Intragenomic Polymorphism of the ITS1-5.8S-ITS2 Region in Invasive Species of the Genus Reynoutria - Cytology and Genetics
Abstract The ITS1-5.8S-ITS2 (ITS1-2) region of the 35S rDNA is widely used for molecular barcoding and in the phylogenetics of plants. It is believed that, due to concerted evolution, all copies of 35S rDNA in eukaryotic genomes should be effectively homogenized. However, the existence of intragenomic polymorphism of the ITS1-2 region in plant genomes has recently been demonstrated, which may be a consequence of hybridization within or between species. In this study, the intragenomic polymorphism of the ITS1-2 region was evaluated using Illumina amplicon sequencing in accessions of two invasive species of the genus Reynoutria, R. japonica and R. sachalinensis, from Ukraine and Romania. Hybridization between these species can lead to the emergence of more aggressive invasive forms. The ITS1-2 sequences of the species studied were found to be represented by some major and minor subclasses/variants, indicating their incomplete homogenization. The number of major variants range from two in R. japonica to six in R. sachalinensis. The ITS1-2 variants that are widespread in the genome of one species may be present at low levels in another species, indicating possible interspecies hybridization. The obtained results show that the ITS1-2 intragenomic polymorphism must be taken into account when performing barcoding, reconstructing the phylogeny of low-level taxa, and for the identification of hybrid forms.
5S Ribosomal DNA in the Family Plumbaginaceae - Cytology and Genetics
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.
Cytology and Genetics