Distribution of 45S and 5S rDNA sites in 23 species of Eleocharis (Cyperaceae)

Abstract

Studies of rDNA location in holocentric chromosomes of the Cyperaceae are scarce, but a few reports have indicated the occurrence of multiple 45S rDNA sites at terminal positions, and in the decondensed state of these regions in prometaphase/metaphase. To extend our knowledge of the number 45S and 5S rDNA sites and distribution in holocentric chromosomes of the Cyperaceae, 23 Brazilian species of Eleocharis were studied. FISH showed 45S rDNA signals always located in terminal regions, which varied from two (E. bonariensis with 2n = 20) to ten (E. flavescens with 2n = 10 and E. laeviglumis with 2n = 60). 5S rDNA showed less variation, with 16 species exhibiting two sites and 7 species four sites, preferentially at terminal positions, except for four species (E. subarticulata, E. flavescens, E. sellowiana and E. geniculata) that showed interstitial sites. The results are discussed in order to understand the predominance of terminal rDNA sites, the mechanisms involved in the interstitial positioning of 5S rDNA sites in some species, and the events of amplification and dispersion of 45S rDNA terminal sites.

Chromosomal dynamics of nucleolar organizer regions (NORs) in the house mouse: micro-evolutionary insights

“…NORs have been widely and successfully used as cytogenetic markers to assess patterns of chromosomal evolution particularly in nonmammalian organisms for which banding data are less tractable (Gallagher et al, 1999;Cabrero and Camacho, 2008;Raskina et al, 2008;Carvalho et al, 2009;Nguyen et al, 2010;da Silva et al, 2010). However, these investigations often included only one or a few individuals per species, so population surveys of NOR variability using FISH remain scarce (Veltsos et al, 2009).…”

“…As the number and position of the rDNA clusters are often species-specific, these chromosomal characters have been widely used in systematics and phylogenetic reconstructions. Studies on NOR variation in numerous plant, insect and vertebrate groups have invariably described changes in the number and chromosomal location of NORs even in closely related species, suggesting that rDNA clusters are highly mobile components of the genome (Gallagher et al, 1999;Datson and Murray, 2006;Cabrero and Camacho, 2008;Nguyen et al, 2010;da Silva et al, 2010;Cazaux et al, 2011). This important inter-species lability is generated either by chromosomal rearrangements or transposition events (Eickbush and Eickbush, 2007).…”

“…This important inter-species lability is generated either by chromosomal rearrangements or transposition events (Eickbush and Eickbush, 2007). When no chromosomal repatterning is observed, several authors have ascribed the high transposition rates of NORs to the existence of transposons in the rDNA clusters; such elements have been observed in plants, invertebrates and recently in intergenic spacer (IGS) repeats of the house mouse (Grozdanov et al, 2003;Raskina et al, 2008;da Silva et al, 2010). The vast majority of these investigations are based on the silverstaining method which presents two drawbacks: it reveals only the active fraction of the rRNA genes, that is, those that were transcribed during the previous interphase, and in some cases, it may lead to nonspecific staining of heterochromatic regions (Dobigny et al, 2003;Cabrero and Camacho, 2008;Carvalho et al, 2009).…”

Evidence of genetic differentiation and karyotype evolution of the sedges Cyperus ligularis L. and C. odoratus L. (Cyperaceae)

“…Contrasting with the significant amount of published data on the karyological features of some genera of Cyperaceae, such as Carex, Eleocharis and Rhynchospora (Vanzela & Guerra 2000;Roalson 2008;Silva et al 2010;Cabral et al 2014), very little is known about the chromatin organization in Cyperus species. In fact, to the best of our knowledge, this is the first time that heterochromatic regions are evidenced in chromosomes of Cyperus species by means of fluorochrome banding.…”

“…In fact, to the best of our knowledge, this is the first time that heterochromatic regions are evidenced in chromosomes of Cyperus species by means of fluorochrome banding. Consequently, it is hard to know if the coincident number of nucleolar organizer regions (NORs), which were evidenced by both CMA/DAPI and silver nitrate staining, indicates some conserved feature within the genus, as reported for other groups of Cyperaceae (Silva et al 2010). Thus, even sharing the same number of active NORs, the different ranges of chromosome number variation among sympatric individuals of C. odoratus and C. ligularis reinforces the assumption of a clear separation of the two species.…”