diverged cytoplasms
Almost identical mitochondrial genome sequences of two recently diverged male-fertile normal and male-sterile CMS-T-like cytoplasms were obtained in onions. A chimeric gene, orf725 , was found to be a CMS-inducing gene.
In onions (Allium cepa L.), cytoplasmic male-sterility (CMS) has been widely used in hybrid seed production. Two types of CMS (CMS-S and CMS-T) have been reported in onions. A complete mitochondrial genome sequence of the CMS-S cytoplasm has been reported in our previous study. Draft mitochondrial genome sequences of male-fertile normal and CMS-T-like cytoplasms are reported in this study. Raw reads obtained from normal and CMS-T-like cytoplasms were assembled into eight and nine almost identical contigs, respectively. After connection and reorganization of contigs by PCR amplification and genome walking, four scaffold sequences with total length of 339 and 180 bp were produced for the normal cytoplasm. A mitochondrial genome sequence of the CMS-T-like cytoplasm was obtained by mapping trimmed reads of CMS-T onto scaffold sequences of the normal cytoplasm. Compared with the CMS-S mitochondrial genome, the normal mitochondrial genome was highly rearranged with 31 syntenic blocks. A total of 499 single nucleotide polymorphisms (SNPs) or insertions/deletions were identified in these syntenic regions. On the other hand, normal and CMS-T-like mitochondrial genome sequences were almost identical except for orf725, a chimeric gene consisting of cox1 with other sequences. Only three SNPs were identified between normal and CMS-T-like syntenic sequences. These results indicate that orf725 is likely to be the casual gene for CMS induction in onions and that CMS-T-like cytoplasm has recently diverged from the normal cytoplasm by introduction of orf725.
This research was supported by Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry (IPET) through Agriculture, Food and Rural Affairs Research Center Support Program (Vegetable Breeding Research Center), funded by the Ministry of Agriculture, Food and Rural Affairs (710011-03), Golden Seed Project (Center for Horticultural Seed Development, No 213007-05-2-SBB10), and a Grant from the Next-Generation BioGreen 21 Program (Plant Molecular Breeding Center No. PJ013400). The authors thank Ji-wha Hur, Jeong-Ahn Yoo, and Su-jung Kim for their dedicated technical assistance.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The authors declare that all experiments complied with current laws of the Republic of Korea.
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