Purification and partial characterization of sugar beet yellows virus

Molecular Characterization of the Complete Coding Sequence of Olive Leaf Yellowing-Associated Virus

Genome organization and phylogenetic relationships of olive leaf yellowing-associated virus (OLYaV) with other members of the Closteroviridae family were determined. The complete coding sequence of OLYaV was obtained by high throughput sequencing of total RNA from a 35-year-old olive tree (cv. Zarzaleña) from Brazil, showing olive leaf yellowing disease and deformations in the wood. This represents the first report of OLYaV in this country. A genomic sequence of 16,700 nt containing 11 open reading frames (ORFs) was recovered, representing the complete virus coding capacity. The knowledge of the nucleotide sequence of the genome including the gene that codes the coat protein will facilitate the development of diagnostic tests, which are limited so far to PCR-based methods targeting the HSP70h gene. Interestingly, a thaumatin-like protein (ORF2), previously reported in other unassigned viruses in the Closteroviridae family, persimmon virus B and actidinia virus 1, was identified in the OLYaV genome. Phylogenetic analysis of shared proteins (ORF1a, ORF1b, HSP70h, HSP90h and CP) with all members of the Closteroviridae family provides new insight into the taxonomic position of these three closteroviruses and suggests they could represent a new genus in the family.

A Short Note on Reflections and Publications on Citrus tristeza virus (CTV) Methodologies

My PhD thesis work of Citrus tristeza virus (CTV) purification was aimed to develop a rapid serological assay to replace biological indexing. The task turned difficult and was achieved after a lengthy struggle, rewarded by allowing (1) the rapid diagnosis of the first incidences of natural spread of a severe CTV-VT strain in our region and (2) finding that the CTV particle isolation protocol, with some modifications, was also useful for Beet yellows virus (BYV) particles, leading to their assignment in the Closterovirus group, the first group of elongated plant viruses with different modal lengths. Later, following the introduction of ELISA for large-scale diagnosis of tristeza-infected citrus trees, the CTV infection rates through the coastal citrus production areas were continually increasing, with many ELISA-positive samples appearing symptomless, prompting the need to develop strain-specific assays. Using CTV-VT cDNA fragments, as hybridization probes, the genetic diversity among local CTV isolates was demonstrated. With the emergence of the PCR technology, we developed a CTV-dsRNA cloning method based on the ligation of known oligonucleotide molecules to dsRNA ends and the use of complementary oligonucleotides for cDNA synthesis and PCR amplification. The method allowed the cloning of a cDNA molecule complementary to a defective dsRNA of 2.4 kb with intact 5 and 3 ends of the CTV-VT genome. A list of publications, resulting from continuous collaborative work with local and foreign associates and students on the development and adaptation of novel CTV methodologies, is present.

A Brief Historical Account of the Family Closteroviridae

The history is outlined of the steps that, starting from the establishment of the "taxonomic group Closterovirus," have brought to the erection of the family Closteroviridae, a taxon comprising plant viruses that possess very long helically constructed filamentous particles and a positive-sense single-stranded, monopartite or bipartite RNA genome and are transmitted either by aphids (genus Closterovirus), pseudococcid mealybugs/soft scale insects (genus Vitivirus), or whiteflies (genus Crinivirus) or have no known vector (genus Velarivirus).

Crinivirus replication and host interactions

Criniviruses comprise one of the genera within the family Closteroviridae. Members in this family are restricted to the phloem and rely on whitefly vectors of the genera Bemisia and/or Trialeurodes for plant-to-plant transmission. All criniviruses have bipartite, positive-sense single-stranded RNA genomes, although there is an unconfirmed report of one having a tripartite genome. Lettuce infectious yellows virus (LIYV) is the type species of the genus, the best studied so far of the criniviruses and the first for which a reverse genetics system was developed. LIYV RNA 1 encodes for proteins predicted to be involved in replication, and alone is competent for replication in protoplasts. Replication results in accumulation of cytoplasmic vesiculated membranous structures which are characteristic of most studied members of the Closteroviridae. These membranous structures, often referred to as Beet yellows virus (BYV)-type vesicles, are likely sites of RNA replication. LIYV RNA 2 is replicated in trans when co-infecting cells with RNA 1, but is temporally delayed relative to RNA 1. Efficient RNA 2 replication also is dependent on the RNA 1-encoded RNA-binding protein, P34. No LIYV RNA 2-encoded proteins have been shown to affect RNA replication, but at least four, CP (major coat protein), CPm (minor coat protein), Hsp70h, and P59 are virion structural components and CPm is a determinant of whitefly transmissibility. Roles of other LIYV RNA 2-encoded proteins are largely as yet unknown, but P26 is a non-virion protein that accumulates in cells as characteristic plasmalemma deposits which in plants are localized within phloem parenchyma and companion cells over plasmodesmata connections to sieve elements. The two remaining crinivirus-conserved RNA 2-encoded proteins are P5 and P9. P5 is 39 amino acid protein and is encoded at the 5' end of RNA 2 as ORF 1 and is part of the hallmark closterovirus gene array. The orthologous gene in BYV has been shown to play a role in cell-to-cell movement and indicated to be localized to the endoplasmic reticulum as a Type III integral membrane protein. The other small protein, P9, is encoded by ORF 4 overlaps with ORF 3 that encodes the structural protein, P59. P9 seems to be unique to viruses in the genus Crinivirus, as no similar protein has been detected in viruses of the other two genera of the Closteroviridae.

Closterovirus infection and mealybug exposure are necessary for the development of mealybug wilt of pineapple disease

ABSTRACT The roles of Pineapple mealybug wilt-associated viruses (PMWaVs) and mealybug (Dysmicoccus spp.) feeding in the etiology of mealybug wilt of pineapple (MWP) were evaluated. Container-grown pineapple (Ananas comosus) plants from five commercially grown Hawaiian proprietary selections and a field study utilizing a randomized complete block design were used to test four treatments for induction of MWP: PMWaV-1-free and PMWaV-1-infected plants maintained mealybug-free, and PMWaV-1-free and PMWaV-1-infected plants that received monthly applications of nonviruliferous mealybugs. A second PMWaV, PMWaV-2, was identified in some of the test plants during the course of these studies and was shown to be an integral factor in MWP etiology. Typical MWP symptoms developed only in plants infected with PMWaV-2 and exposed to mealybugs. MWP did not develop in PMWaV-1-free or PMWaV-1-infected plants that were exposed to mealybugs, or in mealy-bug-free plants infected with PMWaV-1, PMWaV-2, or both viruses. Plants from all five Hawaiian proprietary selections developed MWP when PMWaV-2 infected plants were exposed to mealybug feeding. A PMWaV-2-specific monoclonal antibody was produced that decorated the particles in immunosorbent electron microscopy and detected the virus in tissue blot immunoassays. PMWaV-2 was acquired and transmitted by pink and gray pineapple mealybugs (Dysmicoccus spp.) to pineapple plants, and these plants subsequently developed MWP symptoms while sustaining mealybug populations.

Physiochemical Characterization and Field Assessment of Lettuce Chlorosis Virus

Lettuce chlorosis virus (LCV) was purified and partially characterized, and polyclonal antisera were produced and used to assess disease in the field. The antisera reliably detected LCV by indirect enzyme-linked immunosorbent assay (ELISA) in Nicotiana benthamiana. In Western blots, the LCV antisera distinguished between LCV and lettuce infectious yellows virus (LIYV)-infected plants. LCV particle lengths in partially purified preparations, as observed by transmission electron microscopy, were variable, with the majority between 750 and 950 nm long. A single, high molecular weight dsRNA and several lower molecular weight dsRNAs were isolated from LCV-infected N. benthamiana. A single RNA isolated from purified virion preparations was estimated to be 8,625 nucleotides long and was suspected to be the genomic RNA of LCV. LCV was present in experimental field plots in Holtville, California, during the lettuce growing seasons of 1995 to 1997. The percentage of symptomatic plants and yield of lettuce heads treated with insecticide, as well as dsRNA and ELISA reactions for the plots, are reported. A dsRNA consistent in size with LCV was isolated from four weed species in the Imperial Valley of California.

Purification and Characterization of Peach Mosaic Virus

Virus particles were observed by transmission electron microscopy in preparations extracted from symptomatic leaves of Chenopodium amaranticolor that had been mechanically inoculated with peach mosaic virus. The particles were long, flexuous, filamentous rods with an average length of 888 nm. Purified preparations had an A 260/280 nm ratio of 1.25. RNA extracted from purified virus was approximately 8.1 kilobases, and a capsid protein of approximately 27 kDa was found. Polyclonal rabbit antiserum, produced against purified virus, reacted with samples from peach mosaic and cherry mottle leaf-infected plants when used in Western blot analysis.

Principles of molecular organization, expression, and evolution of closteroviruses: over the barriers

This chapter focuses on the molecular organization, evolution, and expression of closterovirus genomes, as well as on their unique particle structure. The closterovirus group combines several positive-strand RNA viruses with very flexuous filamentous particles, of which beet yellows virus (BYV) is the type virus. Closteroviruses are distinct from other RNA viruses of plants in some important phenomenological aspects. They have genomes of up to 20 kilobases (kb), a value comparable only to those of the animal coronaviruses and toroviruses, which have the largest RNA genomes of all positive-strand RNA viruses. The existence of such genomes having a coding capacity several times that of an average RNA virus genome raises questions as to the trend whereby the long genomes have evolved and the possible novel functions they have acquired. The dramatic increase in the closterovirus genome coding capacity may be linked to the distinct ecological niche they occupy. Thus, closteroviruses are the only elongated plant viruses known so far to cause phloem-limited infections in plants and to persist in their insect vectors for many hours, in contrast to only minutes.

"Rattlesnake" structure of a filamentous plant RNA virus built of two capsid proteins

Elongated particles of simple RNA viruses of plants are composed of an RNA molecule coated with numerous identical capsid protein subunits to form a regular helical structure, of which tobacco mosaic virus is the archetype. Filamentous particles of the closterovirus beet yellow virus (BYV) reportedly contain approximately 4000 identical 22-kDa (p22) capsid protein subunits. The BYV genome encodes a 24-kDa protein (p24) that is structurally related to the p22. We searched for the p24 in BYV particles by using immunoelectron microscopy with specific antibodies against the recombinant p24 protein and its N-terminal peptide. A 75-nm segment at one end of the 1370-nm filamentous viral particle was found to be consistently labeled with both types of antibodies, thus indicating that p24 is indeed the second capsid protein and that the closterovirus particle, unlike those of other plant viruses with helical symmetry, has a "rattlesnake" rather than uniform structure.

Nucleotide sequence of cDNA encoding the coat protein of beet yellows virus

A cDNA clone of beet yellows viral RNA expressed the viral coat protein gene in E. coli. The sequence of the 2724 nucleotide insert revealed three open reading frames, the 3' of which was shown to be the coat protein cistron. This cistron is expressed in E. coli, in spite of there being no obvious ribosome binding site upstream.

Putative 65 kDa protein of beet yellows closterovirus is a homologue of HSP70 heat shock proteins

A portion of the RNA genome of beet yellows closterovirus (BYV) has been sequenced encompassing a complete long open reading frame (ORF) potentially encoding a 65 kDa protein. The sequence of this putative protein was strikingly similar to those of HSP70-related heat shock proteins. The counterparts of all the eight segments strongly conserved in HSP70s could be confidently identified in the BYV 65 kDa protein. It is suggested that some of these segments might be the ATP-binding site(s) and that, similarly to the heat shock proteins, the 65 kDa is probably ATP-binding. Generally, however, the divergence between the 65 kDa sequence and the sequences of the HSP70s was much more pronounced than that between any two members of the latter family, allowing a clearer delineation of clusters of conserved residues that might be crucial for protein function. It is suggested that these observations will be helpful in functional dissection of the proteins of the HSP70 family. Analysis of the sequence of a portion of the ORF found upstream from the 65 kDa ORF showed that the C-terminal domain of the encoded protein could be an RNA-dependent RNA polymerase closely related to those of tricornaviruses, a family of RNA plant viruses with three component genomes.

Molar absorptivity and A1%1 cm values for proteins at selected wavelengths of the ultraviolet and visible regions--XVIII

A table of molar absorptivity and A1cm1% values for more than 180 proteins is given. The conditions used to obtain these values and references to the original literature are also'given.