ARS | Publication request: Physical localization and genetic mapping of fertility restoration gene Rfo in canola (Brassica napus L.)

Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2009
Publication Date: N/A

Interpretive Summary: Canola is a major and important oilseed crop worldwide. Utilization of hybrid seed for canola production has proven to be the most important approach for increasing yield. Like in other major hybrid crops such as maize and rice, commercial production of hybrid seed in canola has been achieved through a set of male-sterile line, maintainer line and restorer line. The Ogu cytoplasm for male fertility and its fertility restorer gene Rfo in canola were originally transferred from radish and have been widely used for canola hybrid production and breeding. The objective of this study was to determine the physical location of the Rfo gene in the canola genome. For physical localization of the Rfo gene, two DNA clones G62 and B420, which were closely linked with the Rfo gene, were used as probes to hybridize with chromosomes of a canola hybrid variety, PHI-46 (46H02), containing the Rfo fragment. The results showed that both clones were physically located at the end of one large chromosome, which morphologically belongs one of three large chromosomes of the C genome. Genetic mapping has confirmed the localization of the Rfo gene to the distal region of linkage group N19 which corresponds to the C genome in canola. This study has provided the evidence of the location of Rfo gene on canola chromosomes and established a basic framework for further physical mapping and manipulation of the gene.

Technical Abstract: The Ogu cytoplasm for male fertility and its fertility restorer gene Rfo in canola (Brassica napus L.) were originally introgressed from radish (Raphanus sativus L.) and have been widely used for canola hybrid production and breeding. The objective of this study was to determine the physical location of the Rfo locus in the canola genome using fluorescence in situ hybridization (FISH) and genetic mapping. For physical localization of the Rfo gene, two BAC (bacterial artificial chromosome) clones G62 and B420, which were closely linked with the Rfo gene, were used as probes to hybridize with the somatic metaphase chromosomes of a canola hybrid variety, PHI-46 (46H02), containing the Rfo fragment. The results showed that both clones were physically located at the end of one large metacentric chromosome. By simultaneous use of two BAC clones and 45S rDNA repeated sequences as the probes, we demonstrated that the large metacentric chromosome probed with the two BAC clones did not carry 45S rDNA repeated sequences. The chromosome was 3.65±0.74 µm in average length (20 cells) and ranked second in size among the chromosomes without 45S rDNAs. The centromere index of the chromosome (20 cells) was calculated as 43.74±4.19. A comparison with previously reported putative karyotypes of B. napus (AACC) and its diploid ancestors B. rapa (AA) and B. oleracea (CC) suggests that the chromosome carrying the Rfo fragment might belong to one of three large metacentric chromosomes of the C genome. Genetic mapping has confirmed the localization of the Rfo fragment to the distal region of linkage group N19 which corresponds to the C genome in B. napus. This study has provided the evidence of the location of Rfo gene on canola chromosomes and established a basic framework for further physical mapping and manipulation of the gene.