The molecular characterization of 16 new sequence variants of Hop stunt viroid reveals the existence of invariable regions and a conserved hammerhead-like structure on the viroid molecule
The molecular characterization of 16 new sequence variants of Hop stunt viroid reveals the existence of invariable regions and a conserved hammerhead-like structure on the viroid molecule
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DOI：
10.1099/0022-1317-82-4-953
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发表时间：
2001-04-01
影响因子：
3.8
通讯作者：
Pallás, V
中科院分区：
文献类型：
--
作者：
Amari, K;Gomez, G;Pallás, V
目前，啤酒花矮化类病毒（HSVd）的分离物分为五组：三大集团（李子型、啤酒花型和柑橘型），每一种都含有仅来自有限数量的分离宿主和两个小群的分离物，这两个小群被认为是来源于主群成员之间的重组事件，在这项工作中，我们提出了从四个地中海国家获得的16个新的HSVd序列变体的特征（塞浦路斯、希腊、摩洛哥和土耳其），这些地方以前没有描述过这种类病毒。考虑到迄今为止表征的序列变体的总体的分子变异性比较显示，大部分的变异性被发现在类病毒分子的致病性和可变结构域中，而末端右（T-R）和左（T-L）结构域分别是低变异性或无变异性的区域，这表明存在限制序列变体的异质性的约束。系统发育分析表明，属于两个小的重组亚组的序列变异比以前认为的更频繁。当考虑十字形结构替代典型的棒状构象时，观察到该结构的上部（发夹I）是严格保守的，而在下部发现减少的变异性。在该下部存在显著的共变异。有趣的是，在HSVd的T-R结构域内发现锤头状序列，并且其在所有序列变体中是严格保守的。HSVd上存在这个基序的进化意义进行了讨论。
At present isolates of Hop stunt viroid (HSVd) are divided into five groups: three major groups (plum-type, hop-type and citrus-type) each containing isolates from only a limited number of isolation hosts and two minor groups that were presumed to derive from recombination events between members of the main groups, In this work we present the characterization of 16 new sequence variants of HSVd obtained from four Mediterranean countries (Cyprus, Greece, Morocco and Turkey) where this viroid had not previously been described. Molecular variability comparisons considering the totality of the sequence variants characterized so far revealed that most of the variability is found in the pathogenic and variable domains of the viroid molecule whereas both the terminal right (T-R) and left (T-L) domains are regions of low or no variability, respectively, suggesting the existence of constraints limiting the heterogeneity of the sequence variants. Phylogenetic analyses revealed that sequence variants belonging to the two minor recombinant subgroups are more frequent than previously thought. When the cruciform structure alternative to the typical rodlike conformation was considered it was observed that the upper part of this structure (hairpin I) was strictly conserved whereas in the lower part a reduced variability was found, The existence of a covariation in this lower part was notable, Interestingly, a hammerhead-like sequence was found within the T-R domain of HSVd and it was strictly conserved in all the sequence variants. The evolutionary implications of the presence of this motif on the HSVd are discussed.