The mitochondrial genome of an asymmetrically cell-fused rapeseed, Brassica napus, containing a radish-derived cytoplasmic male sterility-associated gene.

Shin-Ichi Arimura,Shungo Yanase,Nobuhiro Tsutsumi,Nobuya Koizuka

doi:10.1266/ggs.18-00005

Shin-Ichi Arimura, Shungo Yanase + Show 2 more

Open Access

https://doi.org/10.1266/ggs.18-00005

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Abstract

Cytoplasmic male sterility (CMS) is an agronomically important trait whose causative genes are located in the mitochondrial genome. A CMS rapeseed, Brassica napus 'SW18', was made 25 years ago by an asymmetric (or "donor-recipient") cell fusion between B. napus 'Westar' and a CMS radish (Raphanus sativus 'Kosena'), in order to transfer the radish CMS-associated gene without disturbing the rapeseed features. Here, we determined the nucleotide sequences of the mitochondrial genomes of Kosena radish and SW18. SW18 has a recombinant mitochondrial genome, which includes the whole 222-kb genome of Westar (54 genes) and a total of 23 kb insertions of four fragments from Kosena radish (three genes: orf125, trnfM and atp1). All of the Kosena radish-derived fragments in the SW18 mitochondrial genome had sequences at their ends (ranging from 63 bp to 628 bp) that are identical to the sequences at the sites of insertion on the Westar rapeseed-derived mitochondrial genome. This suggests that these insertions were mediated by homologous recombination. These results confirm at the nucleotide level that a desired CMS-associated gene (orf125) along with a few extraneous genes from radish were successfully transferred.

Highlights

Cytoplasmic male sterility (CMS) is frequently used in F1 hybrid breeding for efficient F1 seed production, because it causes bisexual plants to become female, resulting in secure outcrossing (Chen and Liu, 2014)
We compared the mitochondrial genome of SW18 rapeseed, the asymmetrically cell-fused line, with the mitochondrial genomes of the two parent lines, Westar
The sequences determined in this study were deposited in DDBJ as accession numbers AP018472 (Kosena radish mitochondrial genome), AP018473, AP018474 and AP018475

Summary

Introduction

Cytoplasmic male sterility (CMS) is frequently used in F1 hybrid breeding for efficient F1 seed production, because it causes bisexual plants to become female, resulting in secure outcrossing (Chen and Liu, 2014). Attempts to transfer Ogura cytoplasm to Brassica vegetables by hybridization between radish and rapeseed and backcrossing to the rapeseed failed to produce a good product, because genes other than CMS genes that were acquired from radish mitochondrial or plastid genomes caused inappropriate phenotypes (yellowish and slow-growth)

Results

Conclusion