| Summary: | 碩士 === 國立高雄師範大學 === 生物科學研究所 === 89 === Turnip mosaic virus ( TuMV ) is a member of Potyvirus genus in the family Potyviridae. It is an important virus infecting cruciferous crops and occurring worldwide including Africa, Asia, Australia, Europe, and the north and south America. The conventional methods to identify and classify the TuMV among strains are based on the host range and symptomatology. However they are easily influenced by the environmental factors. Serological method is also indistinguishable for all the strains of TuMV. Therefore we tried to use molecular biology method to differentiate TuMV strains. TuMV-C1 and TuMV-TW could infect the same host plant, Brassica juncea var. 5780, but display different symptom. We believed that they are somehow different in their sequences of nucleotides. The purpose of this study was to clone and sequence the genomic regions of two strains, TuMV-C1and TW, and compare the nucleotide and amino acid sequences with three reported sequences of the TuMV strains, TuMV-CAPP ( from Canada ), TuMV-UK1 ( from United Kindom ), and TuMV-JAP ( from Japan ). All of five TuMV strains showed over 90﹪identities. The P1, P3, and the N terminal of CP gene were more variable regions of the genome. A substitution happened to the TuMV-CAPP at the third position of the DAG motif in the CP gene which is involved with the transmissibility of the Potyvirus. The results also showed that all the NIb genes of five TuMV strains conserved the active site of the core replicase, GDD motif. The 27 kDa NIa protein could cleave itself at the position between Ser-223 and Gly-224 to produce a secondary 25 kDa protein. However TuMV-CAPP mutated at these two positions. Val and Ser were replaced by Ser and Gly. Corresponding to the cleavage sites of NIa protease, TuMV-CAPP had a different cleavage site between CI and 6K2 proteins compared to the other strains. More experiments need to be done to prove that the 25 kDa protein of NIa would cut the site between CI and 6K2 protein. All of the HC-Pro genes of five TuMV strains conserved the KITC and PTK motif. The multiple alignment of the 3'' -nontranslated region showed high homology among strains. The sequence of 3''-nontranslated region was proposed to be able to classify strains of TuMV. However it is not consistent for the five TuMV strains. In conclusion, the comparison of multiple alignments of nucleotide and amino acid sequences among TuMV strains displayed high identities in intraspecies. Comparing the identities of TuMV strains to the other Potyvirus group, Potato virus A ( PVA ) and Zucchini yellow mosaic virus ( ZYMV ) showed that the genes between them were below 70﹪, even more in the P1 and P3 genes which were below 45﹪. The functions of the P1 and P3 proteins were not clear so far. In the phylogenetic analysis, TuMV-C1, TuMV-TW, TuMV-JAP, and TuMV-UK1 have more close relationship other than TuMV-CAPP. It is expected that the result of this study can devote to the construction of the antivirus transgenic plant for controlling TuMV in the future.
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