Determination And Analysis Of The Complete Genomic Sequences Of Turnip Mosaic Virus And Tobacco Vein Banding Mosaic Virus

Turnip mosaic virus (TuMV), Tobacco vein banding mosaic virus (TVBMV) and Beet mosaic virus (BtMV) are worldwide spread and economically important viruses, which mainly infect plants of the families Brassicaceae, Solanaceae and Chenopodiaceae, respectively. In this study, the complete genomic sequences of two TuMV isolates and one TVBMV isolate, and the 3′-terminal genome sequence of one BtMV isolate were determined. Moreover, genetic variability of these three potyviruses was analyzed. The main results read as follows:The complete genomic sequence of two TuMV isolates, WFLB06 and TANX2, collected from radish in Tai'an and Weifang of Shandong Province were investigated. Both of WFLB06 and TANX2 could infect Brassica and Raphanus (BR) plants. Phylogenetic analysis results indicated that both of them belonged to the basal-BR group. This is the first report of complete sequences of Chinese TuMV isolates belonging to basal-BR group.The sequences were examined for evidence of recombination using different sequence comparison methods, and the results showed that recombination existed in both isolates. Isolate WFLB06 were from parents of basal-BR and Asian-BR sequences, with recombination sites located in P1, NIb and CI genes. Isolate TANX2 was intralineage recombinants from basal-BR parents, with recombination sites located in P1, 6K2 and VPg genes. These two recombination type patterns were novel and different from the 37 previously reported ones.The TuMV basal-BR isolates from China and Japan shared high similarities at both nucleotide and amino acid levels. Our study showed that Chinese and Japanese TuMV isolates belonged to the same population, and Chinese TuMV basal-BR isolates might originate from Japan. TuMV populations of China were under purifying or negative selection.The complete genomic sequence of TVBMV isolate HN39, which was collected from tobacco in Henan Provinces and represented Chinese prevalent strain of TVBMV, was determined and analyzed. The genome of TVBMV HN39 is composed of 9 570 nucleotides, excluding the poly(A) tail. This is the second complete genomic sequence of TVBMV available.TVBMV HN39 shared the highest identity with Wild tomato mosaic virus (WTMV) at complete genomic level. However, different genes of HN39 shared the highest identities with different potyviruses. This indicated that different genes of isolate HN39 might evolve from different ancestors.Viral isolate SD was obtained from naturally infected lettuce showing the symptoms of mosaic and stunting in suburb of Tai'an, Shandong Province. The 3′-terminal region ca. 1 700 nt was amplified by RT-PCR with degenerate primers designed for potyviruses. The BLAST results indicated that SD was an isolate of Beet mosaic virus (BtMV). Sequence alignment result showed that the 3′-terminal genomic sequence of BtMV-SD shared identities of 91.1-98.8% with other BtMV isolates previously reported. This is the first report that BtMV can infect lettuce naturally.