Karyotype of Panax ginseng C.A. Meyer Based on FISH of rDNA Families and Newly Identified Ty1/Copia and Ty3/Gypsy LTR Retrotransposons

Panax ginseng C.A. Meyer has been regarded as a very valuable plant owing to its medicinal properties; however, genomic information based on chromosome characterization and physical mapping of cytogenetic markers has been very limited. Its genome is estimated at 3.27 Gbp, which is about 21 and 1.4 times more than that of Arabidopsis thaliana and Zea mays, respectively. Its genome is regarded as a product of polyploidization and accumulation of transposable elements. The latter case has been supported by high abundance of long terminal repeat (LTR) retrotransposons from genomic sequence analyses. Fluorescence in situ hybridization was used to analyze the karyotype and the LTR distribution. The somatic chromosome complement was 2n=48 and the lengths ranged from 3.3 μm to 6.3 μm. One locus each for 5S and 45S rDNA was observed. The karyotype was composed of 12 metacentric, 9 submetacentric, and 3 subtelocentric pairs. DAPI bands were distinctly observed in most chromosomes, which made chromosome identification easier. Del elements of the Ty3/Gypsy LTR family were found to hybridize in the heterochromatic and euchromatic regions while PgDel2 preferentially hybridized to half the complement. PgTat1 (Tat-like element) hybridized at the telomeric and subtelomeric regions while PgTat2 preferred the pericentromeric regions. A representative of the Ty1/Copia LTR family, PgTork, hybridized at the non-DAPI rich heterochromatic and some euchromatic areas. Additionally one unique DNA sequence from BAC H08D23 showed 4 loci in the interphase nucleus. These results would be very valuable in understanding the genomic structure of ginseng and its downstream molecular-cytogenetic applications. This work was supported by the Next-Generation BioGreen21 Program (No. PJ008202), Rural Development Administration, Republic of Korea.