Laboratory Of Cell Biology And Manipulation, Graduate School Of Agriculture, Hokkaido University, Sapporo, Japan.
Mol Plant Microbe Interact. 2010 Mar;23(3):332-9. doi: 10.1094/MPMI-23-3-0332.
Two isolates of Tomato aspermy virus (TAV), V-TAV and C-TAV, can systemically infect Nicotiana benthamiana but only C-TAV can move systemically in N. tabacum. Any pseudorecombinants between the two strains could not move systemically in tobacco as efficiently as C-TAV. However, a pseudorecombinant consisting of RNAs 1 and 3 of V-TAV and RNA 2 of C-TAV (V1C2V3), which cannot infect tobacco systemically, generated progeny with a mutation in V1 and a recombination in C2 (V1(m)C2(r)V3), enabling the virus to move systemically. To avoid further mutation and recombination in the virus, we used Cucumber mosaic virus RNA3 (Y3) for subsequent experiments. Northern blot analyses showed that RNA4A, which encodes the 2b protein (2b), and RNA5 abundantly accumulated in V1(m)C2(r)Y3-infected tobacco. V1(m)C2(r)Y3 actually caused higher accumulation of 2b than did V1C2Y3 in Western blots, and overexpression of 2b by the PVX vector enabled V1C2Y3 to move systemically in tobacco, suggesting that 2b accumulation promotes viral systemic movement. Because RNA-silencing suppressor (RSS) activity of 2b was thought to be involved in systemic movement, we compared the RSS activity of 2b for the two TAV isolates; C-TAV 2b had stronger activity than did V-TAV 2b in tobacco in a transient protoplast assay. Our data also demonstrated that 2b and RNA5 play an important role in the evolution of members of genus Cucumovirus by generating mutant/recombinant viruses and viral systemic movement over RNA silencing.
两种番茄不孕病毒（TAV）分离株，V-TAV 和 C-TAV，可系统感染本氏烟，但只有 C-TAV 可在烟上系统移动。两株之间的任何假重组体在烟草中的系统移动效率均不如 C-TAV。然而，由 V-TAV 的 RNA1 和 RNA3 和 C-TAV 的 RNA2 组成的假重组体（V1C2V3），不能系统地感染烟草，但其生成的后代在 V1 发生突变和 C2 发生重组（V1(m)C2(r)V3），使病毒能够系统移动。为了避免病毒进一步突变和重组，我们在后续实验中使用了黄瓜花叶病毒 RNA3（Y3）。Northern blot 分析表明，编码 2b 蛋白（2b）的 RNA4A 和 RNA5 在 V1(m)C2(r)Y3 感染的烟草中大量积累。在 Western blot 中，V1(m)C2(r)Y3 实际上比 V1C2Y3 引起 2b 的积累更高，而 PVX 载体的 2b 过表达使 V1C2Y3 能够在烟草中系统移动，这表明 2b 的积累促进了病毒的系统移动。由于 2b 的 RNA 沉默抑制（RSS）活性被认为与系统移动有关，我们比较了两种 TAV 分离株 2b 的 RSS 活性；在瞬时原生质体测定中，C-TAV 2b 在烟草中的活性强于 V-TAV 2b。我们的数据还表明，2b 和 RNA5 通过产生突变/重组病毒和 RNA 沉默介导的病毒系统移动，在黄瓜花叶病毒属成员的进化中发挥了重要作用。
