Papers by Sonja Siljak-Yakovlev
PLOS ONE, 2017
In this study we showed that constitutive heterochromatin, GC-rich DNA and rDNA are implicated in... more In this study we showed that constitutive heterochromatin, GC-rich DNA and rDNA are implicated in chromosomal rearrangements during the basic chromosome number changing (dysploidy) in Reichardia genus. This small Mediterranean genus comprises 8-10 species and presents three basic chromosome numbers (x = 9, 8 and 7). To assess genome evolution and differentiation processes, studies were conducted in a dysploid series of six species: R. dichotoma, R. macrophylla and R. albanica (2n = 18), R. tingitana and R. gaditana (2n = 16), and R. picroides (2n = 14). The molecular phylogeny reconstruction comprised three additional species (R. crystallina and R. ligulata, 2n = 16 and R. intermedia, 2n = 14). Our results indicate that the way of dysploidy is descending. During this process, a positive correlation was observed between chromosome number and genome size, rDNA loci number and pollen size, although only the correlation between chromosome number and genome size is still recovered significant once considering the phylogenetic effect. Fluorescent in situ hybridisation also evidenced changes in number, position and organisation of two rDNA families (35S and 5S), including the reduction of loci number and, consequently, reduction in the number of secondary constrictions and nuclear organising regions from three to one per diploid genome. The potential mechanisms of chromosomal and genome evolution, strongly implicating heterochromatin, are proposed and discussed, with particular consideration for Reichardia genus.
Alpine Botany, 2015
Molecular cytogenetics and the study of genome size have been used to understand evolutionary and... more Molecular cytogenetics and the study of genome size have been used to understand evolutionary and systematic relationships in many species. However, this approach has seldom been applied to alpine plants. A group of dysploid-polyploid high mountain Artemisia species, distributed from the European Sierra Nevada to Central Asian mountains, through the Pyrenees, the Alps and the Caucasus, is a good model to consider changes at the genome and chromosome levels. These small perennial Artemisia, found frequently in isolated populations, present highly disjunct distributions. Some are considered rare or even endangered. Here we show results for nine species and 31 populations, including genome size (2C-values), fluorochrome banding and fluorescent in situ hybridisation (FISH) of ribosomal RNA genes (rDNA). Significant intraspecific genome size variation is found in certain populations of A. eriantha and A. umbelliformis, but without taxonomic significance due to the absence of morphological or ecological differentiation. The number and position of GC-rich DNA bands is mostly coincidental with rDNA although there is an expansion of GC-rich heterochromatin in centromeres in some taxa. Ancestral character states have been reconstructed and x=9 is inferred as the likely ancestral base number, while the dysploid x=8 has appeared repeatedly during the evolution of Artemisia. On the basis of cytological observations, Robertsonian translocations are proposed for the appearance of dysploidy in the genus. A remarkable presence of x=8-based species has been detected in the clade including high mountain species, which highlights the important role of dysploidy in the diversification of high mountain Artemisia. Conversely, polyploidy, though present in the alpine species, is more common in the rest of the genus, particularly in arctic species. Hypotheses on the mechanisms underpinning the relative abundance of dysploids and scarcity of polyploids in high mountain Artemisia are discussed.
Botanical Journal of the Linnean Society, 2007
Chromosome counts are reported in 29 populations representing 20 species and one subspecies of th... more Chromosome counts are reported in 29 populations representing 20 species and one subspecies of the genera Callicephalus (one sp.), Klasea (seven spp.), Myopordon (two spp.), Oligochaeta (one sp.), and Rhaponticum (nine spp., one ssp.). Eleven reports are new, the others supplement limited previous data. New and published cytological data are summarized and evaluated critically in light of current taxonomic treatments and evolutionary hypotheses. Basic chromosome numbers are a valuable source of taxonomic information and relate well to the phylogeny. They are quite conserved in Klasea (only x = 15), the sister group of the remaining genera, and in the early branching genera of the Rhaponticum group ( x = 14 for Centaurothamnus and Callicephalus ). However, a more complex pattern of genome evolution is present among the more derived clades, Oligochaeta plus Myopordon ( x = 12, 14) and the genus Rhaponticum ( x = 12, 13). The occurrence of x = 12 in Oligochaeta divaricata and Rhaponticum carthamoides seems to be the result of a recent event of chromosome fusion, as suggested by the fragility of particularly long pairs of chromosomes. The use of chromomycin staining, including an enzymatic digestion step that facilitates spreading and permits a reduction of potential fragmentation, only partially resolves this problem.
PECCENINI S., GALLINO S., SILJAK-YAKOVLEV S. 2003 – Studi citotassonomici sul genere Erysimum (Cruciferae). Informatore Botanico Italiano, 35: 129-131
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Papers by Sonja Siljak-Yakovlev