FISH mapping of rDNA and telomeric repeats in 10 Senna species

Plants of the genus Senna (Fabaceae) are valued for industrial and medicinal properties that have spurred crop improvement through breeding programs. However, there is very little chromosomal data for this genus, limiting the potential for cytogenetics and genomics research. Here, we used fluorescence in situ hybridization (FISH) to perform a comparative analysis of 10 Senna spp. karyotypes (2n = 28 except S. tora with 2n = 26). We detected differences in the distributions of rDNA gene clusters and Arabidopsis -type telomeric repeats (TTTAGGG) n . Only one 5S rDNA pair was detected in all species, but we observed more interspecies variation for 45S rDNA: four pairs in S. didymobotrya, S. spectabilis, and S. viarum ; two pairs in S. candolleana ; and one pair in S. bauhinioides, S. multiglandulosa, S. occidentalis , and S. tora . In both S. leandrii and S. sulfurea , 45S rDNA distribution was hemizygous. While all chromosomes possessed telomeric signals in the terminal region, this signal was also present in the interstitial regions of all S. tora chromosomes and, less obviously (fewer chromosomes, weaker signals), in S. occidentalis . These preliminary data demonstrate interspecific karyotype variation that reveals Senna genome dynamics. Our results facilitate cytogenetic mapping of other major repeats, thus contributing to an improved understanding of Senna genome structure and evolutionary history.