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John Stanley - One of the best experts on this subject based on the ideXlab platform.

  • Biolistic infection of Cassava using cloned components of Indian Cassava Mosaic Virus.
    Archives of Virology, 2005
    Co-Authors: Dirk Rothenstein, Rob W. Briddon, D. Haible, John Stanley, Thomas Frischmuth, Holger Jeske
    Abstract:

    Cassava Mosaic disease (CMD) is a major constraint to Cassava production in Africa and Asia. Of the two begomoViruses associated with CMD on the Indian subcontinent, Indian Cassava Mosaic Virus (ICMV) and Sri Lankan Cassava Mosaic Virus, only the latter has been successfully reintroduced into Cassava to resolve the aetiology of the disease. Here, we report the complete nucleotide sequence of an ICMV isolate from Maharashtra (ICMV-[Mah2]), central India. Biolistic inoculation of the cloned components produced a systemic infection and typical Mosaic symptoms in Cassava, thereby fulfilling Koch’s postulates. The availability of infectious clones will provide a valuable tool to screen new Cassava cultivars for disease resistance under defined conditions.

  • characterisation of sri lankan Cassava Mosaic Virus and indian Cassava Mosaic Virus evidence for acquisition of a dna b component by a monopartite begomoVirus
    Virology, 2002
    Co-Authors: Keith Saunders, Rob W. Briddon, N Salim, Vasant R Mali, V G Malathi, P G Markham, John Stanley
    Abstract:

    Two bipartite begomoViruses, Indian Cassava Mosaic Virus (ICMV) and Sri Lankan Cassava Mosaic Virus (SLCMV), have been isolated from Mosaic-diseased Cassava originating from central India and Sri Lanka, respectively. ICMV was transmitted with low efficiency from Cassava to Nicotiana benthamiana by sap inoculation to give leaf curl symptoms. SLCMV was much more virulent in this host, producing severe stunting, leaf curl, and chlorosis. These symptoms were reproduced when their cloned genomic components (DNAs A and B) were introduced into N. benthamiana by either mechanical or Agrobacterium-mediated inoculation (agroinoculation). SLCMV is more closely related to ICMV (DNA A, 84%; DNA B, 94% nucleotide identity) than African Cassava Mosaic Virus (ACMV) (DNA A, 74%; DNA B, 47% nucleotide identity). Sequence comparisons suggest that SLCMV DNA B originated from ICMV DNA B by a recombination event involving the SLCMV DNA A intergenic region. Pseudorecombinants produced by reassortment of the cloned components of ICMV and ACMV were not infectious in N. benthamiana, emphasising their status as distinct Virus species. In contrast, a pseudorecombinant between ACMV DNA A and SLCMV DNA B was infectious. Consistent with these observations, iteron motifs located within the intergenic region that may be involved in the initiation of viral DNA replication are conserved between SLCMV and ACMV but not ICMV. When introduced into N. benthamiana by agroinoculation, SLCMV DNA A alone produced a severe upward leaf roll symptom, reminiscent of the phenotype associated with some monopartite begomoViruses. Furthermore, coinoculation of SLCMV DNA A and the satellite DNA beta associated with ageratum yellow vein Virus (AYVV) produced severe downward leaf curl in N. glutinosa and yellow vein symptoms in Ageratum conyzoides, resembling the phenotypes associated with AYVV DNA A and DNA beta infection in these hosts. Thus, SLCMV DNA A has biological characteristics of a monopartite begomoVirus, and the Virus probably evolved by acquisition of a DNA B component from ICMV.

  • transactivation of dianthin transgene expression by african Cassava Mosaic Virus ac2
    Virology, 1997
    Co-Authors: Yiguo Hong, Keith Saunders, John Stanley
    Abstract:

    We have recently described a novel strategy for engineering resistance to African Cassava Mosaic Virus (ACMV) in transgenic Nicotiana benthamiana plants using a Virus-inducible promoter to control the expression of a plant ribosome-inactivating protein (RIP) transgene (Y. Hong et al., Virology 220, 119-127, 1996). Here, we have used a potato Virus X (PVX) vector to express the ACMV transactivator protein, AC2, in planta. We confirm that amplification of RIP activity in transgenic plants is mediated by AC2; disruption of AC2 expression by either the introduction of an in-frame stop codon or the deletion of 5'-terminal or 3'-terminal coding sequences reduced RIP expression to the basal level associated with PVX-infected plants. AC2 expression from the PVX vector induced necrosis in nontransformed plants as well as in plants containing the RIP transgene, suggesting that the protein can functionally interact with PVX and/or host factors. The potential of this system to provide a direct and sensitive assay to investigate AC2 function in planta is discussed.

  • regulation of african Cassava Mosaic Virus complementary sense gene expression by n terminal sequences of the replication associated protein ac1
    Journal of General Virology, 1995
    Co-Authors: Yiguo Hong, John Stanley
    Abstract:

    Fragments of the African Cassava Mosaic Virus (ACMV) genome, cloned upstream of the β-glucuronidase (GUS) reporter gene in an expression cassette, were analysed for their ability to direct complementary-sense gene expression in tobacco protoplasts by measuring GUS activity. Five arbitrary domains (A-E) have been designated that contribute to the expression of AC1 (replication-associated protein) and AC4. Consistent with earlier reports, AC1 gene expression was negatively regulated (80% reduction in activity) by its own protein product, and suppression was mimicked by truncated versions of AC1 comprising the N-terminal 57 amino acids. AC1 also suppressed AC4 gene expression to a similar extent. Nucleotide sequences responsible for suppression were mapped to domain A, a 92 bp fragment located immediately upstream of the AC1 initiation codon encompassing the consensus TATA box and transcription start point. Complementary-sense gene expression also decreased by 30–40% in the presence of AV1 (coat protein) although other DNA A-encoded proteins (AV2, AC2, AC3 and AC4) had no effect. The results are discussed in the light of recent advances concerning the initiation of viral DNA replication and the control of gene expression.

  • complementation of african Cassava Mosaic Virus ac2 gene function in a mixed bipartite geminiVirus infection
    Journal of General Virology, 1995
    Co-Authors: Keith Saunders, John Stanley
    Abstract:

    We have previously demonstrated that African Cassava Mosaic Virus (ACMV) DNAs A and B efficiently complement the systemic spread of tomato golden Mosaic Virus (TGMV) DNA A when co-agroinoculated onto Nicotiana benthamiana. Here, we show that a mixture of an ACMV DNA A AC2 mutant and DNA B that is normally unable to systemically infect N. benthamiana can do so at low frequency when co-agroinoculated with TGMV DNA A. Analysis of viral DNA showed that the AC2 mutation was retained during infection. The mixture of genomic components was sap transmissible, indicating that systemic infectivity is not specifically attributable to the use of agroinoculation. In the presence of TGMV DNA A, ACMV coat protein as well as the DNA B gene products BV1 and BC1 were detected in systemically infected tissues. The results demonstrate that dysfunctional AC2 can be complemented in planta by its TGMV homologue AL2.

J P Legg - One of the best experts on this subject based on the ideXlab platform.

  • epidemiological assessment of Cassava Mosaic disease in central african republic reveals the importance of mixed viral infection and poor health of plant cuttings
    Crop Protection, 2013
    Co-Authors: Innocent Zinga, Frédéric Chiroleu, Pierre Lefeuvre, Ephrem Kosh Komba, Silla Semballa, Simplice P. Yandia, Noella Mandakombo, Bernard Reynaud, J P Legg, Jean-michel Lett
    Abstract:

    Cassava is a vital crop in Africa and represents the main food crop in Central African Republic (CAR). CAR has recently faced large reductions in Cassava yields that have led to a surge in market prices. To better understand the causes of the reduction in yield, we identified biotic constraints to Cassava production by means of a large-scale plant epidemiological survey conducted in 2007 and 2008. Standard protocols were used for the assessment of the major Cassava pests and diseases. Cassava Mosaic disease (CMD) was shown to be the most serious constraint to Cassava in CAR, with symptoms observed at all localities surveyed. CMD is distributed throughout the country, with an average incidence of 85%. Importantly, 94% of diseased plants had cutting-derived CMD infection suggesting that farmers mostly use Virus-infected cuttings for planting. PCR amplification and direct sequencing of partial fragments of the Rep ORF revealed that the causal agents of CMD in CAR are African Cassava Mosaic Virus (ACMV) and the Uganda strain of East African Cassava Mosaic Virus (EACMV-UG). We also demonstrated that 58% of CMD samples present mixed infections (ACMV and EACMV-UG) and that these samples had significantly higher symptom severities. Our results suggest that mixed infection and synergism between CMGs, could be an important feature in the yield reduction of Cassava plants in CAR, similar to the other severe CMD epidemics reported in East Africa. (Resume d'auteur)

  • first report of the occurrence of east african Cassava Mosaic Virus uganda eacmv ug in angola
    Plant Pathology, 2009
    Co-Authors: Lava P Kumar, Alfred G. O. Dixon, S A Akinbade, N M Mahungu, M P Mutunda, D Kiala, L Londa, J P Legg
    Abstract:

    Cassava Mosaic disease (CMD) is the major production constraint on Cassava ( Manihot esculenta ) in Angola. Previous reports derived from single samples recorded the presence of African Cassava Mosaic Virus (ACMV) and East African Cassava Mosaic Virus (EACMV) in Angola. Regional CMD monitoring initiatives have predicted the spread into northern Angola of EACMV-Uganda (-UG), the unusually virulent (aggressive) recombinant strain associated with the African CMD pandemic (Legg et al ., 2006). In view of this threat, an assessment survey was conducted in north and central Angola in April 2008. Eighteen Cassava fields were sampled in Bengo, Cuanza Norte, Malanje and Uige Provinces. Moderate to severe CMD symptoms were observed in most fields. Sixty-three of 65 samples obtained from these fields tested positive in TAS-ELISA using monoclonal antibody SCR 20. PCR was performed using primer pairs previously described for the specific identification of ACMV, EACMV, EACMV-UG, East African Cassava Mosaic Cameroon Virus (EACMCV) and Indian Cassava Mosaic Virus (ICMV) (Ogbe et al ., 2003), East African Cassava Mosaic Malawi Virus (EACMMV) (Zhou et al ., 1998), East African Cassava Mosaic Zanzibar Virus (EACMZV) (Were et al ., 2004) and South African Cassava Mosaic Virus (SACMV) in mixed infections. This revealed the occurrence of ACMV, EACMV and EACMV-UG, but not EACMZV, EACMMV, SACMV or ICMV. Single infections of ACMV and EACMV were detected in 32·3 and 9% of samples, respectively. Mixed infections of ACMV with EACMV, EACMV with EACMV-UG and all three Viruses were detected in 35·3, 1·5 and 16·9% of samples, respectively. ACMV, detected in 84·6% of samples, was the predominant species, followed by EACMV (63%) and EACMV-UG (18·5%). Significantly, EACMV-UG occurred most frequently in the northernmost part of the surveyed area (Uige Province) immediately to the south of the Bas Congo region of the Democratic Republic of Congo, already known to be affected by the pandemic. These findings significantly broaden the known geographical extent of the CMD pandemic and draw attention to the urgent need for the large-scale deployment of resistant Cassava varieties, which have been used to reduce losses in pandemic-affected regions of East Africa.

  • identification of a defective molecule derived from dna a of the bipartite begomoVirus of east african Cassava Mosaic Virus
    Plant Pathology, 2006
    Co-Authors: J Ndunguru, J P Legg, I B F Fofana, T A S Aveling, Graham Thompson, Claude M Fauquet
    Abstract:

    GeminiVirus defective interfering DNAs arise spontaneously in mechanically inoculated test plants, and have previously been found with DNA-B of the bipartite Cassava Mosaic geminiViruses, but not DNA-A. Reported here for the first time is the cloning and characterization of a naturally occurring truncated form of Cassava Mosaic geminiVirus DNA-A, which at 1525 nt is around half the expected full size. Sequence analysis has shown it to be a defective (df) form of East African Cassava Mosaic Virus (EACMV) DNA-A that has retained its cis elements essential for replication by the helper Virus, and it has been termed df DNA-A 15. Phylogenetic comparisons placed the df DNA-A 15 molecule close to mild and severe isolates of EACMV-UG2. Biolistic inoculation of Nicotiana benthamiana with infectious df DNA-A 15 clone and East African Cassava Mosaic Cameroon Virus (EACMCV) resulted in symptom amelioration as compared with EACMCV singly inoculated plants, and there was an accumulation of df DNA-A 15 in systemically infected leaves. In addition, the level of EACMV DNA-B accumulation was reduced in the coinoculated plants compared with those inoculated with EACMCV alone. PCR and sequence analysis confirmed the helper Virus as EACMV.

  • the effect of Cassava Mosaic geminiViruses on symptom severity growth and root yield of a Cassava Mosaic Virus disease susceptible cultivar in uganda
    Annals of Applied Biology, 2004
    Co-Authors: J P Legg, B Owor, Geoffrey Okaookuja, R Obonyo, M W Ogengalatigo
    Abstract:

    Summary A study was carried out to assess the effect of different Cassava Mosaic geminiViruses (CMGs) occurring in Uganda on the growth and yield of the susceptible local cultivar ‘Ebwanateraka’. Plants infected with African Cassava Mosaic Virus (ACMV), ‘mild’ and ‘severe’ strains of East African Cassava Mosaic Virus-Uganda (EACMV-UG2) and both ACMV and EACMV-UG2 were grown in two experiments in Kabula, Lyantonde in western Uganda. The most severe disease developed in plants co-infected with ACMV and EACMV-UG2 and in those infected with the ‘severe’ form of EACMV-UG2 alone; disease was least severe in plants infected with the ‘mild’ strain of EACMV-UG2. ACMV-infected plants and those infected with the ‘mild’ strain of EACMV-UG2 were tallest in the 1999–2000 and 2000–2001 trials, respectively; plants dually infected with ACMV and EACMV-UG2 were shortest in both trials. Plants infected with ‘mild’ EACMV-UG2 yielded the largest number and the heaviest tuberous roots followed by ACMV and EACMV-UG2 ‘severe’, respectively, whilst plants dually infected with ACMV and EACMV-UG2 yielded the least considering the two trials together. Reduction in tuberous root weight was greatest in plants dually infected with ACMV and EACMV-UG2, averaging 82%. Losses attributed to ACMV alone, EACMV-UG2 ‘mild’ and EACMV-UG2 ‘severe’ were 42%, 12% and 68%, respectively. Fifty percent and 48% of the plants infected with both ACMV and EACMV-UG2 gave no root yield in 1999–2000 and 2000–2001, respectively. These results indicate that CMGs, whether in single or mixed infections, reduce root yield and numbers of tuberous roots produced and that losses are substantially increased following mixed infection.

  • a distinct bemisia tabaci gennadius hemiptera sternorrhyncha aleyrodidae genotype cluster is associated with the epidemic of severe Cassava Mosaic Virus disease in uganda
    Molecular Ecology, 2002
    Co-Authors: J P Legg, Geoffrey Okaookuja, R French, D Rogan, Judith K Brown
    Abstract:

    : During the 1990s, an epidemic of Cassava Mosaic Virus disease caused major losses to Cassava production in Uganda. Two factors associated with the epidemic were the occurrence of a novel recombinant begomoVirus, EACMV-Ug, and unusually high populations of the whitefly vector, Bemisia tabaci. Here we present molecular evidence for the occurrence of two Cassava-colonizing B. tabaci genotype clusters, Ug1 and Ug2, one of which, Ug2, can be consistently associated with the CMD epidemic in Uganda at the time of collection in 1997. By contrast, a second genotype cluster, Ug1, only occurred 'at' or 'ahead of' the epidemic 'front', sometimes in mixtures with Ug2. Comparison of mitochondrial cytochrome oxidase I gene sequences for Ug1 and Ug2 and well-studied B. tabaci reference populations indicated that the two Ugandan populations exhibited approximately 8% divergence, suggesting they represent distinct sub-Saharan African lineages. Neither Ugandan genotype cluster was identified as the widely distributed, polyphagous, and highly fecund B biotype of Old World origin, with which they both diverged by approximately 8%. Within genotype cluster divergence of Ug1 at 0.61 +/- 0.1% was twice that of Ug2 at 0.35 +/- 0.1%. Mismatch analysis suggested that Ug2 has undergone a recent population expansion and may be of nonUgandan origin, whereas Ug1 has diverged more slowly, and is likely to be an indigenous genotype cluster.

Holger Jeske - One of the best experts on this subject based on the ideXlab platform.

  • different forms of african Cassava Mosaic Virus capsid protein within plants and virions
    Virology, 2019
    Co-Authors: Katharina Hipp, Kerstin Zikeli, Gabi Kepp, Lena Schmid, Robert L Shoeman, Tomasz P Jurkowski, Tatjana Kleinow, Holger Jeske
    Abstract:

    One geminiviral gene encodes the capsid protein (CP), which can appear as several bands after electrophoresis depending on Virus and plant. African Cassava Mosaic Virus-Nigeria CP in Nicotiana benthamiana, however, yielded one band (~ 30 kDa) in total protein extracts and purified virions, although its expression in yeast yielded two bands (~ 30, 32 kDa). Mass spectrometry of the complete protein and its tryptic fragments from virions is consistent with a cleaved start M1, acetylated S2, and partial phosphorylation at T12, S25 and S62. Mutants for additional potentially modified sites (N223A; C235A) were fully infectious and formed geminiparticles. Separation in triton acetic acid urea gels confirmed charge changes of the CP between plants and yeast indicating differential phosphorylation. If the CP gene alone was expressed in plants, multiple bands were observed like in yeast. A high turnover rate indicates that post-translational modifications promote CP decay probably via the ubiquitin-triggered proteasomal pathway.

  • translation modification and cellular distribution of two ac4 variants of african Cassava Mosaic Virus in yeast and their pathogenic potential in plants
    Virology, 2016
    Co-Authors: Katharina Hipp, Peter Rau, Benjamin Schäfer, Jens Pfannstiel, Holger Jeske
    Abstract:

    Plant infecting geminiViruses encode a small (A)C4 protein within the open reading frame of the replication-initiator protein. In African Cassava Mosaic Virus, two in-frame start codons may be used for the translation of a longer and a shorter AC4 variant. Both were fused to green fluorescent protein or glutathione-S-transferase genes and expressed in fission yeast. The longer variant accumulated in discrete spots in the cytoplasm, whereas the shorter variant localized to the plasma membrane. A similar expression pattern was found in plants. A myristoylation motif may promote a targeting of the shorter variant to the plasma membrane. Mass spectrometry analysis of the yeast-expressed shorter variant detected the corresponding myristoylation. The biological relevance of the second start codon was confirmed using mutated infectious clones. Whereas mutating the first start codon had no effect on the infectivity in Nicotiana benthamiana plants, the second start codon proved to be essential.

  • The RXL motif of the African Cassava Mosaic Virus Rep protein is necessary for rereplication of yeast DNA and viral infection in plants.
    Virology, 2014
    Co-Authors: Katharina Hipp, Bruno Gronenborn, Peter Rau, Benjamin Schäfer, Holger Jeske
    Abstract:

    GeminiViruses, single-stranded DNA plant Viruses, encode a replication-initiator protein (Rep) that is indispensable for Virus replication. A potential cyclin interaction motif (RXL) in the sequence of African Cassava Mosaic Virus Rep may be an alternative link to cell cycle controls to the known interaction with plant homologs of retinoblastoma protein (pRBR). Mutation of this motif abrogated rereplication in fission yeast induced by expression of wildtype Rep suggesting that Rep interacts via its RXL motif with one or several yeast proteins. The RXL motif is essential for viral infection of Nicotiana benthamiana plants, since mutation of this motif in infectious clones prevented any symptomatic infection. The cell-cycle link (Clink) protein of a nanoVirus (faba bean necrotic yellows Virus) was investigated that activates the cell cycle by binding via its LXCXE motif to pRBR. Expression of wildtype Clink and a Clink mutant deficient in pRBR-binding did not trigger rereplication in fission yeast.

  • disassembly of african Cassava Mosaic Virus
    Journal of General Virology, 2008
    Co-Authors: Katharina Kittelmann, Holger Jeske
    Abstract:

    The plant-infecting geminiViruses encapsidate their single-stranded DNA genome in characteristic twinned particles that are unique among Viruses. These particles are formed by joining two incomplete T=1 icosahedra. African Cassava Mosaic virions were purified by density-gradient centrifugation from infected Nicotiana benthamiana plants and analysed for their stability with respect to pH changes and heat treatment by using electron microscopy. Negative staining and rotary shadowing revealed stable virions as well as isolated capsomeres between pH 4.0 and 8.5. At pH 9.0 and above, particles disintegrated, whereas they mainly aggregated at a pH below 6.0. Heating the preparations to 55 degrees C and above resulted in the complete loss of any discernible structure. A low proportion (approx. 10 %) of particles ejected their DNA within the pH range of 6.0-8.5. Most virions released their DNA at the top (15.9 %) or the shoulder (71.4 %) of the twin particles and only 12.7 % at the waist. Compared with the expected numbers of pentameric capsomeres at the top (9 %), the shoulder (45.5 %) or the waist (45.5 %), the results revealed a preferential DNA release from the top and shoulder of the geminate particle.

  • tissue and cell tropism of indian Cassava Mosaic Virus icmv and its av2 precoat gene product
    Virology, 2007
    Co-Authors: Dirk Rothenstein, Bjorn Krenz, Olaf Selchow, Holger Jeske
    Abstract:

    In order to establish defined Viruses for challenging plants in resistance breeding programmes, Indian Cassava Mosaic Virus (ICMV; family Geminiviridae) DNA clones were modified to monitor viral spread in plants by replacing the coat protein gene with the green fluorescent protein (GFP) reporter gene. Comparative in situ hybridization experiments showed that ICMV was restricted to the phloem in Cassava and tobacco. GFP-tagged Virus spread similarly, resulting in homogeneous fluorescence within nuclei and cytoplasm of infected cells. To analyze viral intercellular transport in further detail, GFP was fused to AV2, a protein that has been implicated in viral movement. Expressed from replicating Viruses or from plasmids, AV2:GFP became associated with the cell periphery in punctate spots, formed cytoplasmic as well as nuclear inclusion bodies, the latter as conspicuous paired globules. Upon particle bombardment of expression plasmids, AV2:GFP was transported into neighboring cells of epidermal tissues showing that the intercellular transport of the AV2 protein is not restricted to the phloem. The results are consistent with a redundant function of ICMV AV2 acting as a movement protein, presumably as an evolutionary relic of a monopartite geminiVirus that may still increase Virus fitness but is no longer necessary in a bipartite genome. The fusion of ICMV ORF AV2 to the GFP gene is the first example of a reporter construct that follows the whole track of viral DNA from inside the nucleus to the cell periphery and to the next cell.

Judith K Brown - One of the best experts on this subject based on the ideXlab platform.

  • a distinct bemisia tabaci gennadius hemiptera sternorrhyncha aleyrodidae genotype cluster is associated with the epidemic of severe Cassava Mosaic Virus disease in uganda
    Molecular Ecology, 2002
    Co-Authors: J P Legg, Geoffrey Okaookuja, R French, D Rogan, Judith K Brown
    Abstract:

    : During the 1990s, an epidemic of Cassava Mosaic Virus disease caused major losses to Cassava production in Uganda. Two factors associated with the epidemic were the occurrence of a novel recombinant begomoVirus, EACMV-Ug, and unusually high populations of the whitefly vector, Bemisia tabaci. Here we present molecular evidence for the occurrence of two Cassava-colonizing B. tabaci genotype clusters, Ug1 and Ug2, one of which, Ug2, can be consistently associated with the CMD epidemic in Uganda at the time of collection in 1997. By contrast, a second genotype cluster, Ug1, only occurred 'at' or 'ahead of' the epidemic 'front', sometimes in mixtures with Ug2. Comparison of mitochondrial cytochrome oxidase I gene sequences for Ug1 and Ug2 and well-studied B. tabaci reference populations indicated that the two Ugandan populations exhibited approximately 8% divergence, suggesting they represent distinct sub-Saharan African lineages. Neither Ugandan genotype cluster was identified as the widely distributed, polyphagous, and highly fecund B biotype of Old World origin, with which they both diverged by approximately 8%. Within genotype cluster divergence of Ug1 at 0.61 +/- 0.1% was twice that of Ug2 at 0.35 +/- 0.1%. Mismatch analysis suggested that Ug2 has undergone a recent population expansion and may be of nonUgandan origin, whereas Ug1 has diverged more slowly, and is likely to be an indigenous genotype cluster.

  • a distinct bemisia tabaci gennadius hemiptera sternorrhyncha aleyrodidae genotype cluster is associated with the epidemic of severe Cassava Mosaic Virus disease in uganda
    Molecular Ecology, 2002
    Co-Authors: J P Legg, Geoffrey Okaookuja, R French, D Rogan, Judith K Brown
    Abstract:

    During the 1990s, an epidemic of Cassava Mosaic Virus disease caused major losses to Cassava production in Uganda. Two factors associated with the epidemic were the occurrence of a novel recombinant begomoVirus, EACMV-Ug, and unusually high populations of the whitefly vector, Bemisia tabaci. Here we present molecular evidence for the occurrence of two Cassava-colonizing B. tabaci genotype clusters, Ug1 and Ug2, one of which, Ug2, can be consistently associated with the CMD epidemic in Uganda at the time of collection in 1997. By contrast, a second genotype cluster, Ug1, only occurred 'at' or 'ahead of' the epidemic 'front', sometimes in mixtures with Ug2. Comparison of mitochondrial cytochrome oxidase I gene sequences for Ug1 and Ug2 and well-studied B. tabaci reference populations indicated that the two Ugandan populations exhibited approximately 8% divergence, suggesting they represent distinct sub-Saharan African lineages. Neither Ugandan genotype cluster was identified as the widely distributed, polyphagous, and highly fecund B biotype of Old World origin, with which they both diverged by approximately 8%. Within genotype cluster divergence of Ug1 at 0.61 +/- 0.1% was twice that of Ug2 at 0.35 +/- 0.1%. Mismatch analysis suggested that Ug2 has undergone a recent population expansion and may be of nonUgandan origin, whereas Ug1 has diverged more slowly, and is likely to be an indigenous genotype cluster.

Claude M Fauquet - One of the best experts on this subject based on the ideXlab platform.

  • identification of a defective molecule derived from dna a of the bipartite begomoVirus of east african Cassava Mosaic Virus
    Plant Pathology, 2006
    Co-Authors: J Ndunguru, J P Legg, I B F Fofana, T A S Aveling, Graham Thompson, Claude M Fauquet
    Abstract:

    GeminiVirus defective interfering DNAs arise spontaneously in mechanically inoculated test plants, and have previously been found with DNA-B of the bipartite Cassava Mosaic geminiViruses, but not DNA-A. Reported here for the first time is the cloning and characterization of a naturally occurring truncated form of Cassava Mosaic geminiVirus DNA-A, which at 1525 nt is around half the expected full size. Sequence analysis has shown it to be a defective (df) form of East African Cassava Mosaic Virus (EACMV) DNA-A that has retained its cis elements essential for replication by the helper Virus, and it has been termed df DNA-A 15. Phylogenetic comparisons placed the df DNA-A 15 molecule close to mild and severe isolates of EACMV-UG2. Biolistic inoculation of Nicotiana benthamiana with infectious df DNA-A 15 clone and East African Cassava Mosaic Cameroon Virus (EACMCV) resulted in symptom amelioration as compared with EACMCV singly inoculated plants, and there was an accumulation of df DNA-A 15 in systemically infected leaves. In addition, the level of EACMV DNA-B accumulation was reduced in the coinoculated plants compared with those inoculated with EACMCV alone. PCR and sequence analysis confirmed the helper Virus as EACMV.

  • differential roles of ac2 and ac4 of Cassava geminiViruses in mediating synergism and suppression of posttranscriptional gene silencing
    Journal of Virology, 2004
    Co-Authors: Ramachandran Vanitharani, Padmanabhan Chellappan, Justin S Pita, Claude M Fauquet
    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.

  • evidence of synergism between african Cassava Mosaic Virus and a new double recombinant geminiVirus infecting Cassava in cameroon
    Journal of General Virology, 2000
    Co-Authors: V N Fondong, J S Pita, R N Beachy, A De Kochko, Claude M Fauquet
    Abstract:

    Stem cuttings were collected in Cameroon from Cassava plants displaying Cassava Mosaic disease (CMD) symptoms. The nature of the Viruses present was determined by using the PCR with primers specific for the coat protein (CP) genes of African Cassava Mosaic Virus (ACMV) and East African Cassava Mosaic Virus (EACMV). All samples were infected by ACMV and eight of the 50 samples were infected by both ACMV and an EACMV-like Virus. The complete nucleotide sequences of DNA-A and -B of representative ACMV and EACMV-like Viruses were determined. The DNA-A component of the EACMV-like Virus contained evidence of recombination in the AC2–AC3 region and DNA-B also contained evidence of recombination in BC1. However, both components retained gene arrangements typical of bipartite begomoViruses. When Nicotiana benthamiana plants were doubly inoculated with these Cameroon isolates of ACMV and EACMV (ACMV/CM, EACMV/CM) by using sap from Cassava plants or infectious clones, the symptoms were more severe than for plants inoculated with either Virus alone. Southern blot analysis of viral DNAs from infected plants showed that there were significantly higher levels of accumulation of both ACMV/CM components and, to a lesser extent, of EACMV/CM components in mixed-infected plants than in singly infected plants. These results strongly suggest the occurrence of a synergistic interaction between the two Viruses.

  • first report of the presence of east african Cassava Mosaic Virus in cameroon
    Plant Disease, 1998
    Co-Authors: V N Fondong, J S Pita, C Rey, R N Beachy, Claude M Fauquet
    Abstract:

    Cassava Mosaic disease (CMD) occurs in all Cassava-growing regions of Africa, India, and Sri Lanka. Characterized by Mosaic and distortion of Cassava leaves and reduced plant growth, causing high yield losses, CMD is caused by geminiViruses (genus BegomoVirus, family Geminiviridae) transmitted through infected cuttings or by the whitefly, Bemisia tabaci. Three such geminiViruses have been described: African Cassava Mosaic Virus (ACMV) occurs in most of the Cassava-producing zones of Africa; East African Cassava Mosaic Virus (EACMV) in East Africa; and Indian Cassava Mosaic Virus (ICMV) in the Indian subcontinent (1). The two components of ACMV and ICMV genomes, DNA-A and DNA-B, have been sequenced; only DNA-A of EACMV has been identified and sequenced. Variations in symptom expression and severity within the same Cassava variety have been observed in Cameroon. To determine the nature of the Virus species inducing such variations, 50 samples were collected from CMD-infected plants in the savannah and rainf...

  • components of resistance of Cassava to african Cassava Mosaic Virus
    European Journal of Plant Pathology, 1996
    Co-Authors: Denis Fargette, L T Colon, R Bouveau, Claude M Fauquet
    Abstract:

    Components of resistance of Cassava (Manihot esculenta) to African Cassava Mosaic Virus (ACMV) and their interrelationships were confirmed and quantified in a series of experiments at Adiopodoume (Ivory Coast, West-Africa). The response to Virus infection and toBemisia tabaci infestation of a large collection of Cassava, including local cultivars and others derived from inter-specificM. glaziovii hybrids was assessed. A consistent correlation was found between Virus titre, symptom intensity, disease incidence and non-systemicity (recovery) which suggests that they are different expressions of the same genetic resistance. By contrast, there was no correlation between whitefly infestation and incidence of ACMV, suggesting that resistance to Virus and vector are determined by two distinct genetic mechanisms. Several improved cultivars derived from inter-crossing Cassava withM. glaziovii as well as some local cultivars were highly resistant and combined low susceptibility, low symptom intensity, low Virus content and high level of recovery. Although yield losses ranged from 10% to 30% in such resistant cultivars, the combined effect of high field resistance and high rate of recovery lead to low disease incidence and limited yield losses, even in areas of high infection pressure such as Adiopodoume.