Thesis

Genome organization and genetic diversity of Taura syndrome virus (TSV) of Penaeid shrimp (Penaeus sp)

Taura syndrome disease, caused by Taura syndrome virus (TSV), is one of the most important viral diseases of penaeid shrimp in the Western Hemisphere. A 3278 bp eDNA representing the 3' end of the TSV genome was cloned and sequenced. Sequence analyses revealed a 5'-terminal 19 non -coding bases followed by a long open reading frame encoding 10 11 amino acids (aa), and a 3' untranslated region of 225 nts. The deduced aa sequence of TSV showed significant similarities with those of the coat proteins of several insect picomaviruses. A single transcript of approximately 10 kb was detected by Northern blot hybridization suggesting that the TSV coat protein gene is not expressed as a subgenomic RNA. The genome organization ofTSV is similar to insect picornaviruses. Therefore, this is the first molecular evidence of occurrence of a picomavirus in the class Decapoda. The putative VP2 and VP3 capsid protein genes ofTSV from 17 geographical isolates collected from US, Mexico and Taiwan were amplified by RT-PCR to assess the genetic diversity and phylogenetic relationships among isolates. Alignment of the capsid proteins showed nonconservative changes that may be involved in antigenicity and/ or virulence of the isolates. Phylogenetic analyses revealed that the TSV isolates clustered in two main groups, one Mexican group and one mixed group of Mexican, Taiwan and Texas isolates indicating a shared phylogenetic relationship and a possible common origin.

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