Trends in site-number change of rDNA loci during polyploid evolution in Sanguisorba (Rosaceae)

Abstract

To elucidate the evolutionary dynamics of rDNA site number in polyploid plants, we determined 5S and 18S-5.8S-26S rDNA sites for ten species of Sanguisorba (2n=14, 28, 56) and a single species of each of three outgroup genera, Agrimonia (2n=28), Rosa (2n=14), and Rubus (2n=14) by the fluorescence in situ hybridization (FISH) method. We also estimated phylogenetic relationships among these species using matK chloroplast DNA (cpDNA) sequences, and reconstructed the evolutionary history of rDNA site number based on the maximum parsimony method. The 2n=14 and 2n=28 plants of all genera except Rosa carried two 5S rDNA sites, whereas Rosa and 2n=56 plants carried four sites. The 2n=14 plants had two 18S-5.8S-26S rDNA sites, whereas Sanguisorba annua and 2n=28 plants had four or six sites. Phylogenetic analysis showed that polyploidization from 2n=14 to 2n=28 has occurred once or three times in Sanguisorba and Agrimonia. The 5S rDNA sites duplicated during each ancestral polyploidization were evidently lost after each polyploidization. However, the duplicated 18S-5.8S-26S rDNA sites were all conserved after each polyploidization. Thus, the duplicated 5S rDNA sites tend to have been eliminated, whereas those of 18S-5.8S-26S rDNA tend to have been conserved in Sanguisorba. In the most parsimonious hypothesis, 2n=14 in S. annua is a secondary, putatively dysploid state, reduced from 2n=28.

Exploration of Intraspecific Cytomorphological Diversity in Agrimonia eupatoria L. (Rosaceae) from Western Himalayas, India

“…The diploid and tetraploid chromosome numbers conformed the previous reports from Eastern and Western Himalayas by the various workers, whereas the hexaploid chromosome number is newly reported. For genus Agrimonia, the lowest chromosome number is reported to be nϭ14, and the presently as well as previously worked out euploid cytotypes are all multiples of xϭ14, supporting the observations of Mishima et al (2002) and Malin (2004). Hence, the presently worked out materials are designated as 2x, 4x and 6x.…”

Evolutionary implications of permanent odd polyploidy in the stable sexual, pentaploid of Rosa canina L

“…Possibly, paracentric 5S rDNA loci were lost from marker chromosomes 3 and 4 during the evolution of the Caninae. The presence of two 5S rDNA loci per genome in the diploid species R. multiflora (Mishima et al, 2002) and one 18S-26S rDNA locus per genome in most of the rose species investigated by Ma et al (1997) and Fernandez-Romero et al (2001) is consistent with this argument. Ma et al (1997) found one 18S-26S rDNA locus per genome, located terminally on the short arms of small submetacentric chromosomes, in five diploid species and one tetraploid cultivar of Rosa.…”

Intraspecific polymorphism of ribosomal DNA loci number and morphology in Brachypodium pinnatum and Brachypodium sylvaticum

“…However, polymorphism of both rDNA loci number and position has been observed in many plant species, limiting the application of rDNA as reliable chromosome landmarks. Such intraspecific variation in number and chromosomal distribution of rDNA loci has been reported in numerous plant genera, including Brassica, Raphanus, Sinapis [14], Pinus [15] and Sanguisorba [16]. The number and chromosomal distribution of rDNA loci have also been analysed in some species of Brachypodium [17,18].…”