Molecular Genetic Analysis of Host Specificity in Plant Viruses

大多数植物病毒在直接接种于多种植物的细胞中复制，但在启动细胞间和/或维持随后通过植物的系统传播方面表现出精致的宿主特异性。作为对植物病毒基因在运动、系统感染和寄主特异性中的个体和集体作用的分子研究的基础，研究人员已经获得并鉴定了几种不同的、在寄主范围和基因组序列上存在不同差异的具有感染性的完整的cdna克隆。并证明了在这类病毒之间有计划地交换选定的基因和基因片段为识别宿主特异性决定因素和表征它们的行为提供了一种强有力的方法。在这些工具和溴病毒分子生物学强大的一般性特征的基础上，他们现在将：在细胞水平上跟踪感染运动，以确定不同病毒基因改变时系统感染被阻断的不同阶段；将宿主特异性效应定位到几个相关病毒基因的特定功能域，并测试一种基于自然RNA重组的潜在有效的RNA病毒基因定位的新方法；测试初步迹象，与“门控”假设相反，成功的系统性感染需要3a运动基因与1a和2a复制基因之间的相互适应；确定1a和2a基因对系统感染的明显复制后影响是否真的独立于它们在RNA复制中的已知功能；并在3a基因周围的非编码序列中定位观察到的宿主特异性决定因素，并确定它们对3a基因表达的可能影响。结果应该提供关于植物对感染性病毒的反应的明确概念。

Most plant viruses replicate in directly inoculated cells from a wide range of plants, but show exquisite host specificity with respect to initiating cell-to-cell and/or sustaining subsequent systemic spread through the plant. As a foundation for molecular study of the individual and collective role of plant virus genes in movement, systemic infection, and host specificity, the investigators have produced and characterized complete, infectious cDNA clones of several distinct bromoviruses of varying divergence in host range and genome sequence, and demonstrated that designed exchange of selected genes and gene segments between such viruses provides a powerful approach for identifying host specificity determinants and characterizing their behavior. Building on these tools and the strong general characterization of bromovirus molecular biology, they will now: follow infection movement at the cellular level to define the distinct stages at which systemic infection is blocked upon alteration of different virus genes; map host specificity effects to specific functional domains of several implicated virus genes and test a potentially powerful new approach to RNA virus genetic mapping based on natural RNA recombination; test preliminary indications that, contrary to the "gating " hypothesis, successful systemic infection requires mutual adaptation between the 3a movement gene and the 1a and 2a replication genes; determine whether the apparently post-replication influence of the 1a and 2a genes on systemic infection is truly independent of their known functions in RNA replication; and localize observed host specificity determinants in noncoding sequences surrounding the 3a gene and determine their possible influence on 3a gene expression. The results should provide clarifying concepts regarding the plant's response to the infective viruses.