title: Completion of the mitochondrial genome sequence of onion (Allium cepa L.) containing the CMS-S male-sterile cytoplasm and identification of an independent event of the ccmFNgene split.
abstract: Cytoplasmic male-sterility (CMS) conferred by the CMS-S cytoplasm has been most commonly used for onion (Allium cepa L.) F1hybrid seed production. We first report the complete mitochondrial genome sequence containing CMS-S cytoplasm in this study. Initially, seven contigs were de novo assembled from 150-bp paired-end raw reads produced from the total genomic DNA using the Illumina NextSeq500 platform. These contigs were connected into a single circular genome consisting of 316,363 bp (GenBank accession: KU318712) by PCR amplification. Although all 24 core protein-coding genes were present, no ribosomal protein-coding genes, except rps12, were identified in the onion mitochondrial genome. Unusual trans-splicing of the cox2 gene was verified, and the cox1 gene was identified as part of the chimeric orf725 gene, which is a candidate gene responsible for inducing CMS. In addition to orf725, two small chimeric genes were identified, but no transcripts were detected for these two open reading frames. Thirteen chloroplast-derived sequences, with sizes of 126-13,986 bp, were identified in the intergenic regions. Almost 10 % of the onion mitochondrial genome was composed of repeat sequences. The vast majority of repeats were short repeats of <100 base pairs. Interestingly, the gene encoding ccmFNwas split into two genes. The ccmFNgene split is first identified outside the Brassicaceae family. The breakpoint in the onion ccmFNgene was different from that of other Brassicaceae species. This split of the ccmFNgene was also present in 30 other Allium species. The complete onion mitochondrial genome sequence reported in this study would be fundamental information for elucidation of onion CMS evolution.
authors.affiliation: Department of Plant Biotechnology, Biotechnology Research Institute, Chonnam National University, Gwangju, 500-757, Republic of Korea.
authors.forename: Bongju
authors.initials: B
authors.lastname: Kim
authors.affiliation: Department of Plant Science, Plant Genomics and Breeding Institute, Research Institute of Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National University, Seoul, 151-921, Republic of Korea.|Phyzen Genomics Institute, 501-1, Gwanak Century Tower, Gwanak-gu, Seoul, 151-836, Republic of Korea.
authors.forename: Kyunghee
authors.initials: K
authors.lastname: Kim
authors.affiliation: Department of Plant Science, Plant Genomics and Breeding Institute, Research Institute of Agriculture and Life Sciences, College of Agriculture and Life Sciences, Seoul National University, Seoul, 151-921, Republic of Korea.
authors.forename: Tae-Jin
authors.initials: TJ
authors.lastname: Yang
authors.affiliation: Department of Plant Biotechnology, Biotechnology Research Institute, Chonnam National University, Gwangju, 500-757, Republic of Korea. dronion@jnu.ac.kr.
authors.forename: Sunggil
authors.initials: S
authors.lastname: Kim
mesh_terms: D001483:Base Sequence; D016000:Cluster Analysis; D019295:Computational Biology / Q000379:methods; D019143:Evolution, Molecular; D017343:Genes, Plant; D054629:Genome, Mitochondrial; D023281:Genomics; D059014:High-Throughput Nucleotide Sequencing; D058977:Molecular Sequence Annotation; D019697:Onions / Q000235:genetics*; D016366:Open Reading Frames; D010802:Phylogeny; D014158:Transcription, Genetic
keywords: Complete mitochondrial genome sequence; Cytoplasmic male-sterility; Next-generation sequencing; Onion (Allium cepa L.); ccmF N gene split