A Glimpse of Panax ginseng Genome Structure Revealed from Ten BAC Clone Sequences Obtained by SMRT Sequencing Platform

Korean ginseng (Panax ginseng) is a well-known valuable medicinal plant with excellent therapeutic effects, however its complex genome structure has not been elucidated yet. To understand its genome structure, we obtained ten ginseng bacterial artificial chromosome (BAC) clone sequences by single-molecule real-time (SMRT) sequencing platform using a pooled DNA of the BAC clones. Out of the ten BAC clones, nine were completely assembled without any gap and one remained a single gap. The total length of BAC clone sequences was 1,163,364 bp. Sophisticated sequence analysis revealed that the 89.7% of the sequences are high copy repeat regions and the remaining 10.3% are non-repeat regions. Eleven protein-coding genes were identified in the non-repeat regions. Most of the repeat regions show more than 1,000 copies and complex structure of various repetitive elements. Ty3/Gypsy family long terminal repeat retrotransposons (LTR-RTs) are predominant repeats occupying 46.9% of the 1,163-kbp sequence. We identified six novel LTR-RTs and their insertion time. Fluorescence in situ hybridization (FISH) analysis demonstrated that PgDel2 and PgDel5 elements had a subgenome-biased distribution. Collectively, our analysis reveals that ginseng genome has very complex genome structure with abundant repetitive elements and rare gene frequency.