Navas-Castillo J, Albiach-Martí M R, Gowda S, Hilf M E, Garnsey S M, Dawson W O
Citrus Research and Education Center, University of Florida, Lake Alfred 33850, USA.
Virology. 1997 Feb 3;228(1):92-7. doi: 10.1006/viro.1996.8369.
Citrus tristeza virus (CTV), a member of the closterovirus group, is one of the more complex single-stranded RNA viruses. The 5' portion of its 19,296-nt, single-stranded RNA genome is expressed as an approximately 400-kDa polyprotein that is proteolytically processed, while the 10 3' open reading frames are expressed from 3'-coterminal subgenomic RNAs (sg RNAs). As an initial examination of the gene expression of this virus, we found that the kinetics of accumulation of genomic and sg RNAs and coat protein of the T36 isolate of CTV were similar in protoplasts of the natural host, citrus, and the experimental nonhost Nicotiana benthamiana. Newly synthesized genomic RNA was detected 2 days postinoculation and increased to a maximum at 3-5 days. The RNA complementary to the full-length virion RNA increased with similar kinetics, but at approximately one-tenth the concentration of genomic plus strands. Most of the abundant sg RNAs also accumulated in parallel to that of the genomic RNA. However, the smallest sg RNA, which corresponds to the p23 gene, increased earlier. The different sg RNAs accumulated in greatly differing amounts, in general with 3'-most sg RNAs accumulating to higher levels than 5' sg RNAs. However, some 3' sg RNAs (p13 and p18) accumulated to low levels. The two 3'-most sg RNAs (p23 and p20) accumulated to high levels approximately equal to that of the genomic RNA. The accumulation curve for coat protein paralleled that of its mRNA, suggesting that its regulation was transcriptional. Progeny virions from protoplasts were used to sequentially infect new protoplasts, serving as a potential source of virus that could evolve free from the genetic selection in intact plants for aphid transmission and movement.
柑橘衰退病毒（CTV）是长线形病毒属的成员之一，是较为复杂的单链RNA病毒之一。其19296个核苷酸的单链RNA基因组的5'部分表达为一个约400 kDa的多聚蛋白，该多聚蛋白经蛋白水解加工，而10个3'开放阅读框则由3'共末端亚基因组RNA（sg RNA）表达。作为对该病毒基因表达的初步研究，我们发现CTV T36分离株的基因组RNA、sg RNA和外壳蛋白在天然宿主柑橘以及实验性非宿主本氏烟草的原生质体中的积累动力学相似。接种后2天检测到新合成的基因组RNA，并在3 - 5天达到最大值。与全长病毒粒子RNA互补的RNA以相似的动力学增加，但浓度约为基因组正链的十分之一。大多数丰富的sg RNA也与基因组RNA平行积累。然而，对应于p23基因的最小sg RNA增加得更早。不同的sg RNA积累量差异很大，一般来说，最靠近3'端的sg RNA积累水平高于5'端的sg RNA。然而，一些3'端sg RNA（p13和p18）积累水平较低。最靠近3'端的两个sg RNA（p23和p20）积累到高水平，大致与基因组RNA相当。外壳蛋白的积累曲线与其mRNA的积累曲线平行，表明其调控是转录水平的。来自原生质体的子代病毒粒子被用于依次感染新的原生质体，作为一种潜在的病毒来源，其可以在不受完整植物中蚜虫传播和移动的遗传选择影响的情况下进化。
