Submitted to: Chromosome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 17, 2006
Publication Date: May 1, 2006
Citation: Hu, J. 2006. Defining the sunflower (Helianthus annuus L.) linkage group ends with the Arabidopsis-type telomere sequence repeat-derived markers. Chromosome Research. 14:535-548. Interpretive Summary: In eukaryotes, majority of the genetic information is packed in chromosomes. Each chromosome has two terminal ends called telomeres. Although the number of chromosomes varies with species, the sequence of the telomeres is conserved across almost all angiosperm species. Advent of the molecular techniques generated hundreds of markers on the sunflower chromosomes and constructed a dozen of independently published linkage maps for the sunflower genome. However, none of the telomeres has been mapped. This paper reports the application of the target region amplification polymorphism (TRAP) marker technique to generate telomere-associated markers for sunflower using primers derived from the conserved Arabidopsis-type telomere sequences and a set of 92 recombinant inbred lines which had been extensively mapped with SSR markers. One hundred and eighty-three markers were added to the previously established 17 linkage groups of the public sunflower linkage map. Thirty-two markers were mapped to the outermost positions of the linkage groups, defining 21 of the 34 linkage group ends of the sunflower linkage map. The telomere sequence-derived markers mapped to linkage group ends provide an accurate assessment of the completeness of a linkage group. The markers are also potentially useful in tagging important genes located near the telomeres.
Technical Abstract: The target region amplification polymorphism (TRAP) marker technique was employed to develop telomere-associated markers to define the linkage group ends of sunflower (Helianthus annuus L.). The nine fixed primers designed against the conserved Arabidopsis-type telomere sequence repeat (TTTAGGG) worked successfully in generating polymorphic markers in combination with eight arbitrary primers for the F7 recombinant inbred line mapping population descended from the cross RHA280 x RHA801. This population had been used in the construction of the densest sunflower linkage map of 577 simple sequence repeat (SSR) markers. With 18 sets of PCR reactions, 226 TRAP markers were amplified from the DNA samples prepared from the two parental lines and 92 RILs. These telomere sequence-derived TRAP markers integrated very well with the mapped SSR markers. The computer program, Mapmaker, was used to place 183 markers into the established 17 linkage groups. Although most of the added markers spread across the genome, 32 markers were mapped to the outermost positions of the linkage groups, defining 21 of the 34 linkage group ends of the sunflower linkage map. The telomeric origin of a few such markers was confirmed by sequence analyses. These telomere-associated will provide an accurate assessment of the completeness of a linkage group and a better estimates of the actual genetic lengths. The potential application of the telomere mapping to sunflower improvement is discussed.