SEROLOGICAL AND MOLECULAR CHARACTERIZATION OF A HIGH TEMPERATURE-RECOVERED (HT-1) VIRUS BELONGING TO SEROGROUP IV TOSPOVIRUS
PP UENG1, HT HSU2, SD YEH 3, Z YE1, K SUBRAMANIUM1 and RH LAWSON4
1US Dept. of Agriculture, Agricultural Research Service, Mol. Plant Pathol. Lab., and 2US Dept. of Agriculture, Agricultural Research Service, Floral and Nursery Plants Research Unit, Beltsville, MD, USA; 3Dept. of Plant Pathology, National Chung-Hsing
University, Taichung, Taiwan, ROC; 4US Dept. of Agriculture, Agricultural Research Service, National Program Staff, Beltsville, MD, USA
Background and objectives
The Tospovirus genus in the family Bunyaviridae contains viruses infecting both plants and thrips. Viruses included in the genus have an extensive host range including both vegetable and ornamental species. Tospoviruses exhibit a wide range of differences in serological reactions, symptom expression, induced cytological changes and protein profiles. A serologically and morphologically distinct tospovirus, HT-1, was isolated from a Gloxinia plant infected with impatiens necrotic spot virus (INSV) when propagated in a high temperature (27/24°C, light/dark) environment. Mouse monoclonal antibodies (McAb) and rabbit antisera (RbAs) were produced for HT-1 nucleocapsids. We examined the serological relatedness and analyzed and compared the genomic structure of the HT-1 virus with other members of the Tospovirus genus.
Results and conclusions
Both McAb and RbAs produced for INSV nucleocapsids failed to react with the HT-1 culture in ELISA and did not detect HT-1 proteins on Western blots. The HT-1 McAb and RbAs reacted strongly with homologous antigens but failed to react with cultures of INSV and tomato spotted wilt virus (TSWV). However, they reacted in ELISA with watermelon silver mottle virus (WSMoV) from Taiwan and detected the nucleocapsid protein of WSMoV by Western blot. A reciprocal test showed that the antisera prepared to the N protein of WSMoV also reacted with the HT- 1 N protein in Western blot analysis.
The genome structure of the HT-1 virus is similar to those reported in the other tospoviruses. The MRNA contains two open reading frames (ORFs), one in the sense encodes a 308 amino acid (aa) non-structural protein (Srn) and the other in the ambisense a 1122 aa precurser of the G1 and G2 glycoproteins (G1/G2). The S RNA also contains two ORFs, one in the sense encodes a 439 aa non-structural protein (Ss) and the other in the ambisense a 277 aa N protein. The HT-1 virus is distantly related to INSV  and TSWV  as shown by low similarities at the nucleotide (40-52%) and amino acid (28-48%) levels of four ORF sequences. However, the HT-1 virus shares high nucleotide (76-81%) and amino acid (85-92%) identities with peanut bud necrosis virus (PBNV)  and WSMoV .
HT-1 is a member of serogroup IV of the tospoviruses. This is the first time that a tospovirus similar to those found in the far east and in South-East Asia has been identified in the US.
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