Department of Plant Pathology, University of California Davis, CA, USA.
Front Microbiol. 2013 May 20;4:99. doi: 10.3389/fmicb.2013.00099. eCollection 2013.
Criniviruses comprise one of the genera within the family Closteroviridae. Members in this family are restricted to the phloem and rely on whitefly vectors of the genera Bemisia and/or Trialeurodes for plant-to-plant transmission. All criniviruses have bipartite, positive-sense single-stranded RNA genomes, although there is an unconfirmed report of one having a tripartite genome. Lettuce infectious yellows virus (LIYV) is the type species of the genus, the best studied so far of the criniviruses and the first for which a reverse genetics system was developed. LIYV RNA 1 encodes for proteins predicted to be involved in replication, and alone is competent for replication in protoplasts. Replication results in accumulation of cytoplasmic vesiculated membranous structures which are characteristic of most studied members of the Closteroviridae. These membranous structures, often referred to as Beet yellows virus (BYV)-type vesicles, are likely sites of RNA replication. LIYV RNA 2 is replicated in trans when co-infecting cells with RNA 1, but is temporally delayed relative to RNA 1. Efficient RNA 2 replication also is dependent on the RNA 1-encoded RNA-binding protein, P34. No LIYV RNA 2-encoded proteins have been shown to affect RNA replication, but at least four, CP (major coat protein), CPm (minor coat protein), Hsp70h, and P59 are virion structural components and CPm is a determinant of whitefly transmissibility. Roles of other LIYV RNA 2-encoded proteins are largely as yet unknown, but P26 is a non-virion protein that accumulates in cells as characteristic plasmalemma deposits which in plants are localized within phloem parenchyma and companion cells over plasmodesmata connections to sieve elements. The two remaining crinivirus-conserved RNA 2-encoded proteins are P5 and P9. P5 is 39 amino acid protein and is encoded at the 5' end of RNA 2 as ORF 1 and is part of the hallmark closterovirus gene array. The orthologous gene in BYV has been shown to play a role in cell-to-cell movement and indicated to be localized to the endoplasmic reticulum as a Type III integral membrane protein. The other small protein, P9, is encoded by ORF 4 overlaps with ORF 3 that encodes the structural protein, P59. P9 seems to be unique to viruses in the genus Crinivirus, as no similar protein has been detected in viruses of the other two genera of the Closteroviridae.
菜豆黄花叶病毒是该属的模式种，也是迄今为止研究最为深入的克鲁西病毒之一，也是首个开发出反向遗传学系统的病毒。LIYV RNA1 编码的蛋白被预测参与复制，单独就有在原生质体中进行复制的能力。复制导致细胞质囊泡状膜结构的积累，这是大多数研究的 Closteroviridae 成员的特征。这些膜结构通常被称为甜菜黄花叶病毒（BYV）-型囊泡，可能是 RNA 复制的部位。当与 RNA1 共感染细胞时，LIYV RNA2 在转录中复制，但相对于 RNA1 有时间延迟。有效的 RNA2 复制也依赖于 RNA1 编码的 RNA 结合蛋白 P34。没有证据表明 LIYV RNA2 编码的蛋白会影响 RNA 复制，但至少有四个，CP（主要外壳蛋白）、CPm（次要外壳蛋白）、Hsp70h 和 P59 是病毒粒子的结构成分，CPm 是白背飞虱传播能力的决定因素。LIYV RNA2 编码的其他蛋白的作用在很大程度上尚未可知，但 P26 是一种非病毒蛋白，在细胞中积累形成特征性质膜沉积物，在植物中定位于韧皮部薄壁组织和伴胞中，通过胞间连丝与筛管连接。其余两个克鲁西病毒保守的 RNA2 编码蛋白是 P5 和 P9。P5 是一个 39 个氨基酸的蛋白，编码在 RNA2 的 5'端的 ORF1，是标志 Closterovirus 基因阵列的一部分。BYV 的同源基因已被证明在细胞间运动中发挥作用，并被指示定位于内质网作为 III 型整合膜蛋白。另一种小蛋白 P9 由 ORF4 编码，与编码结构蛋白 P59 的 ORF3 重叠。P9 似乎是克鲁西病毒属病毒所独有的，因为在 Closteroviridae 的另外两个属的病毒中没有检测到类似的蛋白。
