#5SrDNA

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Abstract Tandemly arranged repetitive regions (repeats) that encode 5S rRNA (5S rDNA) are an indispensable component of eukaryotic genomes. Typically, 5S rDNA repeats within a genome are very similar due to the concerted nature of the evolution of this type of repeats. Each 5S rDNA repeat consists of an evolutionarily conserved coding sequence (CDS) and a variable intergenic spacer (IGS). 5S rDNA is a popular model for studying the molecular evolution of repetitive sequences, and the high rate of IGS mutations determines its wide use in phylogenetic analysis of closely related taxa. Nevertheless, 5S rDNA remains unexplored for many groups of higher plants, especially for the Plumbaginaceae family. Some taxa of this family are endemic to southern Ukraine and listed in the Red Book. However, their taxonomic status is controversial, and its clarification requires the use of molecular phylogenetic methods. In this work, we examined the molecular organization of 5S rDNA for representatives of four genera of the tribe Limonieae, the largest in the family Plumbaginaceae. It was shown that the CDS of 5S rDNA of representatives of the genera Limonium, Armeria, and Ceratolimon possess single mutations that do not affect the formation of the secondary structure of 5S rRNA. In contrast, in the genomes of Goniolimon species, in addition to functionally normal 5S rDNA repeats, numerous pseudogenes were found that do not evolve in a concerted manner and contain numerous mutations in the CDS that disrupt the secondary structure of 5S rRNA. A significant phylogenetic distance between representatives of the subgenera Pteroclados and Limonium of the genus Limonium indicates that Pteroclados can be considered a separate genus. The high rate of molecular evolution makes 5S rDNA IGS a convenient tool for the reconstruction of phylogenetic relationships within the studied genera of the tribe Limonieae and the barcoding of Ukrainian endemics of the genus Limonium.

Keywords: 5S rDNA genetic polymorphism molecular evolution and phylogeny repetitive sequences pseudogenes Armeria Ceratolimon Goniolimon Limonium

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Abstract The intergenic spacer (IGS) of 5S ribosomal RNA genes (5S rDNA) (that are present in the genome of all living organisms) is characterized by a high variability, due to which it is a convenient and widely used object for clarifying the issues of genome evolution, population genetics, systematics, etc. The aim of this work was to study the IGS of 5S rDNA of the Antarctic pearlwort Colobanthus quitensis. The nucleotide sequence was determined by the methods of molecular genetic analysis, and molecular organization of the C. quitensis 5S rDNA IGS was studied. It was demonstrated that it contains the regulatory elements typical for other vascular plants. The existence of at least two classes of 5S rDNA repeats in the individual genome (that differ significantly in the length and nucleotide sequence of IGS) was established. In addition, based on differences in the length and nucleotide sequence, two subclasses of repeats with a long IGS and three subclasses with a short IGS were identified. A comparison of 5S rDNA IGS sequences in C. quitensis and Silene latifolia Poir. (a member of another section of the Caryophyllaceae family) demonstrated significant differences in the structure of a spacer region of 5S rRNA genes (except for its parts containing regulatory elements). In general, data obtained indicate a significant level of intragenomic polymorphism of C. quitensis 5S rDNA IGS.