Tobacco ringspot virus (TRSV) is an important plant pathogen that causes severe diseases in tobacco plants. In recent years, this virus has been reported in a number of ornamental plants. However, it ...has never been reported from Japanese iris, a famous traditional ornamental plant distributed in Asian countries. In this study, the near-complete bipartite genome of a nepovirus (TRSV-Iris) infecting Japanese iris from Taiwan of China was determined. The RNA1 and RNA2 are 7512 and 3899 nucleotides in length, and encodes a polyprotein of 2303 and 1078 amino acids, respectively. Sequence analysis indicates that TRSV-Iris shares more than 80% amino acid sequence identity, the threshold values of the species demarcation for the genus
Nepovirus
, with known TRSV isolates either in the conserved Pro-Pol or CP regions, respectively. Phylogenetic analysis indicates that TRSV-Iris is a TRSV isolate.
A novel nepovirus was identified and characterised from caraway, and tentatively named caraway yellows virus (CawYV). Tubular structures with isomeric virus particles typical for nepoviruses were ...observed in infected tissues by electron microscopy. The whole genome of CawYV was identified by high throughput sequencing (HTS). It consists of two segments with 8026 nt for RNA1 and 6405 nt for RNA2, excluding the poly(A) tails. CawYV-RNA1 shared closest nt identity to peach rosette mosaic virus (PRMV) with 63%, while RNA2 shared 41.5% with blueberry latent spherical virus (BLSV). The amino acid sequences of the CawYV protease-polymerase (Pro-Pol) and capsid protein (CP) regions share the highest identities with those of the subgroup C nepoviruses. The Pro-Pol region shared highest aa identity with PRMV (80.1%), while the CP region shared 39.6% to soybean latent spherical virus. Phylogenetic analysis of the CawYV-Pro-Pol and -CP aa sequences provided additional evidence of their association with nepoviruses subgroup C. Based on particle morphology, genomic organization and phylogenetic analyses, we propose CawYV as a novel species within the genus Nepovirus subgroup C.
The cell death response known as the hypersensitive response (HR) is a central feature of gene-for-gene plant disease resistance. A mutant line of Arabidopsis thaliana was identified in which ...effective gene-for-gene resistance occurs despite the virtual absence of HR cell death. Plants mutated at the DND1 locus are defective in HR cell death but retain characteristic responses to avirulent Pseudomonas syringae such as induction of pathogenesis-related gene expression and strong restriction of pathogen growth. Mutant dnd1 plants also exhibit enhanced resistance against a broad spectrum of virulent fungal, bacterial, and viral pathogens. The resistance against virulent pathogens in dnd1 plants is quantitatively less strong and is differentiable from the gene-for-gene resistance mediated by resistance genes RPS2 and RPM1. Levels of salicylic acid compounds and mRNAs for pathogenesis-related genes are elevated constitutively in dnd1 plants. This constitutive induction of systemic acquired resistance may substitute for HR cell death in potentiating the stronger gene-for-gene defense response. Although cell death may contribute to defense signal transduction in wild-type plants, the dnd1 mutant demonstrates that strong restriction of pathogen growth can occur in the absence of extensive HR cell death in the gene-for-gene resistance response of Arabidopsis against P. syringae
The complete nucleotide (nt) sequence of Grapevine deformation virus (GDefV) RNA-1 has been determined. It consists of 7386nt, excluding the poly(A) tail, and contains a single open reading frame ...(ORF) encoding a polyprotein (p1) of 252kDa. P1 comprises the 1APro-cof proteinase cofactor, the 1BHel NTP-binding protein, the 1CVPg viral protein genome-linked, the 1DProt proteinase and the 1EPol RNA-dependent RNA polymerase, all of which are conserved domains in polyproteins of different members of the order Picornavirales. The amino acid (aa) sequence of GDefV RNA1 p1 has the highest identity with the homologous products of Grapevine fanleaf virus (GFLV, 86–88%) and Arabis mosaic virus (ArMV, 73–74%), two nepoviruses of subgroup A. Four cleavage sites for proteins processing were predicted (C/A, C/S, G/E and R/G) and found similar to those of GFLV RNA1. Phylogenetic trees constructed with the complete aa sequences of protein p1 and the RNA2-encoded protein p2 of GDeFV, GFLV and ArMV, showed an incongruent allocation of GDefV in these trees. Pairwise alignment and prediction of recombination sites of both RNA segments showed that GDefV RNA2 has a mosaic structure resulting from recombination events between GFLV and ArMV at the level of the 2AHP (homing protein), 2BMP (movement protein), 2CCP (capsid protein) and the 3′NCR (non coding region). This strongly suggests that GDefV originated from the interspecific recombination between isolates of GFLV and ArMV.
Grapevine fanleaf virus (GFLV), responsible for fanleaf degeneration, one of the most severe virus diseases of grapevines worldwide, causes substantial crop losses, reduces fruit quality and shortens ...longevity of grapevines. GFLV is transmitted from grapevine to grapevine by the ectoparasitic nematode Xiphinema index and belongs to genus Nepovirus, family Comoviridae. Since the discovery of the nematode vector in the late _50s and the identification of GFLV as the agent of fanleaf degeneration in the early _60s, a wealth of information was accumulated on its transmission, biological properties and serological characteristics, as well as on structure and expression of GFLV genome. Although dissemination of virus through propagation material has been drastically reduced over the past two decades by implementing rigorous certification schemes and establishing quarantine facilities, effective strategies are still needed to control GFLV in vineyards. Recently, significant progress has been made on the elucidation of the functions of most GFLV proteins, in particular the ones involved in critical steps of virus multiplication cycle, including RNA replication, cell-to-cell movement and transmission by X. index. New insights have also been gained into population structure and genomic variability among isolates from naturally infected vineyards, which have opened new pathways for designing alternative control strategies. This review article offers a comprehensive overview of the most significant advances made over the past 15 years on GFLV and discusses novel control strategies for one of the major threats to grapevine industry worldwide
Il Virus della foglia a ventaglio della vite (GFLV), responsabile della degenerazione a ventaglio, una delle più gravi malattie della vite a livello mondiale, causa rilevanti perdite produttive, riduce la qualità dell'uva e la longevità delle piante. Il GFLV viene trasmesso dal nematode ectoparassita Xiphinema index e appartiene al genere Nepovirus, famiglia Comoviridae. Dalla scoperta del vettore alla fine degli anni '50 e dall'identificazione del GFLV come agente della degenerazione a ventaglio nei primi anni '60, sono state accumulate molte informazioni su trasmissione, proprietà biologiche, caratteri sierologici e struttura ed espressione del genoma del GFLV. Sebbene la diffusione del virus col materiale di moltiplicazione sia stata ridotta drasticamente negli ultimi venti anni con rigorosi schemi di certificazione e strutture per la quarantena, sono tuttora necessarie strategie efficaci per il controllo del GFLV. Recentemente sono stati conseguiti progressi significativi sul chiarimento delle funzioni della maggior parte delle proteine del GFLV, in particolare quelle coinvolte nei passaggi critici del ciclo di moltiplicazione, comprendenti la replicazione dell'RNA, il movimento da cellula a cellula e la trasmissione tramite X. index. Sono state inoltre acquisite nuove informazioni sulla struttura e variabilità genomica delle popolazioni negli isolati provenienti da vigneti infetti naturalmente, che hanno aperto nuove strade per mettere a punto strategie di controllo alternative. Questa rassegna offre un panorama dei progressi più significativi conseguiti negli ultimi 15 anni sul GFLV e discute le strategie innovative di controllo di una delle maggiori minacce per la viticoltura mondiale
A disease complex was observed on grapevine var. Chardonnay (Vitis vinifera) in a commercial vineyard in Missouri that destroyed the affected vineyard. Conspicuous vein-clearing symptoms on the ...leaves of originally diseased Chardonnay vines and bud-grafted Chardonnay, V. vinifera ‘Cabernet Franc', V. vinifera ‘Baco Blanc', and hybrid ‘LN-33' vines are characteristics of the disease complex, which is referred to as the grapevine vein-clearing complex (GVCC). By applying reverse-transcription polymerase chain reaction (RT-PCR) using virus-specific primers, we detected combinations of Grapevine fanleaf virus (GFLV), Tomato ringspot virus (ToRSV) and Grapevine rupestris stem pitting-associated virus (GRSPaV), in symptomatic Chardonnay vines. Sequencing of RT-PCR amplified DNA fragments confirmed the identity of each virus, indicating the occurrence of ToRSV yellow vein strain, and two distinct strains of GRSPaV in the GVCC-affected Chardonnay vines. This is the first report of the co-infection of two nepoviruses and GRSPaV in var. Chardonnay. This study demonstrated that mixed infections of grapevine viruses belonging to different taxonomic groups pose a great threat to vineyards under certain climatic and soil conditions.
Two generic PCR protocols were developed to detect nepoviruses in subgroups A and B using degenerate primers designed to amplify part of the RNA-dependent RNA polymerase (RdRp) gene. It was observed ...that detection sensitivity and specificity could be improved by adding a 12-bp non-complementary sequence to the 5′ termini of the forward, but not the reverse, primers. The optimized PCR protocols amplified a specific product (∼340
bp and ∼250
bp with subgroups A and B, respectively) from all 17 isolates of the 5 virus species in subgroup A and 3 species in subgroup B tested. The primers detect conserved protein motifs in the RdRp gene and it is anticipated that they have the potential to detect unreported or uncharacterised nepoviruses in subgroups A and B.
Based on the nucleotide sequence homology of RNA-1 and RNA-2 of nepoviruses isolated from grapevines, three sets of degenerate primers, one for each of the three subgroups of the genus (A, B and C), ...were designed and proved effective for RT-PCR detection of subgroups in infected grapevines and herbaceous hosts. Primers designed specifically for detecting subgroup A species amplified a fragment of 255
bp from samples infected by
Grapevine fanleaf virus (GFLV),
Arabis mosaic virus (ArMV),
Tobacco ringspot virus (TRSV) and Grapevine deformation virus (GDefV), but not from samples infected by other nepovirus species. Similarly, primers for detection of subgroup B nepoviruses amplified a 390
bp product from samples infected by
Grapevine chrome mosaic virus (GCMV),
Tomato black ring virus (TBRV), Grapevine Anatolian ringspot virus (GARSV) and
Artichoke Italian latent virus (AILV). The third set of primers amplified a 640
bp fragment, only from samples infected by subgroup C nepoviruses, i.e
Tomato ringspot virus (ToRSV)
Grapevine Bulgarian latent virus (GBLV), and
Grapevine Tunisian ringspot virus (GTRSV). These primers were able to detect simultaneously all viral species belonging to the same subgroup and to discriminate species of different subgroups. Multiplex-PCR detection of subgroup A and B nepoviruses was obtained using a specific primer (
sense for subgroup A and
antisense for subgroup B) for each of the species of the same subgroup in combination with the degenerate subgroup-specific primers. In this way it was possible to detect four different viral species in single samples containing mixtures of viruses of the same subgroup. In particular, for viruses of subgroup A (TRSV, GFLV, ArMV and GDefV) amplicons of 190, 259, 301 and 371
bp were obtained, whereas amplicons of 190, 278, 425 and 485
bp, respectively, were obtained from samples infected with viruses of subgroup B (GCMV, AILV, GARSV and TBRV).
Summary
Data on the distribution of Longidoridae and nepoviruses in Bulgaria and Slovenia are summarized. Six species of
Longidorus
(
L. apulus, L. attenuatus, L. arthensis, L. fasciatus, L. ...elongatus, L. macrosoma
), one
Paralongidorus
species (
P. maximus
) and three
Xiphinema
species (
X. diversicaudatum, X. index, X. rivesi
) are known as natural vectors of nine nepoviruses in Europe. Currently, 10 and 13 species of
Xiphinema
; 6 and 15 of
Longidorus
are reported to occur in Slovenia and Bulgaria, respectively.
Paralongidorus maximus
has been reported only in Bulgaria. Among the virus vector species
X. index, X. diversicaudatum
and
L. elongatus
occur in both countries,
X. rivesi
only in Slovenia and
L. attenuatus, L. macrosoma, X. italiae
and
P. maximus
only in Bulgaria. A report of
X. index
and Grapevine fanleaf virus (GFLV) in Bulgaria was related to transgenic grape tolerance to the same virus. Nepoviruses have been reported from Slovenia, but despite an evident relationship in the occurrence of GFLV and
X. index
in several vineyards the only laboratory proven transmission is that of TRSV and ToRSV to bait plants by a Slovenian population of
X. rivesi
.
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