qRT-PCR investigation of transcription levels of genes involved in the resistance provided by Mi-1.2 gene against Meloidogyne incognita

Root-knot nematodes are one of the pests that cause yield and quality loss in tomatoes. In tomato, Mi-1.2 gene confers resistance against the most common root-knot nematode species, Meloidogyne incognita, M. javanica and M. arenaria. However, the increasing prevalence of Mi-1.2 virulent populations severely limits the effectiveness of this gene. In the site where the nematode begins to feed, changes are observed in the expression of many genes in compatible and incompatible relationship between the nematode and the plant. Many genes are effective in the resistance provided by the Mi-1.2 gene. Knowing the expression levels of these genes in the nematode infection process might be important in the development of management strategies. In this thesis, beside Mi-1.2 gene, PR-1a, PR-2, PR-5, WRKY72a, WRKY72b, WRKY45, WRKY3, glycogenin glucosyltransferase, HsfA1a, Hsp90 and peroxidase genes, which are thought to be related to resistance, were studied. Changes in gene expressions as a result of the response of resistant and susceptible tomato plants carrying these genes to Mi-1.2-virulent (V30) and avirulent (S6) isolates of Meloidogyne incognita were investigated with qRT-PCR. A difference was found between the control group and inoculated plants on the 2nd day after inoculation with the FjMi-1.2 primer sets used to determine the expression level of the Mi-1.2 gene, and on the 5th day with the ToMi-1.2 primer sets. There was no statistically significant difference between the ΔCT values obtained for Mi-1.2 of plants versus Mi-1.2 virulent and avirulent isolates. The ΔCT values of the PR-1a gene in resistant and susceptible tomato plants did not change compared to the Mi-1.2 virulent and avirulent isolate of M. incognita. The expression of the PR-2 gene in the susceptible plant decreased until the 3rd day after nematode inoculation and then started to increase, however, in the resistant plant, it did not change according to the days and the isolate. The expression of the PR-5 gene increased up to 5 days after nematode inoculation in susceptible plant, whereas it increased 3 days after inoculation of Mi-1.2 virulent isolate in resistant plant. There was no difference between the ΔCT values of SIWRKY72a, SIWRKY72b, SIWRKY45 and SIWRKY3 genes obtained in the same day from resistant plants inoculated with Mi-1.2-virulent and avirulent isolates of M. incognita and control plants without nematode inoculation. The ΔCT values of the SIWRKY72a gene in the first 5 days after nematode inoculation in susceptible tomato cultivars did not differ statistically from the control plant. In susceptible plants inoculated with avirulent and Mi-1.2 virulent isolates of M. incognita, a significant difference was observed between the ΔCT values obtained 2 days after inoculation for SIWRKY72b and SIWRKY3 genes and 4 days for SIWRKY45. It was observed that glycogenin glucosyltransferase and HsfA1a genes were not stimulated after inoculation with avirulent and Mi-1.2 virulent isolates of M. incognita in susceptible and resistant plants. Expression of the Hsp90 gene increased on days 4 and 5 after inoculation in resistant plant inoculated with Mi-1.2 virulent isolate of M. incognita, but this was not observed in susceptible plants. Expression of peroxidase gene in susceptible plant was determined at the highest level 2 days after inoculation of avirulent and Mi-1.2 virulent isolates of M. incognita. In the resistant plant, the expression level in the plants infected with avirulent isolate was lower than the plants inoculated with Mi-1.2 virulent isolate. The results show that PR genes may be involved in basal defense against nematodes in susceptible tomato plants. It is thought that this thesis study will enable the establishment of basic scientific information for the successful use of the Mi-1.2 gene against virulent populations for a longer period.