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A Novel Approach to Engineering Tomato Spotted Wilt Virus Infectious Clones by Disarming Key Nodes in Antiviral Defenses.

Tomato spotted wilt virus (TSWV) is an economically devastating pathogen that rapidly overcomes genetic resistance in major crops. Reverse genetic systems are crucial for investigating plant-virus interactions and resistance-breaking mechanisms, and developing these tools for segmented ambisense RNA viruses remains a crucial challenge. Current TSWV clones rely on extensively modified Asian isolates requiring co-delivery of multiple replication helpers and viral silencing suppressors. Streamlining these systems for regionally significant strains with minimal genetic alterations is essential. Here, we developed the first infectious clone of a U.S. TSWV isolate (PA01). Three binary plasmids contain cDNAs for the antigenomic L and S segments, as well as the genomic M segment, with enhanced GFP replacing NSs on the S segment. Co-delivery of the cucumovirus 2b alone or in combination with tombusvirus P19 or begomovirus AL2 achieved a high proportion of systemically infected Nicotiana benthamiana and Capsicum annuum plants. In N. tabacum, co-delivering the Caenorhabditis elegans cell death suppressor CED-9 or using NahG transgenic plants produced 30 to 33% systemically infected plants. Co-delivery of 2b boosted infection levels in NahG plants to 62%. These data indicate that in addition to the antiviral RNA-silencing machinery, additional host defense pathways influence TSWV rescue and systemic infection from cDNA. [Formula: see text] Copyright © 2026 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Tospovirus

Host ESCRT machinery orchestrates the assembly of tomato spotted wilt virus ribonucleoproteins.

The genomic RNA of negative-strand RNA viruses is encapsidated by nucleocapsid proteins and associates with RNA polymerase to form a ribonucleoprotein (RNP) complex. Lacking both a 5' cap and a 3' poly (A) tail, viral RNAs are highly unstable and prone to degradation by cellular nucleases. Therefore, newly synthesized genomic and complementary-strand RNAs must be rapidly protected through RNP formation. However, the molecular mechanisms governing RNP assembly in cytoplasm-replicating negative-strand RNA viruses remain largely unknown. Here, we screened a yeast knockout library and isolated mutants in several components of the endosomal sorting complexes required for transport (ESCRT) genes that affected RNA replication of tomato spotted wilt virus (TSWV). In wild-type (WT) yeast cells, TSWV nucleocapsid (N) and RNA polymerase (L) proteins colocalize at the trans-Golgi network (TGN) in a replicon-RNA-dependent manner, suggesting that TSWV RNPs accumulate at the TGN. However, in the snf7Δ, bro1Δ, and doa4Δ mutant cells, N localization to TGN and RNP formation were impaired. Another RNA replication-defective mutant, vps36Δ, showed normal N localization, and SNF7, BRO1, and DOA4 were recruited to the TGN by TSWV N or L proteins, implying that the ESCRT components have additional roles in TSWV RNA replication beyond facilitating N transport. These findings suggest that ESCRT components play multifaceted roles in TSWV RNA replication, including the intracellular transport of N to the TGN-where RNA replication takes place-thereby ensuring accurate and efficient RNP assembly.

Tospovirus

First report of tomato spotted wilt virus (Orthotospovirus tomatomaculae) and phytoplasma in China aster and development of duplex PCR, LAMP, and qPCR assays for rapid detection.

UNLABELLED: China aster (Callistephus chinensis) is an economically important ornamental crop widely cultivated for cut flowers and landscaping. During field surveys conducted in three districts of Karnataka, India, China aster plants exhibiting chlorotic and necrotic ring spots, leaf deformation, and witches' broom symptoms were collected and analyzed to determine the causal agents. Mechanical inoculation of symptomatic leaf sap onto cowpea (Vigna unguiculata cv. C-152) produced characteristic chlorotic and necrotic ring spots on newly emerging leaves indicating the presence of an infectious viral agent. Serological assay by DAC-ELISA followed by RT-PCR confirmed the presence of tomato spotted wilt virus (TSWV, Orthotospovirus tomatomaculae) in symptomatic plants. Similarly the plants exhibiting witches' broom symptoms tested positive for phytoplasma infection using universal and Nested primers PCR assays targeting the 16S rRNA gene. Sequence analysis of TSWV CP gene revealed more than 97% nucleotide identity with TSWV isolates reported from India and other countries. Based on these results, one representative isolate was selected for complete genome sequencing. The complete sequences of the L, M, S RNA segements were amplified cloned, and sequenced showing more than 97% nucleotide identity with global TSWV isolates available in database. Sequence analysis of 16S rRNA gene of the phytoplasma associated with witches' broom symptoms was identified as 'Candidatus Phytoplasma australasiaticum' belonging to the 16SrII-D subgroup, sharing 99.2% nucleotide identity with previously reported isolates. Phylogenetic analysis further supported the placement of both the TSWV and phytoplasma isolates within their respective taxonomic groups. To facilitate rapid and sensitive diagnosis, quantitative PCR (qPCR) and RT-LAMP assays were developed for TSWV detection. In addition a duplex PCR assay was optimized for simultaneous detection of TSWV and phytoplasma from infected China aster plants in a single reaction. This study represents the first reports of the complete genome characterization of TSWV and phytoplasma infection in China aster in India along with the development of sensitive qPCR, RT-LAMP, and duplex PCR assays for rapid detection of these pathogens providing valuable tools for disease diagnosis, epidemiological studies. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at https://doi.org/10.1007/s13205-026-05038-w.

China aster