Cloning And Comparing Analysis Of Viral Resistance-related Genes In Tomato

As one of the most widely cultivated vegetable tomato is an important economic crop in China and all over the world. ToMV (Tomato mosaic virus) and CMV (Cucumber mosaic virus) often lead to serious loss of yield and quality in tomato crops. Studying on the mechanism of viral infection has important significance to prevent viral diseases. In this experiment, we cloned and analyzed the viral resistance-related genes in tomato which have different reactions against infection of the two viruses above.ToMV-N5 is a necrosis strain of ToMV. By host biology research, it has found to cause different symptoms in different tomato varieties. ToMV-N5 induced symptoms of necrosis in tomato cv. Hezuo 903, whereas the symptoms of light mosaic in another varieties tomato cv. Zhongshu 4. In our study, this was speculated related to the types of resistance gene Tm2 in different tomato varieties. Tm2 is a class of R genes in tomato with resistance to ToMV. It includes three alleles, resistance genes Tm-2~2, Tm-2 and susceptible gene tm-2. The expressing of the two resistance genes brought necrotic spot and system necrosis symptoms in resistance response. We identified the types of Tm2 genes of tomato cv. Hezuo 903 and tomato cv. Zhongshu 4. The results showed that tomato cv. Hezuo 903 contained both resistance gene Tm-2~2 and susceptible gene tm-2. In another variety, tomato cv. Zhongshu 4 was found to include susceptible gene tm-2 only. Two tomato varieties were very different on this gene. We speculated that different infection symptoms caused by ToMV-N5 were related to the type of Tm2.CMV-Fny is well-known strain of CMV. It causes typical mosaic and leaf deformation in tomato leaves. In this work, interference between CMV-Fny and ToMV-N5 was observed in tomato cv. Hezuo 903. When plants were first inoculated with CMV-Fny, and followed by a second inoculation with ToMV-N5 after 6~8 days, plants co-infected by CMV-Fny and ToMV-N5 expressed mosaic and leaf deformation only, with no necrosis observed. This interference effect was existence whether the CMV-Fny carrying satellite RNA or not. This phenomenon was speculated related to plant's Pathogenesis Related Protein (PR), which is a class of immune proteins induced by pathological or environmental stress. PR plays important roles in host defense responses. And studies have shown that induction of different PRs is related to the several pathogen infection symptoms. In this study, we detected that the expressing levels of mRNA of PR-1a1 and PR-2 in plants infected with CMV-Fny and ToMV-N5 single or double infection. Results showed that there was no expression of PR-1a1 and PR-2 in CMV-Fny single or combined with ToMV-N5 inoculated plants. But we detected the expression of these two genes when ToMV-N5 infected tomato cv. Hezuo 903 singly. The expressions of these two genes were so different in single and double infections. It indicated that these two genes were connected with necrosis initiated by ToMV-N5 and could be interfered by pre-inoculation with CMV strains.