Investigation of the effects of salt stress on DNA methylation in Arabidopsis thaliana epigenetic mutants

The gradual increase in the world population increases the need for food. However, reasons such as the destruction of agricultural lands and climatic fluctuations expose crops to various biotic and abiotic stress conditions. This situation reduces crop productivity and causes an increase in the hunger threat. It is known that plants develop various molecular mechanisms, including epigenetic arrangements, to tolerate changing environmental conditions. In order to make plants resistant to stress and sustain this resistance for generations, firstly molecular mechanisms must be understood well. One of the biggest threats to crop yields is salinity stress. It is known that NaCl application causes hypomethylation in Arabidopsis thaliana Col-0 plants and there are considerable differences between plants and callus tissues in terms of DNA methylation. In this thesis study, the null mutants met1-7 and met1-3, in which the MET1 enzyme of A. thaliana plant was not synthesized, were exposed to salt stress in vitro, morphological changes were observed and methylation levels at the genome level were compared. At the same time, the effects of salt stress applied to mutants were tested by analysis of the expressions of DRM2, Pol IV and Pol V genes known to be involved play in DNA methylation in plants. Gene expression analyzes were made by real-time PCR method, and the relationship between the hypomethylation caused by NaCl application and the MET1 gene was tried to be understood. By comparing the results obtained with homozygous mutants of the MET1 gene with previous data, information about the role of methylation in the plant's response to salinity stress can be obtained. It was observed that NaCl application affected the met1-7 and met1-3 mutants morphologically more than the Col-0 plant. By looking at the number of leaves, leaf surface area and root length of the plants, it was determined that the increasing NaCl concentration has negative effect in all parameters. It is known that morphological changes in plants are also connected to many epigenetic regulations such as DNA methylation, histone modifications, histone variants, and regulation via siRNAs. Therefore, in this study, genome-level methylation levels of Col-0, met1-7 and met1-3 plants exposed to salt stress were measured with an ELISA-based kit, and salt stress was found to cause hypomethylation in all groups, with a higher rate in mutants. The effect of NaCl application on DRM2, Pol IV and Pol V genes, which are known to be involved in epigenetic regulations, was also analyzed by real-time PCR. As a result of the studies, it was determined that the expressions of the examined genes increased at different rates in mutant plants. In conclusion, with this thesis, it is thought that the morphological and molecular data obtained about the effects of NaCl application on mutants where MET1 enzyme is not synthesized will help us to understand the epigenetic basis of stress mechanisms.