Research Of Geminivirus On Sweet Potato

Our research is about geminivirus on sweet potato in Dalian, Liaoning province of China. Sweet potato (Ipomoea batatas) showing leaf curl symptoms in Liaoning province in China was collected. The 2.8kb fragment obtained by amplification with BM primers which was used as universal primers for amplification of the geminivirus DNA-A fragment. The result suggests that the plant was infected with geminivirus. Stem scions from the plant were graft-inoculated to I. purpurea. Three weeks later, the indicator developed symptoms of leaf curling and interveinal chlorosis. The geminivirus can be transmitted by whitefly. The virus was considered preliminary as sweet potato leaf curl virus (SPLCV) and was named as SPLCV-CN (sweet potato leaf curl virus in China).The PCR products were fractionated by electrophoresis, cloned into PMD-18T vector and competent Escherichia coli cells were transformed. Sequences of DNA-A of SPLCV-CN were determined. The length of DNA-A is 2771bp. SPLCV-CN has genome organization similar to that of begomoviruses. The DNA-A had two ORFs (AV1 and AV2) in the virion sense strand and four ORFs (AC1, AC2, AC3 and AC4) in the complementary sense strand. The intergenic region ( IR ) contains a conserved stem-loop motif, a conserved nanonucleotide, TATA box and three incomplete direct repeat iterons. The position of these iterative elements is similar to those of begomoviruses from the old world. These structures are needed in replication, transcription and package of geminivirus. Sequence comparisons showed that the DNA-A sequence of SPLCV-CN were closely related to those of sweet potato leaf curl Georgia virus-[16] (SPLCGV-[16]), Ipomoea yellow vein virus (IYVV-SI) and sweet potato leaf curl virus (SPLCuV ) with nucleotide sequence identity ranging from 88% to 91%. Comparison of individual encoded proteins between SPLCV-CN and that of three other SPLCV isolates showed the coat protein (AV1) shared amino acid sequence identity (93%-96%) . The relationships between SPLCV-CN and other whitefly-transmitted geminiviruses were investigated by using phylogeny of derived AV1, AC1 and AV2 amino acid sequences with Neighbor-joining and Parsimony of MEGA 3.0. In all phylogenetic trees, SPLCV-CN clustered with three other isolates of SPLCV. The result indicates that it is a strain of SPLCV. This is the first report of the natural occurrence of SPLCV in China. Based on the structure of the DNA-A and phylogenetic analyses, SPLCV originate in the Old World.