DR-OPC01 sequence disperses throughout the Drosera rotundifolia-derived genomes in the allohexaploid sundew Drosera tokaiensis

Drosera genomes show variation in chromosome size. DNA sequences contributing to the size changes have not been fully characterized for Drosera species. This study aimed to identify DNA sequences that contribute to changes in chromosome size in a polyploid group of the genus Drosera using a random amplified polymorphic DNA (RAPD). RAPD fragment named DR-OPC01 was isolated from D. rotundifolia (2n=2x=20, 2C=2,333 Mbp, 45.4% GC ratio), which possessed 20 middle-sized chromosomes (m-chromosomes). The DNA fragment DR-OPC01 was also amplified in the allohexaploid D. tokaiensis (2n=6x=60, 2C=3,048 Mbp, 43.0% GC ratio), which has a hybrid origin between D. rotundifolia and D. spatulata (2n=4x=40, 2C=1,079 Mbp, 42.4% GC ratio). However, the fragment was not amplified in D. spatulata, which possessed 40 small chromosomes (s-chromosomes). The sequence length of DR-OPC01 was 669 bp with 10-bp palindromic repeat sequences of the RAPD primer OPC-01 at both ends. The GC ratio of the DR-OPC01 sequence was 49.6%, which was higher than that of the three Drosera species. In dot-blot hybridization, hybridized signals from the DR-OPC01 probe were clearly detected with dot-blots of genomic DNA from D. rotundifollia and D. tokaiensis, but not D. spatulata. Fluorescence in situ hybridization on the somatic chromosome of D. tokaiensis revealed that the DR-OPC01 probe hybridized to the entire m-chromosomes, but not to all s-chromosomes.