Transmission mechanism of Benyvirus (BNYVV) by the fungus Polymyxa betae

甜菜坏死黄脉病毒（Beetnecrotiveyellowveinvirus，BNYVV）是甜菜丛根病的病原，由甜菜多黏菌（Polymyxabetae）传播。BNYVV有5种RNA（RNA 1 -5）。RNA 1和RNA 2参与病毒RNA复制、装配和细胞间移动，RNA 3至5与甜菜根中载体介导的感染和疾病发展相关。通过将GFP基因引入BNYVV RNA 2的外壳蛋白通读结构域，构建了GFP标记的BNYVV（BNYVV-GFP）。BNYVV-GFP对局部病斑和系统性宿主植物具有有效的感染性，并且通过表达绿色荧光来跟踪感染部位。然而，构建的几种GFP病毒不能通过甜菜夜蛾传播，因此我们不能使用BNYVV-GFP进行传播实验。用BNYVV-GFP检测了甜菜植物中BNYVV的维管运动。当病毒摩擦接种到叶片中时，病毒很难从表皮细胞移动到韧皮部组织。在根中，病毒在小根的任何组织中都能繁殖，但病毒很难从小根组织侵入主根和茎的韧皮部组织。对RNA 4编码的p31的分子分析表明，BNYVV p31在有效的载体传播、增强的症状表达和根特异性沉默抑制中起多功能作用。RNA 3编码的p25蛋白负责产生丛根病症状。p25蛋白的存在也被发现与抗性植物的抗性反应有关。BNYVV株系与甜菜植株之间存在基因型特异性互作。三个氨基酸残基68、70和179在决定耐药表型方面很重要，并且宿主基因型特异性由位置68处的单个氨基酸变化控制。BNYVV在根和叶中的抗性机制可能不同，叶中的抗性比根中的抗性强。

Beet necrotic yellow vein virus (BNYVV, Benyvirus) causes rhizomania disease of sugar beet and is transmitted by Polymyxa betae. BNYVV has five RNA species (RNA1-5). RNA1 and RNA2 are involved in viral RNA replication, assembly, and cell-to-cell movement, and RNA3 to 5 are associated with vector-mediated infection and disease development in sugar beet roots. GFP-tagged BNYVV (BNYVV-GFP) was constructed by introducing the GFP gene into the coat protein readthrough domain of BNYVV RNA2. BNYVV-GFP was efficiently infectious to local lesion and systemic host plants and infection sites were followed up by expressing the green fluorescence. However, several GFP viruses constructed were not transmitted by P. betae so that we were not able to conduct transmission experiments using BNYVV-GFP. The vascular movement of BNYVV in beet plants was examined using BNYVV-GFP. The virus had difficulty to move from epidermal cells to phloem tissues when rub-inoculated into leaves. In roots, the vector-inoculated virus propagated in any tissues of rootlets, but it was difficult for virus to invade from rootlet tissues into phloem tissues of taproots and stems. Molecular analyses of RNA4-encoded p31 showed that BNYVV p31 plays a multifunctional role in efficient vector transmission, enhanced symptom expression and root-specific silencing suppression. The RNA3-encoded p25 protein is responsible for production of rhizomania symptoms. The presence of the p25 protein also was found to be associated with resistance response in resistant plants. There was a genotype-specific interaction between BNYVV strains and the beet plants. Three amino acid residues 68, 70, and 179 are important in determining the resistance phenotype, and that the host-genotype specificity is controlled by single amino acid changes at position 68. BNYVV resistance mechanisms in root and leaf may be different: the resistance appearing in leaves was stronger than that appearing in roots.