Influence of retinoblastoma-related gene silencing on the initiation of DNA replication by African cassava mosaic virus Rep in cells of mature leaves in Nicotiana benthamiana plants

ABSTRACT Posttranscriptional gene silencing (PTGS) in plants is a natural defense mechanism against virus infection. In mixed infections, virus synergism is proposed to result from suppression of the host defense mechanism by the viruses. Synergistic severe mosaic disease caused by simultaneous infection with isolates of the Cameroon strain of African cassava mosaic virus (ACMV-[CM]) and East African cassava mosaic Cameroon virus (EACMCV) in cassava and tobacco is characterized by a dramatic increase in symptom severity and a severalfold increase in viral-DNA accumulation by both viruses compared to that in singly infected plants. Here, we report that synergism between ACMV-[CM] and EACMCV is a two-way process, as the presence of the DNA-A component of ACMV-[CM] or EACMCV in trans enhanced the accumulation of viral DNA of EACMCV and ACMV-[CM], respectively, in tobacco BY-2 protoplasts. Furthermore, transient expression of ACMV-[CM] AC4 driven by the Cauliflower mosaic virus 35S promoter (p35S-AC4) enhanced EACMCV DNA accumulation by ∼8-fold in protoplasts, while p35S-AC2 of EACMCV enhanced ACMV-[CM] DNA accumulation, also by ∼8-fold. An Agrobacterium-based leaf infiltration assay determined that ACMV-[CM] AC4 and EACMCV AC2, the putative synergistic genes, were able to suppress PTGS induced by green fluorescent protein (GFP) and eliminated the short interfering RNAs associated with PTGS, with a correlated increase in GFP mRNA accumulation. In addition, we have identified AC4 of Sri Lankan cassava mosaic virus and AC2 of Indian cassava mosaic virus as suppressors of PTGS, indicating that geminiviruses evolved differently in regard to interaction with the host. The specific and different roles played by these AC2 and AC4 proteins of cassava geminiviruses in regulating anti-PTGS activity and their relation to synergism are discussed.

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The size of encapsidated single-stranded DNA determines the multiplicity of African cassava mosaic virus particles

Journal of General Virology ◽

10.1099/0022-1317-82-3-673 ◽

2001 ◽

Vol 82 (3) ◽

pp. 673-676 ◽

Cited By ~ 28

Author(s):

Thomas Frischmuth ◽

Margit Ringel ◽

Cornelia Kocher

Keyword(s):

Electron Microscopy ◽

Mosaic Virus ◽

Nicotiana Benthamiana ◽

Southern Blotting ◽

African Cassava Mosaic Virus ◽

Dna Virus ◽

Virus Particles ◽

20 Nm ◽

And Control ◽

Cassava Mosaic Virus

Transgenic Nicotiana benthamiana plants harbouring a defective interfering (DI) DNA of African cassava mosaic virus (ACMV) and control plants were inoculated with ACMV. Virus particles were purified from infected plants, separated in sucrose gradients and fractions were analysed by Southern blotting. Transgenic plant-derived virus particles taken from the top fractions of sucrose gradients contained DI DNA, middle fractions contained a mixture of genomic and DI DNA and bottom fractions contained a mixture of multimeric, genomic and DI DNA. Virus particles from selected top, middle and bottom fractions were analysed by electron microscopy. In fractions containing only DI DNA, isometric particles of 18–20 nm were detected. In fractions containing DI DNA as well as genomic size DNA, isometric and geminate particles were found. Fractions containing multimeric size DNA were found to comprise particles consisting of three subunits adjacent to geminate particles. From these data, it is concluded that the size of encapsidated DNA determines the multiplicity of ACMV particles.

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Nitric oxide associated protein 1 is associated with chloroplast perturbation and disease symptoms in Nicotiana benthamiana infected with South African cassava mosaic virus

Virus Research ◽

10.1016/j.virusres.2017.05.022 ◽

2017 ◽

Vol 238 ◽

pp. 75-83 ◽

Cited By ~ 2

Author(s):

Imanu Mwaba ◽

Marie Emma Christine Rey

Keyword(s):

Nitric Oxide ◽

Mosaic Virus ◽

South African ◽

Nicotiana Benthamiana ◽

African Cassava Mosaic Virus ◽

Disease Symptoms ◽

Cassava Mosaic Virus

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Short Interfering RNA Accumulation Correlates with Host Recovery in DNA Virus-Infected Hosts, and Gene Silencing Targets Specific Viral Sequences

Journal of Virology ◽

10.1128/jvi.78.14.7465-7477.2004 ◽

2004 ◽

Vol 78 (14) ◽

pp. 7465-7477 ◽

Cited By ~ 150

Author(s):

Padmanabhan Chellappan ◽

Ramachandran Vanitharani ◽

Claude M. Fauquet

Keyword(s):

Gene Silencing ◽

Mosaic Virus ◽

Defense Mechanism ◽

African Cassava Mosaic Virus ◽

Molecular Evidence ◽

Plant Host ◽

C Terminus ◽

Symptom Recovery ◽

Ssdna Viruses ◽

Cassava Mosaic Virus

ABSTRACT Viruses are both inducers and targets of posttranscriptional gene silencing (PTGS), a natural defense mechanism in plants. Here we report molecular evidence of the ability of single-stranded DNA (ssDNA) viruses to induce PTGS in infected plants irrespective of the severity of or recovery from the symptoms. Our results reveal that five distinct species of cassava-infecting geminiviruses were capable of triggering PTGS by producing two classes of virus-specific short interfering RNAs (siRNAs) of 21 to 26 nucleotides in two plant hosts, tobacco (Nicotiana benthamiana) and cassava (Manihot esculenta, Crantz). However, the efficacy of virus-induced PTGS varied depending on the intrinsic features of the virus and its interaction with the plant host. We found that symptom recovery over time in plants infected with the isolates of African cassava mosaic virus (ACMV-[CM]) or Sri Lankan cassava mosaic virus was associated with a much higher level of virus-derived siRNA accumulation compared to plants infected with viruses that do not show symptom recovery. Furthermore, we determined that the C terminus of AC1 that overlaps with the N terminus of AC2 early viral genes involved in virus replication were the primary targets for ACMV-[CM]-induced PTGS, whereas the C terminus of BC1 was targeted for the East African cassava mosaic Cameroon virus. In addition, our results reveal the possibility for double-stranded RNA formation during transcription in ssDNA viruses, which explains in part how these viruses can trigger PTGS in plants.

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