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The first complete genome sequence of iris yellow spot virus from South America and comparative analysis with isolates of different geographic origin.

We report the first complete nucleotide sequence of an isolate of iris yellow spot virus (IYSV; Orthotospovirus iridimaculaflavi) from Brazil. Isolate Br-25 was collected in 2025 in Imbuia, Santa Catarina, from symptomatic onion scapes. The genome of IYSV-Br-25 consisted of L, M and S genomic RNAs of 8879, 4866 and 3223 nt, respectively. Comparison of the L segment nucleotide (nt) sequence showed identities ~96% to most of the available L segment sequences from IYSV isolates of different geographic origin, with the exception of isolate DSMZ PV-0528, which showed 89.0% nt identity. The M and S segment nt sequences showed highest identity to an isolate recently reported from sugarbeet in Idaho, USA. In silico-generated Hinf1 digestion profile assigned the isolate to the previously defined IYSVBR genotype. This work provides valuable novel information on the genetic diversity of IYSV.

Genome, Viral

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

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