Nucleotide sequence of the coat protein coding region of the potyvirus tobacco vein-banding mosaic virus

Development of Attenuated Viruses for Effective Protection against Pepper Veinal Mottle Virus in Tomato Crops

Tomato (Solanum lycopersicum) is the most important vegetable and fruit crop in the family Solanaceae worldwide. Numerous pests and pathogens, especially viruses, severely affect tomato production, causing immeasurable market losses. In Taiwan, the cultivation of tomato crops is mainly threatened by insect-borne viruses, among which pepper veinal mottle virus (PVMV) is one of the most prevalent. PVMV is a member of the genus Potyvirus of the family Potyviridae and is non-persistently transmitted by aphids. Its infection significantly reduces tomato fruit yield and quality. So far, no PVMV-resistant tomato lines are available. In this study, we performed nitrite-induced mutagenesis of the PVMV tomato isolate Tn to generate attenuated PVMV mutants. PVMV Tn causes necrotic lesions in Chenopodium quinoa leaves and severe mosaic and wilting in Nicotiana benthamiana plants. After nitrite treatment, three attenuated PVMV mutants, m4-8, m10-1, and m10-11, were selected while inducing milder responses to C. quinoa and N. benthamiana with lower accumulation in tomato plants. In greenhouse tests, the three mutants showed different degrees of cross-protection against wild-type PVMV Tn. m4-8 showed the highest protective efficacy against PVMV Tn in N. benthamiana and tomato plants, 100% and 97.9%, respectively. A whole-genome sequence comparison of PVMV Tn and m4-8 revealed that 20 nucleotide substitutions occurred in the m4-8 genome, resulting in 18 amino acid changes. Our results suggest that m4-8 has excellent potential to protect tomato crops from PVMV. The application of m4-8 in protecting other Solanaceae crops, such as peppers, will be studied in the future.

Molecular variability of Tobacco vein banding mosaic virus populations

The incidence of Tobacco vein banding mosaic virus (TVBMV) on tobacco increases dramatically in China recently and it has caused great economic losses. To gain insights into the evolutionary mechanisms of TVBMV, a total of 40 TVBMV isolates were collected from different tobacco production regions in China and their genomic regions encoding helper component-proteinase (HC-Pro), the third protein (P3), the first 6K protein (6K1) and coat protein (CP) were sequenced. Phylogenetic analyses revealed that TVBMV isolates can be divided into two evolutionary divergent groups based on P3, the frame-shifting pipo and 6K1 genes, and three groups on HC-Pro and CP genes. The populations from most parts of mainland China (MC) showed frequent gene flow; those from Yunnan province in south western China always formed a separate group (YN) and also had frequent within-group gene flow. However, the gene flow between groups MC and YN was uncommon. Our results revealed that all the tested TVBMV genes were under negative selection and the HC-Pro gene was under the strongest constraints. Recombination events were identified in 13 of the 42 analyzed isolates. This study suggested that negative selection, gene flow and recombination were important evolutionary factors driving the genetic diversification of TVBMV.

Complete genome sequence of a tobacco isolate of the tobacco vein banding mosaic virus strain prevailing in China

Tobacco vein banding mosaic virus (TVBMV) is a species of the largest plant virus genus Potyvirus. Its incidence has been increasing in Chinese tobacco-growing area. TVBMV isolates can be clustered into three genetic groups that are corresponding with their geographical origin. We have reported the complete genomic sequence of TVBMV isolate YND with unique NIb/CP cleavage site. Here, we determined and analyzed the complete genomic sequence of isolate HN39, which was collected from tobacco in Henan Province and represented Chinese prevalent strain of TVBMV. HN39 has similar host range with YND, but induce mild vein banding symptom in Nicotiana tabacum cv. Samsun. The genome of TVBMV-HN39 is composed of 9,570 nucleotides, excluding the poly(A) tail. It contains a large ORF of 9,240 nucleotides and encode a polyprotein of 3,079 amino acids. The putative NIa-Pro cleavage site for NIb/CP is Q/G. The identities between the complete genomes of isolates HN39 and YND were 90.0% at nucleotide level and 95.4% at amino acid level. As for other potyviruses, HN39 shared the highest identity with wild tomato mosaic virus (WTMV) at complete genomic level, while different genes shared the highest identities with different potyviruses. This is the second complete genomic sequence of TVBMV reported.

The complete genomic sequence of Tobacco vein banding mosaic virus and its similarities with other potyviruses

The complete genomic sequence of an isolate of Tobacco vein banding mosaic virus (TVBMV-YND) from Yunnan, China was determined by sequencing overlapping cDNA fragments obtained by RT-PCR with degenerate and/or specific primers. The genome is composed of 9,570 nucleotides (nt) excluding the 3'-terminal poly (A) tail and contains one single open reading frame of 9,240 nt encoding a large polyprotein of 3,079 amino acids with predicted Mr of 348.6 kDa. Phylogenetic analysis of complete genomic sequences confirmed that TVBMV is a distinct species of the genus Potyvirus. Different parts of TVBMV-YND genome shared different levels of identity with other species of potyviruses, while most parts showed greatest identity with Chilli veinal mottle virus among the potyviruses with available complete genomic sequences. TVBMV-YND had a rare Q/N cleavage site for NIb/CP and uncommon RITC motif in HC-Pro that is crucial for aphid transmission of potyviruses.

Molecular diversity of tobacco vein banding mosaic virus

Tobacco vein banding mosaic virus (TVBMV) is of increasing importance in tobacco production on the Chinese mainland. The 3'-terminal genomic sequences (1624 nucleotides) of 12 TVBMV isolates from China were determined and compared to the sequences of only four TVBMV isolates available in databanks. The results revealed that TVBMV consists of several phylogenetically distinguishable strains that show a degree of correlation with the geographical origin. Two isolates from Yunnan had a unique putative NIb/CP proteolytic cleavage site of Q/N that is uncommon for potyviruses, whereas other TVBMV isolates had the more typical Q/G amino acids at that site. One isolate (ZB6) from Zibo, Shandong Province, was predicted to have experienced recombination within the characterized genomic region.