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Transient overexpression of Nb-CAR7 inhibited TMV RNA accumulation in N. benthamiana plants. a Schematic structure of Nb-CAR7 overexpression vector, 35S-NbCAR7-GFP. b The relative expression level of Nb-CAR7 was increased in plant leaves at 3 days post infiltration with 35S-NbCAR7-GFP vector, using plants infiltrated with 35S-GFP vector as controls. c After TMV inoculation of the plants pre-infiltrated with 35S-NbCAR7-GFP vector, the relative expression level of TMV RNA at 7 dpi was decreased in the TMV-inoculated leaves but increased in the upper leaves. d After TMV inoculation of the plants pre-infiltrated with 35S-NbCAR7-GFP vector, the relative expression level of Nb-CAR7 in the TMVinoculated leaves was higher than that of control plants at 7 dpi, whereas was lower in the upper leaves than that of control plants. * represents P < 0.05 compared with control group
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Abstract Tobacco mosaic virus (TMV) is a positive-sense single-stranded RNA virus. The 3′ end of TMV genome is consisted of an upstream pseudoknot domain (UPD) and a tRNA-like structure (TLS), both of which are important RNA elements to enhance TMV replication and translation. Deep-sequencing analysis revealed that TMV-specific viral small interfer...
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... from mock-inoculated plants ( Fig. 2c), indicating the specificity of TMV-vsiRNA 22 nt-directed cleavage of the Nb-CAR7 transcript in TMVinfected N. benthamiana plants. To examine the effect of Nb-CAR7 on TMV infection, Nb-CAR7 overexpression construct driven by the 35S promoter with GFP tag was agro-infiltrated into N. benthamiana leaves ( Fig. 3a). At 3 days after infiltration, the expression level of Nb-CAR7 was significantly increased in the 35S-NbCAR7-GFP-infiltrated leaves, as compared to that of GFP-expressed control plants (Fig. 3b). After TMV was inoculated onto the infiltrated leaves, TMV RNA accumulation was significantly reduced in the inoculated leaves of ...
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... of Nb-CAR7 on TMV infection, Nb-CAR7 overexpression construct driven by the 35S promoter with GFP tag was agro-infiltrated into N. benthamiana leaves ( Fig. 3a). At 3 days after infiltration, the expression level of Nb-CAR7 was significantly increased in the 35S-NbCAR7-GFP-infiltrated leaves, as compared to that of GFP-expressed control plants (Fig. 3b). After TMV was inoculated onto the infiltrated leaves, TMV RNA accumulation was significantly reduced in the inoculated leaves of Nb-CAR7-overexpressed plants at 7 dpi, whereas was higher in the upper leaves of the same plant, as compared with that of the control plants (Fig. ...
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... leaves, as compared to that of GFP-expressed control plants (Fig. 3b). After TMV was inoculated onto the infiltrated leaves, TMV RNA accumulation was significantly reduced in the inoculated leaves of Nb-CAR7-overexpressed plants at 7 dpi, whereas was higher in the upper leaves of the same plant, as compared with that of the control plants (Fig. ...
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... TMV inoculation, the transcript levels of Nb-CAR7 in the inoculated leaves and upper leaves of infiltrated plants at 7 dpi were also analysed (Fig. 3d). The transcript level of Nb-CAR7 in the TMV-inoculated leaves was higher than that of control plants. Conversely, Nb-CAR7 level in the upper leaves was lower than that of ...
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... overexpression of Nb-CAR7 through agrobacterium infiltration was restricted to plant cells in the infiltrated region. Therefore, TMV RNA accumulation was decreased only in the infiltrated leaves but not in the upper leaves after TMV was inoculated into the agrobacterium-infiltrated leaves. (Fig. 3c). RNA silencing of Nb-CAR7 occurred in the upper leaves due to transient overexpression of Nb-CAR7 in the infiltrated leaves, which led to a lower amount of Nb-CAR7 in the upper leaves (Fig. 3d). Therefore, the accumulation of TMV RNA remained high in the upper leaves. In contrast, silencing of Nb-CAR7 through TRV-based and VIGSinduced ...
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... accumulation was decreased only in the infiltrated leaves but not in the upper leaves after TMV was inoculated into the agrobacterium-infiltrated leaves. (Fig. 3c). RNA silencing of Nb-CAR7 occurred in the upper leaves due to transient overexpression of Nb-CAR7 in the infiltrated leaves, which led to a lower amount of Nb-CAR7 in the upper leaves (Fig. 3d). Therefore, the accumulation of TMV RNA remained high in the upper leaves. In contrast, silencing of Nb-CAR7 through TRV-based and VIGSinduced gene silencing occurred throughout the entire plant. After TMV infection, silencing of Nb-CAR7 led to a higher viral RNA accumulation in both inoculated and upper leaves of Nb-CAR7-silenced ...
Citations
... Nb-CAR7 plays a critical role in ABA signaling, an important hormone in plant responses to abiotic stresses as well as to plant pathogens, including viruses. Consistently, Nb-CAR7-overexpressing plants show a decrease in TMV RNA accumulation, while dowregulation of Nb-CAR7 resulted in a higher TMV RNA accumulation [35] (Figure 1, panel II). ...
Small RNAs (sRNAs) are the hallmark and main effectors of RNA silencing and therefore are involved in major biological processes in plants, such as regulation of gene expression, antiviral defense, and plant genome integrity. The mechanisms of sRNA amplification as well as their mobile nature and rapid generation suggest sRNAs as potential key modulators of intercellular and interspecies communication in plant-pathogen–pest interactions. Plant endogenous sRNAs can act in cis to regulate plant innate immunity against pathogens, or in trans to silence pathogens’ messenger RNAs (mRNAs) and impair virulence. Likewise, pathogen-derived sRNAs can act in cis to regulate expression of their own genes and increase virulence towards a plant host, or in trans to silence plant mRNAs and interfere with host defense. In plant viral diseases, virus infection alters the composition and abundance of sRNAs in plant cells, not only by triggering and interfering with the plant RNA silencing antiviral response, which accumulates virus-derived small interfering RNAs (vsiRNAs), but also by modulating plant endogenous sRNAs. Here, we review the current knowledge on the nature and activity of virus-responsive sRNAs during virus–plant interactions and discuss their role in trans-kingdom modulation of virus vectors for the benefit of virus dissemination.
... On the other hand, mutations can also lead to increased virus reproduction and/or symptom development. An example is an increase of TMV replication due to disruptions in its the secondary structure [44]. Since the expression of sub-genomic viral RNA is regulated by sub-genomic promoter and enhancer elements, disruption of the relevant motifs also leads to changes in protein expression [45]. ...
... HTS of these plants revealed that TMV-vsiRNA possessed high sequence complementarity to a host gene which encodes a C2-domain abscisic acid (ABA)-related (CAR) 7-lke protein. CAR proteins play a crucial role in the ABA signaling pathway [44]. If an acute virus infection can have a more complex host-virus relationship than a disease damaging its host, it is perhaps easier to imagine that an asymptomatic infection can turn out to be a mutualistic relationship with the host. ...
Tobamoviruses are among the most well-studied plant viruses and yet there is still a lot to uncover about them. On one side of the spectrum, there are damage-causing members of this genus: such as the tobacco mosaic virus (TMV), tomato brown rugose fruit virus (ToBRFV) and cucumber green mottle mosaic virus (CGMMV), on the other side, there are members which cause latent infection in host plants. New technologies, such as high-throughput sequencing (HTS), have enabled us to discover viruses from asymptomatic plants, viruses in mixed infections where the disease etiology cannot be attributed to a single entity and more and more researchers a looking at non-crop plants to identify alternative virus reservoirs, leading to new virus discoveries. However, the diversity of these interactions in the virosphere and the involvement of multiple viruses in a single host is still relatively unclear. For such host–virus interactions in wild plants, symptoms are not always linked with the virus titer. In this review, we refer to latent infection as asymptomatic infection where plants do not suffer despite systemic infection. Molecular mechanisms related to latent behavior of tobamoviruses are unknown. We will review different studies which support different theories behind latency.
... Interestingly, Nb-CAR7 expression level is negatively correlated with the TMV RNA accumulation. Also, Nb-CAR7 mediates its antiviral role by modulating the expression of host abscisic acid responsive genes (Guo and Wong, 2020). ...
Virus-derived siRNAs (vsiRNAs) generated by the host RNA silencing mechanism are effectors of plant’s defense response and act by targeting the viral RNA and DNA in post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS) pathways, respectively. Contrarily, viral suppressors of RNA silencing (VSRs) compromise the host RNA silencing pathways and also cause disease-associated symptoms. In this backdrop, reports describing the modulation of plant gene(s) expression by vsiRNAs via sequence complementarity between viral small RNAs (sRNAs) and host mRNAs have emerged. In some cases, silencing of host mRNAs by vsiRNAs has been implicated to cause characteristic symptoms of the viral diseases. Similarly, viroid infection results in generation of sRNAs, originating from viroid genomic RNAs, that potentially target host mRNAs causing typical disease-associated symptoms. Pathogen-derived sRNAs have been demonstrated to have the propensity to target wide range of genes including host defense-related genes, genes involved in flowering and reproductive pathways. Recent evidence indicates that vsiRNAs inhibit host RNA silencing to promote viral infection by acting as decoy sRNAs. Nevertheless, it remains unclear if the silencing of host transcripts by viral genome-derived sRNAs are inadvertent effects due to fortuitous pairing between vsiRNA and host mRNA or the result of genuine counter-defense strategy employed by viruses to enhance its survival inside the plant cell. In this review, we analyze the instances of such cross reaction between pathogen-derived vsiRNAs and host mRNAs and discuss the molecular insights regarding the process of pathogenesis.
Host plants deploy the small RNA (sRNA)-directed RNA silencing pathway to resist invasion by acellular microorganisms (viruses/viroids/satellites), and, in turn, this pathway is exploited by pathogenic agents to create an environment conducive to infection. Previous known sRNA-RNA systems consist of host endogenous microRNAs (miRNAs) mediating the regulation of host mRNAs and virus/viroid/satellite-derived small interfering RNAs (vsiRNAs) targeting their genomic RNAs. However, more in-depth explorations have substantially expanded the understanding of the complexity of sRNA-RNA regulatory networks. Here, we review some recently discovered sRNA-mediated regulatory systems. Specifically, in addition to virus-encoded proteins acting as virulence factors, vsiRNAs can serve as important pathogenic determinants targeting host mRNAs and noncoding RNAs to promote virus/viroid/satellite infection and trigger symptoms that may be side effects of infection. Additionally, virus-activated but host-derived siRNAs (vasiRNAs) regulate endogenous plant gene expression related to virus resistance or pathogenicity. The inhibitory effect of miRNAs on plant endogenous mRNAs and viral RNAs (vRNAs) has also been identified. Furthermore, siRNA-based interregulation occurring between viruses and their parasite satellite RNAs (satRNAs) enables coexisting virus-satRNA-plant homeostasis. Thus, the underlying mechanisms of plant–virus/viroid/satellite competition and symbiosis are largely obscured by these diverse sRNA-RNA combinations. Guided by the intricate regulatory network-based principle at the RNA level, practically applicable and feasible strategies have been developed for the management of plant viruses/viroids/satellites for which effective control measures are lacking.
