Five-color fluorescence in situ hybridization system for karyotyping of Panax ginseng

Abstract

Chromosomal mapping of repetitive elements is invaluable in understanding genome structure and evolution. Repetitive elements constitute ~ 80% of the allotetraploid ginseng (Panax ginseng) genome. Preparing sporophytic metaphase chromosomes of ginseng is laborious; therefore, it would be advantageous to maximize the information obtained from a single slide. Here, we investigated the suitability of simultaneous five-color fluorescence in situ hybridization using major ginseng repeats, namely PgDel1, PgDel2, PgTel, and Pg167TR. For Pg167TR, we generated two degenerate probe libraries (Pg167TRa and Pg167TRb) based on the chromosomal target coverage. We labeled the probes with dark-red, blue, red, orange, and green fluorochromes and used excitation/emission filter sets specific to each fluorochrome to detect fluorescence in situ hybridization signals. PgDel1 was distributed across all 24 chromosome pairs, except for the secondary constriction region of chromosome 16, whereas PgDel2 was distributed over 12 of the 24 pairs. PgTel was localized in the termini of chromosomes and in an intercalary region in chromosome 13. Pg167TRa and Pg167TRb were distributed among 22 chromosome pairs with loci polymorphisms. These results showed the utility of five-color fluorescence in situ hybridization for chromosomal mapping of five repeats to expedite karyotyping and facilitate genome evolution studies in ginseng and other plant species.