Identification of Partitivirus-like RdRPs in the Brevipalpus yothersi Genome Supports Viral-to-Arthropod Horizontal Gene Transfer

Discovery of novel viruses related to the Potyviridae family reveals expanded diversity, a broad host range, and evidence of fungal and oomycete infections

The family Potyviridae represents the largest and most economically important group of plant-infecting RNA viruses. Despite extensive study of crop-associated members, the full diversity, host range, and evolutionary history of potyvirids remain poorly understood. Here, we conducted a large-scale mining of publicly available RNA-seq datasets to systematically search for novel potyvirid sequences. This approach enabled the identification and assembly of 47 previously undescribed members of the family, distributed across eight recognized genera and, importantly, putative new groups. Beyond expanding the known genetic diversity of Potyviridae, our analyses revealed a distinct and deeply divergent lineage of potyvirid-like viruses associated with fungi and oomycetes. These viruses possess compact genomes and atypical genomic organizations, including the absence of canonical plant cell-to-cell movement factors and the presence of HCPro-like proteins arranged in tandem. Comparative structural and phylogenetic analyses indicate that these leader proteases are more closely related to fungal hypoviral counterparts than to canonical potyvirid HCPro factors. Together, our findings substantially expand the host range of Potyviridae, provide compelling evidence that potyvirid-like viruses likely infect fungi and oomycetes in nature, and offer new insights into the evolutionary pathways that have shaped this major virus family.

Characterization and classification of a novel bacteriophage, vB_RsoP_HXg1W, infecting Ralstonia pseudosolanacearum: a new member of the genus Serkorvirus in the family Autotranscriptaviridae

Systematic profiling of nudivirus-like genes reveals conserved and differentiated roles in a domesticated endogenous virus

Cotesia vestalis bracovirus (CvBV) is a type of domesticated endogenous virus (DEV) derived from ancestral nudiviruses that is integrated into the genome of the parasitoid wasp Cotesia vestalis. The CvBV proviral genome is composed of two distinct components: one encoding genes associated with virion morphogenesis and assembly, and the other harboring virulence genes that are excised, circularized, and packaged into virions. CvBV replication and particle assembly occur exclusively in the ovaries of female wasps. While prior studies have largely focused on the function of virulence genes during parasitization, the molecular mechanisms underlying CvBV replication and assembly remain poorly understood. Here, we identified 71 nudivirus-like genes in the C. vestalis genome through integrated transcriptomic and proteomic analyses. Using gene silencing and microscopy-based imaging approaches, we functionally characterized 24 key genes involved in DNA replication (helicase, integrase-1, and integrase-2), transcriptional regulation (p47, lef-5, and lef-9), capsid formation (vp39, PmV, HzNVorf9–1, HzNVorf9–2, HzNVorf106, 38k, 27b, and K425_459), envelope formation (11k, 17a-1, 35a-1, 35a-2, and K425_461), virion assembly (vlf-1, HzNVorf140–1, and HzNVorf140–2), and viral infectivity (pif-0 and vp91). Although the functions of most nudivirus-like genes are generally conserved among baculoviruses, nudiviruses, and bracoviruses, lef-5, K425_459, 11k, and vp91 appear to have undergone functional divergence relative to their homologs in baculoviruses, nudiviruses, and Microplitis demolitor bracovirus, highlighting lineage-specific adaptations in CvBV. Collectively, our work provides a molecular framework for understanding CvBV assembly and serves as a valuable resource for investigating bracovirus evolution.

Cilevirus and dichorhavirus glycoproteins target overlapping host proteins in the Brevipalpus yothersi vector

Enveloped plant viruses are rare, and accumulating evidence suggests deep evolutionary ties to arthropod hosts. Brevipalpus-transmitted viruses (BTVs), which include cileviruses, higreviruses, and dichorhaviruses, are transmitted exclusively by Brevipalpus mites, causing localized infections in plants. Some cileviruses and dichorhaviruses can also replicate within vector cells. Despite their enveloped virions, the involvement of virion structural proteins mediating the interaction with the vector remains unresolved. Here, we investigated the putative glycoproteins P61 of citrus leprosis virus C (CiLV-C; Cilevirus, Kitaviridae) and G of clerodendrum chlorotic spot virus (ClCSV; Dichorhavirus, Rhabdoviridae) to define their interaction networks in the Brevipalpus yothersi vector. Using membrane-based yeast two-hybrid screening with a B. yothersi cDNA library, we identified 73 interactors for P61 and 162 for G, including a shared core set enriched for membrane-associated proteins involved in intracellular trafficking, ER–Golgi dynamics, protein synthesis and folding, and signal transduction. Numerous hypothetical membrane proteins emerged as strong candidates for viral receptors or co-receptors. Three proteins (ARF1, SERP2, and a hypothetical transmembrane protein) were validated by BiFC and Co-IP in Spodoptera frugiperda (Sf9) cells, confirming interactions with both viral proteins in an arthropod-like environment. Together, this work provides the first comprehensive interactome of BTV glyco-like proteins with those of its natural vector and reveals partially convergent host-interaction strategies between phylogenetically distinct viruses, establishing a mechanistic basis for dissecting BTV transmission. IMPORTANCE BTV’s damage economically important crops worldwide, and citrus leprosis (CL) is a significant disease in the Brazilian citrus belt. Brazil is responsible for over 75% of global sweet orange juice production and widely cited estimates indicate that CL causes >US$69 million in annual yield losses and acaricide-based control of Brevipalpus yothersi, the vector of CiLV-C and several other BTVs. Despite this impact, the molecular basis of BTV acquisition, persistence, and transmission by Brevipalpus spp. remains largely unexplored. Here, we provide the first systematic map of mite proteins interacting with glycoproteins from two BTVs belonging to distinct viral families. These interactomes reveal key components of the cellular machinery targeted by cileviruses and dichorhaviruses in their arthropod vector, offering mechanistic insight into how these viruses establish and maintain infections in mites. This work establishes a foundational framework for future studies aimed at disrupting BTV transmission and developing sustainable control strategies.

Molecular and biological characterisation of Magnaporthe oryzae botourmiavirus 15

The efficacy of RNA interference against the microsporidia Vairimorpha ceranae in honeybees Apis mellifera. Can it be enhanced to the level of antiviral and anti-mite activity shown for the Remebee-I and Vadescana dsRNA?

Microsporidia Vairimorpha ceranae are virulent pathogens of the European honeybee Apis mellifera. About ten studies have confirmed that RNA interference (RNAi)-based silencing of the parasite’s genes inhibits microsporidia growth. To further evaluate the RNAi effectiveness against V. ceranae and methods for enhancing it, we synthesized in vitro double-stranded RNA (dsRNA) fragments of five genes encoding microsporidian DNA replication enzymes, their chimeric variants composed of predicted small interfering RNAs (siRNAs), and the fragments of four host genes. Fragments of the parasite’s genes encoding the PTP3 and SWP8 proteins, effective against V. ceranae at low concentrations, were used as positive controls. Ten-day feeding of individually infected and individually maintained young bees with dsRNA was followed by spore counting. This demonstrated (1) increased mortality of individually housed bees, (2) more effective infection suppression at lower dsRNA concentrations, and (3) the effectiveness of siRNA-containing chimeras and a gene fragment encoding a putative host apoptosis inhibitor in reducing spore load. Unfortunately, we were unable to enhance the RNAi efficiency by mixing the V. ceranae PTP3 fragment with polyethyleneimine and chitosan polymers, and V. ceranae growth was also unaffected when hive-derived bees of different ages were fed with E. coliexpressed dsRNA, effective in young insects. Analysis of the RNAi application to control bee pathogens indicates the need to further improve the efficiency of V. ceranae inhibition by searching for new target genes, optimizing the fragment concentration in syrup, and using the most effective dsRNA or siRNA, nanoparticles and liposomes.