In this master's thesis, we used qPCR to study the expression of genes related to DNA methylation in hop plants infected with the CBCVd viroid. Hops are an important agricultural crop threatened by various pathogens, with CBCVd infection being particularly problematic. We focused on the genes DRM2, AGO4, CLSY1, RDR2, HEN1, and DCL3, which are associated with DNA methylation, an epigenetic mechanism by which plants rapidly adapt to biotic and abiotic stimuli. The experiment was conducted on three hop varieties at three different time points post-infection. Our hypothesis was that gene expression would differ between infected and uninfected plants, with higher expression expected in infected plants, indicating active methylation as a defense response to the infection. The results showed statistically significant differences in the expression of the AGO4, HEN1, and DCL3 genes, but only at certain time points. Surprisingly, the expression of these genes was higher in uninfected plants. For the variety Celeia, which is sensitive to infection, we expected higher gene expression compared to the tolerant varieties Styrian Styrian Cardinal and Styrian Styrian Wolf. However, a statistically significant difference in expression was observed only for the AGO4 gene, where expression was higher in the reportedly tolerant Styrian Styrian Wolf variety, highlighting the complexity of plant responses to viroid infections and the need for further research in this area.
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