Browsing by Subject "Tomato mosaic virus (ToMV)"

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    Analyse von Pathogenresistenzmechanismen in Tomate (Solanum lycopersicum L.)
    (2008) Gerhardts, Anja; Pfitzner, Artur J. P.
    For many organisms plants serve as a source of nutrients and energy, but because of their static location they are exposed to various harmful environmental influences. Due to this factor they have developed complex defence mechanisms e. g. for protection against pathogens. An important aspect of these defence mechanisms is the expression of intrinsic resistance genes (R) that detect pathogenic avirulence gene products (Avr) thereby causing a hypersensitive response (HR) in the infected cells and consequently inhibiting the systemic infection of the plant. In this work the resistance genes Tm-2 and Tm-2² of tomato were isolated, cloned and sequenced. The allelic R genes are members of the CC-NBS-LRR group of resistance genes, which is widely spread in plants, and differ only in four amino acids. This is surprising because using resistance breaking ToMV strains Weber et al. (2004) showed that both resistance gene products interact differently with the movement protein (30 kDa MP = Avr) of the virus. To gain further insight into this phenomenon of different pathogen detection, chimeric exchange constructs (A1 and A2) were designed through restriction in the region between the NBS and the LRR domain. These four constructs were used for transformation of MM tomatoes as well as NN and nn tobacco plants. The expression of the resistance gene constructs in MM an nn lines did not confer the expected resistance to ToMV. Nevertheless in older infected nn transformants a formation of spontaneous necrosis was observed, which indicates a delayed development of HR. One possible explanation could be that the presence of only the resistance gene product is not sufficient to detect the viral movement protein and that other host cellular components are involved in this process (as in the guard hypothesis by Dangl and Jones, 2001). This assumption is supported by our yeast two hybrid interaction experiments which showed that a direct interaction of Tm-2 and 30 kDa MP can be excluded. For the NN transformants differences in functionality of the constructs was observed. While NN/Tm-2 and NN/A2 plants showed extreme resistance to ToMV wild type (ToMV0) and the Tm-2² resistance breaking strain ToMV2², the Tm-2² and A1 constructs conferred less resistance to ToMV0 and the Tm-2 resistance breaking strain ToMV1-2. This finding also supports the assumption that there is a difference in pathogen detection between the two alleles. Furthermore it shows that the detection takes place within the LRR region because the exchange construct that behaves in the same way as the endogenous resistance gene carries the C-terminal LRR domain of this allele. The hydroxycinnamoyl-CoA:tyramine N-(Hydroxycinnamoyl)transferase (THT) was found to be another candidate for transmission of pathogen resistance during HR (Gerhardts, 2003). Our in vivo results show that the products of the THT enzymatic reaction induced during HR does not only have an antimicrobiotic effect on the pathogen (von Roepenack-Lahaye et al., 2003; Newman et al., 2001) but also has an apoptotic effect on the plant cell itself.