Identification Of The Promoters From Satellite DNA Associated With Two Different Begomoviruses

DNAβis a novel satellite DNA that was associated with monopartite geminiviruses, and is required by geminiviruses for inducing typical symptoms in natural hosts. The geneβC1 has been found in all reported DNAβmolecule on its complementary strand, which is conserved in both position and size and is found to be a symptom determinant. Tomato yellow leaf curl China virus (TYLCCNV) and Malvastrum yellow vein virus (MYVV) were both monopartite geminiviruses associated with DNAβmolecule. In this study, we isolated and identified theβC1 promoters in the two geminiviruses.Agrobacterium-mediated transient expression assay was used to identify theβC1 promoter of DNAβof MYVV isolate Y47 (MYVV-Y47). With GUS and GFP gene as reporter gene, respectively, promoter activity was determined by both histochemical and fluorometric assay. The results showed that a 991 nuclueotide (nt) fragment upstream the translation start site ofβC1 ORF of MYVV-Y47 DNAβwas functional and the 5'- and A-rich region deletions of the fragment maintained its activity. The activity of the 991 nt fragment was about 28.05% that of the 35S promoter from Cauliflower mosaic virus. Histochemical assay revealed that the 991 nt fragment can drive GUS gene to be expressed constitutively in the transformed tobacco plants. Further studies indicated that a 214 nt fragment from 3' end of the 991 nt fragment was responsible for basic promoter activity and can confers a constitutive GUS expression pattern in transgenic tobacco plants.Following the same method, we also analyzed theβC1 promoter of DNAβof TYLCCNV-Y25. The result revealed that 982 nt fragment upstream the translation start site ofβC1 was functional and its activity was about 46.23% that of the 35S promoter from Cauliflower mosaic virus. Besides, the 206 nt fragment from 3' end of the promoter kept nearly the same activity to that of the entire 982 nt fragment.