A minimum length of N gene sequence in transgenic plants is required for RNA-mediated tospovirus resistance

Jan, Fuh-Jyh; Fagoaga, Carmen; Pang, Sheng‐Zhi; Gonsalves, D.

doi:10.1099/0022-1317-81-1-235

Cited by 57 publications

(35 citation statements)

References 54 publications

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“…It can be induced systemically, not only in cells that contained the primary virus, but also in cells that were not preinfected with the primary virus. The mechanism targets nearly identical RNA sequences; thus, the introduction of homologous sequences, in some cases as short as 23 nucleotides, into genomes of heterologous viruses has been shown to induce degradation of RNA molecules containing those sequences (30,49,67,72). For a number of plant viruses, RNA silencing was suggested as a mechanism that confers homologous interference of viruses (48,49,68; reviewed in references 21 and 29).…”

Section: Discussionmentioning

confidence: 99%

Superinfection Exclusion Is an Active Virus-Controlled Function That Requires a Specific Viral Protein

Folimonova

2012

J Virol

175

146

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Superinfection exclusion, a phenomenon in which a preexisting viral infection prevents a secondary infection with the same or a closely related virus, has been described for various viruses, including important pathogens of humans, animals, and plants. The phenomenon was initially used to test the relatedness of plant viruses. Subsequently, purposeful infection with a mild isolate has been implemented as a protective measure against virus isolates that cause severe disease. In the medical and veterinary fields, superinfection exclusion was found to interfere with repeated applications of virus-based vaccines to individuals with persistent infections and with the introduction of multicomponent vaccines. In spite of its significance, our understanding of this phenomenon is surprisingly incomplete. Recently, it was demonstrated that superinfection exclusion of Citrus tristeza virus (CTV), a positive-sense RNA closterovirus, occurs only between isolates of the same strain, but not between isolates of different strains of the virus. In this study, I show that superinfection exclusion by CTV requires production of a specific viral protein, the p33 protein. Lack of the functional p33 protein completely eliminated the ability of the virus to exclude superinfection by the same or a closely related virus. Remarkably, the protein appeared to function only in a homology-dependent manner. A cognate protein from a heterologous strain failed to confer the exclusion, suggesting the existence of precise interactions of the p33 protein with other factors involved in this complex phenomenon. Superinfection exclusion or homologous interference is defined as the ability of an established virus infection to interfere with a secondary infection by the same or a closely related virus. The phenomenon has been described for various virus-host systems, including viruses that cause serious diseases in humans, animals, and plants (2, 9, 10, 11, 14, 19-21, 23, 28, 29, 31, 35, 37, 38, 55, 61-64, 74-77). From an evolutionary standpoint, superinfection exclusion can be a powerful strategy that determines the genetic structure of the virus population. Superinfection exclusion protects the virus from a related competing secondary virus targeting the cell that has been successfully infected by the primary virus. Besides elimination of competition for host resources, the phenomenon could function as a means to maintain the stability of viral sequences because it prevents replication of two or more viral genomes in the same cell, thus reducing the likelihood of the recombination or reassortment of viral genes, with the latter event of particular importance for the evolution of segmented viruses (18,27). From a practical standpoint, superinfection exclusion can have both positive and negative attributes. Referred to as cross-protection, this phenomenon has been implemented as an agricultural practice in which purposeful infection with a mild isolate was used as a protective measure against isolates of the virus that cause severe disease (reviewed in...

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Section: Discussionmentioning

confidence: 99%

Superinfection Exclusion Is an Active Virus-Controlled Function That Requires a Specific Viral Protein

Folimonova

2012

J Virol

175

146

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“…RNA silencing, which has been shown to be a major host defense mechanism against viruses in plants and in invertebrate animals, can be induced systemically in both infected and uninfected cells (59,62,76,92,97). The mechanism targets nearly identical RNA sequences and, thus, introduction of homologous sequences, in some cases as short as 23 nucleotides, into genomes of heterologous viruses has been shown to induce degradation of RNA molecules containing these sequences (42,70,90,98). These characteristics parallel the observations of superinfection exclusion of CTV and could explain the exclusion of closely related isolates and lack of exclusion of isolates of distinct strains.…”

Section: Discussionmentioning

confidence: 99%

“…The observation that superinfection exclusion occurred only with isolates of the same strains, which were defined based on the levels of sequence similarity, suggested that RNA silencing might be a component of the exclusion mechanism. Numerous examples from various virushost systems demonstrated that expression of homologous sequences from a virus genome in a host can trigger sequencespecific degradation of viral RNA, and some examples of superinfection exclusion have been attributed to RNA silencing (42,70,98). To examine the role of homologous sequences in superinfection exclusion, we created a series of hybrids in which sequences from one virus were substituted into a virus of a different strain.…”

Section: Assessment Of Superinfection Exclusion For Different Combinamentioning

confidence: 99%

Infection with Strains of Citrus Tristeza Virus Does Not Exclude Superinfection by Other Strains of the Virus

Folimonova

Robertson

Shilts

et al. 2010

J Virol

112

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Superinfection exclusion or homologous interference, a phenomenon in which a primary viral infection prevents a secondary infection with the same or closely related virus, has been observed commonly for viruses in various systems, including viruses of bacteria, plants, and animals. With plant viruses, homologous interference initially was used as a test of virus relatedness to define whether two virus isolates were "strains" of the same virus or represented different viruses, and subsequently purposeful infection with a mild isolate was implemented as a protective measure against isolates of the virus causing severe disease. In this study we examined superinfection exclusion of Citrus tristeza virus (CTV), a positive-sense RNA closterovirus. Thirteen naturally occurring isolates of CTV representing five different virus strains and a set of isolates originated from virus constructs engineered based on an infectious cDNA clone of T36 isolate of CTV, including hybrids containing sequences from different isolates, were examined for their ability to prevent superinfection by another isolate of the virus. We show that superinfection exclusion occurred only between isolates of the same strain and not between isolates of different strains. When isolates of the same strain were used for sequential plant inoculation, the primary infection provided complete exclusion of the challenge isolate, whereas isolates from heterologous strains appeared to have no effect on replication, movement or systemic infection by the challenge virus. Surprisingly, substitution of extended cognate sequences from isolates of the T68 or T30 strains into T36 did not confer the ability of resulting hybrid viruses to exclude superinfection by those donor strains. Overall, these results do not appear to be explained by mechanisms proposed previously for other viruses. Moreover, these observations bring an understanding of some previously unexplained fundamental features of CTV biology and, most importantly, build a foundation for the strategy of selecting mild isolates that would efficiently exclude severe virus isolates as a practical means to control CTV diseases.Superinfection exclusion or homologous interference is a phenomenon in which a preexisting viral infection prevents a secondary infection with the same or a closely related virus, whereas infection by unrelated viruses can be unaffected. The phenomenon was first observed by McKinney (57,58) between two genotypes of Tobacco mosaic virus (TMV) and later with bacteriophages (21, 94). Since that time, the phenomenon has been observed often for viruses of animals (1, 13, 18, 34, 43, 47, 50, 85, 86-88, 102, 103) and plants (11,30,31,32,39,40,49,77,99,100). In plant virology, homologous interference initially was used as a test of virus relatedness to define whether two virus isolates were "strains" of the same virus or represented different viruses (58, 77). Subsequently, it was developed into a management tool to reduce crop losses by purposely infecting plants with mild isolates of a virus ...

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“…The sequences of the 35S-3END-S and 34S-3END-AS constructs were T36-like, whereas the sequence of the 34S-3END-S construct was more similar to stem pitting isolates (data not shown). The size of the 3END insert was chosen based on work by others suggesting that a minimum viral transgene length of about 400 bp is necessary in order to induce resistance (Jan et al 2000).…”

Section: Plasmid Constructsmentioning

confidence: 99%

Characterization of grapefruit plants (Citrus paradisi Macf.) transformed with citrus tristeza closterovirus genes

et al. 2003

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Grapefruit (Citrus paradisi Macf. cv Duncan) plants were transformed with several sequences from citrus tristeza closterovirus (CTV) that varied in terms of position in the CTV genome and virus strain origin in an attempt to obtain resistant plants. The sequences included the capsid protein gene from three different strains, a nontranslatable version of the capsid protein gene, the replicase (RdRp), the minor capsid protein (p27), a highly transcribed gene of unknown function (p20) and the more conserved 3' end of the genomic RNA. Transgenic plants were generated from all of the constructs, except from the p20 and p27 genes. Southern and Western blot analyses demonstrated that stably transformed grapefruit plants were obtained and that at least some transgenes were expressed. In a first effort at virus challenge, 25 transgenic lines were graft inoculated with a severe strain of CTV. Although some transgenic plants averaged lower titers of virus than controls, there was great variability in titer in both controls and transgenic plants, and all were apparently susceptible to the virus.

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A minimum length of N gene sequence in transgenic plants is required for RNA-mediated tospovirus resistance

Cited by 57 publications

References 54 publications

Superinfection Exclusion Is an Active Virus-Controlled Function That Requires a Specific Viral Protein

Superinfection Exclusion Is an Active Virus-Controlled Function That Requires a Specific Viral Protein

Infection with Strains of Citrus Tristeza Virus Does Not Exclude Superinfection by Other Strains of the Virus

Characterization of grapefruit plants (Citrus paradisi Macf.) transformed with citrus tristeza closterovirus genes

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