Kyrychenko A. Pathogenicity, structure-function organization and genomics of plant viruses with a monopartite (+)RNA genome.

The thesis is devoted to the study of biological and physicochemical characteristics of the monopartite (+)RNA genomic plant viruses prevailing in Ukraine as well as the structure and function of their genomes, virus-specific products and cellular components at different levels of cell organization of infected plants. Much attention is paid to the computer analysis regulatory elements in the genomic sequences of (+)RNA viruses. For the first time, it was investigated a genetic structure (variability and strain diversity) of bean yellow mosaic virus population circulating in agrocenoses in the different crops of a region – bean (Phaseolus vulgaris L.), soybean (Glycine max L.) and lupine (Lupinus luteus L.). Сomparative genomic sequence analysis revealed a high level of identity of the isolates and their belonging to the same bean yellow mosaic virus strain. Ukrainian isolates showed high sequence homology to isolates from Russia, Australia and Argentina. Bean common mosaic virus isolates by the reaction of differential bean cultivars was assigned to pathogroup PG VII. The partial coat protein sequence data of Ukrainian isolate show 100 % identity with sequences from 125 bean common mosaic virus strains that are widespread worldwide in bean growing regions. The plum pox virus isolates distributed in different regions of the Central Ukraine have been studied. Molecular characterization indicated that the isolates belong to the D strain of the virus. Ukrainian isolates have shown high identity (95-99,4 %) with all of 33 plum pox virus isolates from different countries and host plants tested in our study. The presence of a mixed infection with two viruses (Hosta Virus X and Tobacco Rattle Virus) in Hosta plants was confirmed by the RT-PCR as well as biological assay and electron microscopy methods. It was shown that virus infection disturbs plant physiology causing developmental abnormalities and other phenotypic manifestations that are considered as disease symptoms. Physiological and biochemical alterations including changes in the photosynthetic apparatus of chloroplasts, photosynthetic pigments, proteins and carbohydrates metabolism disorders have been studied in virus-infected plants. The pathological influence of bean yellow mosaic virus on the growth and development of the callus cell culture has been established. The date obtained indicates a high level of seed transmission of the bean common mosaic virus. The viral RNA has been detected in plant generative organs and some components of the seed and flower. Also, virus particles were found in pollen grains of Phaseolus vulgaris plant. Phylogenetic properties and comparative sequence analyses of viruses as well as a computer analysis of regulatory elements in the genomic sequences of RNA-containing viruses have been performed. The presence of similar regulatory nucleotide motifs within groups of viruses isolated from different plant species was established. Computer analysis of conserved nucleotide motifs and secondary structures in the genomic and subgenomic promoters of tobamoviruses indicates that both nucleic acid secondary structure and nucleotide sequences are essential for tobamovirus sgRNA promoter activity. The groups of tobamoviruses containing different strains and species with similar nucleotide substitutions supplement a limited demonstration of Vavilov’s homologous series at the molecular level, and are also consistent with our assumption about the molecular mechanism of homologous series – the possibility of fixing only those nucleotide substitutions that do not disturb of finely balanced functioning of several genetic codes in one cell. Hypothetical models of subgenomic and genomic tobamovirus RNAs synthesis have been proposed. The models are well consistent with our results and published data and can be used to study the mechanisms of replication and transcription of viral RNAs. Key words: plant viruses, genomic sequences, callus tissue culture, liposomal glycan-glycolipid complexes, promoters, computer analysis of sequences