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Title: High-resolution tyramide-FISH mapping of markers tightly linked to the male-fertility restoration (Ms) locus of onion

Author
item KHRUSTALEVA, L - Russian Agrarian University
item JIANG, J - University Of Wisconsin
item Havey, Michael

Submitted to: Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2015
Publication Date: 12/24/2015
Publication URL: http://handle.nal.usda.gov/10113/61913
Citation: Khrustaleva, L., Jiang, J., Havey, M.J. 2015. High-resolution tyramide-FISH mapping of markers tightly linked to the male-fertility restoration (Ms) locus of onion. Theoretical and Applied Genetics. 129(3):535-545. doi: 10.1007/s00122-015-2646-2.

Interpretive Summary: Using a highly sensitive fluorescent technique, genetic markers linked to the Ms locus were physically located on onion chromosomes. Relatively short genomic amplicons (846 to 2251 bp) and a cDNA clone (666 bp) were visualized in 9 to 42% of observed cells. The genetic markers were assigned to proximal locations close to the centromere on the long arm of chromosome 2. This is the first report of physical mapping to an onion chromosome of molecular markers linked to an important locus. Because the markers tightly linked to Ms are located close to the centromere, a region of significantly lower recombination, they are likely physically distant from Ms. Although these markers are still useful for marker-aided selection, our results indicate that eventual map-based cloning of Ms will be difficult due to reduced recombination near the gene. These results will be of interest to onion breeders and geneticists working in the private and public sectors as a standard technique to determine the best way to clone onion genes.

Technical Abstract: Fluorescence in situ hybridization (FISH) has not been readily exploited for physical mapping of molecular markers in plants due to the technical challenge to visualize small single-copy probes. Signal amplification using tyramide (tyr) FISH can increase sensitivity up to 100 fold. We used tyr-FISH to physically assign to an onion chromosome molecular markers tightly linked to the nuclear male-fertility (Ms) restoration locus. Because numerous molecular markers linked to the Ms locus have been reported, many of which were identified after screening relatively few DNA clones or primers and segregating progenies, our goal was to determine if the Ms locus is located in a region of the onion genome with low recombination. Using tyr-FISH, markers linked to the Ms locus were physically located on mitotic metaphase, pachytene, and super-stretched pachytene chromosomes. Relatively short genomic amplicons (846 to 2251 bp) and a cDNA clone (666 bp) were visualized in 9 to 42% of observed cells. The markers were assigned to proximal locations close to the centromere on the long arm of chromosome 2. This is the first report of physical mapping to an onion chromosome of molecular markers linked to an important locus. Because the markers tightly linked to Ms are located close to the centromere, a region of significantly lower recombination, they may be physically distant from Ms. Although these markers are still useful for marker-aided selection, our results indicate that eventual map-based cloning of Ms will be difficult due to reduced recombination near the gene.