Comparative triple-color FISH mapping in eleven Senna species using rDNA and telomeric repeat probes

Senna is a diverse and paraphyletic genus in the subfamily Caesalpinioideae (Fabaceae Lindl.) comprising various species of industrial and medicinal value. To date, the genome-based taxonomic relationship among several Senna species remains enigmatic. Cytogenetic information is invaluable in deciphering phylogenetic relationships and evolutionary history. However, insufficient chromosomal research for many Senna species impedes comparative cytotaxonomic analyses aimed at understanding their genomic evolution. To provide additional Senna -related molecular cytogenetic information, we karyotyped 11 Senna species by employing triple-color fluorescence in situ hybridization using 5S rDNA, 45S rDNA, and Arabidopsis thaliana -type telomeric pre-labeled oligonucleotide probes. Chromosome numbers were predominantly 2 n = 28, but 2 n = 22 ( S. marilandica ) and 2 n = 24 ( S. uniflora ) were also observed. While most species revealed only one interstitial 5S rDNA locus, except for S. uniflora which has two loci, a range of one to three 45S rDNA loci were detected at distal chromosomal regions. Additionally, we observed a hemizygous 45S rDNA locus in S. auriculata . In addition to chromosome termini, weak signals for telomeric repeats were found in interstitial regions in S. hirsuta, S. corymbosa , and S. alexandrina . These cytogenetic data can be integrated with molecular phylogenetic data for more comprehensive Senna cytotaxonomic analyses.