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Induction of DGIs and recovery. (A) Symptoms of BP infection in the systemically infected leaves in N. benthamiana. (B) A DGI on the chlorotic leaf systemically infected with BP. (C) The upper systemically infected leaves on BP-infected HCpro-transgenic plants showed no recovery. (D to G) DGIs in the systemic leaves of nontransgenic plants (D and E) and their absence on systemically infected leaves of the HCpro-transgenic plants (F), compared with a symptomless, healthy leaf (G). (H and I) Comparison of BP infection in HCpro-transgenic (H) and nontransgenic (I) plants. Arrows indicate the recovered leaves.
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RNA silencing is a natural defense mechanism against genetic stress factors, including viruses. A mutant hordeivirus (Barley stripe mosaic virus [BSMV]) lacking the γb gene was confined to inoculated leaves in Nicotiana benthamiana, but systemic infection was observed in transgenic N. benthamiana expressing the potyviral silencing suppressor protei...
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... and appeared at different times. In plants infected with BSMV ND18 , mild yellowing symptoms were observed in the upper, noninocu- lated leaves at 10 to 12 dpi. In the plants inoculated with BP, however, symptoms were observed earlier (5 to 6 dpi), and they were more severe. Initially the leaves displayed severe mosaic symptoms and malformations (Fig. 4A) and later (9 to 12 dpi) developed necrosis. These results showed that replacement of the b gene in BSMV with the corresponding gene of PSLV enhances symptom severity and infection rate in N. benthami- ana, providing additional evidence for the involvement of hor- deivirus b in virus movement and virulence ...
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... systemically infected with BP and showing chlorosis developed discrete patterns of DGIs (Fig. 4B) at 12 to 40 dpi. DGI tissue was excised from the leaves and analyzed for viral CP, viral RNA, and siRNAs diagnostic of RNA silencing. Ac- cumulation of viral CP (Fig. 5A) and RNA (data not shown) was reduced by 50-fold in DGIs compared with the sur- rounding chlorotic leaf tissue. The minute quantities of viral CP and RNA detected in ...
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... 21 to 40 dpi, most of the new leaves in plants infected with BP were symptomless, indicating recovery from the viral infection (Fig. 4I), but some leaves still showed severe mosaic symptoms including DGIs. Thereafter, all new leaves were asymptomatic, whereas the new leaves in all plants infected with BSMV ND18 continued to display symptoms. The symp- tomless leaves of BP-infected plants contained only very low or no detectable amounts of viral CP (Fig. 5B) and viral ...
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... the recovery from infection with BSMV/ PSLV chimera. A total of nine HCpro-transgenic plants and nine nontransgenic (wt) N. benthamiana plants were inocu- lated with BP in two experiments. The symptoms induced by BP in the HCpro-transgenic plants were different from those observed in wt plants as the former group had fewer and smaller DGIs (Fig. 4E and F). As before, wt plants recovered from infection at 21 to 40 dpi (Fig. 4I), but the upper leaves of all HCpro-transgenic plants continued to be infected, display- ing the typical yellow mosaic and leaf malformation symptoms ( Fig. 4C and H). Viral CP and RNA were detected in the newly developing, symptomatic leaves of the ...
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... plants and nine nontransgenic (wt) N. benthamiana plants were inocu- lated with BP in two experiments. The symptoms induced by BP in the HCpro-transgenic plants were different from those observed in wt plants as the former group had fewer and smaller DGIs (Fig. 4E and F). As before, wt plants recovered from infection at 21 to 40 dpi (Fig. 4I), but the upper leaves of all HCpro-transgenic plants continued to be infected, display- ing the typical yellow mosaic and leaf malformation symptoms ( Fig. 4C and H). Viral CP and RNA were detected in the newly developing, symptomatic leaves of the HCpro-transgenic plants but not in the symptomless leaves of the wt N. benthami- ana ...
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... plants were different from those observed in wt plants as the former group had fewer and smaller DGIs (Fig. 4E and F). As before, wt plants recovered from infection at 21 to 40 dpi (Fig. 4I), but the upper leaves of all HCpro-transgenic plants continued to be infected, display- ing the typical yellow mosaic and leaf malformation symptoms ( Fig. 4C and H). Viral CP and RNA were detected in the newly developing, symptomatic leaves of the HCpro-transgenic plants but not in the symptomless leaves of the wt N. benthami- ana plants (Fig. 5B). The siRNAs were not detected in HCpro- transgenic plants at 28 dpi (Fig. 5C). Our studies on transgeni- cally overexpressed potyviral HCpro uncovered ...
Citations
... Viral determinants for seed transmission of BSMV, PEBV, and PSbMV have been reported to be the γb protein, 12K protein (12K), and helper-component protease (HC-Pro), respectively [14,26,61]. Although RNA silencing is a major plant defense mechanism against plant RNA viruses, the γb protein and HC-Pro are known to suppress RNA silencing (RSS activity), and 12K has high similarity to the protein with RSS activity of tobacco rattle virus [4,35,49,65]. Hence, RNA silencing may play an important role in inhibiting seed transmission of plant RNA viruses. ...
Raspberry bushy dwarf virus (RBDV) is transmitted through seed in infected red raspberry plants after pollination with pollen grains from healthy red raspberry plants. Here, we show that RBDV is not transmitted through seeds in infected Nicotiana benthamiana (Nb) plants after pollination with virus-free Nb pollen grains. Chromogenic in situ hybridization revealed that the virus invades the shoot apical meristem and the ovule, including the embryo sac, of RBDV-infected Nb plants; however, in seeds that developed from infected embryo sacs after fertilization by virus-free sperm cells, RBDV was absent in the embryos and present in the endosperms. When we analyzed seed transmission of RBDV in Nb mutants with mutations in dicer-like enzyme 2 and 4 (NbDCL2&4) or RNA-dependent RNA polymerase 6 (NbRDR6), RBDV was not present in the offspring from seeds with embryos and endosperms that did not express NbDCL2&4 or NbRDR6. These results suggest that seed transmission of RBDV is prevented by evasion of infection by the embryo and that RNA silencing is not essential for preventing seed transmission of RBDV in Nb plants.
... In this sense, the reduced accumulation of encapsidated RNAs in the evolved chimeric AMV constructs will permit increase in the number of BMV MP-RNA complexes, allowing for more efficient virus transport. Accordingly, all evolved chimeric AMV constructs showed increased cell-to-cell transport, which is critical for the systemic transport (33), probably by avoiding the plant defense mechanisms (21,(51)(52)(53)(54). Interestingly, a BMV MP mutant lacking the C-terminal 42 amino acids was competent to mediate cell-to-cell transport of BMV in the absence of CP, but did not support systemic transport, even in the presence of the CP (36), probably due to its incapacity to interact with the virus particles and/or the encapsidated viral RNAs, as observed herein. ...
Although the coat protein (CP) has a relevant role in the long-distance movement of alfalfa mosaic virus (AMV) and brome mosaic virus (BMV), its precise function is not fully understood. Previous results showed that a specific interaction between the C termini of the movement protein (MP) and the cognate CP is required for systemic transport. Thus, we have performed a compensatory evolution experiment using an AMV RNA3 derivative defective in long-distance transport that carries a BMV MP lacking the C-terminal 48 residues and unable to interact with the AMV CP. After several passages, five independent evolution lineages were able to move long distance. The analysis of the viral RNA of these lineages showed the presence of three different modifications located exclusively at the 5' untranslated region (5' UTR). The three evolved 5' UTR variants accumulated comparable levels of viral RNA and CP but reduced the accumulation of virus particles and the affinity between the 5' UTR and the AMV CP. In addition, the evolved 5' UTR increased cell-to-cell transport for both the AMV RNA3 carrying the BMV MP and that carrying the AMV MP. Finally, the evolved 5' UTRs allowed the systemic transport of an AMV RNA3 carrying a CP mutant defective in virus particles and increased the systemic transport of several AMV RNA3 derivatives carrying different viral MPs associated with the 30K superfamily. Altogether, our findings indicate that virus particles are not required for the systemic transport of AMV but also that BMV MP is competent for the short- and long-distance transport without the interaction with the CP. IMPORTANCE The results obtained in the present work could challenge the view of the role of the virus particle in the systemic transport of plant viruses. In this sense, we show that two different MPs are competent to systemically transport the AMV genome without the requirement of the virus particles, as reported for viruses lacking a CP (e.g., Umbravirus). The incapability of the viral MP to interact with the CP triggered virus variants that evolved to reduce the formation of virus particles, probably to increase the accessibility of the MP to the viral progeny. Our results point to the idea that virus particles would not be necessary for the viral systemic transport but would be necessary for vector virus transmission. This idea is reinforced by the observation that heterologous MPs also increased the systemic transport of the AMV constructs that have reduced encapsidation capabilities.
... Barley stripe mosaic virus (BSMV), a type member of the genus Hordeivirus, is composed of three plus-sense genomic RNAs named RNAa, RNAb and RNAc that encode seven major proteins (Jackson et al., 2009;Jiang et al., 2021). Among them, RNAc-encoded cb is a 17 kDa multifunctional protein that acts as a viral suppressor of RNA silencing (VSR) (Yelina et al., 2002; and pathogenicity determinant and is responsible for seed transmission of BSMV in barley (Hordeum vulgare) and wheat (Triticum aestivum) (Edwards, 1995;Li et al., 2021). Our recent studies indicated that cb can promote BSMV replication by enhancing the unwinding of RNA duplexes (Zhang et al., 2017) and can facilitate viral cell-to-cell movements by enhancing the ATPase activity of the BSMV Triple Gene Block1 (TGB1) protein (Jiang et al., 2020). ...
Posttranslational modifications (PTMs) play important roles in virus–host interplay. We previously demonstrated that Barley stripe mosaic virus (BSMV) γb protein is phosphorylated by different host kinases to support or impede viral infection. However, whether and how other types of PTMs participate in BSMV infection remains to be explored.
Here, we report that S‐adenosylmethionine decarboxylase 3 (SAMDC3) from Nicotiana benthamiana or wheat (Triticum aestivum) interacts with γb. BSMV infection induced SAMDC3 expression. Overexpression of SAMDC3 led to the destabilization of γb and reduction in viral infectivity, whereas knocking out NbSAMDC3 increased susceptibility to BSMV.
NbSAMDC3 positively regulated the 26S proteasome‐mediated degradation of γb via its PEST domain. Further mechanistic studies revealed that γb can be ubiquitinated in planta and that NbSAMDC3 promotes the proteasomal degradation of γb by increasing γb ubiquitination. We also found evidence that ubiquitination occurs at nonlysine residues (Ser‐133 and Cys‐144) within γb.
Together, our results provide a function for SAMDC3 in defence against BSMV infection through targeting of γb abundance, which contributes to our understanding of how a plant host deploys the ubiquitin–proteasome system to mount defences against viral infections.
... Additionally, the presence of synergistically interacting WSMV and TriMV in tripartite and quadripartite interactions might have prevented the negative effects of BMV on WSMV and TriMV. Perhaps, the weak nature of RNA silencing suppressor protein of BSMV (Yelina et al., 2002;Bragg and Jackson, 2004;Zhang et al., 2017) is not enough to overcome the host defense and compete with robust BMV replication; thus, BMV dominates replication of BSMV in co-infected wheat. ...
Field-grown wheat ( Triticum aestivum L.) plants can be co-infected by multiple viruses, including wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), brome mosaic virus (BMV), and barley stripe mosaic virus (BSMV). These viruses belong to four different genera in three different families and are, hence, genetically divergent. However, the impact of potential co-infections with two, three, or all four of them on the viruses themselves, as well as the wheat host, has yet to be examined. This study examined bi-, tri-, and quadripartite interactions among these viruses in wheat for disease development and accumulation of viral genomic RNAs, in comparison with single virus infections. Co-infection of wheat by BMV and BSMV resulted in BMV-like symptoms with a drastic reduction in BSMV genomic RNA copies and coat protein accumulation, suggesting an antagonism-like effect exerted by BMV toward BSMV. However, co-infection of either BMV or BSMV with WSMV or TriMV led to more severe disease than singly infected wheat, but with a decrease or no significant change in titers of interacting viruses in the presence of BMV or BSMV, respectively. These results were in stark contrast with exacerbated disease phenotype accompanied with enhanced virus titers caused by WSMV and TriMV co-infection. Co-infection of wheat by WSMV, TriMV, and BMV or BSMV resulted in enhanced synergistic disease accompanied by increased accumulation of TriMV and BMV but not WSMV or BSMV. Quadripartite interactions in co-infected wheat by all four viruses resulted in very severe disease synergism, leading to the death of the most infected plants, but paradoxically, a drastic reduction in BSMV titer. Our results indicate that interactions among different viruses infecting the same plant host are more complex than previously thought, do not always entail increases in virus titers, and likely involve multiple mechanisms. These findings lay the foundation for additional mechanistic dissections of synergistic interactions among unrelated plant viruses.
... Therefore, VSRs have evolved independently with no structural similarities, repressing antiviral RNA silencing in hosts by affecting the involved core components (Li and Wang 2019) ( Table 2, Fig. 2). Yelina et al. (2002) and Merai et al. (2006) Pecluvirus PCV (+)ssRNA P15 Binds to siRNA size selectively and interferes with the miRNA pathway to suppress antiviral silencing Dunoyer et al. (2004) and Merai et al. (2006) Tobamovirus ...
RNA silencing is an evolutionarily homology-based gene inactivation mechanism and plays critical roles in plant immune responses to acute or chronic virus infections, which often pose serious threats to agricultural productions. Plant antiviral immunity is triggered by virus-derived small interfering RNAs (vsiRNAs) and functions to suppress virus further replication via a sequence-specific degradation manner. Through plant-virus arms races, many viruses have evolved specific protein(s), known as viral suppressors of RNA silencing (VSRs), to combat plant antiviral responses. Numerous reports have shown that VSRs can efficiently curb plant antiviral defense response via interaction with specific component(s) involved in the plant RNA silencing machinery. Members in the family Closteroviridae (closterovirids) are also known to encode VSRs to ensure their infections in plants. In this review, we will focus on the plant antiviral RNA silencing strategies, and the most recent developments on the multifunctional VSRs encoded by closterovirids. Additionally, we will highlight the molecular characters of phylogenetically-associated closterovirids, the interactions of these viruses with their host plants and transmission vectors, and epidemiology.
... Notably, sgRNA-γ-b accumulated at much higher levels than gRNAs and other sgRNAs taken together (Figure 6), which may reflect an important function of the 16 kDa cysteine-rich protein γ-b at a given stage of infection in the symptomatic privet leaf. Indeed, the hordeiviral γ-b proteins and other small cysteine-rich proteins of + ssRNA viruses have been implicated in RNA binding and suppression of RNA silencing (Yelina et al., 2002;Bragg and Jackson, 2004;Li et al., 2020). In a previous study also using Northern blot analysis with a 3 -CR specific probe, sgRNA-γ was found to be the most abundant viral RNA in LRSV-infected N. benthamiana (Jiang et al., 2018). ...
... Since DCL4 is known to be a primary Dicer targeting cytoplasmic RNA viruses, while DCL2 is activated when DCL4 activity is diminished or suppressed (reviewed in Csorba et al., 2015;Pooggin, 2016Pooggin, , 2018, the predominance of 22 nt viral siRNAs, which accumulated at levels exceeding those of 21 nt viral siRNAs (Figure 7B), suggests that DCL4 activity in LigMV-infected privet cells might be suppressed by a viral silencing suppressor protein. As mentioned above, the γ-b protein translated from the most abundant sgRNA is a silencing suppressor (Yelina et al., 2002;Bragg and Jackson, 2004;Li et al., 2020) that can potentially target DCL4 and perhaps other components of the plant RNAi machinery, as demonstrated for other viral suppressor proteins (reviewed in Csorba et al., 2015;Pooggin, 2016). However, viral suppressor activity does not appear to prevent massive production of viral 21-22 nt siRNAs. ...
Wild plants serve as a large reservoir of known and yet-unknown viruses and as a source of viral pathogens of cultivated plants. Yellow mosaic disease of forest shrub Ligustrum vulgare (privet) was recurrently observed in Europe for more than 100 years. Using a universal virus identification approach based on deep sequencing and de novo assembly of viral small interfering (si)RNAs we identified a causative agent of this disease in Switzerland and reconstructed its complete 3-segmented RNA genome. Notably, a short 3-terminal common region (CR) attached to each segment via a ∼53-71 nucleotide poly(A) tract, as determined by RT-PCR sequencing, was initially identified as an orphan siRNA contig with conserved tRNA-like secondary structure. Phylogenomic analysis classified this virus as a novel member in the genus Hordeivirus of family Virgaviridae, which we named ligustrum mosaic virus (LigMV). Similar to other hordeiviruses, LigMV formed rod-shape virions (visualized by electron microscopy), was transmitted through seeds and could also be mechanically transmitted to herbaceous hosts Chenopodium quinoa and Nicotiana benthamiana. Blot hybridization analysis identified genomic and subgenomic RNAs, sharing the 3-CR and likely serving as monocistronic mRNAs for seven evolutionarily-conserved viral proteins including two subunits of viral RNA-dependent RNA polymerase, coat protein, triple gene block proteins mediating viral movement and cysteine-rich suppressor of RNA silencing. Analysis of size, polarity, and hotspot profiles of viral siRNAs suggested that they are produced by the plant antiviral Dicer-like (DCL) proteins DCL2 and DCL4 processing double-stranded intermediates of genomic RNA replication. Whole genome sequencing of French and Austrian isolates of LigMV revealed its genetic stability over a wide geographic range (>99% nucleotide identity to Swiss isolates and each other), suggesting its persistence and spread in Europe via seed dispersal.
... The cb protein encoded by RNAc plays a versatile role in multiple steps of the BSMV infection cycle and interferes with several basal host defenses during BSMV-host interactions . In addition to functioning as a viral suppressor of RNA silencing (VSR; Yelina et al, 2002;, cb is a determinant of viral systemic movement (Petty et al, 1990;Yelina et al, 2002), viral pathogenesis (Donald & Jackson, 1994;, and seed transmission (Edwards, 1995). Moreover, cb is also phosphorylated by PKA-like kinase to sustain virus infection and evade the host necrotic antiviral responses . ...
... The cb protein encoded by RNAc plays a versatile role in multiple steps of the BSMV infection cycle and interferes with several basal host defenses during BSMV-host interactions . In addition to functioning as a viral suppressor of RNA silencing (VSR; Yelina et al, 2002;, cb is a determinant of viral systemic movement (Petty et al, 1990;Yelina et al, 2002), viral pathogenesis (Donald & Jackson, 1994;, and seed transmission (Edwards, 1995). Moreover, cb is also phosphorylated by PKA-like kinase to sustain virus infection and evade the host necrotic antiviral responses . ...
... These results demonstrate that His-85 of cb is a key amino acid that determines cb binding to NbNTRC. Considering that cb is a classic VSR (Yelina et al, 2002;, we also tested whether the His-85 mutation affected VSR activity. The GFP protein was co-expressed with either cb-3xFlag or its mutants (cb H85A and cb H85C ) in N. benthamiana leaves . ...
The plant antioxidant system plays important roles in response to diverse abiotic and biotic stresses. However, the effects of virus infection on host redox homeostasis and how antioxidant defense pathway is manipulated by viruses remain poorly understood. We previously demonstrated that the Barley stripe mosaic virus (BSMV) γb protein is recruited to the chloroplast by the viral αa replicase to enhance viral replication. Here, we show that BSMV infection induces chloroplast oxidative stress. The versatile γb protein interacts directly with NADPH-dependent thioredoxin reductase C (NTRC), a core component of chloroplast antioxidant systems. Overexpression of NbNTRC significantly impairs BSMV replication in Nicotiana benthamiana plants, whereas disruption of NbNTRC expression leads to increased viral accumulation and infection severity. To counter NTRC-mediated defenses, BSMV employs the γb protein to competitively interfere with NbNTRC binding to 2-Cys Prx. Altogether, this study indicates that beyond acting as a helicase enhancer, γb also subverts NTRC-mediated chloroplast antioxidant defenses to create an oxidative microenvironment conducive to viral replication.
... The cb protein is a multifunctional protein that participates in different stages of virus infection. Its functions include singlestranded viral RNA binding during replication (Donald and Jackson, 1996), suppression of RNA silencing (Yelina et al., 2002;Bragg and Jackson, 2004), inhibition of peroxisomal reactive oxygen species burst (Yang et al., 2018a), subversion of autophagy-mediated antiviral defense (Yang et al., 2018b), mediating systemic virus movement (Yelina et al., 2002), viral pathogenesis (Donald and Jackson, 1994), and facilitating viral transmission through seed (Edwards, 1995). BSMV replicates its RNA genome on the cytosolic side of the chloroplast outer membrane (Zhang et al., 2017;Jin et al., 2018). ...
... The cb protein is a multifunctional protein that participates in different stages of virus infection. Its functions include singlestranded viral RNA binding during replication (Donald and Jackson, 1996), suppression of RNA silencing (Yelina et al., 2002;Bragg and Jackson, 2004), inhibition of peroxisomal reactive oxygen species burst (Yang et al., 2018a), subversion of autophagy-mediated antiviral defense (Yang et al., 2018b), mediating systemic virus movement (Yelina et al., 2002), viral pathogenesis (Donald and Jackson, 1994), and facilitating viral transmission through seed (Edwards, 1995). BSMV replicates its RNA genome on the cytosolic side of the chloroplast outer membrane (Zhang et al., 2017;Jin et al., 2018). ...
... NbSTY46 has no discernable effect on the VSR activity of cb As a viral suppressor of RNA silencing (VSR), BSMV cb protein promotes virus pathogenicity and long-distance movement (Yelina et al., 2002;Bragg and Jackson, 2004). To determine the effects of NbSTY46 on cb VSR activity, we measured whether NbSTY46 can interfere with the suppression of positive-sense GFP (sGFP)-induced RNA silencing by cb (Dong et al., 2016;Zhang et al., 2018). ...
Protein phosphorylation is a common post-translational modification that frequently occurs during plant-virus interaction. Host protein kinases often regulate virus infectivity and pathogenicity by phosphorylating viral proteins. The Barley stripe mosaic virus (BSMV) γb protein plays versatile roles in virus infection and the coevolutionary arms race between plant defense and viral counter-defense. Here, we identified that the autophosphorylated cytosolic serine/threonine/tyrosine (STY) protein kinase 46 of Nicotiana benthamiana (NbSTY46) phosphorylates and directly interacts with the basic motif domain (aa 19-47) of γb in vitro and in vivo. Overexpression of wild-type NbSTY46, either transiently or transgenically, suppresses BSMV replication and ameliorates viral symptoms, whereas silencing of NbSTY46 leads to increased viral replication and exacerbated symptom. Moreover, the antiviral role of NbSTY46 requires its kinase activity, as the NbSTY46T436A mutant, lacking kinase activity, not only loses the ability to phosphorylate and interact with γb but also fails to impair BSMV infection when expressed in plants. NbSTY46 could also inhibit the replication of Lychnis ringspot virus, another chloroplast-replicating hordeivirus. In summary, we report a function of the cytosolic kinase STY46 in defending against plant viral infection by phosphorylating a viral protein in addition to its basal function in plant growth, development, and abiotic stress responses.
... The recombinant pCB301-FLRaV binary plasmid was transformed into A. tumefaciens strain EHA105. Equal volumes of Agrobacterium cultures harboring pCB301-FLRaV as well as constructs expressing two RNA silencing suppressors, barley stripe mosaic virus (BSMV) γb and tomato bushy stunt virus (TBSV) p19, were mixed and co-infiltrated into four-week-old N. benthamiana leaves [26][27][28]. The plants were then maintained in a growth chamber at 25 • C with a 14:10 h photoperiod. ...
A novel RNA virus was identified in firespike (Odontonema tubaeforme) plants exhibiting leaf curling and chlorosis. The molecular features of the viral genomic RNA and proteins resemble those of ampeloviruses. Based on sequence comparisons and phylogenetic analysis, we propose a new species in the genus Ampelovirus, which we have tentatively named Firespike leafroll-associated virus (FLRaV). Bioassays showed that the virus is mechanically transmissible to Nicotiana benthamiana. In addition, a full-length cDNA clone of FLRaV could successfully infect N. benthamiana via agroinfiltration.
... The application of homologous recombination technology to construct chimeric viruses provide important tools to unravel the functions of specific viral RNA sequences or the coding proteins during infection (Yelina et al., 2002;Lukhovitskaya et al., 2013;Tuo et al., 2015;Yu et al., 2019). In a previous study, we generated a PMMoV infectious clone and several chimeric clones to clarify critical RNA sequences required for efficient virus infection (Yu et al., 2019). ...
... Application of chimeric viruses containing heterologous sequence substitution can provide important messages to clarify the critical functions of the RNA sequences or the coding proteins of plant viruses during infection (Yelina et al., 2002;Lukhovitskaya et al., 2013;Tuo et al., 2015;Yu et al., 2019). Table 2. Asterisks indicate a statistically significant difference compared with TMV, " * " indicate a significant difference (P < 0.05) and " * * " indicate an extremely significant difference (P < 0.01). ...
In the pathogen infection and host defence equilibrium, plant viruses have evolved to efficiently replicate their genomes, to resist the attack from host defence responses and to avoid causing severe negative effect on growth and metabolism of the hosts. In this study, we generated chimeric tobacco mosaic virus (TMV) variants, in which the coat protein (CP) sequences were substituted with that of cucumber green mottle mosaic virus (CGMMV) or pepper mild mottle virus (PMMoV) to address the role of these in virus infection and host symptomology. The results showed that the chimeric viruses (TMV-CGCP or TMV-PMCP) induce stunting and necrotic symptoms in tobacco plants. We analyzed the transcriptomic changes in tobacco plants after infection of TMV and its chimeras using a high-throughput RNA sequencing approach and found that infection of the chimeric TMV induced significant up-regulation of host defence responsive genes together with salicylic (SA) or abscisic acid (ABA) responsive genes, but down-regulation of auxin (Aux) responsive genes. We further confirmed the increase in the levels of SA and ABA, together with the reduced levels of Aux after infection of chimeric TMV in tobacco plants. These data suggest novel roles of tobamovirus CP in induction of host symptoms and defence responses.
