Biomedical subjects

C Fauquet

Publications and source records attributed to C Fauquet.

At least 19 recordsLinked to original sources

PubMed2006

Molecular ecology and emergence of tropical plant viruses.

An appreciation of the risks caused by emergent plant viruses is critical in tropical areas that rely heavily on agriculture for subsistence and rural livelihood. Molecular ecology, within 10 years, has unraveled the factors responsible for the emergence of several of the economically most important tropical plant viruses: Rice yellow mottle virus (RYMV), Cassava mosaic geminiviruses (CMGs), Maize streak virus (MSV), and Banana streak virus (BSV). A large range of mechanisms--most unsuspected until recently--were involved: recombination and synergism between virus species, new vector biotypes, genome integration of the virus, host adaptation, and long-distance dispersal. A complex chain of molecular and ecological events resulted in novel virus-vector-plant-environment interactions that led to virus emergence. It invariably involved a major agricultural change: crop introduction, cultural intensification, germplasm movement, and new genotypes. A current challenge is now to complement the analysis of the causes by an assessment of the risks of emergence. Recent attempts to assess the risks of emergence of virulent virus strains are described.

Ecosystem↗

PubMed2005

Physiological responses during submaximal interval swimming training: effects of interval duration.

The aim of the present study was to determine the time sustained near VO2max in two interval training (IT) swimming sessions comprising 4x400 m (IT(4x400)) or 16x100 (IT(16xl00)). Elite swimmers (Mean+/-SD age 18+/-2 yrs; body mass 66.9+/-6.5 kg: swim VO2max 55.7+/-5.8 ml.kg(-1).min(-1)) completed three experimental sessions at a 50-m indoor pool over a one week period. The first test comprised a 5 x 200-m incremental test to exhaustion for determination of the pulmonary ventilation threshold (VT, m.s(-1)), VO2max, the velocity associated with VO2max (VO2max, m(s(-1)) and maximum heart rate (HR(max), b.min(-1)). The remaining two tests involved the IT(4x400) and IT(16xl00) performed in a randomised order. The two IT sessions where completed at a velocity representing 25% of the difference between the VT and the VO2max (delta25%) and in the same work to rest ratio. During the IT sessions VO2 as well as HR were measured. The duration (s) >90% VO2max, also the duration (s) >90% HR(max), were not significantly different in the IT(16x100) and IT(4x400). However, limits of agreement (LIM(AG)) analysis demonstrated considerable individual variation in the time >90% VO2max (mean difference +/-2SD = 222+/-819 s) and the time >90% HRmax (mean difference +/-2SD = 61+/-758 s) between the two IT sessions. This factor deserves further research to establish the characteristics of those athletes which influence the physiological responses in IT of short or longer duration repetitions.

Adolescent↗

PubMed2003

Cotton leaf curl disease is associated with multiple monopartite begomoviruses supported by single DNA beta.

For bipartite begomoviruses (family Geminiviridae) trans-replication of the DNA B component by the DNA A-encoded replication-associated protein (Rep) is achieved by virtue of a shared sequence, the "common region", which contains repeated motifs (iterons) which are sequence-specific Rep binding sites and form part of the origin of replication. Recently cotton leaf curl disease (CLCuD), a major constraint to cotton production on the Indian subcontinent, has been shown to be caused by a monopartite begomovirus ( Cotton leaf curl Multan virus [CLCuMV]) and a novel single-stranded DNA satellite molecule termed CLCuD DNA beta. The satellite molecule is trans-replicated by CLCuMV but does not possess the iteron sequences of this virus. We have investigated the ability of CLCuD DNA beta to interact with three further clones of monopartite begomoviruses, isolated from cotton, that have distinct Rep binding specificities. All three cloned viruses were capable of trans-replicating the satellite molecule and inducing CLCuD symptoms in cotton, indicating that the interaction between begomovirus and DNA beta is relaxed in comparison to the interaction between DNA A and DNA B components. Field surveys across all the cotton growing regions of Pakistan indicate that dual and multiple infections are the norm for CLCuD with no evidence of synergism. Despite the diversity of begomoviruses associated with CLCuD, only a single class of DNA beta has been detected, suggesting that this satellite has the capacity to be recruited by unrelated begomoviruses.

Animals↗

PubMed2002

Comparison of molecular and immunological typing of isolates of Rice yellow mottle virus.

Isolates of Rice yellow mottle virus (RYMV) were typed at the molecular level through the sequences of the open reading frame (ORF) 4 (coding for the coat protein) and ORF1 (coding for the movement protein), and serologically by means of polyclonal and monoclonal antibodies. The overall patterns of diversity shown by molecular and serological analyses were similar: East-African isolates differed from West-African ones, and the West-African isolates from forest differed from the savannah ones. Each major strain had a different serological profile. However, molecular typing was more discriminating than immunological typing since several sequence variants belonged to the same serotype. In rare instances, there were explainable discrepancies between molecular and serological typing. Two amino acids at positions 115 (alanine vs threonine) and 191 (valine vs threonine) consistently discriminated between the major serotypes. These positions were located in antigenic sites as revealed by Spot-scan method and were recognised by discriminating monoclonal antibodies. One shared epitope, lying within a conserved region, may be responsible for the cross-reactivity between RYMV isolates. A rationale for the correlation between molecular and immunological typing of RYMV and other sobemoviruses is proposed.

Amino Acid Sequence↗

PubMed1999

The Arabidopsis transposon Tag1 is active in rice, undergoing germinal transposition and restricted, late somatic excision.

Tag1 is an autonomous transposable element of Arabidopsis thaliana that displays tight developmental control of its excision during shoot development. To determine how Tag1 behaves in a monocotyledonous species, Tag1 was inserted in a 35S-GUS marker gene and the construct was introduced into rice. Tag1 showed somatic excision activity in four out of eleven transgenic lines examined. In leaves, excision was primarily restricted to vascular bundles and produced sectors composed of only a few cells. Excision events in flowers occurred predominantly in or near the major veins of the palea and lemma to produce small sectors. In roots, small sectors were evident, but they were few in number. These data show that the timing of Tag1 excision during rice shoot development is late and mimics the late excision behavior of Tag1 in Arabidopsis. One of the transgenic rice lines, which had a high frequency of somatic excision, produced several germinal revertants, one of which was characterized by a new Tag1 insertion band. The pattern of Tag1 transcripts and the footprint sequences left behind after excision in rice were found to be very similar to those in Arabidopsis. These results show that key properties of Tag1 transposition and behavior are conserved between monocots and dicots and that Tag1 has the potential to serve as an insertional mutagen in rice.

Arabidopsis↗

PubMed1998

Expression of the rice yellow mottle virus P1 protein in vitro and in vivo and its involvement in virus spread.

Rice yellow mottle sobemovirus (RYMV) is responsible for the yellow mottle disease on rice in Africa. The expression and function of the protein P1 (17.8 kDa) encoded by the first open reading frame (ORF) of RYMV was investigated. Using an antibody raised against purified P1, two proteins with apparent molecular masses of 18 and 19 kDa were identified in in vitro translation reactions of transcripts of the full-length cDNA of RYMV. Likewise, gene products with similar molecular mass were detected in inoculated and systemically infected rice leaves and in infected rice protoplasts. A mutant from which ORF1 nucleotides 88 to 547 were deleted and a frameshift mutant that resulted in truncation of 83 amino acids from the C terminus of P1 were incapable of replicating in protoplasts. In contrast, a mutant that does not express P1 due to a mutation at the initiation codon replicated efficiently in protoplasts but at a reduced level (about 0.5- to 2-fold less) compared to replication of wild-type RNA. None of these mutants caused systemic infection in rice plants. Transgenic rice plants that express P1 complemented the initiation codon mutant, but not the deletion mutants, and produced systemic infection. These experiments demonstrate that P1 of RYMV is dispensible for virus replication, although nucleotide deletions or additions in ORF1 are apparently lethal for virus replication. Furthermore, P1 of RYMV is required for the infection of plants and is important for virus spread.

Animals↗

PubMed1998

Movement of rice yellow mottle virus between xylem cells through pit membranes.

The translocation of rice yellow mottle virus (RYMV) within tissues of inoculated and systemically infected Oryza sativa L. leaves was characterized by Western immunoblotting, Northern blotting, and electron microscopy of thin sections. In inoculated leaves, RYMV RNA and coat protein first were detected at 3 and 5 days postinoculation, respectively. By 6 days postinoculation, RYMV had spread systemically to leaves, and virus particles were observed in most cell types, including epidermal, mesophyll, bundle sheath, and vascular parenchyma cells. Most of the virions accumulated in large crystalline patches in xylem parenchyma cells and sieve elements. Colocalization of a cell wall marker for cellulosic beta-(1-4)-D-glucans and anti-RYMV antibodies over vessel pit membranes suggests a pathway for virus migration between vessels. We propose that the partial digestion of pit membranes resulting from programmed cell death may permit virus migration through them, concomitant with autolysis. In addition, displacement of the Ca2+ from pit membranes to virus particles may contribute to the disruption of the pit membranes and facilitate systemic virus transport.

Biological Transport↗

PubMed1998

Cassava vein mosaic virus (CsVMV), type species for a new genus of plant double stranded DNA viruses?

The complete sequence of 8159 nucleotides of the double stranded DNA genome of cassava vein mosaic virus (CsVMV) was determined (# U59751) and revealed a significant difference in genome organization when compared with a previous report (# U20341). When transferred to cassava plants by microbombardment, the full length CsVMV clone was infectious, confirming the genome organization here described. Sequence comparisons between CsVMV and members of the genera Caulimovirus and Badnavirus revealed high homologies between consensus sequences of several proteins that are indispensable for virus replication, including a potential transactivator factor not reported previously. The presence of a sequence complementary to a plant Met tRNA confirms that CsVMV is a plant pararetrovirus and is most closely related to members of the genus Caulimovirus as previously assessed. However, differences in genome organization, number and size of the ORFs, in addition to sequence comparisons with other plant pararetroviruses, shows that either the genetic variability of caulimoviruses is much greater than previously thought, or that CsVMV is the unique representative of a new genus within the Caulimoviridae family. On the basis of this study, it is proposed to upgrade the floating genus Caulimovirus to the family level and to divide the Caulimoviridae family into at least three genera with CsVMV being the type member of a new genus.

Amino Acid Sequence↗

PubMed1998

Functional organization of the cassava vein mosaic virus (CsVMV) promoter.

Cassava vein mosaic virus (CsVMV) is a pararetrovirus that infects cassava plants in Brazil. A promoter fragment isolated from CsVMV, comprising nucleotides -443 to +72, was previously shown to direct strong constitutive gene expression in transgenic plants. Here we report the functional architecture of the CsVMV promoter fragment. A series of promoter deletion mutants were fused to the coding sequence of uidA reporter gene and the chimeric genes were introduced into transgenic tobacco plants. Promoter activity was monitored by histochemical and quantitative assays of beta-glucuronidase activity (GUS). We found that the promoter fragment is made up of different regions that confer distinct tissue-specific expression of the gene. The region encompassing nucleotides -222 to -173 contains cis elements that control promoter expression in green tissues and root tips. Our results indicate that a consensus as1 element and a GATA motif located within this region are essential for promoter expression in those tissues. Expression from the CsVMV promoter in vascular elements is directed by the region encompassing nucleotides -178 to -63. Elements located between nucleotides -149 and -63 are also required to activate promoter expression in green tissues suggesting a combinatorial mode of regulation. Within the latter region, a 43 bp fragment extending from nucleotide -141 to -99 was shown to interact with a protein factor extracted from nuclei of tobacco seedlings. This fragment showed no sequence homology with other pararetrovirus promoters and hence may contain CsVMV-specific regulatory cis elements.

Binding Sites↗

PubMed1998

Xa21D encodes a receptor-like molecule with a leucine-rich repeat domain that determines race-specific recognition and is subject to adaptive evolution.

The rice Xa21 gene confers resistance to Xanthomonas oryzae pv oryzae in a race-specific manner. Analysis of the inheritance patterns and resistance spectra of transgenic plants carrying six Xa21 gene family members indicated that one member, designated Xa21D, displayed a resistance spectrum identical to that observed for Xa21 but conferred only partial resistance. Xa21D encodes a receptor-like protein carrying leucine-rich repeat (LRR) motifs in the presumed extracellular domain. The Xa21D transcript terminates shortly after the stop codon introduced by the retrotransposon Retrofit. Comparison of nucleotide substitutions in the LRR coding regions of Xa21 and Xa21D provided evidence of adaptive selection. Both functional and evolutionary evidence indicates that the Xa21D LRR domain controls race-specific pathogen recognition.

Adaptation, Physiological↗

PubMed1997

Analysis of the sequence diversity of the P1, HC, P3, NIb and CP genomic regions of several yam mosaic potyvirus isolates: implications for the intraspecies molecular diversity of potyviruses.

Partial sequences from serologically characterized yam mosaic potyvirus (YMV) isolates were determined in conserved (helper-component proteinase, HC; nuclear inclusion b, NIb) and variable (first protein, P1; third protein, P3; and coat protein, CP) regions of the potyviral genome in order to investigate the intraspecies molecular diversity of YMV. Multiple sequence alignments and pairwise comparisons were used to quantify the sequence polymorphism in these regions. Two levels of diversity were observed among YMV isolates: above 90% nucleotide (nt) sequence identities were found between YMV isolates of the same group (intragroup) regardless of the region considered, whereas identities between isolates from different groups (intergroup) were lower and depended upon the protein chosen. For instance, the average intergroup nt sequence identity between YMV isolates was about 65% in the P1 protein and the N terminus of the CP while there was more than 80% nt identity in the HC, P3 and NIb proteins. Thus P3 appeared to be conserved between YMV isolates even though this region was variable between potyvirus species. Similar analysis of the intraspecies molecular diversity of other potyviruses (potato virus Y, zucchini yellow mosaic virus, plum pox virus, pea seed-borne mosaic virus) led to the same results: (i) two levels of intraspecies molecular diversity were found (intragroup and intergroup); (ii) intraspecies molecular diversity differed from interspecies molecular diversity in the P3, P1 and N-terminal regions.

Amino Acid Sequence↗

PubMed1996

Isolation and expression in transgenic tobacco and rice plants, of the cassava vein mosaic virus (CVMV) promoter.

The cassava vein mosaic virus (CVMV) is a double stranded DNA virus which infects cassava plants (Manihot esculenta Crantz) and has been characterized as a plant pararetrovirus belonging to the caulimovirus subgroup. Two DNA fragments, CVP1 of 388 nucleotides from position -368 to +20 and CVP2 of 511 nucleotides from position -443 to +72, were isolated from the viral genome and fused to the uidA reporter gene to test promoter expression. The transcription start site of the viral promoter was determined using RNA isolated from transgenic plants containing the CVMV promoter:uidA fusion gene. Both promoter fragments were able to cause high levels of gene expression in protoplasts isolated from cassava and tobacco cell suspensions. The expression pattern of the CVMV promoters was analyzed in transgenic tobacco and rice plants, and revealed that the GUS staining pattern was similar for each construct and in both plants. The two promoter fragments were active in all plant organs tested and in a variety of cell types, suggesting a near constitutive pattern of expression. In both tobacco and rice plants, GUS activity was highest in vascular elements, in leaf mesophyll cells, and in root tips.

Base Sequence↗

PubMed1996

The complete nucleotide sequence of yam mosaic virus (Ivory Coast isolate) genomic RNA.

The complete nucleotidic sequence of the yam mosaic virus (YMV) RNA was determined following the cloning of partial segments of the genome by reverse transcription and polymerase chain reactions (RT-PCR) using degenerate and/or specific oligonucleotide primers. YMV genomic RNA is 9,608 nucleotides in length and contains one open reading frame (ORF) encoding a polyprotein of 3,103 amino acids (aa) with a calculated Mr of 350,915. The 5' leader sequence of YMV RNA preceding the ORF is 134 nucleotides (nt) long while the 3' untranslated region (UTR) is 165 nt excluding the poly(A) tail. A computer algorithm predicted that the 3'UTR forms four stem loop structures which form a cloverleaf-like secondary structure. These structures apparently share some homologies with those observed in the 3'UTR of the potato virus Y-NL1 strain. Seven potential recognition sites for the NIa protease were found: one putative cleavage site for the P1 proteinase and one for the HC proteinase. The organization of the YMV genome is therefore similar to the other members of the genus Potyvirus based upon conserved sequence motifs common amongst members of this group. Despite its similarity with the other potyviruses in these conserved regions, YMV appears to be a distinct potyvirus species based upon a comparison of its sequence with those of other potyviruses.

Amino Acid Sequence↗

PubMed1996

Regeneration of transgenic cassava plants (Manihot esculenta Crantz) from microbombarded embryogenic suspension cultures.

A protocol was established for the introduction of DNA into embryogenic suspension-derived tissues of cassava via microparticle bombardment, for the selection of genetically transformed cells, and for the regeneration of fully transgenic plants from these cells. The plasmid DNA used for bombardment contained a gene encoding neomycin phosphotransferase (nptII) and a gene encoding beta-glucuronidase (uidA). Selection of bombarded tissue with paromomycin resulted in the establishment of putative transgenic embryogenic calli. In most of these calli, beta-glucuronidase was detected histochemically. Molecular analysis of paromomycin-resistant embryogenic calli and of plants regenerated from these calli, confirmed the stable integration of bombarded DNA into the cassava genome.

Biolistics↗

PubMed1995

A receptor kinase-like protein encoded by the rice disease resistance gene, Xa21.

The rice Xa21 gene, which confers resistance to Xanthomonas oryzae pv. oryzae race 6, was isolated by positional cloning. Fifty transgenic rice plants carrying the cloned Xa21 gene display high levels of resistance to the pathogen. The sequence of the predicted protein, which carries both a leucine-rich repeat motif and a serine-threonine kinase-like domain, suggests a role in cell surface recognition of a pathogen ligand and subsequent activation of an intracellular defense response. Characterization of Xa21 should facilitate understanding of plant disease resistance and lead to engineered resistance in rice.

Amino Acid Sequence↗

PubMed1995

Synthesis of an infectious full-length cDNA clone of rice yellow mottle virus and mutagenesis of the coat protein.

A full-length cDNA clone of rice yellow mottle sobemovirus (RYMV) was synthesized and placed adjacent to a bacteriophage T7 RNA polymerase promoter sequence. Capped-RNA transcripts produced in vitro were infectious when mechanically inoculated onto rice plants (Oryza sativa L). Individual full-length clones varied in their degree of infectivity but all were less infectious than native viral RNA. A representative clone, designated RYMV-FL5, caused a disease phenotype identical to that produced by viral RNA except that symptoms were somewhat slower to appear than those induced by viral RNA. The infectivity of RYMV-FL5 was verified by ELISA, Western blot analysis, Northern blot hybridization, RT-PCR, and Southern blot hybridization. Frameshift and deletion mutations introduced into the coat protein cistron demonstrated that the coat protein was dispensable for RNA replication in rice protoplasts. However, the coat protein was required for full infectivity in rice plants, presumably by playing a role in phloem-mediated long-distance movement and possibly in cell-to-cell movement.

Base Sequence↗

PubMed1994

Nucleotide sequence and genome characterization of rice yellow mottle virus RNA.

The genome of rice yellow mottle virus (RYMV) is a single-stranded positive-sense RNA that is not polyadenylated, and has an M(r) of 1.4 x 10(6). We present here the 4550 nucleotide (nt) sequence of RYMV RNA, and its predicted genomic organization. The RYMV genomic RNA contains four open reading frames (ORFs). The first (nt 80 to 553) encodes a protein containing 157 amino acids with a predicted M(r) of 17.8K. No function has yet been attributed to this product. ORF2 (nt 608 to 3607) encodes a polyprotein of 999 amino acids, with a predicted M(r) of 110.7K. The first 134 amino acids of ORF2 are predicted to be the genome-linked protein, VPg, followed by the viral protease, the helicase and the RNA-dependent RNA polymerase. ORF3 is within the boundaries of ORF2 and is predicted to encode a polypeptide with 126 amino acids and an M(r) of 13.7K. No function has yet been attributed to this protein. ORF4 (nt 3447 to 4166), which overlaps the 3' terminus of ORF2, encodes a 26K protein. This polypeptide has been identified as the RYMV coat protein. The data presented here confirm that RYMV belongs to the sobemovirus group and thus is a member of the picorna-like family of plant viruses.

Amino Acid Sequence↗

PubMed1993

Comparative epidemiology of three tropical whitefly-transmitted geminiviruses.

Spatial and temporal patterns of spread of African cassava mosaic, okra leaf curl and tobacco leaf curl viruses in West Africa, East Africa and India share some general characteristics. By comparing the results and running new analyses on available data, it is shown that the epidemiology of these viruses is controlled by the same key variables. For instance, spatial spread is characterised by strong border effects due to accumulation of whitefly vectors (Bemisia tabaci) on the wind-exposed field borders under the influence of the prevailing wind. This results in pronounced environmental gradients of disease. Temporal patterns of virus spread are driven by the sinusoidal fluctuation of temperature over the year which correspond with changes of whitefly populations.

Animals↗