Characterization of Bean Necrotic Mosaic Virus: A Member of a Novel Evolutionary Lineage within the Genus Tospovirus

BackgroundTospoviruses (Genus Tospovirus, Family Bunyaviridae) are phytopathogens responsible for significant worldwide crop losses. They have a tripartite negative and ambisense RNA genome segments, termed S (Small), M (Medium) and L (Large) RNA. The vector-transmission is mediated by thrips in a circulative-propagative manner. For new tospovirus species acceptance, several analyses are needed, e.g., the determination of the viral protein sequences for enlightenment of their evolutionary history. Methodology/Principal FindingsBiological (host range and symptomatology), serological, and molecular (S and M RNA sequencing and evolutionary studies) experiments were performed to characterize and differentiate a new tospovirus species, Bean necrotic mosaic virus (BeNMV), which naturally infects common beans in Brazil. Based upon the results, BeNMV can be classified as a novel species and, together with Soybean vein necrosis-associated virus (SVNaV), they represent members of a new evolutionary lineage within the genus Tospovirus. Conclusion/SignificancesTaken together, these evidences suggest that two divergent lineages of tospoviruses are circulating in the American continent and, based on the main clades diversity (American and Eurasian lineages), new tospovirus species related to the BeNMV-SVNaV clade remain to be discovered. This possible greater diversity of tospoviruses may be reflected in a higher number of crops as natural hosts, increasing the economic impact on agriculture. This idea also is supported since BeNMV and SVNaV were discovered naturally infecting atypical hosts (common bean and soybean, respectively), indicating, in this case, a preference for leguminous species. Further studies, for instance a survey focusing on crops, specifically of leguminous plants, may reveal a greater tospovirus diversity not only in the Americas (where both viruses were reported), but throughout the world.背景：番茄斑萎病毒属（Tospovirus）、布尼亚病毒科（Bunyaviridae）是一类植物病原物，在全球范围内造成严重的作物减产。它们拥有三段负义兼义RNA基因组片段，分别命名为S（小）、M（中）和L（大）RNA。其媒介传播由蓟马以循回增殖型方式介导。对于新型番茄斑萎病毒物种的认定，需开展多项分析，例如测定病毒蛋白序列以阐明其演化历史。 材料与方法/主要发现：研究开展了生物学（宿主范围与症状学）、血清学及分子生物学（S、M RNA测序与演化分析）实验，对一种在巴西自然侵染普通菜豆的新型番茄斑萎病毒物种——菜豆坏死花叶病毒（Bean necrotic mosaic virus, BeNMV）进行了鉴定与区分。基于实验结果，BeNMV可被归类为新物种，其与大豆叶脉坏死相关病毒（Soybean vein necrosis-associated virus, SVNaV）一同构成番茄斑萎病毒属内一个全新的演化支系。 结论与意义：综合上述证据，番茄斑萎病毒存在两个分化支系在美洲大陆传播；结合主要进化枝的多样性（美洲支系与欧亚支系），与BeNMV-SVNaV进化枝相关的新型番茄斑萎病毒物种仍有待发掘。这种潜在的更丰富的番茄斑萎病毒多样性，可能意味着更多作物成为其自然宿主，进而加剧其对农业的经济影响。这一推论亦得到佐证：BeNMV与SVNaV分别自然侵染非典型宿主（普通菜豆与大豆），表明该类病毒在此类宿主中偏好豆科物种。后续开展的相关研究，例如以作物尤其是豆科植物为目标的调查，不仅可在已有这两种病毒报道的美洲地区，更可在全球范围内揭示更多此前未被发现的番茄斑萎病毒多样性。