Submitted to: Chromosome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 13, 2011
Publication Date: May 1, 2011
Citation: Iovene, M., Cavagnaro, P.F., Simon, P.W., Senalik, D.A., Buell, C.R., Jiang, J. 2011. Comparative FISH mapping of Daucus species (Apiaceae family). Chromosome Research. 19:493-506. Interpretive Summary: Carrots are a widely grown crop but little is known about their genetics. Researchers have developed genetic maps but the relationship between these carrot genetic maps and carrot chromosomes has not been established. Short pieces of chromosomes called BACs have been prepared for the carrot genome, and some of these carrot BACs are known to have specific genes on them. Using a procedure called BAC fluorescent in situ hybridization (FISH) or BAC-FISH we were able to locate 17 genes from the carrot genetic map to carrot chromosomes in this study. One of the BACs was useful in identifying an important region of all carrot chromosomes called the centromere. The centromere is essential for organizing chromosomes during cell division. We were then able to take carrot BACs and use the BAC-FISH technique to locate most of these 17 genes on the chromosomes of two wild species that are related to carrot but have different numbers of chromosomes than carrot has. This research established a framework of chromosomal structure that provides insights into carrot chromosome structure and chromosome evolution in carrot relatives. Researchers and geneticists studying chromosomes of all organisms will find this research of interest in providing insights to gene location, chromosome structure, and chromosome evolution.
Technical Abstract: The genus Daucus (Apiaceae family) contains about 20 mostly diploid species with n=9, 10 and 11, including carrot (D. carota L., 2n=18). Here, we report a pachytene chromosome-based karyotype of carrot. We integrated the carrot linkage groups with chromosomes by fluorescent in situ hybridization (FISH) mapping of bacterial artificial chromosome (BAC) clones anchored by linkage group-specific genetic markers. We have isolated a satellite repeat from the centromeric regions of the carrot chromosomes which aided chromosome identification and karyotype development, and demonstrated that heterochromatic domains were mainly confined to the pericentromeric regions of each carrot chromosome. Chromosome-specific BACs were used to: 1) physically locate additional DNA sequences that were either genetically unanchored or mapped in genetic backgrounds unrelated to the mapping population used to construct the carrot reference linkage map; 2) reveal relationships between genetic distances and physicaldistances; and 3) address chromosome synteny and evolution studies in Daucus. Most carrot BACs generated distinct FISH signals in 22-chromosome Daucus species and provided evidence for syntenic chromosome segments, as well as several chromosomal rearrangements among these species. These results provide a foundation for further cytogenetic characterization of the carrot genome and to aid chromosome evolution studies in Daucus and likely other Apiaceae.