Determinants Of Symptom On DNA β Associated With Tomato Yellow Leaf Curl Virus And Tobacco Curly Shoot Virus

Geminiviruses are a group of plant single-stranded viruses characterized by their unique twinned particles, and are currently emerging as a major threat to crop production all over the world. Geminiviruses have been reported in several provinces in southern parts of China, and disease incidence has been increasing in recent years. Geminiviruses have also been identified in Zhejiang Province and Shanghai recently. Tomato yellow leaf curl China virus (TYLCCNV) and Tobacco curly shoot virus (TbCSV) induce distinct set of symptom phenotypes on Nicotiana spp. TYLCCNV and its DNAβinduce severe leaf curling, dwarf and enations, while TbCSV and its DNAβcomplex induce severe leaf curling and dwarf symptoms in Nicotiana benthamiana, N. tabacum, N, glutinosa and Lycopersicon esculentum. By making pseudorecombinant, we found that some symptom phenotypes, such as enation, were related to TYLCCNV DNAβ. In this thesis, determinants of symptom phenotypes on DNAβmolecule of Tobacco curly shoot virus isolate Y35 (TbCSV-Y35) and Tomato yellow leaf curl China virus isolate Y10 (TYLCCNV-Y10) were investigated.The 430 nt fragments containing the promoter and A-rich region in TYLCCNV-Y10 and TbCSV-Y35 DNAβwere amplified and chimeric satellites were constructed using Overlap Extension PCR. When using either TbCSV or TYLCCNV as helper virus, symptoms induced by the chimeric satellite Y10-35AP (TYLCCNV-Y10 DNAβsatellite containing TbCSV-Y35 DNAβpromoter and. -rich region) were similar to those induced by TYLCCNV-Y10 DNAβ, and enation were observed on inoculate leaves. However, the chimeric satellite Y35-10AP (TbCSV-Y35 DNAβsatellite containing TYLCCNV-Y10 DNAβpromoter and -rich region) did not develop enation when co-inoculated with TYLCCNV-Y10 or TbCSV-Y35, but produced leaf curling and stunt.symptoms similar to those induced by TbCSV-Y35 and its DNAβor TbCSV-Y35 and TYLCCNV-Y10 DNAβ. The results above indicate that enation is determined by theβC1 gene in DNAβmolecule, but the promoter region is also related with symptom severity and phenotype.