Transmission mechanism of plant viruses transmitted by the fungus Polymyxa betae

甜菜坏死性黄脉病毒(BNYVV)由土壤传播的甜菜多粘菌(Polymyxa Betae)传播，含有5种单链RNA(RNA1~5)。BNYVV是由甜菜上的烟草小蜂生物型传播的，而不是由藜菜、反枝苋和马齿苋的其他生物型传播的。虽然BNYVV和该载体的寄主范围仅限于藜科等少数物种，但甜菜疫霉游动孢子侵染的植物种类很广，其中几种植物的根也感染BNYVV。本氏烟草是很好的指示寄主。外壳蛋白由RNA2的5‘端ORF编码，该ORF的末端密码子可以被抑制，从而产生一个75 kDa的通读(RT)蛋白。突变分析表明，RT结构域N-末端的一个区域参与病毒组装，而C-末端蛋白包含对真菌传播重要的序列。建立了BNYVV RNA3、4和5的感染性克隆。对含有RNA3、RNA4和RNA5不同组合的菌株进行的真菌接种试验表明，RNA3和RNA5参与了症状表达。RNA3编码的25KDA蛋白是甜菜感病品种根瘤病的致病基因，也参与了甜菜抗病品种的抗性反应。当编码26KDA蛋白的RNA5存在时，根症状更强烈，获得了针对25KDA和26KDA蛋白的抗血清。这表明这些蛋白在受侵染的植物中的表达与症状的发展密切相关。RNA4与症状表达无关，但具有增加传播效率和稳定性的作用。RNA4与RNA3或RNA5之间存在协同作用。

Beet necrotic yellow vein virus (BNYVV), which is transmitted by the soil-borne fungus Polymyxa betae, contains five ssRNA species (RNAs 1 to 5). BNYVV was transmitted by the biotype of P. batae from sugar beets, but not by the other biotypes from Chenopodium album, Amaranthus retroflexus and Portulaca oleracea. Although host ranges of BNYVV and the vector were thought to be limited to only few species such as Chenopdiaceae species, P. betae zoospores were found to infect a wide range of plant species, and also BNYVV infected roots of several plant species of them. Nicotiana benthamiana is a good indicator host. The coat protein is encoded by the 5' proximal ORF of RNA2, and the terminal codon of this ORF can be suppressed, which results in the production of a 75 kDa readthrough (RT) protein. Mutagenic analysis revealed that a region within the N-terminal half of the RT domain is involved in virus assembly, whereas the C-terminal protein contains sequences important for fungus transmission. Infectious cDNA clones to BNYVV RNAs 3,4 and 5 were established. Fungal inoculation tests with isolates containing different combinations of RNAs 3, 4 and 5 showed that RNA3 and RNA5 are involved in symptom expression. The 25 kDA protein encoded by RNA3 was responsible for rhizomania of susceptible cultivars of sugar beet, and also was involved in resistant reaction in resistant cultivars. When RNA5, encoding the 26 kDA protein, was present, the root symptoms were more intense, Antisera against 25 kDA AND 26 kDA protein, were obtained. It was suggested that expressions of these proteins in infected plant are strongly involved in symptom development. RNA4 was not associated with symptom expression, but acted as increasing transmission efficiency and stability. Synergistic effects were found between RNA4 and RNA3 or RNA5.