Complete Genome Sequence of Mulberry Vein Banding Associated Virus, a New Tospovirus Infecting Mulberry.

Jiaorong Meng,Pingping Liu,Jieqiu Li,Baoshan Chen,Chengwu Zou,Liling Zhu,Hanu R Pappu

doi:10.1371/journal.pone.0136196

Abstract

Mulberry vein banding associated virus (MVBaV) that infects mulberry plants with typical vein banding symptoms had been identified as a tentative species of the genus Tospovirus based on the homology of N gene sequence to those of tospoviruses. In this study, the complete sequence of the tripartite RNA genome of MVBaV was determined and analyzed. The L RNA has 8905 nucleotides (nt) and encodes the putative RNA-dependent RNA polymerase (RdRp) of 2877 aa amino acids (aa) in the viral complementary (vc) strand. The RdRp of MVBaV shares the highest aa sequence identity (85.9%) with that of Watermelon silver mottle virus (WSMoV), and contains conserved motifs shared with those of the species of the genus Tospovirus. The M RNA contains 4731 nt and codes in ambisense arrangement for the NSm protein of 309 aa in the sense strand and the Gn/Gc glycoprotein precursor (GP) of 1,124 aa in the vc strand. The NSm and GP of MVBaV share the highest aa sequence identities with those of Capsicum chlorosis virus (CaCV) and Groundnut bud necrosis virus (GBNV) (83.2% and 84.3%, respectively). The S RNA is 3294 nt in length and contains two open reading frames (ORFs) in an ambisense coding strategy, encoding a 439-aa non-structural protein (NSs) and the 277-aa nucleocapsid protein (N), respectively. The NSs and N also share the highest aa sequence identity (71.1% and 74.4%, respectively) with those of CaCV. Phylogenetic analysis of the RdRp, NSm, GP, NSs, and N proteins showed that MVBaV is most closely related to CaCV and GBNV and that these proteins cluster with those of the WSMoV serogroup, and that MVBaV seems to be a species bridging the two subgroups within the WSMoV serogroup of tospoviruses in evolutionary aspect, suggesting that MVBaV represents a distinct tospovirus. Analysis of S RNA sequence uncovered the highly conserved 5’-/3’-ends and the coding regions, and the variable region of IGR with divergent patterns among MVBaV isolates.

Highlights

The mulberry (Morus spp.) is an economically important plant grown widely throughout Asia, for the cultivation of the silkworms (Bombyx mori Linn.) and for the sericulture industry
Our results show that Mulberry vein banding associated virus (MVBaV) is a distinct member of Tospovirus belonging to the Watermelon silver mottle virus (WSMoV) serogroup
In term of molecular differentiation, N protein sequence identity of 90% has been set as the threshold to establish a new species of tospovirus

Summary

Introduction

The mulberry (Morus spp.) is an economically important plant grown widely throughout Asia, for the cultivation of the silkworms (Bombyx mori Linn.) and for the sericulture industry. Diverse virus-like symptoms, including mosaic, vein banding, vein necrosis, chlorotic ringspots, and leaf deformation were frequently observed on mulberry. The viral diseases have been a major factor restricting yield and quality of mulberry. Two mulberry-infecting viruses, Mulberry latent virus (Genus Carlavirus) [1] and the Mulberry ringspot virus (Genus Nepovirus) [2], have been partly characterized in Japan. A mulberry-infecting Tospovirus, temporarily named Mulberry vein banding virus (MuVBV), was found in China and identified to be a new species of Tospovirus based on the homology of N protein sequence to other Tospovirus species [3]. Tospoviruses cause significant loss of yield and quality to vegetables, legumes, and ornamental crops worldwide and are transmitted by thrips in a circulative and propagative manner [4, 5]. The 3' termini of all RNA segments are highly conserved in the first 9 nucleotides and show inverted complementarity to the 5' ends [7]

Methods

Results

Conclusion