The thesis is aimed at the study of the molecular organization and evolution of 5S ribosomal DNA of the Poeae tribe members (family Poaceae) and the taxonomic application of this molecular marker.
The first section of the study presents the analysis of the published information regarding the taxonomy of the Poaceae family. In particular, it describes the current approaches used in the taxonomy of this family, and provides the examples of application as a molecular marker of the genomic regions encoding 5S ribosomal RNA (or 5S rDNA). These regions belong to the class of the tandemly arranged repeated sequences and consist of evolutionarily conservative coding regions and variable spacers that separate them. Due to the occurrence of all eukaryotic organisms in the genomes and the presence of variable spacer regions in its composition, 5S rDNA has been successfully used for the investigation of the evolution of repeated sequences as well as in phylogenetic studies. However, the molecular organization of 5S rDNA of such a large and important group of plants as the family Poaceae still remains poorly investigated. Therefore, the aim of the study was to analyze the molecular organization, polymorphism and evolution of 5S rDNA in the members of the Poeae tribe, the largest one in the Poaceae family, and to evaluate the possibility of using this genomic region in taxonomic research.
To achieve the aim it was necessary to solve the following tasks:
• To clone and sequence 5S rDNA of different genera of the Poeae tribe.
• To evaluate polymorphism and to elucidate the nature of 5S rDNA variability in populations of the Antarctic plant Deschampsia antarctica and other species of this genus.
• To analyze the structure and evolution of 5S rDNA sequence in different genera of the Poeae tribe.
• To assess the possibility of 5S rDNA usage in the molecular taxonomy of the Poeae tribe.
• To use the obtained data for the clarification of the phylogenetic relationships in the Poeae tribe.
The object of research is the structural and functional organization and evolution of 5S rDNA in plants. A set of modern molecular genetics and bioinformatics methods were used in the thesis.
For the first time, the 5S rDNA repeated units were cloned and sequenced and their molecular organization, polymorphism and evolution were analyzed for 4 species of the genus Deschampsia and 14 other members of the Poeae tribe. In particular, the 5S rDNA polymorphism in plants from 19 populations of the Antarctic species Deschampsia antarctica was studied in detail. It was shown that three structural classes of 5S rDNA, two of which include subclasses, are present in the genomes of Deschampsia species. Three structural classes of 5S rDNA appeared at an early stage of speciation in the genus, before the divergence of modern species from a common ancestor, whereas the subclasses emerged later and are partially species-specific. In the genus Deschampsia, transcripts of 5S rDNA repeats of all structural classes are mostly able to form a canonical secondary structure, indicating their functional activity. However, some 5S rDNA repeats show transformation into pseudogenes. High intragenomic 5S rDNA polymorphism is a unique feature of the genus Deschampsia, in contrast to the high similarity of 5S rDNA repeats in the genomes of other studied plants. The obtained data confirms the hypotheses about the exclusion of two species, namely Avenela flexuosa and Vahlodea atropurpurea, from the genus Deschampsia. Taking everything into account, the results demonstrate the feasibility of using 5S rDNA to clarify the phylogenetic relationships between the species and the genera of the tribe Poeae.
The results of the study can be used to reveal the mechanisms of plant evolution in extreme environmental conditions and in environment protection practice for plant genotyping in the development of strategies for the conservation of genetic diversity.
