Size and location of radish 1 chromosome regions carrying the fertility restorer Rfk1 gene in spring turnip rape

TL;DR

This study localizes the radish chromosome region carrying the Rfk1 fertility restorer gene in turnip rape using GISH and BAC-FISH, revealing its unstable integration as monosomic or disomic addition lines.

Contribution

It provides the first physical localization of the Rfk1 gene in turnip rape chromosomes and identifies its specific chromosomal position and stability issues.

Findings

Rfk1 gene located on radish chromosome regions in turnip rape.

Restorer lines are monosomic or disomic addition lines with unstable fertility restoration.

Homologous regions in B. rapa genome identified near Rfk1 location.

Abstract

In spring turnip rape (Brassica rapa L. spp. oleifera) the most promising F1 hybrid system would be the Ogu-INRA CMS/Rf system. A Kosena fertility restorer gene Rfk1, homologue of the Ogura restorer gene Rfo, was successfully transferred from oilseed rape into turnip rape and that restored the fertility in female lines carrying Ogura cms. The trait was, however, unstable in subsequent generations. The physical localization of the radish chromosomal region carrying the Rfk1 gene was investigated using 8 GISH (genomic in situ hybridization) and BAC-FISH (bacterial artificial chromosome fluorescence in situ hybridization) methods. The metaphase chromosomes were hybridized using radish DNA as the genomic probe and BAC64 probe, which is linked with Rfo gene. Both probes showed a signal in the chromosome spreads of the restorer line 4021-2 Rfk of turnip rape but not in the negative control line 4021B. The GISH analyses clearly showed that the turnip rape restorer plants were either monosomic (2n=2x=20+1R) or disomic (2n=2x=20+2R) addition lines with one or two copies of a single alien chromosome region originating from radish. In the BAC-FISH analysis, double dot signals were detected in sub-terminal parts of the radish chromosome arms showing that the fertility restorer gene Rfk1 was located in this additional radish chromosome. Detected disomic addition lines were found to be unstable for turnip rape hybrid production. Using the BAC-FISH analysis, weak signals were sometimes visible in two chromosomes of turnip rape and a homologous region of Rfk1 in chromosome 9 of the B. rapa A genome was verified with BLAST analysis. In the future this homologous area in A genome could be substituted with radish chromosome area carrying the Rfk1 gene.