Biomedical subjects

A C de Avila

Publications and source records attributed to A C de Avila.

10 recordsLinked to original sources

PubMed2004

A novel melon flexivirus transmitted by whitefly.

In recent years, a viral disease on melon plants has become a serious problem in Brazil. Symptoms were principally yellowing and mottling on older leaves. Long filamentous virus particles, resembling those of carlaviruses, were seen in symptomatic leaves. In this study, the 3' terminal region of the virus genome isolated from an infected plant, including the last two ORFs, was cloned and sequenced. The sequence comprised a polyadenilated tail and two ORFs, one exhibiting similarity to potexvirus and carlavirus coat protein gene and the second to a carlavirus protein with potential nucleic acid-binding property. The sequence analysis, the genome organization and the particle morphology indicated that the virus could be classified as a novel whitefly-transmitted flexivirus. The name Melon yellowing-associated virus (MYaV) is tentatively suggested for this virus.

Amino Acid Sequence↗

PubMed2002

Pepper yellow mosaic virus, a new potyvirus in sweetpepper, Capsicum annuum.

A potyvirus was found causing yellow mosaic and veinal banding in sweetpepper in Central and Southeast Brazil. The sequence analysis of the 3' terminal region of the viral RNA revealed a coat protein of 278 amino acids, followed by 275 nucleotides in the 3'-untranslated region preceding a polyadenylated tail. The virus shared 77.4% coat protein amino acid identity with Pepper severe mosaic virus, the closest Potyvirus species. The 3'-untranslated region was highly divergent from other potyviruses. Based on these results, the virus found in sweetpepper plants could be considered as a new potyvirus. The name Pepper yellow mosaic virus (PepYMV) is suggested.

3' Untranslated Regions↗

PubMed2001

Sequence diversity of NS(M) movement protein of tospoviruses.

In order to determine the diversity of the movement protein (NS(M)) among tospoviruses, the NSM genes of five distinct tospovirus species occurring in Brazil (Tomato chlorotic spot virus, Groundnut ring spot virus, Chrysanthemum stem necrosis virus, Zucchini lethal chlorosis virus and Iris yellow spot virus) were cloned, sequenced and compared with NS(M) sequences of other available tospoviruses. The 'D-motif', a conserved region present in the majority of '30K superfamily' virus movement proteins, is present in all NSM amino acid sequences available. In addition to the 'D-motif', a conserved phospholipase A2 motif was found. The NSM amino acid sequence comparisons among tospovirus species revealed several conserved regions located in the internal part of the protein and diverse domains mainly located in the amino-terminus. Prediction of secondary structure showed similar patterns among all NS(M) proteins analyzed. Considering the geographical prevalence and phylogenetic analysis of N and NS(M) proteins, tospoviruses were tentatively clustered in 'American' and 'Eurasian' groups. Both phylogenetic trees may reflect the natural evolution of tospovirus species within distinct ecological niches. The sequence information obtained in this work would facilitate functional analysis of NS(M) during the tospovirus infection process.

Amino Acid Sequence↗

PubMed1993

Distinct levels of relationships between tospovirus isolates.

The taxonomic relations of a number of tospovirus isolates, collected in different geographical areas and from different host plants, were studied. To delineate these isolates, properties such as susceptibility of a limited range of host plants, symptomatology, cytopathology, nucleocapsid composition, serology of their nucleocapsid proteins, and nucleotide sequence homology were compared. The results show that isolates which have previously been discriminated as members of three different serogroups, should in fact be regarded as representatives of at least three distinct virus species in the tospovirus genus.

Blotting, Northern↗

PubMed1993

Classification of tospoviruses based on phylogeny of nucleoprotein gene sequences.

The nucleotide sequences of the nucleoprotein (N) genes of seven tospovirus isolates representing three serogroups were determined and used to establish phylogenetic parameters to delineate species within the Tospovirus genus of the Bunyaviridae. A high sequence divergence (55.9% identity at the nucleotide level) was observed between isolates of serogroup I (tomato spotted wilt virus) and isolates of serogroup III (Impatiens necrotic spot virus). The serogroup II isolates take an intermediate position. Their N genes have 75% identity with those of serogroup I isolates and 57% with those of serogroup III isolates. Whereas the isolates within serogroups I or III have almost identical sequences, the two isolates BR-03 and SA-05 of serogroup II diverged significantly from each other (82.1% sequence identity). The results obtained support the conclusion that, in addition to the species TSWV and INSV, the serogroup II isolates BR-03 and SA-05 have to be considered as distinct species within the genus Tospovirus for which the names tomato chlorotic spot virus and groundnut ringspot virus, respectively, are proposed.

Amino Acid Sequence↗

PubMed1992

The nucleotide sequence of the S RNA of Impatiens necrotic spot virus, a novel tospovirus.

Impatiens necrotic spot virus (INSV) shares a number of properties with tomato spotted wilt virus (TSWV), the type species of the genus tospovirus within the family Bunyaviridae. INSV, however, differs from TSWV in plant host range and serology. In order to define the genomic structure and the taxonomic status of this TSWV-like virus, the nucleotide sequence of its genomic S RNA segment has been determined. The molecular data obtained demonstrate that, like TSWV, INSV has an ambisense S RNA molecule, encoding a non-structural protein in viral sense and the nucleocapsid protein in viral complementary sense. The level of nucleotide sequence homology between their S RNAs, as well as the divergence in amino acid sequence homology of their gene products, confirm previous conclusions from serological studies that INSV and TSWV represent distinct virus species within the newly created genus, tospovirus.

Amino Acid Sequence↗

PubMed1992

Defective interfering L RNA segments of tomato spotted wilt virus retain both virus genome termini and have extensive internal deletions.

Defective interfering (DI) RNA molecules derived from the genomic L RNA segment of tomato spotted wilt virus (TSWV) were generated during sequential passage of the virus at high multiplicity. Characterization of DI RNAs from four distinct isolates by Northern blot analysis and sequence determination revealed that both the 5' and 3' genomic termini were retained in these molecules. Each DI RNA contained a single internal deletion of approximately 60% to 80% of the L RNA segment. All DI RNAs studied maintain an open reading frame (ORF) which suggests that these defective molecules should be translatable by ribosomes. Detection of only defective molecules with ORFs indicates either that association with ribosomes or translation is a prerequisite for the selection and maintenance of replicating DI RNAs, or that the truncated proteins produced play a role in their selection or replication. Analysis of the junction sites in the DI RNAs showed that short nucleotide sequences are repeated, one at the release and another at the reinitiation point on the L RNA. One of these is lost during the generation of the DI molecules. The presence of repeated sequences at the junction sites seems to be unique for tospovirus DI L RNAs; they have not been described for other DI systems of either positive- or negative-strand RNA viruses. A model for TSWV DI RNA generation is proposed in which the viral polymerase can 'jump' across the internal sequences from one secondary structure to another containing the repeated sequences, during the replication of the viral complementary L RNA segment.

Base Sequence↗

PubMed1991

Generation of envelope and defective interfering RNA mutants of tomato spotted wilt virus by mechanical passage.

During a series of mechanical transfers of tomato spotted wilt virus, two distinct types of mutants were generated. Firstly, a morphologically defective isolate was obtained which had lost the ability to produce the membrane glycoproteins and, as a consequence, was not able to form enveloped particles. Analysis of the genomic RNAs of this isolate suggested that this defect was caused by either point mutations or very small deletions in the medium genomic RNA segment. Secondly, isolates were obtained which had accumulated truncated forms of the large (L) RNA segment. These shortened L RNA molecules most likely represented defective interfering RNAs, since they replicated more rapidly than full-length L RNA and their appearance was often associated with symptom attenuation. Defective L RNAs of different sizes were generated after repeated transfers, and hybridization analysis using L RNA-specific cDNA probes showed that the internal regions deleted varied in length. The presence of defective L RNAs in nucleocapsid fractions as well as in enveloped virus particles indicates that all defective molecules retained the sequences required for replication, encapsidation by nucleocapsid proteins and packaging of the nucleocapsid into virus particles.

Blotting, Northern↗

PubMed1990

Serological differentiation of 20 isolates of tomato spotted wilt virus.

Twenty tomato spotted wilt virus (TSWV) isolates were serologically compared in ELISA employing five different procedures using a rabbit polyclonal antiserum against nucleocapsid proteins (NuAbR) and mouse monoclonal antibodies (MAbs), two directed to nucleocapsid proteins (N1 and N2) and four directed to glycoproteins G1 to G4. All the antisera were raised against TSWV-CNPH1. The 20 isolates were differentiated into two distinct serogroups. Serogroup I consisting of 16 isolates strongly reacted with NuAbR. The other four isolates were poorly recognized by NuAbR and were placed in another serogroup, designated II. The panel of MAbs differentiated the TSWV isolates into three serotypes. The 16 isolates forming serogroup I reacted strongly with the MAbs generated and were identified as serotype I isolates. The four isolates which made up serogroup II were split into serotypes II and III. The serotype II isolates did not respond or responded poorly with MAbs N1, N2 and G3. The two other isolates placed in serotype III were recognized by N1 but not by N2 and G3. Two isolates became defective after several mechanical passages and failed to respond or responded very poorly with MAbs directed to glycoproteins. Our results show that ELISA employing polyclonal and monoclonal antisera is a useful tool to differentiate TSWV isolates and to detect defective forms. The results also strongly suggest that TSWV nucleocapsid proteins are less conserved than the glycoproteins.

Antibodies, Monoclonal↗

PubMedDate not supplied

Immuno-electron microscopical detection of tomato spotted wilt virus and its nucleocapsids in crude plant extracts.

Tomato spotted wilt virus (TSWV) particles were identified in thin sections and in crude extracts of leaves from plants infected with different TSWV isolates, using gold labelled protein A and antibodies prepared against purified virus particles or against nucleocapsid preparations. In addition, both in thin sections and in dip preparations aggregates were detected using either gold-labelled antiserum. These aggregates were not detected using antisera against envelope proteins or against the non-structural protein NSs. They were the only detectably labelled material in preparations made from plants infected by morphologically defective isolates of TSWV, i.e. isolates that did not produce enveloped particles. The aggregates were discerned in dip preparations as cloudy amorphous structures having a cottonwool boll-like appearance. These 'cotton bolls' were interpreted as being the in vitro structures of the nucleocapsid aggregates occurring in plant cells infected by isolates maintained by mechanical inoculation and are the only structures in cells infected by morphologically defective isolates (Ie, 1982; Kitajima et al., 1992). The detection of the 'cotton boll-like' structures in crude extracts provides an adequate and rapid method to establish the presence of nucleocapsid aggregates in cells of infected plants, irrespective of whether they are infected by morphologically defective isolates or not.

Capsid↗