| Abstract |
During the co-evolution of plants and their pathogens, the former have developed specific immunity mechanisms in order to become resistant to several diseases and therefore to be able to survive and grow (Zhang, et al., 2019). Plant defense mechanisms can be divided into two categories: (1) the preliminary, basal defense, pathogen-associated molecular pattern (PAMP) triggered immunity (Monaghan & Zipfel, 2012) (2) the secondary defense, effector-triggered immunity (ETI) (Eitas & Dangl, 2010).
Plants can perceive the infection of pathogens by recognizing the conserved microbe-associated or pathogen-associated molecular patterns (MAMPs or PAMPs) via the cell surface-localized pattern recognition receptors (PRRs) (Monaghan & Zipfel, 2012). In order to manipulate host processes and promote infection, pathogens employ several virulence effectors and establish successful infection, called effector triggered immunity (ETI). Plants recognize pathogen effectors using specific receptors called NLRs (containing nucleotide binding site and leucine rich repeats) and then transfer the signals to the downstream of defense genes (Takken & Goverse, 2012). The complex NLR function became apparent with the discovery of specific domains integrated in NLRs (integrated domains, IDs), that mostly constitute targets of the effectors. This led to the development of the integrated decoy model (Dang & Jonathan, 2001). ETI is often accompanied by cell death at the area of the infection of the host by the pathogen, known as hypersensitive response (HR) (Dodds & Rathjen, 2010).
The aim of this master thesis was to study the role of a genetically linked pair of NLR receptors from the Brassica napus plant, RPR1 and RPR2. In order to do so, specific truncations of the RPR1 gene were constructed, eliminating an integrated domain each time, using TA or Golden Gate cloning. These constructs in Agrobacteria cells were infiltrated in leaves of Nicotiana benthamiana or Nicotiana tabacum. The plants were checked for the cause of HR and the protein localization was observed through the confocal microscope. Following the same procedure, the role of the 5’ UTR of the RPR1 gene was also examined. Lastly, the two NLR receptors were checked for their interaction with specific virulence effector proteins, HcPro and VPg from the Turnip Mosaic virus (TuMV), through BiFc (Bimolecular fluorescence complementation) and Yeast 2 Hybrid (Y2H) assays. The results indicate a crucial role of the TFIIS domain of the RPR1 gene, which contains an NLS signal that guides the protein to the nucleus. Absence of this domain leads to the stay of the RPR1 protein in the cytoplasm and does not cause HR to the leaf when infiltrated. Additionally, the presence of the 5’UTR results in lower expression levels of the RPR1 gene, a fact that remains to be verified through qPCR experiments. Moreover, Y2H and BiFc assays have not shown, so far, an interaction of the RPR1 receptor with the HcPro effector. Further experiments need to be conducted for our hypothesis to be clarified.
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Studying the role of a genetically linked pair of plant NLR Immunity receptors
