Taliansky M E, García-Arenal F
Departamento de Patología Vegetal, E.T.S.I. Agrónomos, Ciudad Universitaria, Madrid, Spain.
J Virol. 1995 Feb;69(2):916-22. doi: 10.1128/JVI.69.2.916-922.1995.
Direct evidence is presented for a host-specific role of the cucumovirus capsid protein in long-distance movement within infected plants. Cucumber (Cucumis sativus L.) is a systemic host for cucumber mosaic cucumovirus (CMV). Tomato aspermy cucumovirus, strain 1 (1-TAV), multiplied to the levels of CMV (i.e., replicated, moved from cell to cell, and formed infectious particles) in the inoculated leaves of cucumbers but was completely unable to spread systemically. The defective long-distance systemic movement of 1-TAV was complemented by CMV in mixed infections. Coinfection of cucumbers with 1-TAV RNA with various combinations of transcripts from full-length cDNA clones of CMV genomic RNA 1, RNA2, and RNA3 showed that CMV RNA3 alone complemented 1-TAV long-distance movement. We obtained mutants containing mutations in the two open reading frames in CMV RNA3 encoding the 3a protein and the capsid protein (CP), both of which are necessary for cell-to-cell movement of CMV. Complementation experiments with mutant CMV RNA3 showed that only 3a protein mutants, i.e., those with an intact CP, complemented the long-distance movement of 1-TAV in cucumbers. Since CMV and TAV have common systemic host plants, the results presented here are strong evidence for an active, host-specific function of the CPs of these two cucumoviruses for long-distance spread in the phloem. The results also suggest that the plasmodesmata in the vascular system and/or at the boundary between the mesophyll and the vascular system, involved in long-distance movement through the phloem, and those in the mesophyll, involved in cell-to-cell movement, differ functionally.
有直接证据表明黄瓜花叶病毒衣壳蛋白在受感染植物的长距离移动中具有宿主特异性作用。黄瓜（Cucumis sativus L.）是黄瓜花叶黄瓜病毒（CMV）的系统宿主。番茄不孕黄瓜病毒1号株系（1-TAV）在黄瓜接种叶片中增殖至CMV的水平（即复制、细胞间移动并形成感染性颗粒），但完全无法进行系统传播。在混合感染中，1-TAV缺陷的长距离系统移动可被CMV互补。黄瓜与1-TAV RNA以及CMV基因组RNA 1、RNA 2和RNA 3全长cDNA克隆转录本的各种组合共感染表明，单独的CMV RNA3可互补1-TAV的长距离移动。我们获得了在CMV RNA3中编码3a蛋白和衣壳蛋白（CP）的两个开放阅读框中发生突变的突变体，这两者都是CMV细胞间移动所必需的。用突变型CMV RNA3进行的互补实验表明，只有3a蛋白突变体（即CP完整的突变体）能互补1-TAV在黄瓜中的长距离移动。由于CMV和TAV有共同的系统宿主植物，此处给出的结果有力证明了这两种黄瓜花叶病毒的CP在韧皮部长距离传播中具有活跃的宿主特异性功能。结果还表明，参与通过韧皮部长距离移动的维管系统和/或叶肉与维管系统边界处的胞间连丝，以及参与细胞间移动的叶肉中的胞间连丝，在功能上存在差异。
