Substantial portions of the 5' and intercistronic noncoding regions of cowpea chlorotic mottle virus RNA3 are dispensable for systemic infection but influence viral competitiveness and infection pathology.
Substantial portions of the 5' and intercistronic noncoding regions of cowpea chlorotic mottle virus RNA3 are dispensable for systemic infection but influence viral competitiveness and infection pathology.
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豇豆褪绿斑驳病毒RNA3的5端和顺反子间非编码区的大部分对于全身性感染是可有可无的，但会影响病毒竞争力和感染病理学。
DOI：
10.1016/0042-6822(92)90318-j
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发表时间：
1992
期刊：
影响因子：
3.7
通讯作者：
Ahlquist,P
中科院分区：
文献类型：
--
作者：
Pacha,RF;Ahlquist,P
豇豆褪绿斑驳病毒（CCMV）基因组为三重正链RNA。基因组RNA 3（2.2kb）编码3a非结构蛋白和外壳蛋白，它们是原生质体中病毒RNA合成所必需的，但是系统感染整株植物所必需的。在原生质体中，CCMV RNA 3的5′端和顺反子间非编码区的部分也被转录，用于RNA 3的复制和亚基因组外壳蛋白mRNA的转录。为了确定这些非编码序列是否是系统性感染所必需的，检测了RNA 3中一系列5′和顺反子间缺失对豇豆植物（CCMV的天然宿主）感染的影响。结果进一步完善了CCMVRNA 3亚基因组mRNA启动子的定位，并表明CCMVRNA 3的5′端非编码区至少有144个碱基和顺反子间非编码区至少有125个碱基与系统感染有关。对于在这些区域内具有缺失的突变体，在感染传播速率方面没有发现差异，并且接种后10-14天在全身感染组织中的病毒积累水平是野生型（wt）的60-100%。然而，最大的可行的顺反子间的缺失转化的野生型CCMV感染，以广泛的，明亮的黄色褪绿，几乎无菌的外观，表明感染病理学可以改变的突变与监管，而不是蛋白质编码字符。此外，在全植物共感染实验中，5′和顺反子间缺失突变体都不能有效地与wt CCMV竞争;即，在与wtCCMV共接种后，在全身感染的组织中检测不到这种突变体。因此，尽管CCMV RNA 3的5′和顺反子间非编码区的相当大一部分对于个体的系统性感染是不稳定的，但这些片段有助于病毒的竞争适应性，并影响与宿主的相互作用，如症状反应所证明的。
Cowpea chlorotic mottle virus (CCMV) has a tripartite, positive strand RNA genome. Genomic RNA3 (2.2 kb) encodes the 3a nonstructural protein and the coat protein, which are dispensable for viral RNA synthesis in protoplasts, but required for systemic infection of whole plants. In protoplasts, portions of the 5′ and intercistronic noncoding regions of CCMV RNA3 are also dispensable for RNA3 replication and for transcription of the subgenomic coat protein mRNA. To determine whether these noncoding sequences are required for systemic infection, a series of 5′ and intercistronic deletions in RNA3 were tested for their effects on the infection of cowpea plants, a natural host of CCMV. The results refine the mapping of the subgenomic mRNA promoter and show that at least 144 bases in the 5′ noncoding region and at least 125 bases in the intercistronic noncoding region of CCMV RNA3 are dispensable for systemic infection. For mutants with deletions within these regions, no differences were noted in the rate of infection spread, and the level of virus accumulation in systemically infected tissue 10–14 days postinoculation was 60–100% of wild type (wt). However, the largest viable intercistronic deletion transformed the nearly symptomless appearance of wt CCMV infections to an extensive, bright yellow chlorosis, showing that infection pathology can be altered by mutations with a regulatory rather than a protein-coding character. In addition, neither 5′ nor intercistronic deletion mutants competed effectively with wt CCMV in whole plant co-infection experiments; i.e., such mutants were not detectable in systemically infected tissue after co-inoculation with wt CCMV. Thus, although substantial portions of both the 5′ and the intercistronic noncoding regions of CCMV RNA3 are dispensable for individual systemic infection, these segments contribute to the competitive fitness of the virus and influence interaction with the host, as evidenced by symptom response.