Molecular and Cytogenetic Analysis of rDNA Evolution in Crepis Sensu Lato

Abstract

Although Crepis was the first model plant group in which chromosomal changes were considered to play an important role in speciation, their chromosome structure and evolution have been barely investigated using molecular cytogenetic methods. The aim of the study was to provide a better understanding of the patterns and directions of Crepis chromosome evolution, using comparative analyses of rDNA loci number and localisation. The chromosome base number and chromosomal organisation of 5S and 35S rDNA loci were analysed in the phylogenetic background for 39 species of Crepis, which represent the evolutionary lineages of Crepis sensu stricto and Lagoseris, including Lapsana communis. The phylogenetic relationships among all the species were inferred from nrITS and newly obtained 5S rDNA NTS sequences. Despite high variations in rDNA loci chromosomal organisation, most species had a chromosome with both rDNA loci within the same (usually short) chromosomal arm. The comparative analyses revealed several independent rDNA loci number gains and loci repositioning that accompanied diversification and speciation in Crepis. Some of the changes in rDNA loci patterns were reconstructed for the same evolutionary lineages as descending dysploidy.

The Chromosome Number and rDNA Loci Evolution in Onobrychis (Fabaceae)

“…In some cases, rDNA loci are robust chromosome markers, allowing comparative analyses of karyotypes, especially of wild and neglected species [ 22 , 71 , 72 , 73 ]. In angiosperms, most often 35S rDNA loci are placed in the subterminal while most 5S rDNA loci are in the interstitial region of the chromosome [ 21 , 74 ].…”

Cytomolecular Organisation of the Nuclear Genome

“…The article by Senderowicz et al [ 17 ] provides a comprehensive study on the chromosomal organisation and evolution of rDNA loci in the complex and taxonomically challenging genus Crepis in the Asteraceae family. Using fluorescent bandings, FISH with rDNA probes and nr-ITS-based phylogenetic analyses, the authors determined the number and chromosomal location of 5S and 35S rDNA loci, reconstructed their ancestral numbers within the genus, and inferred the patterns of their evolution.…”