Search

The different types of epitopes found in viral antigens are described. The BIAcore has been used successfully to map the location of epitopes in viral antigens and several examples of such studies are presented. Knowledge of the affinity of viral antibodies is important for understanding the molecular basis of viral antigenicity and the mechanism of infectivity neutralization by antibodies. The use of the BIAcore for measuring binding constants of viral antibodies is described. Affinity constants of antibodies binding to virus particles are easily obtained using sensor chips on which the virus is immobilized by a first layer of antibodies. Affinity constants obtained with the BIAcore agree closely with values obtained by several other methods of affinity determination. By comparing the binding properties of neutralizing and nonneutralizing viral antibodies with the BIAcore, it should be possible to establish whether there is a relationship between affinity and neutralizing capacity of antibodies. By immobilizing synthetic peptides corresponding to viral epitopes on sensor chips, the BIAcore can also be used to quantitate antibody to specific epitopes present in polyclonal antiserum.

Synthetic peptides conjugated to a protein carrier were used to immunise rabbits in an attempt to produce antisera specific for the different classes of gliadins and for the low M r glutenin subunits of wheat. Eight peptides were selected from regions of low homology situated in the N and C-terminal domains of these proteins. The anti-peptide antisera were assayed gliadin and glutenin fractions of the bread wheat Hardy by immunoblotting after SDS-PAGE separation and by ELISA. Six of the peptides, i.e. N-terminal peptides of α,β-type, γ-type and ω-type gliadins and low M r glutenin subunits and a C-terminal peptide of α,β-type gliadins, induced antibodies that reacted specifically with the cognate proteins. C-terminal peptides of γ-type gliadins induced antibodies that cross-reacted with ω-type gliadins.

Association (ka) and dissociation (kd) rate constants of three monoclonal antibodies raised against tobacco mosaic virus were determined using a biosensor technique based on surface plasmon resonance (BIAcore, Pharmacia). Dissociation rates were constant over the 4-400 nM antibody concentration range whereas apparent association rates decreased over this range probably due to an increased saturation level of the antigen. Affinity constants K calculated from the ratio of ka/kd were in reasonable agreement with values obtained under equilibrium conditions by two standard methods based on enzyme immunoassay.

In the present study, we developed new turn scales based on the occurrence of amino acids at each of the four positions of a turn using a structural database comprised of 87 proteins. We found that the scales correctly predicted a fraction of the turn regions in proteins with approximately 80% confidence. We used the turn scales for predicting the location of antigenic sites in proteins. The method was developed with the specific aim of predicting only a few peaks for each protein (two or three). We found that it leads to a high level of accurate prediction (70% of correct prediction of known epitopes). Our method should be useful for selecting protein regions to be synthesized in order to produce anti-peptide antibodies cross-reacting with the parent protein.

The suitability of two ELISA procedures for detecting serologically closely related as well as distantly related cucumoviruses has been compared. When antibodies to a single strain were used, closely related strains of cucumber mosaic virus could be detected by both direct and indirect ELISA. However, only the indirect ELISA procedure was capable of detecting distantly related viruses such as tomato aspermy, peanut stunt and cucumber mosaic viruses.

Ten monoclonal antibodies (McAbs) against cucumber mosaic virus (CMV) have been raised from fusion experiments performed after immunizing mice with different CMV antigens. Their reactivities with members of the three CMV serotypes, CMV-DTL, CMV-ToRS, and CMV-Co were tested in a double antibody sandwich format of enzyme immunosorbent assay (ELISA). Several of the McAbs were specific for different members of the CMV-DTL and CMV-ToRS groups while two allowed the detection of CMV-Co. By using a mixture of two McAbs, any member of the three major CMV serotypes could be detected in infected plant sap. One of the antibodies made it possible to discriminate between subunits and whole virions of CMV-D when it was used in ELISA simultaneously as coating antibody and as biotin-conjugate. McAbs were shown to be useful for quantifying the amount of CMV present in plant sap.

UMR BGPI Equipe 2 Mention d'édition : Third Edition; International audience; Viruses have evolved a remarkable diversity of strategies for spreading efficiently from one host to the next. Organisms feeding on infected hosts and actively traveling in between hosts in the environment are all potential useful means for virus transport. Such organisms, designated vectors, are found among fungi, nematodes, and arthropods, particularly insects. Several different interaction patterns have evolved between viruses and vectors, and this diversity is well illustrated in plant viruses transmitted by insects. Over half a century, a tremendous amount of studies has been carried out on the insect transmission of viruses, and a classification of the strategies observed has been established and regularly updated. This classification, originally established for the insect transmission of plant viruses, is comprehensive enough to illustrate all strategies described so far for virus–vector interactions, including animal viruses (though not addressed in detail here) and the cases of transmission by non-insect vectors such as mites, nematodes, and fungi. This article presents an overview of this classification, illustrated by appropriate examples.

Recessive resistance genes have been recognized for a long time and appear more prevalent for resistance to viruses than for resistance to fungal or other plant pathogens for which resistance is primarily a dominant trait. The isolation and characterization of a few of these recessive genes in the 2000s strongly indicate that their prevalence is related to peculiarities of the virus biology. Because the small genome of plant viruses encodes few proteins, the ability of a virus to invade a host relies on host cellular components. Therefore, absence or inadequacy of one of these host components may lead to the inability for the virus to establish a compatible interaction. Such a mechanism was recently associated with recessive resistance genes. This article presents a catalog of recessive resistance factors identified in the natural diversity of crops and the plant model Arabidopsis and discusses phenotypic and molecular characteristics of this type of resistance against plant viruses.

Rice yellow mottle virus (RYMV) causes the most important rice disease in Africa. RYMV belongs to the genus Sobemovirus. RYMV has icosahedral particles of 25 nm in diameter. The virions contain a single coat protein (CP) of 29 kDa, a genomic RNA, and one subgenomic RNA molecule. The genomic RNA is one single-stranded messenger-sense molecule, 4450 nt in size. The 5′ terminus of the RNAs has a genome-linked protein (VPg), and lacks a poly(A) tail. RYMV often encapsidates, in addition to its genomic RNA, a viroid-like satellite RNA. The RYMV genome is organized in four overlapping open reading frames (ORFs). The ORF1 encodes a protein P1 required for cell-to-cell movement of the virus. P1 is a suppressor of posttranslational gene silencing. The ORF2a contains sequence motifs for the proteinase and the VPg. The ORF2b encodes the RNA-dependent RNA polymerase. The ORF4 is translated from the subgenomic RNA and encodes the CP. The natural host range of RYMV is restricted to a few members of the Poaceae family. Transmission is due to chrysomelidae vectors and to contact during cultural practices. The more efficient resistance called high resistance encodes the translation initiation factor eIF(iso)4G. This resistance is overcome by a point mutation in the VPg. The evolution of RYMV has been inferred from its genetic diversity.

Mention d'édition : 3. ed.; International audience