Contrasting patterns of the 5S and 45S rDNA evolutions in the Byblis liniflora complex (Byblidaceae)

Abstract

To clarify the evolutionary dynamics of ribosomal RNA genes (rDNAs) in the Byblis liniflora complex (Byblidaceae), we investigated the 5S and 45S rDNA genes through (1) chromosomal physical mapping by fluorescence in situ hybridization (FISH) and (2) phylogenetic analyses using the nontranscribed spacer of 5S rDNA (5S-NTS) and the internal transcribed spacer of 45S rDNA (ITS). In addition, we performed phylogenetic analyses based on rbcL and trnK intron. The complex was divided into 2 clades: B. aquatica–B. filifolia and B. guehoi–B. liniflora–B. rorida. Although members of the complex had conservative symmetric karyotypes, they were clearly differentiated on chromosomal rDNA distribution patterns. The sequence data indicated that ITS was almost homogeneous in all taxa in which two or four 45S rDNA arrays were frequently found at distal regions of chromosomes in the somatic karyotype. ITS homogenization could have been prompted by relatively distal 45S rDNA positions. In contrast, 2–12 5S rDNA arrays were mapped onto proximal/interstitial regions of chromosomes, and some paralogous 5S-NTS were found in the genomes harboring 4 or more arrays. 5S-NTS sequence type-specific FISH analysis showed sequence heterogeneity within and between some 5S rDNA arrays. Interlocus homogenization may have been hampered by their proximal location on chromosomes. Chromosomal location may have affected the contrasting evolutionary dynamics of rDNAs in the B. liniflora complex.

Chromosomal diversification and karyotype evolution of diploids in the cytologically diverse genus Prospero(Hyacinthaceae)

“…Thus, despite the high frequency of chromosomal rearrangements within and between populations of the P. autumnale complex - inversions, supernumerary segments, translocations, B-chromosomes [24,25,37,42] - all diploid cytotypes possess unique and stable locations of their rDNA loci (except for two B 6 B 6 plants in this study with translocations). By contrast 5S rDNA proved to be more variable in locus number and location (Figure 2), a phenomenon observed in other plant groups [5,15,16,43,44]. Despite this variability, 5S rDNA is frequently more stable in its position than 35S rDNA, which may vary substantially in distribution between related species (e.g., in Aloe [45]) and even between cells in individuals of species of genus Allium [46].…”

Non-Random Distribution of 5S rDNA Sites and Its Association with 45S rDNA in Plant Chromosomes

“…In most genera with linked sites, this condition was present in a subset of species, as in Aristolochia [Berjano et al, 2009], Avena [Shelukhina et al, 2007[Shelukhina et al, , 2008a, Brassica [Hasterok et al, 2006], and Byblis [Fukushima et al, 2011]. The retention of adjacent sites in an extensive taxonomic lineage was observed only in the subfamily Aurantioideae, in which at least one pair of adjacent sites was found in species of 10 out of 11 analyzed genera.…”

“…Likewise, in accordance to the general distribution observed for 5S and 45S rDNA sites, 71.5% of the adjacent sites were located on the terminal regions, mostly with the 45S rDNA distally positioned, as for example in different species of Nemesia [Datson and Murray, 2006] or in Citrus and related genera [Barros e Silva et al, 2013]. In several species where the adjacent 5S-45S rDNA sites occurred at the proximal position this orientation was often inverted, with the 5S rDNA site more terminally located, as for example in Poncirus [Brasileiro-Vidal et al, 2007], Crotalaria Morales et al, 2011], Solanum [Brasileiro-Vidal et al, 2009], and Byblis [Fukushima et al, 2011].…”

Divergence between<b><i> C. melo</i></b> and African <b><i>Cucumis</i></b> Species Identified by Chromosome Painting and rDNA Distribution Pattern

“…Physical mapping of the 5S and 45S rDNA by fluorescence in situ hybridization (FISH) can provide valuable information on the interrelationships of closely related species [Adams et al, 2000;Ran et al, 2001;Shan et al, 2003;Weiss-Schneeweiss et al, 2008;Fukushima et al, 2011;Lan and Albert, 2011;Chacón et al, 2012;Li et al, 2016]. To date, the distribution of 5S and 45S rDNA loci has only been reported in C. sativus and C. melo of the genus Cucumis [Han et al, 2008;Liu et al, 2010].…”