The Natural Occurrence of Two Distinct Begomoviruses Associated with DNAbeta and a Recombinant DNA in a Tomato Plant from Indonesia

Emergence and diversity of begomoviruses infecting solanaceous crops in East and Southeast Asia

Over the past three decades diseases caused by whitefly-transmitted geminiviruses (begomoviruses) have emerged to be important constraints to the production of solanaceous crops, particularly tomato (Solanum lycopersicum) and peppers (Capsicum spp.), in many tropical and subtropical regions of the world. The most studied of these is Tomato yellow leaf curl virus (TYLCV), which has spread to many other areas from its likely origin in the Mediterranean basin region. The virus is usually associated with the polyphagous and virus-vectoring-efficient B-biotype of its vector whitefly (Bemisia tabaci). However, in Southeast and East Asia, a wide variety of distinct local begomovirus species have been identified from tomato and pepper crops over this period, and TYLCV was detected in Japan only in about 1996, China in 2006 and Korea in 2008, despite B-biotype whiteflies being present in several of the countries of the region since at least the early 1990s. Continental Southeast Asia appears to be a major center of diversity for begomoviruses and some species may have spread across the region; Tomato yellow leaf curl Thailand virus (TYLCTHV) appears to have spread from the Thailand-Myanmar region into southern China and is now displacing the local tomato-infecting species in Taiwan, and Tomato yellow leaf curl Kanchanaburi virus (TYLCKaV) appears to have spread from the Thailand-Vietnam region to Java, Indonesia. Since many of the native tomato- or pepper-infecting begomoviruses and associated satellite DNAs have also been detected in local weed species, it seems likely that their ancestors originated in these weed hosts, but with the expansion and intensification of tomato and pepper production in the region, there was selection for recombinant or mutant forms with greater virulence on tomato and/or pepper. Expansion and intensification of these crops may also have resulted in increased populations of local, and if present, B- or Q-biotype whiteflies, aiding the increase and spread of local begomovirus species.

Association of an alphasatellite with tomato yellow leaf curl virus and ageratum yellow vein virus in Japan is suggestive of a recent introduction

Samples were collected in 2011 from tomato plants exhibiting typical tomato leaf curl disease symptoms in the vicinity of Komae, Japan. PCR mediated amplification, cloning and sequencing of all begomovirus components from two plants from different fields showed the plants to be infected by Tomatoyellowleafcurlvirus (TYLCV) and Ageratumyellowveinvirus (AYVV). Both viruses have previously been shown to be present in Japan, although this is the first identification of AYVV on mainland Japan; the virus previously having been shown to be present on the Okinawa Islands. The plant harboring AYVV was also shown to contain the betasatellite Tomato leaf curl Java betasatellite (ToLCJaB), a satellite not previously shown to be present in Japan. No betasatellite was associated with the TYLCV infected tomato plants analyzed here, consistent with earlier findings for this virus in Japan. Surprisingly both plants were also found to harbor an alphasatellite; no alphasatellites having previously been reported from Japan. The alphasatellite associated with both viruses was shown to be Sida yellow vein China alphasatellite which has previously only been identified in the Yunnan Province of China and Nepal. The results suggest that further begomoviruses, and their associated satellites, are being introduced to Japan. The significance of these findings is discussed.

Complete nucleotide sequence of a monopartite Begomovirus and associated satellites infecting Carica papaya in Nepal

Carica papaya (papaya) is a fruit crop that is cultivated mostly in kitchen gardens throughout Nepal. Leaf samples of C. papaya plants with leaf curling, vein darkening, vein thickening, and a reduction in leaf size were collected from a garden in Darai village, Rampur, Nepal in 2010. Full-length clones of a monopartite Begomovirus, a betasatellite and an alphasatellite were isolated. The complete nucleotide sequence of the Begomovirus showed the arrangement of genes typical of Old World begomoviruses with the highest nucleotide sequence identity (>99 %) to an isolate of Ageratum yellow vein virus (AYVV), confirming it as an isolate of AYVV. The complete nucleotide sequence of betasatellite showed greater than 89 % nucleotide sequence identity to an isolate of Tomato leaf curl Java betasatellite originating from Indonesian. The sequence of the alphasatellite displayed 92 % nucleotide sequence identity to Sida yellow vein China alphasatellite. This is the first identification of these components in Nepal and the first time they have been identified in papaya.

Subcellular localization of V2 protein of Tomato leaf curl Java virus by using green fluorescent protein and yeast hybrid system

Tomato leaf curl Java virus-A (ToLCJV-A[ID]) from Southeast Asia is a new member of the emerging group of monopartite begomoviruses that require a betasatellite component for symptom induction. Previously, we have elucidated the role of V1 ORF encoded by ToLCJV-A[ID] in cell-to-cell movement. In this study, the role of V2 (PreCP) in localization was determined. Subcellular localization of ToLCJV-A[ID] V2 in plant tissues showed that this protein is co-localized to the cell cytoplasm, perinuclear and associated with the endoplasmic reticulum network. The results obtained from deletion analysis indicate that fusion of N-terminal part of the V2, containing the nuclear export signals (NES), directed the accumulation of fluorescence towards the cell cytoplasm. Furthermore, functionality of the NES ((20)LAVKYLQLV(29)) in the N-terminal part of the V2 protein was confirmed by one-hybrid yeast system. Taken together, these results suggest that V2 enhances the coat protein-mediated nuclear export of ToLCJV-A[ID] and is consistent with the model in which V2 mediates viral DNA export from the nucleus to the plasmodesmata.

Molecular analysis of new isolates of Tomato leaf curl Philippines virus and an associated betasatellite occurring in the Philippines

Three new begomovirus isolates and one betasatellite were obtained from a tomato plant exhibiting leaf curl symptom in Laguna, the Philippines. Typical begomovirus DNA components representing the three isolates (PH01, PH02 and PH03) were cloned, and their full-length sequences were determined to be 2754 to 2746 nucleotides. The genome organizations of these isolates were similar to those of other Old World monopartite begomoviruses. The sequence data indicated that PH01 and PH02 were variants of strain B of the species Tomato leaf curl Philippines virus, while PH03 was a variant of strain A of the species Tomato leaf curl Philippines virus. These isolates were designated ToLCPV-B[PH:Lag1:06], ToLCPV-B[PH:Lag2:06], and ToLCPV-A[PH:Lag3:06], respectively. Phylogenetic analysis revealed that the present isolates form a separate monophyletic cluster with indigenous begomoviruses reported earlier in the Philippines. A betasatellite isolated from same sample belongs to the betasatellite species Tomato leaf curl Philippines betasatellite and designated Tomato leaf curl Philippines betasatellite-[Philippines:Laguna1:2006], ToLCPHB-[PH:Lag1:06]. When co-inoculated with this betasatellite, tomato leaf curl Philippines virus induced severe symptoms in N. benthamiana and Solanum lycopersicum plants. Using a PVX-mediated transient assay, we found that the C4 and C2 proteins of tomato leaf curl Philippines virus and the βC1 protein of ToLCPHB-[PH:Lag1:06] function as a suppressor of RNA silencing.

Identification of the virulence factors and suppressors of posttranscriptional gene silencing encoded by Ageratum yellow vein virus, a monopartite begomovirus

Ageratum yellow vein disease (AYVD) is caused by the association of a Tomato leaf curl Java betasatellite [Indonesia:Indonesia 1:2003] (ToLCJB-[ID:ID1:03]) with a begomovirus component. Our previous results demonstrated that ToLCJB-[ID:ID:03] is essential for induction of leaf curl symptoms in plants and transgene expression of its betaC1 gene in Nicotiana benthamiana plants induces virus-like symptoms. Here we show that Ageratum yellow vein virus-Indonesia [Indonesia: Tomato] (AYVV-ID[ID:Tom]) alone could systemically infect the plants and induced upward leaf curl symptoms. ToLCJB-[ID:ID1:03] was required, in addition to AYVV-ID[ID:Tom], for induction of severe downward leaf curl disease in N. benthamiana plants. However, DNAbeta01fsbetaC1, which encompasses a frameshift mutation, did not induce severe symptoms in N. benthamiana when co-inoculated with AYVV-ID[ID:Tom]. The infectivity analysis of AYVV-ID[ID:Tom] and its associated betasatellite encoded genes using Potato virus X (PVX) vector were carried out in N. benthamiana, indicate that the V2 and betaC1 genes are symptom determinants. We have identified the DNA encoded V2 and its betasatellite, ToLCJB-[ID:ID1:03], encoded betaC1 proteins as efficient silencing suppressors of posttranscriptional gene silencing (PTGS) by using an Agrobacterium co-infiltration or heterologous PVX vector assays. However, the results also showed weak suppression of gene silencing activities for C2 and C4 induced by GFP and mRNA associated with GFP was detected. Furthermore, confocal imaging analysis of ToLCJB-[ID:ID1:03] betaC1 in the epidermal cells of N. benthamiana shows that this protein is accumulated towards the periphery of the cell and around the nucleus, however, V2 accumulated in the cell cytoplasm, C4 associated with plasma membrane and C2 exclusively targeted into nucleus. In this study, we identified as many as four distinct suppressors of RNA silencing encoded by AYVV-ID[ID:Tom] and its cognate betasatellite in the family Geminiviridae, counteracting innate antiviral response.

Tomato leaf curl Java virus V2 protein is a determinant of virulence, hypersensitive response and suppression of posttranscriptional gene silencing

We previously identified the Tomato leaf curl Java virus-A (ToLCJV-A[ID]) from Southeast Asia as a new member of the emerging group of monopartite begomoviruses that require a betasatellite component for symptom induction. In this study, the role of V2 in viral pathogenesis and posttranscriptional gene silencing (PTGS) was studied. Our results showed V2 of ToLCJV-A[ID] elicits a reaction resembling the hypersensitive response (HR) associated with the induction of necrosis and a systemic burst of H(2)O(2) production when expressed from a potato virus X vector in Nicotiana species and tomato. Transient expression of ToLCJV-A[ID] V2 after agroinfiltration of Nicotiana benthamiana and tomato also triggered HR-like cell death, demonstrating that ToLCJV-A[ID] V2 is a target of host defense responses. Deletion of 58 amino acids (aa) from the N-terminus did not affect the HR, suggesting that this region has no role in the HR, while deletion of 58 aa from the C-terminus of V2 abolished both the HR response and V2 silencing suppressor activity, suggesting that these sequences are required for the HR-like response and suppression of PTGS. This finding demonstrated that ToLCJV-A[ID] V2 is a pathogenicity determinant that elicits an HR-like response.

Interaction of tomato yellow leaf curl virus with diverse betasatellites enhances symptom severity

The complete nucleotide sequence was determined for a begomovirus isolated from tomato exhibiting leaf curling and yellowing symptoms in Tochigi Prefecture in Japan. The genome organization of this virus was similar to those of other Old World monopartite begomoviruses. Neither a DNA betasatellite nor a DNA-B component was detected. It had the highest total nucleotide sequence identity (99%) with tomato yellow leaf curl virus-Israel[Japan:Tosa:2005] (TYLCV-IL[JR:Tos:05]) and TYLCV-Israel[Japan:Haruno:2005] (TYLCV-IL[JR:Han:05]). Its coat protein V1 also showed an identical amino acid sequence with those of TYLCV-IL[JR:Tos:05] and TYLCV-IL[JR:Han:05]. Thus, the begomovirus was determined to be an isolate of TYLCV-IL designated as TYLCV-Israel[Japan:Tochigi:2007] (TYLCV-IL[JR:Toc:07]). We investigated the interaction of TYLCV-IL[JR:Toc:07] with two known satellites associated with tomato yellow dwarf disease in Japan, tobacco leaf curl Japan betasatellite [Japan:Ibaraki:2006] and honeysuckle yellow vein mosaic betasatellite [Japan:Nara:2006], as well as with tomato leaf curl Philippines betasatellite [Philippines:Laguna1:2008], in tomato and Nicotiana benthamiana plants. TYLCV-IL[JR:Toc:07] trans-replicated these betasatellites, inducing more severe tomato yellow leaf curl disease-related symptoms than TYLCV-IL[JR:Toc:07] alone.

Characterization of signals that dictate nuclear/nucleolar and cytoplasmic shuttling of the capsid protein of Tomato leaf curl Java virus associated with DNA beta satellite

Transport of the viral genome into the nucleus is an obligatory step in the replication cycle of geminiviruses. Capsid proteins (CPs) of geminiviruses are multifunctional proteins thought to be involved in this process. The CP of monopartite geminiviruses is absolutely essential for virus movement. To more precisely examine the role of CP, we have constructed a series of single and double deletions into the coding sequence of Tomato leaf curl Java virus (ToLCJAV) CP and examined sub-cellular localization using transient expression of GFP fusion proteins. In this report, the domains of the CP encoded by ToLCJAV localized in the nucleus/nucleolus and cytoplasm in transfected cells were mapped. Deletion analysis revealed that the Arg-rich cluster from amino acids (aa) (16)KVRRR(20) in the N-terminal region of CP functioned as nuclear/nucleolar localization signals (NLSs). The region from aa (52)RKPR(55) contained basic amino acid cluster was capable to redirect the CP to the nucleus. Further, both transient expression and yeast hybrid assays demonstrated that CP was capable of shuttling between the nucleus and cytoplasm of the cell. Deletion mutant analysis revealed that this property was attributed to a nuclear export signal (NES) sequence consisted of aa ((245)LKIRIY(250)) reside at C-terminal part of CP. This hydrophobic region caused transport of GFP to the cytoplasm. However, ToLCJAV CP NLSs and NES show peculiarities in the number and position of basic residues. Taken together, these results demonstrated that ToLCJAV CP shuttles between the nucleus and cytoplasm, such an activity homolog to bipartite geminivirus BV1 ORF.

A severe symptom phenotype in tomato in Mali is caused by a reassortant between a novel recombinant begomovirus (Tomato yellow leaf curl Mali virus) and a betasatellite

Tomato production in West Africa has been severely affected by begomovirus diseases, including yellow leaf curl and a severe symptom phenotype, characterized by extremely stunted and distorted growth and small deformed leaves. Here, a novel recombinant begomovirus from Mali, Tomato yellow leaf curl Mali virus (TYLCMLV), is described that, alone, causes tomato yellow leaf curl disease or, in combination with a betasatellite, causes the severe symptom phenotype. TYLCMLV is an Old World monopartite begomovirus with a hybrid genome composed of sequences from Tomato yellow leaf curl virus-Mild (TYLCV-Mld) and Hollyhock leaf crumple virus (HoLCrV). A TYLCMLV infectious clone induced leaf curl and yellowing in tomato, leaf curl, crumpling and yellowing in Nicotiana benthamiana and common bean, mild symptoms in N. glutinosa, and a symptomless infection in Datura stramonium. In a field-collected sample from a tomato plant showing the severe symptom phenotype in Mali, TYLCMLV was detected together with a betasatellite, identified as Cotton leaf curl Gezira betasatellite (CLCuGB). Tomato plants co-agroinoculated with TYLCMLV and CLCuGB developed severely stunted and distorted growth and small crumpled leaves. These symptoms were more severe than those induced by TYLCMLV alone, and were similar to the severe symptom phenotype observed in the field in Mali and in other West African countries. TYLCMLV and CLCuGB also induced more severe symptoms than TYLCMLV in the other solanaceous hosts, but not in common bean. The increased symptom severity was associated with hyperplasia of phloem-associated cells, but relatively little increase in TYLCMLV DNA levels. In surveys of tomato virus diseases in West Africa, TYLCMLV was commonly detected in plants with leaf curl and yellow leaf curl symptoms, whereas CLCuGB was infrequently detected and always in association with the severe symptom phenotype. Together, these results indicate that TYLCMLV causes tomato yellow leaf curl disease throughout West Africa, whereas TYLCMLV and CLCuGB represent a reassortant that causes the severe symptom phenotype in tomato.

Strains of a new bipartite begomovirus, pepper yellow leaf curl Indonesia virus, in leaf-curl-diseased tomato and yellow-vein-diseased ageratum in Indonesia

The complete nucleotide sequences of begomoviruses from pepper with leaf curl and yellowing symptoms, tomato with leaf curl symptoms, and ageratum with yellow vein in Indonesia were determined. On the basis of genome organization and sequence homology, they were proposed to belong to a new species, Pepper yellow leaf curl Indonesia virus (PepYLCIV), which includes the new strains PepYLCIV-Tomato and PepYLCIV-Ageratum. These viruses had bipartite genomes. Pepper virus DNAs from Indonesia (PepYLCIV, PepYLCIV-Tomato and PepYLCIV-Ageratum DNA-As) were noticeably distinct, forming a separate branch from the viruses infecting pepper. Considerable divergence was observed in the common region (CR) of the genomic components of PepYLCIV (77%), PepYLCIV-Tomato (82%) and PeYLCIV-Ageratum (75%). A stem-loop-forming region and a Rep-binding motif were identical in the CR of the three viruses. The CRs of PepYLCIV-Ageratum DNA-A was approximately 10 nucleotides longer than that of PepYLCIV DNA-A and PepYLCIV-Tomato DNA-A. A similar insertion was also found in the CR of PepYLCIV-Ageratum DNA-B. PepYLCIV DNA-A alone was infectious in pepper and Nicotiana benthamiana plants, and association with DNA-B increased symptom severity.

The begomoviruses Honeysuckle yellow vein mosaic virus and Tobacco leaf curl Japan virus with DNAbeta satellites cause yellow dwarf disease of tomato

The complete nucleotide sequences of two begomoviruses (Nara virus-1 and Nara virus-2), a satellite DNA (DNAbeta-Nara) and defective DNAs were obtained from honeysuckle (Lonicera japonica) showing characteristic yellow vein mosaic symptoms in Nara Prefecture, Japan. One begomovirus (Ibaraki virus) and a satellite DNA (DNAbeta-Ibaraki) was isolated and cloned from honeysuckle plants exhibited typical yellowing of veins and small elliptical shaped enations along veins on the under side of the leaves in Ibaraki Prefecture, Japan. The genome organization of the three viruses is the same as those of other Old World monopartite begomoviruses. Nara virus-1 had overall nucleotide sequence identity with Nara virus-2 of 94% and Ibaraki virus of 90%. DNAbeta-Nara had overall nucleotide sequence identity with DNAbeta-Ibaraki of 83%. Comparison of the nucleotide sequences with other begomoviruses revealed that Nara virus-1 and Nara virus-2 are strains of Honeysuckle yellow vein mosaic virus (HYVMV), hence named as HYVMV-Nara1 and HYVMV-Nara2, whereas Ibaraki virus was a strain of Tobacco leaf curl Japan virus (TbLCJV), designated as TbLCJV-Hs[Iba]. HYVMV-Nara1 and HYVMV-Nara2 have hybrid genomes, which are likely to have formed recombination between HYVMV and TbLCJV. TbLCJV-Hs[Iba] or HYVMV-Nara2 could infect and cause yellowing, leaf crinkling and stunting symptoms when partial tandem dimeric constructs were agroinoculated on tomato plants. However, in the presence of DNAbeta, both TbLCJV-Hs[Iba] or HYVMV-Nara2 produced more severe stunting symptoms in tomato plants. Therefore, these viruses along with their satellites are causal agents of tomato yellow dwarf disease in Japan, and honeysuckle acts as a potential reservoir host. Previously available evidence indicated that DNAbeta elements do not contain iteron sequences of their helper viruses; hence this is the first evidence that DNAbeta satellites have the iteron of their helper virus.

Evidence of local evolution of tomato-infecting begomovirus species in West Africa: characterization of tomato leaf curl Mali virus and tomato yellow leaf crumple virus from Mali

Tomato yellow leaf curl (TYLC) and tomato leaf curl (ToLC) diseases are serious constraints to tomato production in Mali and other countries in West Africa. In 2003 and 2004, samples of tomato showing virus-like symptoms were collected during a survey of tomato virus diseases in Mali. Three predominant symptom phenotypes were observed: (1) TYLC/ToLC (stunted upright growth and upcurled leaves with interveinal yellowing and vein purpling), (2) yellow leaf crumple and (3) broccoli or bonsai (severe stunting and distorted growth). Squash blot (SB) hybridization with a general begomovirus probe and/or SB/PCR analyses revealed begomovirus infection in plants with each of these symptom phenotypes and no evidence of phytoplasma infection. Sequence analysis of PCR-amplified begomovirus fragments revealed two putative new begomovirus species associated with the TYLC/ToLC and yellow leaf crumple symptom phenotypes, respectively. Full-length clones of these begomoviruses were obtained using PCR and overlapping primers. When introduced into N. benthamiana and tomato plants, these clones induced upward leaf curling and crumpling (the TYLC/ToLC-associated begomovirus) or downward leaf curl/yellow mottle (yellow leaf crumple-associated begomovirus) symptoms. Thus, these begomoviruses were named tomato leaf curl Mali virus (ToLCMLV) and tomato yellow leaf crumple virus (ToYLCrV). The genome organization of both viruses was similar to those of other monopartite begomoviruses. ToLCMLV and ToYLCrV were most closely related to each other and to tobacco leaf curl Zimbabwe virus (TbLCZV-[ZW]) and tomato curly stunt virus from South Africa (ToCSV-ZA). Thus, these likely represent tomato-infecting begomoviruses that evolved from indigenous begomoviruses on the African continent. Mixed infections of ToLCMLV and ToYLCrV in N. benthamiana and tomato plants resulted in more severe symptoms than in plants infected with either virus alone, suggesting a synergistic interaction. Agroinoculation experiments indicated that both viruses induced symptomatic infections in tomato and tobacco, whereas neither virus induced disease symptoms in pepper, common bean, small sugar pumpkin, African eggplant, or Arabidopsis. Virus-specific PCR primers were developed for detection of ToLCMLV and ToYLCrV and will be used to further investigate the distribution and host range of these viruses.

Infection and disease in reservoir and spillover hosts: determinants of pathogen emergence

Infection and disease in reservoir and spillover hosts determine patterns of infectious agent availability and opportunities for infection, which then govern the process of transmission between susceptible species. In this chapter, using the zoonotic agents Hendra virus and Nipah virus as examples, the pathogenesis of infection in various species including the wildlife reservoirs and domestic spillover hosts is reviewed with an emphasis on the aspects of pathogenesis which contribute to the dissemination of infection. Through these discussions, the emergence of these zoonotic agents is explored.

Suppressor of RNA silencing encoded by the monopartite tomato leaf curl Java begomovirus

We previously isolated the monopartite begomovirus tomato leaf curl Java virus (ToLCJAV) and satellite DNAbeta02 from the same naturally infected tomato source in Indonesia. ToLCJAV induced mild leaf curl symptoms in Nicotiana benthamiana plants; DNAbeta02 encoded the betaC1 gene and produced severe leaf curl symptoms when co-inoculated with ToLCJAV in N. benthamiana. However, DNAbeta02mbetaC1, which contains a frame shift mutation, did not induce severe symptoms in N. benthamiana when co-inoculated with ToLCJAV. Expression of the betaC1 gene in N. benthamiana using a potato virus X (PVX) vector induced virus-like symptoms in the absence of ToLCJAV infection. When betaC1 and green fluorescent protein (GFP) genes were co-expressed in the GFP-expressing N. benthamiana line 16c from a PVX vector, betaC1 was able to suppress posttranscriptional gene silencing (PTGS) induced by GFP and eliminated the short interfering RNA (siRNA) associated with GFP expression, with a correlated increase in GFP mRNA accumulation. When C2 or C4 genes of ToLCJAV and the GFP gene were co-expressed in the GFP-expressing N. benthamiana line 16c, C2 showed a weak suppressor activity and C4 was unable to suppress PTGS induced by GFP, and siRNA associated with GFP was detected. The results of the sub-cellular localization of ToLCJAV-betaC1 in the epidermal cells of N. benthamiana and onion tissues showed that this protein is accumulated towards the periphery of the cell.

A begomovirus associated with Ageratum yellow vein disease in Indonesia: evidence for natural recombination between tomato leaf curl Java virus and Ageratum yellow vein virus-[Java]

A begomovirus (2747 nucleotides) and a satellite DNA beta component (1360 nucleotides) have been isolated from Ageratum conyzoides L. plants with yellow vein symptoms growing in Java, Indonesia. The begomovirus is most closely related to Tomato leaf curl Java virus (ToLCJV) (91 and 98% in the total nucleotide and coat protein amino acid sequences, respectively), although the products of ORFs C1 and C4 are more closely related to those of Ageratum yellow vein virus-[Java] (91 and 95% identity, respectively). For this reason, the begomovirus it is considered to be a strain of ToLCJV and is referred to as ToLCJV-Ageratum. The virus probably derives from a recombination event in which nucleotides 2389-2692 of ToLCJV have been replaced with the corresponding region of the AYVV-[Java] genome, which includes the 5' part of the intergenic region and the C1 and C4 ORFs. Infection of A. conyzoides with ToLCJV-Ageratum alone produced no symptoms, but co-infection with DNAbeta induced yellow vein symptoms. Symptoms induced in Nicotiana benthamiana by ToLCJV-Ageratum, ToLCJV and AYVV-[Java] are consistent with the exchange of pathogenicity determinant ORF C4 during recombination.