Patent Application
20050032041
The present invention relates to Rupestris stem pitting associated virus (“RSPaV”) proteins, DNA molecules encoding these proteins, and diagnostic and other uses thereof.
The world's most widely grown fruit crop, the grape (Vitis sp.), is cultivated on all continents except Antarctica. However, major grape production centers are in European countries (including Italy, Spain, and France), which constitute about 70% of the world grape production (Mullins et al., Biology of the Grapevine, Cambridge, U.K.:University Press (1992)). The United States, with 300,000 hectares of grapevines, is the eighth largest grape grower in the world. Although grapes have many uses, a major portion of grape production (˜80%) is used for wine production. Unlike cereal crops, most of the world's vineyards are planted with traditional grapevine cultivars, which have been perpetuated for centuries by vegetative propagation. Several important grapevine virus and virus-like diseases, such as grapevine leafroll, corky bark, and Rupestris stem pitting (“RSP”), are transmitted and spread through the use of infected vegetatively propagated materials. Thus, propagation of certified, virus-free materials is one of the most important disease control measures. Traditional breeding for disease resistance is difficult due to the highly heterozygous nature and outcrossing behavior of grapevines, and due to polygenic patterns of inheritance. Moreover, introduction of a new cultivar may be prohibited by custom or law. Recent biotechnology developments have made possible the introduction of special traits, such as disease resistance, into an established cultivar without altering its horticultural characteristics.
Many plant pathogens, such as fungi, bacteria, phytoplasmas, viruses, and nematodes can infect grapes, and the resultant diseases can cause substantial losses in production (Pearson et al., Compendium of Grape Diseases, American Phytopathological Society Press (1988)). Among these, viral diseases constitute a major hindrance to profitable growing of grapevines. About 34 viruses have been isolated and characterized from grapevines. The major virus diseases are grouped into: (1) the grapevine degeneration caused by the fanleaf nepovirus, other European nepoviruses, and American nepoviruses, (2) the leafroll complex, and (3) the rugose wood complex (Martelli, ed., Graft Transmissible Diseases of Grapevines, Handbook for Detection and Diagnosis, FAO, UN, Rome, Italy (1993)).
Rugose wood (RW) complex is a term to describe a group of graft-transmissible diseases which are important and widespread on grapevines grown world-wide. Symptoms of RW are characterized by pitting, grooving, or distortion to the woody cylinder of the grapevine scion, rootstock, or both. Based on symptoms developed on different indicator plants after graft inoculation, RW complex can be divided into four components: Kober 5BB stem grooving (KSG), LN 33 stem grooving (LNSG), grapevine corky bark (GCB), and Rupestris stem pitting (RSP) (Martelli, “Rugose Wood Complex,” in Graft-Transmissible Diseases of Grapevines. Handbook for Detection and Diagnosis, pp.45-54, Martelli, ed., Food and Agriculture Organization of the United Nations, Rome, Italy (1993)). Because RW can cause severe decline and death to grapevines (Savino et al., “Rugose Wood Complex of Grapevine: Can Grafting to Vitis Indicators Discriminate Between Diseases?”, in Proceedings of the 9th Meetings of the International Council for the Study of Viruses and Virus Diseases of the Grapevine, Anavim, Israel (1989); Credi and Babini, “Effect of Virus and Virus-like Infections on the Growth of Grapevine Rootstocks,” Adv. Hort. Sci., 10:95-98 (1996)), it has been included in healthy grapevine detection schemes used in major grapevine growing countries including Italy, France, and the United States.
RSP was discovered in California in the late 1970s (Prudencio, “M. Sc. Thesis: Comparative Effects of Corky Bark and Rupestris Stem Pitting Diseases on Selected Germplasm Lines of Grapes,” University of California, Davis, California, 36 pages (1985); Goheen, “Rupestris Stem Pitting,” in Compendium of Grape Diseases, p. 53, Pearson and Goheen, eds., American Phytopathological Society Press, St. Paul, Minn., USA (1988) (“Goheen”)). The disease was defined by Goheen as follows: after graft inoculation with a chip bud from an infected grapevine, the woody cylinder of the indicator plant Vitis rupestris Scheele St. George (“St. George”) develops a narrow strip of small pits extending from the inoculum bud to the root zone. Grafted St. George plants were checked for wood symptoms 2 to 3 years after inoculation. In contrast to GCB, which elicits pitting and grooving on St. George and LN 33, RSP does not produce symptoms on the latter (Goheen, “Rupestris Stem Pitting,” in Compendium of Grape Diseases, p. 53, Pearson and Goheen, eds., American Phytopathological Society Press, St. Paul, Minn., USA (1988)).
RSP is probably the most common component of the RW complex on grapevines. Surveys in California revealed a high disease incidence in many grapevine cultivars imported from Western Europe and Australia (Goheen, “Rupestris Stem Pitting,” in Compendium of Grape Diseases, p. 53, Pearson and Goheen, eds., American Phytopathological Society Press, St. Paul, Minn., USA (1988)). An examination of indexing records in California compiled over 23 years revealed RSP infection in 30.5% of 6482 grapevine selections introduced from around the world (Golino and Butler, “A Preliminary Analysis of Grapevine Indexing Records at Davis, California,” in Proceedings of the 10th Meeting of the ICVG, pp. 369-72, Rumbos et al., eds., Volos, Greece (1990)). Indexing in New York State showed that 66% of 257 grapevines tested on St. George developed typical small pits below the inoculum bud or around the woody cylinder (Azzam and Gonsalves, Abstract: “Survey of Grapevine Stem-Pitting in New York and Isolation of dsRNA from a Grapevine Selection Infected with Stem Pitting,” Phytopathology 78:1568 (1988)). Furthermore, several reports have indicated that RSP is the most frequently detected component of the RW complex in Italy (Borgo and Bonotto, “Rugose Wood Complex of Grapevine in Northeastern Italy: Occurrence of Rupestris Stem Pitting and Kober Stem Grooving,” in Extended Abstracts of the 11 th Meeting of the International Council for the Study of Viruses and Virus Diseases of the Grapevine (ICVG), pp. 61-62, Gugerli, ed., Montreux, Switzerland (1993); Credi, “Differential Indexing Trials on Grapevine Rugose Wood Syndrome,” Extended Abstracts of the 11th Meeting of the International Council for the Study of Viruses and Virus Diseases of the Grapevine (ICVG), p. 63, Gugerh, P., ed., Montreux, Switzerland (1993)).
The effect of RSP on growth, yield, and grapevine quality is not well understood and, thus, subject to debate. The reason for this ambiguity is the absence of a rapid and sensitive diagnostic tool. RSP is the most difficult grapevine disease to diagnose. Serological or molecular methods are not available for diagnosing RSP. Biological indexing on St. George, as described above, has remained the only approach to diagnose RSP. Biological indexing is labor intensive, time consuming (i.e., often requiring up to about three years to obtain results), and, by its very nature, subjective. Moreover, symptoms on St. George can be variable and not exactly as those defined by Goheen. In particular, Credi, “Characterization of Grapevine Rugose Wood Sources from Italy,” Plant Disease, 82:1288-92 (1997), recently showed that some RSP infected grapevines induced pitting that is restricted to below the inoculum bud, while others induced pitting around the woody cylinder of inoculated St. George. Thus, the present method of identifying the presence of RSP is not entirely adequate.
The etiology of RSP is unknown. Efforts to isolate virus particles from RSP-infected grapevines and to mechanically transfer the causal virus(es) to herbaceous host plants failed (Azzam and Gonsalves, “Detection of in Grapevines Showing Symptoms of Rupestris Stem Pitting Disease and the Variabilities Encountered,” Plant Disease, 75:96-964 (1991)). However, a major dsRNA species of ca. 8.3 kb, accompanied by a smaller dsRNA of ca. 7.6 kb, was consistently isolated from one Pinot Gris and four Pinot Noir clones that had been indexed positive for RSP (Walter and Cameron, “Double-Stranded RNA Isolated from Grapevines Affected by Rupestris Stem Pitting Disease,” Am. J. of Enology and Viticulture, 42:175-79 (1991)). In addition, a third dsRNA of ca. 5.5 kb was observed in three clones. Likewise, an apparently similar dsRNA species of ca. 8.0 and 6.7 kbp was isolated from dormant canes of RSP-infected grapevines collected from California, Canada, and New York (Azzam and Gonsalves, “Detection of dsRNA in Grapevines Showing Symptoms of Rupestris Stem Pitting Disease and the Variabilities Encountered,” Plant Disease, 75:960-64 (1991)). Six of eight Californian and three of five Canadian samples contained these two dsRNA species. However, results of New York samples were not consistent. Among eight RSP infected grapevine selections tested, only one showed these two dsRNAs. Using explants growing in tissue culture as source materials, dsRNA of ca. 359 bp was isolated from 21 of 31 grapevine cultivars, all of which were previously indexed on St. George and considered to be infected with RSP (Monette et al., “Double-Stranded RNA from Rupestris Stem Pitting-Affected Grapevines,” Vitis 28:137-44 (1989)).
In view of the serious risk RSP poses to vineyards and the absence of an effective treatment of it, the need to prevent this affliction continues to exist. Moreover, the absence of a rapid and accurate diagnostic assay prevents proper identification of RSP. The present invention is directed to overcoming these deficiencies in the art.
The present invention relates to an isolated protein or polypeptide corresponding to a protein or polypeptide of a RSP virus. The encoding RNA molecule or DNA molecule, in either isolated form or incorporated in an expression system, a host cell, or a transgenic Vitis scion or rootstock cultivar, are also disclosed.
Another aspect of the present invention relates to a method of imparting RSP virus resistance to Vitis scion or rootstock cultivars by transforming them with a DNA molecule encoding the protein or polypeptide corresponding to a protein or polypeptide of a RSP virus.
The present invention also relates to an antibody or binding portion thereof or probe which recognizes proteins or polypeptides of the present invention.
Still another aspect of the present invention relates to diagnostic tests which involve methods for detecting the presence of a RSP virus in a sample. The methods include the use of an antibody or binding portion of the present invention (i.e., in an immunoassay), or a nucleic acid probe obtained from a DNA molecule of the present invention (i.e., in a nucleic acid hybridization assay or gene amplification detection procedure). The antibody or binding portion thereof, or nucleic acid probe, is introduced into contact with the sample, whereby the presence of Rupestris stem pitting virus in the sample is detected using an assay system.
The characterization of an RSP virus is particularly desirable because it will allow for the determination of whether the virus is associated to the specific (restricted) or nonspecific (nonrestricted) pitting symptoms of RSP, or to both. Also, RSP virus resistant transgenic variants of the current commercial grape cultivars and rootstocks allows for more complete control of the virus while retaining the varietal characteristics of specifics cultivars. Furthermore, these variants permit control over RSP virus transmitted by infected scions or rootstocks. Moreover, the diagnostic tests offer significant improvement over conventional diagnostic means currently employed, namely, rapid results and greater accuracy.
FIGS. 5A-D are comparative sequence listings of amino acid sequences for ORF2, ORF3, ORF74, and a C-terminal part of ORF5 (CP) of RSPaV-1, respectively, with ASPV and PVM carlavirus. In
FIGS. 7A-B are photographs comparing the results of RT-PCR of grapevines using RSP 149 primers (
The present invention relates to isolated DNA molecules encoding for the proteins or polypeptides of a Rupestris stem pitting associated virus. Since the nucleotide sequence was derived from cDNA clones of the dsRNA that was associated with RSP, the viral agent has been designated as Rupestris stem pitting associated virus (“RSPaV”). RSP is likely caused by one or a number of viral strains. The genome of each RSPaV has a plurality of open reading frames, each containing DNA molecules in accordance with the present invention. The complete genome of one strain has been sequenced and the strain is designated RSPaV-1. Substantial portions of the genomes of two other RSPaV strains have also been sequenced. These strains are designated by their clone names, RSP47-4 and RSP158.
The DNA molecule which constitutes the complete RSPaV-1 genome comprises the nucleotide sequence corresponding to SEQ. ID. No. 1 as follows:
The DNA molecule of SEQ. ID. No. 1 contains at least five open reading frames (e.g., ORF 1-ORF5), each of which encodes a particular protein or polypeptide of RSPaV-1, and a 3′ untranscribed region downstream of ORF5.
Another DNA molecule of the present invention (RSPaV-1 ORF 1) includes nucleotides 62-6547 of SEQ. ID. No. 1. The DNA molecule of RSPaV-1 ORF1 encodes for a RSPaV-1 replicase and comprises a nucleotide sequence corresponding to SEQ. ID. No. 2 as follows:
The RSPaV-1 replicase has a deduced amino acid sequence corresponding to SEQ. ID. No. 3 as follows:
The replicase of SEQ. ID. No. 3 has a molecular weight of about 240 to 246 kDa, preferably about 244 kDa.
Another DNA molecule of the present invention (RSPaV-1 ORF2) includes nucleotides 6578-7243 of SEQ. ID. No. 1. The DNA molecule of RSPaV-1 ORF2 encodes for a first protein or polypeptide of an RSPaV-1 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 4 as follows:
The first protein or polypeptide of the RSPaV-1 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 5 as follows:
The first protein or polypeptide of the RSPaV-1 triple gene block has a molecular weight of about 20 to 26 kDa, preferably 24.4 kDa.
Another DNA molecule of the present invention (RSPaV-1 ORF3) includes nucleotides 7245-7598 of SEQ. ID. No. 1. The DNA molecule of RSPaV-1 ORF3 encodes for a second protein or polypeptide of the triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 6 as follows:
The second protein or polypeptide of the RSPaV-1 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 7 as follows:
The second protein or polypeptide of the RSPaV-1 triple gene block has a molecular weight of about 10 to 15 kDa, preferably 12.8 kDa.
Yet another DNA molecule of the present invention (RSPaV-1 ORF4) includes nucleotides 7519-7761 of SEQ. ID. No. 1. The DNA molecule of RSPaV-1 ORF4 encodes for a third protein or polypeptide of the RSPaV-1 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 8 as follows:
The third protein or polypeptide of the RSPaV-1 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 9 as follows:
The third protein or polypeptide of the RSPaV-1 triple gene block has a molecular weight of about 5 to 10 kDa, preferably 8.4 kDa.
Still another DNA molecule of the present invention (RSPaV-1 ORF5) includes nucleotides 7771-8550 of SEQ. ID. No. 1. The DNA molecule of RSPaV-1 ORF5 encodes for a RSPaV-1 coat protein and comprises a nucleotide sequence corresponding to SEQ. ID. No. 10 as follows:
The RSPaV-1 coat protein has a deduced amino acid sequence corresponding to SEQ. ID. No. 11 as follows:
The RSPaV-1 coat protein has a molecular weight of about 25 to 30 kDa, preferably 28 kDa.
The DNA molecule which constitutes the substantial portion of the RSPaV strain RSP474 genome comprises the nucleotide sequence corresponding to SEQ. ID. No. 12 as follows:
The RSP47-4 strain contains five open reading frames (i.e., ORF1-5). ORF1 and ORF5 are only partially sequenced. RSP47-4 is 79% identical in nucleotide sequence to the corresponding region of RSPaV-1. The amino acid sequence identities between the corresponding ORFs of RSP47-4 and RSPaV-1 are: 94.1% for ORF1, 88.2% for ORF2, 88.9% for ORF3, 86.2% for ORF4, and 92.9% for ORF5. The nucleotide sequences of the five potential ORFs of RSP47-4 are given below.
Another DNA molecule of the present invention (RSP47-4 incomplete ORF1) includes nucleotides 1-768 of SEQ. ID. No. 12. This DNA molecule is believed to code for a polypeptide portion of a RSP47-4 replicase and comprises a nucleotide sequence corresponding to SEQ. ID. No. 13 as follows:
The polypeptide has a deduced amino acid sequence corresponding to SEQ. ID. No. 14 as follows:
Another DNA molecule of the present invention (RSP47-4 ORF2) includes nucleotides 857-1522 of SEQ. ID. No. 12. This DNA molecule codes for a first protein or polypeptide of an RSP47-4 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 15 as follows:
The first protein or polypeptide of the RSP47-4 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 16 as follows:
The first protein or polypeptide of the RSP47-4 triple gene block has a molecular weight of about 20 to 26 kDa., preferably 24.3 kDa.
Another DNA molecule of the present invention (RSP47-4 ORF3) includes nucleotides 1524-1877 of SEQ. ID. No. 12. This DNA molecule codes for a second protein or polypeptide of the RSP47-4 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 17 as follows:
The second protein or polypeptide of the RSP47-4 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 18 as follows:
The second protein or polypeptide of the RSP47-4 triple gene block has a molecular weight of about 10 to 15 kDa., preferably 12.9 kDa.
Another DNA molecule of the present invention (RSP47-4 ORF4) includes nucleotides 1798-2040 of SEQ. ID. No. 12. This DNA molecule codes for a third protein or polypeptide of the RSP47-4 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 19 as follows:
The third protein or polypeptide of the RSP47-4 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 20 as follows:
The third protein or polypeptide of the RSP47-4 triple gene block has a molecular weight of about 5 to 10 kDa., preferably 8.3 kDa.
Yet another DNA molecule of the present invention (RSP474 ORF5) includes nucleotides 2050-2680 of SEQ. ID. No. 12. This DNA molecule codes for a partial RSP47-4 coat protein or polypeptide and comprises a nucleotide sequence corresponding to SEQ. ID. No. 21 as follows:
The polypeptide has a deduced amino acid sequence corresponding to SEQ. ID. No. 22 as follows:
The DNA molecule which constitutes a substantial portion of the RSPaV strain RSP158 genome comprises the nucleotide sequence corresponding to SEQ. ID. No. 23 as follows:
The RSP158 strain contains five open reading frames (i.e., ORF1-5). ORF1 and ORF5 are only partially sequenced. The nucleotide sequence of RSP158 is 87.6% identical to the corresponding region of RSPaV-1 (type strain). The numbers of amino acid residues of corresponding ORFs of RSP158 and RSPaV-1 (type strain) are exactly the same. In addition, the amino acid sequences of these ORFs have high identities to those of RSPaV-1: 99.3% for ORF1, 95% for ORF2, 99.1% for ORF3, 88.8% for ORF4, and 95.1% for ORF5. The nucleotide and amino acid sequence information of the RSP158 ORFs are described below.
Another DNA molecule of the present invention (RSP158 incomplete ORF1) includes nucleotides 1-447 of SEQ. ID. No. 23. This DNA molecule is believed to code for a polypeptide portion of a RSP158 replicase and comprises a nucleotide sequence corresponding to SEQ. ID. No. 24 as follows:
The polypeptide encoded by the nucleotide sequence of SEQ. ID. No. 24 has a deduced amino acid sequence corresponding to SEQ. ID. No. 25 as follows:
Another DNA molecule of the present invention (RSP158 ORF2) includes nucleotides 506-1171 of SEQ. ID. No. 23. This DNA molecule codes for a first protein or polypeptide of the RSP158 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 26 as follows:
The first protein or polypeptide of the RSP158 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 27 as follows:
The first protein or polypeptide of the RSP158 triple gene block has a molecular weight of about 20 to 26 kDa., preferably 24.4 kDa.
Another DNA molecule of the present invention (RSP158 ORF3) includes nucleotides 1173-1526 of SEQ. ID. No. 23. This DNA molecule codes for a second protein or polypeptide of the RSP158 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 28 as follows:
The second protein or polypeptide of the RSP158 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 29 as follows:
The second protein or polypeptide of the RSP158 triple gene block has a molecular weight of about 10 to 15 kDa., preferably 12.9 kDa.
Another DNA molecule of the present invention (RSP158 ORF4) includes nucleotides 1447-1689 of SEQ. ID. No. 23. This DNA molecule codes for a third protein or polypeptide of the RSP158 triple gene block and comprises a nucleotide sequence corresponding to SEQ. ID. No. 30 as follows:
The third protein or polypeptide of the RSP158 triple gene block has a deduced amino acid sequence corresponding to SEQ. ID. No. 31 as follows:
The third protein or polypeptide of the RSP158 triple gene block has a molecular weight of about 5 to 10 kDa., preferably 8.4 kDa.
Yet another DNA molecule of the present invention (RSP158 ORF5) includes nucleotides 1699-2009 of SEQ. ID. No. 23. This DNA molecule codes for a partial RSP158 coat protein or polypeptide and comprises a nucleotide sequence corresponding to SEQ. ID. No. 32 as follows:
The polypeptide has a deduced amino acid sequence corresponding to SEQ. ID. No. 33 as follows:
The following seven cDNA clones are located at the central part of the ORF1 of RSPaV-1 and all have high identities (83.6-98.4%) in nucleotide sequence with the comparable regions of RSPaV-1. When their nucleotide sequences are aligned with MegAlign (DNAStar), a highly conserved region of ca. 600 nucleotides was found. The universal primers BM98-3F/BM98-3R (SEQ. ID. Nos. 51 and 52, infra) were designed based on the conserved nucleotide sequences of this region.
Portions of the genome from yet other strains of Rupestris stem pitting associated viruses have also been isolated and sequenced. These include strains designated 140/94-19 (T7+R1), 140/94-24 (T7+R1), 140/94-2 (T3+F1), 140/94+42 (T7+R1), 140/94-64 (T+R1), 140-94-72 (T7+R1), and 140/94-6 (T3+BM98-3F+F2).
The nucleotide sequence of 140/94-19 (T7+R1) corresponds to SEQ. ID. No. 34 as follows:
The nucleotide sequence of 140/94-24 (T7+R1) corresponds to SEQ. ID. No. 35 as follows:
The nucleotide sequence of 140/94-2 (T3+F1) corresponds to SEQ. ID. No. 36 as follows:
The nucleotide sequence of 140/94-42 (T7+R1) corresponds to SEQ. ID. No. 37 as follows:
The nucleotide sequence of 140/94-6 (T3+BM98-3F+F2) corresponds to SEQ. ID. No. 38 as follows:
The nucleotide sequence of 140/94-64 (T7+R1) corresponds to SEQ. ID. No. 39 as follows:
The nucleotide sequence of 140-94-72 (T7+R1) corresponds to SEQ. ID. No. 40 as follows:
Also encompassed by the present invention are fragments of the DNA molecules of the present invention. Suitable fragments capable of imparting RSP resistance to grape plants are constructed by using appropriate restriction sites, revealed by inspection of the DNA molecule's sequence, to: (i) insert an interposon (Felley et al., “Interposon Mutagenesis of Soil and Water Bacteria: A Family of DNA Fragments Designed for in vitro Insertion Mutagenesis of Gram-negative Bacteria,” Gene 52:147-15 (1987), which is hereby incorporated by reference) such that truncated forms of the RSP virus polypeptide or protein, that lack various amounts of the C-terminus, can be produced or (ii) delete various internal portions of the protein. Alternatively, the sequence can be used to amplify any portion of the coding region, such that it can be cloned into a vector supplying both transcription and translation start signals.
Suitable DNA molecules are those that hybridize to a DNA molecule comprising a nucleotide sequence of at least 15 continuous bases of SEQ. ID. No. 1 under stringent conditions characterized by a hybridization buffer comprising 0.9M sodium citrate (“SSC”) buffer at a temperature of 37° C. and remaining bound when subject to washing with SSC buffer at 37° C.; and preferably in a hybridization buffer comprising 20% formamide in 0.9M saline/0.9M SSC buffer at a temperature of 42° C. and remaining bound when subject to washing at 42° C. with 0.2×SSC buffer at 42° C.
Variants may also (or alternatively) be modified by, for example, the deletion or addition of nucleotides that have minimal influence on the properties, secondary structure and hydropathic nature of the encoded protein or polypeptide. For example, the nucleotides encoding a protein or polypeptide may be conjugated to a signal (or leader) sequence at the N-terminal end of the protein which co-translationally or post-translationally directs transfer of the protein. The nucleotide sequence may also be altered so that the encoded protein or polypeptide is conjugated to a linker or other sequence for ease of synthesis, purification, or identification of the polypeptide.
The protein or polypeptide of the present invention is preferably produced in purified form (preferably, at least about 80%, more preferably 90%, pure) by conventional techniques. Typically, the protein or polypeptide of the present invention is isolated by lysing and sonication. After washing, the lysate pellet is re-suspended in buffer containing Tris-HCl. During dialysis, a precipitate forms from this protein solution. The solution is centrifuged, and the pellet is washed and re-suspended in the buffer containing Tris-HCl. Proteins are resolved by electrophoresis through an SDS 12% polyacrylamide gel.
The DNA molecule encoding the RSP virus protein or polypeptide of the present invention can be incorporated in cells using conventional recombinant DNA technology. Generally, this involves inserting the DNA molecule into an expression system to which the DNA molecule is heterologous (i.e., not normally present). The heterologous DNA molecule is inserted into the expression system or vector in proper sense orientation and correct reading frame. The vector contains the necessary elements for the transcription and translation of the inserted protein-coding sequences.
U.S. Pat. No. 4,237,224 to Cohen and Boyer, which is hereby incorporated by reference, describes the production of expression systems in the form of recombinant plasmids using restriction enzyme cleavage and ligation with DNA ligase. These recombinant plasmids are then introduced by means of transformation and replicated in unicellular cultures including procaryotic organisms and eukaryotic cells grown in tissue culture.
Recombinant genes may also be introduced into viruses, such as vaccinia virus. Recombinant viruses can be generated by transfection of plasmids into cells infected with virus.
Suitable vectors include, but are not limited to, the following viral vectors such as lambda vector system gt11, gt WES.tB, Charon 4, and plasmid vectors such as pBR322, pBR325, pACYC177, pACYC184, pUC8, pUC9, pUC18, pUC19, pLG339, pR290, pKC37, pKCO101, SV 40, pBluescript II SK +/− or KS+/− (see “Stratagene Cloning Systems” Catalog (1993) from Stratagene, La Jolla, Calif., which is hereby incorporated by reference), pQE, pIH821, pGEX, pET series (see Studier et. al., “Use of T7 RNA Polymerase to Direct Expression of Cloned Genes,” Gene Expression Technology, vol. 185 (1990), which is hereby incorporated by reference), and any derivatives thereof. Suitable vectors are continually being developed and identified. Recombinant molecules can be introduced into cells via transformation, transduction, conjugation, mobilization, or electroporation. The DNA sequences are cloned into the vector using standard cloning procedures in the art, as described by Maniatis et al., Molecular Cloning: A Laboratory Manual, Cold Springs Laboratory, Cold Springs Harbor, N.Y. (1982), which is hereby incorporated by reference.
A variety of host-vector systems may be utilized to express the protein-encoding sequence(s). Primarily, the vector system must be compatible with the host cell used. Host-vector systems include but are not limited to the following: bacteria transformed with bacteriophage DNA, plasmid DNA, or cosmid DNA; microorganisms such as yeast containing yeast vectors; mammalian cell systems infected with virus (e.g., vaccinia virus, adenovirus, etc.); insect cell systems infected with virus (e.g., baculovirus); and plant cells infected by bacteria or transformed via particle bombardment (i.e. biolistics). The expression elements of these vectors vary in their strength and specificities. Depending upon the host-vector system utilized, any one of a number of suitable transcription and translation elements can be used.
Different genetic signals and processing events control many levels of gene expression (e.g., DNA transcription and messenger RNA (“mRNA”) translation).
Transcription of DNA is dependent upon the presence of a promoter which is a DNA sequence that directs the binding of RNA polymerase and thereby promotes mRNA synthesis. The DNA sequences of eukaryotic promoters differ from those of procaryotic promoters. Furthermore, eukaryotic promoters and accompanying genetic signals may not be recognized in or may not function in a procaryotic system, and, further, procaryotic promoters are not recognized and do not function in eukaryotic cells.
Similarly, translation of mRNA in procaryotes depends upon the presence of the proper procaryotic signals which differ from those of eukaryotes; Efficient translation of mRNA in procaryotes requires a ribosome binding site called the Shine-Dalgarno (“SD”) sequence on the mRNA. This sequence is a short nucleotide sequence of mRNA that is located before the start codon, usually AUG, which encodes the amino-terminal methionine of the protein. The SD sequences are complementary to the 3′-end of the 16S rRNA (ribosomal RNA) and probably promote binding of mRNA to ribosomes by duplexing with the rRNA to allow correct positioning of the ribosome. For a review on maximizing gene expression, see Roberts and Lauer, Methods in Enzymology, 68:473 (1979), which is hereby incorporated by reference.
Promoters vary in their “strength” (i.e., their ability to promote transcription). For the purposes of expressing a cloned gene, it is desirable to use strong promoters in order to obtain a high level of transcription and, hence, expression of the gene. Depending upon the host cell system utilized, any one of a number of suitable promoters may be used. For instance, when cloning in E. coli, its bacteriophages, or plasmids, promoters such as the T7 phage promoter, lac promoter, trp promoter, recA promoter, ribosomal RNA promoter, the PR and PL promoters of coliphage lambda and others, including but not limited, to lacUV5, ompF, bla, Ipp, and the like, may be used to direct high levels of transcription of adjacent DNA segments. Additionally, a hybrid trp-lacV5 (tac) promoter or other E. coli promoters produced by recombinant DNA or other synthetic DNA techniques may be used to provide for transcription of the inserted gene.
Bacterial host cell strains and expression vectors may be chosen which inhibit the action of the promoter unless specifically induced. In certain operons, the addition of specific inducers is necessary for efficient transcription of the inserted DNA. For example, the lac operon is induced by the addition of lactose or IPTG (isopropylthio-beta-D-galactoside). A variety of other operons, such as trp, pro, etc., are under different controls.
Specific initiation signals are also required for efficient gene transcription and translation in procaryotic cells. These transcription and translation initiation signals may vary in “strength” as measured by the quantity of gene specific messenger RNA and protein synthesized, respectively. The DNA expression vector, which contains a promoter, may also contain any combination of various “strong” transcription and/or translation initiation signals. For instance, efficient translation in E. coli requires a Shine-Dalgarno (“SD”) sequence about 7-9 bases 5′ to the initiation codon (“ATG”) to provide a ribosome binding site. Thus, any SD-ATG combination that can be utilized by host cell ribosomes may be employed. Such combinations include but are not limited to the SD-ATG combination from the cro gene or the N gene of coliphage lambda, or from the E. coli tryptophan E, D, C, B or A genes. Additionally, any SD-ATG combination produced by recombinant DNA or other techniques involving incorporation of synthetic nucleotides may be used.
Once the isolated DNA molecules encoding the various Rupestris stem pitting associated virus proteins or polypeptides, as described above, have been cloned into an expression system, they are ready to be incorporated into a host cell. Such incorporation can be carried out by the various forms of transformation noted above, depending upon the vector/host cell system. Suitable host cells include, but are not limited to, bacteria, virus, yeast, mammalian cells, insect, plant, and the like.
The present invention also relates to RNA molecules which encode the various RSP virus proteins or polypeptides described above. The transcripts can be synthesized using the host cells of the present invention by any of the conventional techniques. The mRNA can be translated either in vitro or in vivo. Cell-free systems typically include wheat-germ or reticulocyte extracts. In vivo translation can be effected, for example, by microinjection into frog oocytes.
One aspect of the present invention involves using one or more of the above DNA molecules encoding the various proteins or polypeptides of a RSP virus to transform grape plants in order to impart RSP resistance to the plants. The mechanism by which resistance is imparted in not known. In one hypothetical mechanism, the transformed plant can express the coat protein or polypeptide, and, when the transformed plant is inoculated by a RSP virus, such as RSPaV-1, the expressed coat protein or polypeptide surrounds the virus, thereby preventing translation of the viral DNA.
In this aspect of the present invention, the subject DNA molecule incorporated in the plant can be constitutively expressed. Alternatively, expression can be regulated by a promoter which is activated by the presence of RSP virus. Suitable promoters for these purposes include those from genes expressed in response to RSP virus infiltration.
The isolated DNA molecules of the present invention can be utilized to impart RSP virus resistance for a wide variety of grapevine plants. The DNA molecules are particularly well suited to imparting resistance to Vitis scion or rootstock cultivars. Scion cultivars which can be protected include those commonly referred to as Table or Raisin Grapes, such as Alden, Almeria, Anab-E-Shahi, Autumn Black, Beauty Seedless, Black Corinth, Black Damascus, Black Malvoisie, Black Prince, Blackrose, Bronx Seedless, Burgrave, Calmeria, Campbell Early, Canner, Cardinal, Catawba, Christmas, Concord, Dattier, Delight, Diamond, Dizmar, Duchess, Early Muscat, Emerald Seedless, Emperor, Exotic, Ferdinand de Lesseps, Fiesta, Flame seedless, Flame Tokay, Gasconade, Gold, Himrod, Hunisa, Hussiene, Isabella, Italia, July Muscat, Khandahar, Katta, Kourgane, Kishmishi, Loose Perlette, Malaga, Monukka, Muscat of Alexandria, Muscat Flame, Muscat Hamburg, New York Muscat, Niabell, Niagara, Olivette blanche, Ontario, Pierce, Queen, Red Malaga, Ribier, Rish Baba, Romulus, Ruby Seedless, Schuyler, Seneca, Suavis (IP 365), Thompson seedless, and Thomuscat. They also include those used in wine production, such as Aleatico, Alicante Bouschet, Aligote, Alvarelhao, Aramon, Baco blanc (22A), Burger, Cabernet franc, Cabernet, Sauvignon, Calzin, Carignane, Charbono, Chardonnay, Chasselas dore, Chenin blanc, Clairette blanche, Early Burgundy, Emerald Riesling, Feher Szagos, Fernao Pires, Flora, French Colombard, Fresia, Furmint, Gamay, Gewurztraminer, Grand noir, Gray Riesling, Green Hungarian, Green Veltliner, Grenache, Grillo, Helena, Inzolia, Lagrein, Lambrusco de Salamino, Malbec, Malvasia bianca, Mataro, Melon, Merlot, Meunier, Mission, Montua de Pilas, Muscadelle du Bordelais, Muscat blanc, Muscat Ottonel, Muscat Saint-Vallier, Nebbiolo, Nebbiolo fino, Nebbiolo Larnpia, Orange Muscat, Palomino, Pedro Ximenes, Petit Bouschet, Petite Sirah, Peverella, Pinot noir, Pinot Saint-George, Primitivo di Gioa, Red Veltliner, Refosco, Rkatsiteli, Royalty, Rubired, Ruby abernet, Saint-Emilion, Saint Macaire, Salvador, Sangiovese, Sauvignon blanc, Sauvignon gris, Sauvignon vert, Scarlet, Seibel 5279, Seibel 9110, Seibel 13053, Semillon, Servant, Shiraz, Souzao, Sultana Crimson, Sylvaner, Tannat, Teroldico, Tinta Madeira, Tinto cao, Touriga, Traminer, Trebbiano Toscano, Trousseau, Valdepenas, Viognier, Walschriesling, White Riesling, and Zinfandel. Rootstock cultivars which can be protected include Couderc 1202, Couderc 1613, Couderc 1616, Couderc 3309, Dog Ridge, Foex 33 EM, Freedom, Ganzin 1 (A×R #1), Harmony, Kober 5BB, LN33, Millardet & de Grasset 41B, Millardet & de Grasset 420A, Millardet & de Grasset 101-14, Oppenheim 4 (SO4), Paulsen 775, Paulsen 1045, Paulsen 1103, Richter 99, Richter 110, Riparia Gloire, Ruggeri 225, Saint-George, Salt Creek, Teleki 5A, Vitis rupestris Constantia, Vitis California, and Vitis girdiana.
Plant tissue suitable for transformation include leaf tissue, root tissue, meristems, zygotic and somatic embryos, and anthers. It is particularly preferred to utilize embryos obtained from anther cultures.
The expression system of the present invention can be used to transform virtually any plant tissue under suitable conditions. Tissue cells transformed in accordance with the present invention can be grown in vitro in a suitable medium to impart RSPaV resistance. Transformed cells can be regenerated into whole plants such that the protein or polypeptide imparts resistance to RSPaV in the intact transgenic plants. In either case, the plant cells transformed with the recombinant DNA expression system of the present invention are grown and caused to express that DNA molecule to produce one of the above-described RSPaV proteins or polypeptides and, thus, to impart RSPaV resistance.
In producing transgenic plants, the DNA construct in a vector described above can be microinjected directly into plant cells by use of micropipettes to transfer mechanically the recombinant DNA. Crossway, Mol. Gen. Genetics, 202:179-85 (1985), which is hereby incorporated by reference. The genetic material may also be transferred into the plant cell using polyethylene glycol. Krens, et al., Nature, 296:72-74 (1982), which is hereby incorporated by reference.
One technique of transforming plants with the DNA molecules in accordance with the present invention is by contacting the tissue of such plants with an inoculum of a bacteria transformed with a vector comprising a gene in accordance with the present invention which imparts RSPaV resistance. Generally, this procedure involves inoculating the plant tissue with a suspension of bacteria and incubating the tissue for 48 to 72 hours on regeneration medium without antibiotics at 25-28° C.
Bacteria from the genus Agrobacterium can be utilized to transform plant cells. Suitable species of such bacterium include Agrobacterium tumefaciens and Agrobacterium rhizogenes. Agrobacterium tumefaciens (e.g., strains C58, LBA4404, or EHA105) is particularly useful due to its well-known ability to transform plants.
Heterologous genetic sequences can be introduced into appropriate plant cells, by means of the Ti plasmid of A. tumefaciens or the R1 plasmid of A. rhizogenes. The Ti or R1 plasmid is transmitted to plant cells on infection by Agrobacterium and is stably integrated into the plant genome. J. Schell, Science, 237:1176-83 (1987), which is hereby incorporated by reference.
After transformation, the transformed plant cells must be regenerated.
Plant regeneration from cultured protoplasts is described in Evans et al., Handbook of Plant Cell Cultures, Vol. 1: (MacMillan Publishing Co., New York, 1983); and Vasil I. R. (ed.), Cell Culture and Somatic Cell Genetics of Plants, Acad. Press, Orlando, Vol. I, 1984, and Vol. III (1986), which are hereby incorporated by reference.
It is known that practically all plants can be regenerated from cultured cells or tissues, including but not limited to, all major species of sugarcane, sugar beets, cotton, fruit trees, and legumes.
Means for regeneration vary from species to species of plants, but generally a suspension of transformed protoplasts or a petri plate containing explants is first provided. Callus tissue is formed and shoots may be induced from callus and subsequently rooted. Alternatively, embryo formation can be induced in the callus tissue. These embryos germinate as natural embryos to form plants. The culture media will generally contain various amino acids and hormones, such as auxin and cytokinins. It is also advantageous to add glutamic acid and proline to the medium. Efficient regeneration will depend on the medium, on the genotype, and on the history of the culture. If these three variables are controlled, then regeneration is usually reproducible and repeatable.
After the expression cassette is stably incorporated in transgenic plants, it can be transferred to other plants by sexual crossing. Any of a number of standard breeding techniques can be used, depending upon the species to be crossed.
Once transgenic plants of this type are produced, the plants themselves can be cultivated in accordance with conventional procedure so that the DNA construct is present in the resulting plants. Alternatively, transgenic seeds are recovered from the transgenic plants. These seeds can then be planted in the soil and cultivated using conventional procedures to produce transgenic plants.
Another approach to transforming plant cells with a gene which imparts resistance to pathogens is particle bombardment (also known as biolistic transformation) of the host cell. This can be accomplished in one of several ways. The first involves propelling inert or biologically active particles at cells. This technique is disclosed in U.S. Pat. Nos. 4,945,050, 5,036,006, and 5,100,792, all to Sanford et al., and in Emerschad et al., “Somatic Embryogenesis and Plant Development from Immature Zygotic Embryos of Seedless Grapes (Vitis vinifera),” Plant Cell Reports, 14:6-12 (1995) (“Emerschad (1995)”), which are hereby incorporated by reference. Generally, this procedure involves propelling inert or biologically active particles at the cells under conditions effective to penetrate the outer surface of the cell and to be incorporated within the interior thereof. When inert particles are utilized, the vector can be introduced into the cell by coating the particles with the vector containing the heterologous DNA. Alternatively, the target cell can be surrounded by the vector so that the vector is carried into the cell by the wake of the particle. Biologically active particles (e.g., dried bacterial cells containing the vector and heterologous DNA) can also be propelled into plant cells.
Once a grape plant tissue is transformed in accordance with the present invention, it is regenerated to form a transgenic grape plant. Generally, regeneration is accomplished by culturing transformed tissue on medium containing the appropriate growth regulators and nutrients to allow for the initiation of shoot meristems. Appropriate antibiotics are added to the regeneration medium to inhibit the growth of Agrobacterium and to select for the development of transformed cells. Following shoot initiation, shoots are allowed to develop tissue culture and are screened for marker gene activity.
The DNA molecules of the present invention can be made capable of transcription to a messenger RNA that does not translate to the protein. This is known as RNA-mediated resistance. When a Vitis scion or rootstock cultivar is transformed with such a DNA molecule, the DNA molecule can be transcribed under conditions effective to maintain the messenger RNA in the plant cell at low level density readings. Density readings of between 15 and 50 using a Hewlet ScanJet and Image Analysis Program are preferred.
A portion of one or more DNA molecules of the present invention as well as other DNA molecules can be used in a transgenic grape plant in accordance with U.S. patent application Ser. No. 09/025,635, which is hereby incorporated herein by reference.
The RSPaV protein or polypeptide can also be used to raise antibodies or binding portions thereof or probes. The antibodies can be monoclonal or polyclonal.
Monoclonal antibody production may be effected by techniques which are well-known in the art. Basically, the process involves first obtaining immune cells (lymphocytes) from the spleen of a manunal (e.g., mouse) which has been previously immunized with the antigen of interest either in vivo or in vitro. The antibody-secreting lymphocytes are then fused with (mouse) myeloma cells or transformed cells, which are capable of replicating indefinitely in cell culture, thereby producing an immortal, immunoglobulin-secreting cell line. The resulting fused cells, or hybridomas, are cultured, and the resulting colonies screened for the production of the desired monoclonal antibodies. Colonies producing such antibodies are cloned, and grown either in vivo or in vitro to produce large quantities of antibody. A description of the theoretical basis and practical methodology of fusing such cells is set forth in Kohler and Milstein, Nature, 256:495 (1975), which is hereby incorporated by reference.
Mammalian lymphocytes are immunized by in vivo immunization of the animal (e.g., a mouse) with the protein or polypeptide of the present invention. Such immunizations are repeated as necessary at intervals of up to several weeks to obtain a sufficient titer of antibodies. Following the last antigen boost, the animals are sacrificed and spleen cells removed.
Fusion with mammalian myeloma cells or other fusion partners capable of replicating indefinitely in cell culture is effected by standard and well-known techniques, for example, by using polyethylene glycol (“PEG”) or other fusing agents. (See Milstein and Kohler, Eur. J. Immunol., 6:511 (1976), which is hereby incorporated by reference.) This immortal cell line, which is preferably murine, but may also be derived from cells of other mammalian species, including but not limited to rats and humans, is selected to be deficient in enzymes necessary for the utilization of certain nutrients, to be capable of rapid growth, and to have good fusion capability. Many such cell lines are known to those skilled in the art, and others are regularly described.
Procedures for raising polyclonal antibodies are also well known. Typically, such antibodies can be raised by administering the protein or polypeptide of the present invention subcutaneously to New Zealand white rabbits which have first been bled to obtain pre-immune serum. The antigens can be injected at a total volume of 100 μl per site at six different sites. Each injected material will contain synthetic surfactant adjuvant pluronic polyols, or pulverized acrylamide gel containing the protein or polypeptide after SDS-polyacrylamide gel electrophoresis. The rabbits are then bled two weeks after the first injection and periodically boosted with the same antigen three times every six weeks. A sample of serum is then collected 10 days after each boost. Polyclonal antibodies are then recovered from the serum by affinity chromatography using the corresponding antigen to capture the antibody. Ultimately, the rabbits are euthanized with pentobarbital 150 mg/Kg IV. This and other procedures for raising polyclonal antibodies are disclosed in Harlow et. al., editors, Antibodies: A Laboratory Manual (1988), which is hereby incorporated by reference.
In addition to utilizing whole antibodies, binding portions of such antibodies can be used. Such binding portions include Fab fragments, F(ab′)2 fragments, and Fv fragments. These antibody fragments can be made by conventional procedures, such as proteolytic fragmentation procedures, as described in Goding, Monoclonal Antibodies: Principles and Practice, New York: Academic Press, pp. 98-118 (1983), which is hereby incorporated by reference.
The present invention also relates to probes found either in nature or prepared synthetically by recombinant DNA procedures or other biological procedures. Suitable probes are molecules that bind to RSP viral antigens identified by the polyclonal antibodies of the present invention or bind to the nucleic acid of RSPaV. Such probes can be, for example, proteins, peptides, lectins, or nucleic acids.
The antibodies or binding portions thereof or probes can be administered to RSPaV infected scion cultivars or rootstock cultivars. Alternatively, at least the binding portions of these antibodies can be sequenced, and the encoding DNA synthesized. The encoding DNA molecule can be used to transform plants together with a promoter which causes expression of the encoded antibody when the plant is infected by an RSPaV. In either case, the antibody or binding portion thereof or probe will bind to the virus and help prevent the usual stem pitting response.
Antibodies raised against the proteins or polypeptides of the present invention or binding portions of these antibodies can be utilized in a method for detection of RSPaV in a sample of tissue, such as tissue from a grape scion or rootstock. Antibodies or binding portions thereof suitable for use in the detection method include those raised against a replicase, proteins or polypeptides of the triple gene block, or a coat protein or polypeptide in accordance with the present invention. Any reaction of the sample with the antibody is detected using an assay system which indicates the presence of RSPaV in the sample. A variety of assay systems can be employed, such as enzyme-linked immunosorbent assays, radioimmunoassays, gel diffusion precipitin reaction assays, immunodiffusion assays, agglutination assays, fluorescent immunoassays, protein A immunoassays, or immunoelectrophoresis assays.
Alternatively, the RSPaV can be detected in such a sample using the DNA molecules of the present, RNA molecules of the present invention, or DNA or RNA fragments thereof, as probes in nucleic acid hybridization assays for detecting the presence of complementary virus DNA or RNA in the various tissue samples described above. The nucleotide sequence is provided as a probe in a nucleic acid hybridization assay or a gene amplification detection procedure (e.g., using a polymerase chain reaction procedure). The nucleic acid probes of the present invention may be used in any nucleic acid hybridization assay system known in the art, including, but not limited to, Southern blots (Southern, E. M., “Detection of Specific Sequences Among DNA Fragments Separated by Gel Electrophoresis,” J. Mol. Biol. 98:503-17 (1975), which is hereby incorporated by reference), Northern blots (Thomas, P. S., “Hybridization of Denatured RNA and Small DNA Fragrnents Transferred to Nitrocellulose,” Proc. Nat'l Acad. Sci. USA, 77:5201-05 (1980), which is hereby incorporated by reference), and Colony blots (Grunstein, M., et al., “Colony Hybridization: A Method for the Isolation of Cloned cDNAs that Contain a Specific Gene,” Proc. Nat'l Acad. Sci. USA, 72:3961-65 (1975), which is hereby incorporated by reference). Alternatively, the isolated DNA molecules of the present invention or RNA transcripts thereof can be used in a gene amplification detection procedure (e.g., a polymerase chain reaction). Erlich, H. A., et. al., “Recent Advances in the Polymerase Chain Reaction,” Science 252:1643-51 (1991), which is hereby incorporated by reference. Any reaction with the probe is detected so that the presence of RSP virus in the sample is indicated. Such detection is facilitated by providing the DNA molecule of the present invention with a label. Suitable labels include a radioactive compound, a fluorescent compound, a chemiluminescent compound, an enzymatic compound, or other equivalent nucleic acid labels.
Depending upon the desired scope of detection, it is possible to utilize probes having nucleotide sequences that correspond with conserved or variable regions of the ORF or UTR. For example, to distinguish RSPaV from other related viruses (as described herein), it is desirable to use probes which contain nucleotide sequences that correspond to sequences more highly conserved among all RSPaV strains. Also, to distinguish between different RSPaV strains (e.g., RSPaV-1, RSP47-4, RSP158), it is desirable to utilize probes containing nucleotide sequences that correspond to sequences less highly conserved among the RSP virus strains.
Nucleic acid (DNA or RNA) probes of the present invention will hybridize to complementary RSPaV-1 nucleic acid under stringent conditions. Less stringent conditions may also be selected. Generally, stringent conditions are selected to be about 50° C. lower than the thermal melting point (Tm) for the specific sequence at a defined ionic strength and pH. The Tm is the temperature (under defined ionic strength and pH) at which 50% of the target sequence hybridizes to a perfectly matched probe. The Tm is dependent upon the solution conditions and the base composition of the probe, and may be calculated using the following equation:
Tm=79.8° C.+(18.5×Log[Na+])+
+(58.4° C.×%[G+C])
−(820/#bp in duplex)
−(0.5×% formamide)
Nonspecific binding may also be controlled using any one of a number of known techniques such as, for example, blocking the membrane with protein-containing solutions, addition of heterologous RNA, DNA, and SDS to the hybridization buffer, and treatment with RNase. Generally, suitable stringent conditions for nucleic acid hybridization assays or gene amplification detection procedures are as set forth above. More or less stringent conditions may also be selected.
The development of a rapid detection method for RSP is a major breakthrough, because the only detection method now available is through inoculation of St. George grape indicators, which takes two to three years to develop symptoms. A serological or nucleic acid based detection tests developed for RSP will take only 1 to 2 days and it is less expensive. The woody indicator test on St. George costs $250 per sample, while a serological or nucleic acid based test would cost $30-50 per sample. Moreover, the rapid tests will speed up the introduction of grape imports into the US from the current three years to about six months. These applications will be valuable wherever grapes are grown. Since RSP is part of the rugose wood complex, development of rapid detection methods will be invaluable in determining the significance of RSP in the rugose wood complex. This will allow an investigator to determine whether RSP alone can cause the rugose wood complex or if other components are needed. In addition, these rapid detection methods are very useful to evaluate the resistance of transgenic plants to Rupestris stem pitting associated virus.
The following examples are provided to illustrate embodiments of the present invention but are by no means intended to limit its scope.
Samples from 15 accessions that induced pitting on graft-inoculated St. George were collected from the National Grapevine Germplasm Repository of the USDA Plant Genetic Resources Unit (PGRU) at Geneva and used for dsRNA analysis. Positive controls used included Thompson Seedless (RSP105) (Golino, “The Davis Grapevine Virus Collection,” Am. J. Enology Viticulture, 43:200-05 (1992), which is hereby incorporated by reference) from the FPMS, University of California (Davis) and Pinot Noir (SVP1186-09A2), which was kindly provided by Dr. R. Johnson of Center for Plant Health, Agriculture Canada, Sidney, British Columbia. Negative controls as judged by indexing on St. George included Freedom from the PGRU at Geneva, N.Y., and Verduzzo 233A. The latter was kindly provided by Dr. P. Silvano of the Sezione di Fitovirologia, ERSA Servizio Chimico-Agrario e della Certificazione, Pozzuolo del Friuh (UD), Italy.
Dormant cuttings of 138 grapevine selections were collected from USA, Canada, Italy, and Portugal over three years. Samples included Vitis vinifera cultivars, hybrids, V. riparia, and rootstocks. 117 grapevine selections were indexed on St. George for RSP and other RW diseases. Pinot noir (1186-9A2) from Agriculture Canada, Center for Plant Health (Sidney, Canada) and Thompson seedless (RSP105) from University of California (Davis) were included as positive controls. Sauvignon blanc, generated from shoot tip tissue culture and tested free of viruses and viroids was provided by Dr. J. Semancik (University of California at Riverside) and used as a healthy control. In addition, six seedlings of five Vitis species were also included as negative controls.
Methods for isolating dsRNA were described by Hu et al., “Characterization of Closterovirus-like Particles Associated with Grapevine Leafroll Disease,” J. Phytopathology, 128:1-14 (1990), which is hereby incorporated by reference, except that 1×STE with 15% ethanol (instead of 16.5%) was used to wash CF-11 cellulose columns prior to elution of dsRNAs. The dsRNAs were isolated from leaves, petioles, and the phloem tissue of dormant canes, electrophoresed on 1% agarose or low melting temperature agarose gels, and analyzed by staining with ethidium bromide (EtBr). Hind EII digested lambda DNA was used as markers to estimate the sizes of the dsRNA molecules.
The extremely low yield of dsRNA and the limited quantity of RSP-infected grape materials precluded the use of a single RSP-infected grapevine accession as the source of dsRNA for cloning purpose. Therefore, dsRNA preparations from Colobel 257, Ravat 34, Couderc 28-112, and Seyval were pooled and used as templates for cDNA synthesis. In order to get pure templates for cloning, dsRNA bands were excised from low melting temperature agarose gels after electrophoresis and recovered by extraction with phenol and chloroform (Sambrook et al., Molecular Cloning: A LaboratorEy Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989), which is hereby incorporated by reference). The same recovery procedure was repeated once more. The purified dsRNA was denatured with 20 mM methyl mercuric hydroxide and cDNAs were synthesized using slightly modified methods of Jelkmann et al., “Cloning of Four Viruses from Small Quantities of Double-Stranded RNA,” Phytopathology, 79:1250-53 (1989), which is incorporated herein be reference. The cDNA fragments were first blunt-ended with T4 DNA polymerase at 12° C. T4 DNA ligase was used to add EcoR I adapters to both ends of the cDNAs. Subsequently, the cDNA molecules with cohesive ends were ligated to EcoR I-prepared arms of lambda ZAP II. Finally, the resulting recombinant phages were packed into Gigapack II packaging extract following manufacturer's instructions (Stratagene, La Jolla, Calif.).
Plaque hybridization was used to screen cDNA clones by transferring recombinant cDNA plaques to nylon membranes and hybridizing to 32P-labeled first-strand cDNA probes generated from the dsRNA according to manufacturer's recommendations (Du Pont, 1987). Clones with strong hybridization signals were converted into pBluescript SK through in vivo excision (Stratagene, 1991). After digestion of the resulting plasmids with EcoR I, 20 clones were selected and further analyzed in Southern hybridization with radio labeled first strand cDNA probes synthesized from the dsRNA. The specificity of two selected clones to the dsRNA was confirmed by Northern analysis using 32P labeled inserts of the two clones.
To bridge the gap between clones RSP3 and RSP94, a pair of specific primers were used in RT-PCR to generate cDNA fragments from the dsRNA. RSP3-RSP94 primer 1 (sense, nt 3629-3648) has a nucleotide sequence corresponding to SEQ. ID. No. 41 as follows:
RSP3-RSP94 primer 2 (antisense, nt 4350-4366) has a nucleotide sequence corresponding to SEQ. ID. No. 42 as follows:
After gel electrophoresis, PCR amplified cDNA bands were excised from gels and recovered with the phenol/chloroform method (Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989), which is hereby incorporated by reference).
The same strategy was employed to bridge the gap between clones RSP94 and RSP95. RSP94—RSP95 primer 1 (sense, nt 5272-5291) has a nucleotide sequence corresponding to SEQ. ID. No. 43 as follows:
RSP94-RSP95 primer 2 (antisense, nt 6791-6808) has a nucleotide sequence corresponding to SEQ. ID. No. 44 as follows:
To obtain the terminal 3′ end sequences, a primer (sense, nt 8193-8210) having a nucleotide sequence corresponding to SEQ. ID. No. 45 as follows:
and a (dT) 18 primer were used in RT-PCR to amplify cDNA from the dsRNA. Resulting PCR products were cloned into TA vector pCRII (Invitrogen) and sequenced. This approach was based on the assumption that the RSP associated dsRNA contained a poly (A) tail. For the terminal 5′ end, the dsRNA was first tagged with poly (A) using yeast Poly (A) polymerase (USB) (Pappu et al., “Nucleotide Sequence and Organization of Eight 3′ Open Reading Frames of the Citrus tristeza Closterovirus Genome,” Virology 199:35-46 (1994), which is hereby incorporated by reference) and then used as templates to generate cDNA fragments by RT-PCR using (dT) 18 primer and primer (antisense, nt 429-449) having a nucleotide sequence corresponding to SEQ. ID. NO. 46 as follows:
CsCl or alkaline/PEG (polyethylene glycol) purified plasmids (Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989), which is hereby incorporated by reference; Applied Biosystems, Inc.) and RT-PCR amplified cDNA fragments were sequenced for completion on both strands. Nucleotide sequencing was done manually with Sequenase version 2.0 kit (USB) or automatically on ABI 373 automated sequencer with Taq DyeDeoxy™ terminator cycle sequencing kit (Applied Biosystems, Inc.). Vector primers (T3, T7, M13 Forward, and M13 Reverse) were used in initial sequencing and sequences were completed by primer walking strategy.
Two pairs of primers were designed for RT-PCR: (1) RSP95F1 and RSP95R1; and (2) RSP149F1 and RSP149R1. Primer RSP95F1, an antisense strand primer, has a nucleotide sequence corresponding to SEQ. ID. NO. 47 as follows:
Primer RSP95R1, a sense strand primer, has a nucleotide sequence corresponding to SEQ. ID. No. 48 as follows:
Primer RSP149F1, an antisense strand primer, has a nucleotide sequence corresponding to SEQ. ID. No. 49 as follows:
Primer RSP149R1, a sense strand primer, has a nucleotide sequence corresponding to SEQ. ID. No. 50 as follows:
RSP95F1/R1 were used in RT-PCR to test samples collected in 1994. RSP149R1/F1, alone or together with RSP95F1I/R1, were used to test samples collected in 1995 and 1996. To avoid bias in the judgment of RT-PCR results, blind tests were conducted for samples from Canada in 1995 and 1996. The indexing results of these samples were kept untold until the RT-PCR tests were complete.
dsRNAs were denatured with methylmercuric hydroxide (CH4HgOH) and reverse transcribed into cDNAs with Moloney murine leukemia virus (MMLV) or Avian Myeloblastosis Virus (AMV) reverse transcriptases (Promega) at 42° C. for 1 to 3 h. Five of 20 μl of the RT reactions were added to PCR mix and amplified in thermal cycler (HYBAID OmniGene, National Labnet Company) with Taq DNA polymerase (buffer B, Promega) using the following parameters: initial denaturation at 94° C. for 5 min, 40 cycles of amplification at 94° C. for 45 s, 52° C. for 1 min, and 72° C. for 1 min, and a final extension at 72° C. for 10 min. PCR products were analyzed by electrophoresis on 1% agarose gels containing ethidium bromide. Hae III digested Phix 174 fragments were used as molecular weight markers.
DNA fragments amplified by PCR from cDNA clone RSP149 with primers RSP149F1/R1 were labeled with 32P by random priming and used as probes. Products of RT-PCR of randomly selected grapevines including 26 positives and 6 negatives by RT-PCR were electrophoresed on an 0.8% agarose gel, transferred to nylon membranes, and hybridized to the probes following manufacturer's instructions (Du Pont).
Sequences were assembled with SeqMan program and potential open reading frames were generated with MapDraw program (DNASTAR, Madison, Wis.). BLAST program of the NCBI (the National Center for Biotechnology Information) was used to search for homologies in DNA and protein databases. Clustal analysis (with identity weight table) of MegAlign (DNASTAR) was employed to reveal sequence similarities between the putative proteins of RSPaV-1 and the analogous proteins of ASPV (Jelkmann, “Nucleotide Sequences of Apple Stem Pitting Virus and of the Coat Protein of a Similar Virus from Pear Associated with Vein Yellows Disease and Their Relationship with Potex- and Carlaviruses,” J. General Virology, 75:1535-42 (1994), which is hereby incorporated by reference) and PVM (Zavriev et al., “Complete Nucleotide Sequence of Genomic RNA of the Potato M-Virus,” Molecular Biology (Mosk.) 25:761-69 (1991), which is hereby incorporated by reference). In addition, nucleotide sequences of the untranslated regions (UTR) of these three viruses were also compared using MagAlign, as shown in
The 15 grapevine accessions used in this study were previously indexed on St. George where 12 accessions induced typical RSP symptoms (i.e., a narrow strip of small pits below the inoculum bud).
George, did not reveal visible dsRNA. Although two dsRNA bands were observed in Verduzzo 233A (which was indexed free of RSP on St. George), they were not specific to RSP based on the fact that they were larger or smaller than the 8.7 kb dsRNA associated with RSP (
Symbols:
*Probe used was insert from cDNA clone RSP149.
†A faint dsRNA band could be observed on the gel after electrophoresis but no hybridization signal could be seen in Northern analysis.
‡Although two dsRNA bands were observed in Verduzzo 233A, they were not specific to RSP, because they were either larger or smaller than the RSP-associated 8.7 kbp dsRNA and they did not hybridize to the probe in Northern analysis.
The yield of dsRNA was low and varied significantly among different accessions. When a comparable amount of phloem tissue (14 g for Bertille Seyve 5563 and Couderc 28-112; 18.5 g for the others) was used to isolate dsRNA, Colobel 257, Seyval, Ravat 34, Grande Glabre, and Seyve Villard 14-287 displayed strong dsRNA bands, while Bertille Seyve 5563, Couderc 28-112, Joffre, and Verdelet showed weak bands after staining with EtBr, as shown in
A total of 182 clones were selected after plaque hybridization. Eighty clones with strong hybridization signals were subcloned into pBluescript SK through in vivo excision. Resulting plasmids were shown to have inserts ranging from 0.3 to 3.0 kb. A total of 20 clones with inserts of ca. 0.8 kb or larger were selected. Southern analysis of these 20 clones to radio labeled first strand cDNA probes derived from the dsRNA resulted in 15 clones with strong hybridization signals. Several of these clones were used to determine the genome sequence of the dsRNA: RSP3, RSP28, RSP94, RSP140, RSP95, and TA5. Another clone (RSP149), which was 97% similar in nucleotide sequence to RSP95, was used as one of the two probes in Northern hybridization.
Northern hybridization was employed to confirm the specific relationship of clones RSP95 and RSP149 to the isolated dsRNA. These two clones gave the strongest reaction in Southern analysis described above. Initial experiments showed that RSP95 insert hybridized with the dsRNA isolated from three accessions (Colobel 257, Seyval, and Ravat 34), from which the template dsRNAs used in cDNA synthesis were isolated. As shown in
Six cDNA clones and three RT-PCR amplified cDNA fragments (identified as RSPA, RSPB, and RSPC) were sequenced on both strands and used to obtain the complete nucleotide sequence of a viral agent, which is shown in
MapDraw analysis, shown at
The arrangement of the ORFs and the amino acid sequences of RSPaV-1 showed similarities to those of PVX (Skryabin et al., “The Nucleotide Sequence of Potato Virus X RNA,” Nucleic Acids Res. 16: 10929-30 (1988), which is hereby incorporated by reference), PVM (Zavriev et al., “Complete Nucleotide Sequence of Genomic RNA of the Potato M-Virus,” Molecular Biology (Mosk.) 25:761-69 (1991), which is hereby incorporated by reference), and ASPV (Jelkmann, “Nucleotide Sequences of Apple Stem Pitting Virus and of the Coat Protein of a Similar Virus from Pear Associated with Vein Yellows Disease and Their Relationship with Potex- and Carlaviruses,” J. General Virology 75:1535-42 (1994), which is hereby incorporated by reference), with the latter two being the most similar to RSPaV-1. A representation of the sequence comparison is shown in
When the total amino acid sequence of RSPaV-1 ORF 1 was used for comparison, it showed 39.6% and 37.6% identities with the replicases of ASPV and PVM respectively (Table 2). These homologies were mainly found in regions I (aa 1 to 372) and II (aa 1354-2161), which are at the N and C terminal portions of the putative replicase, respectively, shown at
The triple gene block is a common feature of several groups of plant viruses including carlaviruses, potexviruses, and ASPV. Comparison of RSPaV-1 ORF2 with those of PVM and ASPV showed evenly distributed homologies in amino acid sequence: 38.0% identity to ASPV and 34.8% to PVM (Table 2). The N terminal region of the 24.4K protein (ORF2) contained the consensus sequence “GXGKS S/T” (aa 31 to 36) (
A sequence similarity search in a DNA database revealed identities between the putative protein encoded for by RSPaV-1 ORF5 to the coat proteins (CPs) of several groups of plant viruses, indicating that RSPaV-1 ORF5 may code for the coat protein. MegAlign analysis revealed that RSPaV-1 ORF5 had 31.3% and 21.2% identities with the CPs of ASPV and PVM, respectively (Table 2). Most of the identities were found in the C terminal portion of the coat proteins (aa 142 to 245 for RSPaV-1), while the N terminal portions were quite variable in the numbers and sequences of amino acid residues. When the C terminal portion of RSPaV-1 CP was compared to the corresponding regions of ASPV and PVM, it showed 49.5% and 33.3% identities with ASPV and PVM, respectively (Table 2). In addition, the “RR/QX-XFDF” motif was found in the central region of RSPaV-1 CP (
MegAlign analysis, shown in
It has been have shown that an 8.7 kbp dsRNA is consistently associated with grapevines that indexed positively on St. George for RSP. Sequence analyses of the dsRNA provide evidence that a virus is involved in RSP, which has now been named RSPaV-1. The complete nucleotide sequence of RSPaV-1 was determined from overlapping cDNA clones and RT-PCR-amplified cDNA fragments generated from the dsRNA. The RSPaV-1 genome has five ORFs coding for the putative replicase (ORF1), the triple gene block (ORF24), and the CP(ORF5). The existence of these ORFs and their potential to code for structural and non-structural viral proteins were further supported by the identification of conserved motifs which are the signatures of various viral proteins.
This work confirms and extends the findings of Walter and Cameron (“Double-stranded RNA Isolated from Grapevines Affected by Rupestris Stem Pitting Disease,” Am. J. Enology and Viticulture 42:175-79 (1991), which is hereby incorporated by reference), and Azzam and Gonsalves (“Detection of dsRNA in Grapevines Showing Symptoms of Rupestris Stem Pitting Disease and the Variabilities Encountered,” Plant Disease 75:960-64 (1991), which is hereby incorporated by reference), who observed a major dsRNA species of about 8.0-8.3 kbp in RSP-infected grapevines. In addition, such work also observed a smaller dsRNA of ca. 6.6 kbp. A dsRNA of similar size was also observed here, but it was consistently detected in only Colobel 257 and Seyval. The relationship, if any, of this smaller dsRNA to RSP remains to be determined. The small dsRNA of ca. 0.359 kbp, which Monette et al. (“Double-stranded RNA from Rupestris Stem Pitting-Affected Grapevines,” Vitis 28:13744 (1989), which is hereby incorporated by reference) isolated from RSP-infected grapevines growing in tissue culture, was not observed.
Electron microscopy evidence also suggests that RSP is caused by filamentous virus(es). Tzeng et al. (“Anatomical and Tissue Culture Studies of Rupestris Stem Pitting-Affected Grapevines,” Botan. Bulletin of Acad. Sinica (Taipei) 34:73-82 (1993), which is hereby incorporated by reference) observed flexuous filamentous virus aggregates in the phloem parenchyma cells of young shoots of Sylvner grapevines that had indexed positively for RSP. Monette and Godkin (“Detection of Capillovirus-like Particles in a Grapevine Affected with Rugose Wood,” Vitis 34:24142 (1995), which is hereby incorporated by reference) observed a filamentous virus in Sauvignon blanc infected by RSP and LNSG. The relationship of these virus particles to RSP disease remains to be studied.
Evidence suggests that the cDNA library generated from the isolated dsRNA templates is not homogeneous for only RSPaV-1. During the process of sequencing cDNA clones, several clones (e.g., RSP474 and RSP158) were identified with high, but not identical, sequence similarities to RSPaV-1.
RSPaV-1 has the most similarities to ASPV, which has not yet been grouped into a virus genus. Both viruses have the same genome organization and their ORFs code for putative proteins of similar sizes, except that the coat protein of ASPV is significantly larger (44 kDa) than that of RSPaV-1 (28 kDa). Comparisons of RSPaV-1 with PVM carlavirus show some similarities in genome organization except that RSPaV-1 lacks ORF6 which is located at the 3′ end of PVM genome. Although the genome organization of RSPaV-1 is similar to PVX potexvirus, the latter has a much smaller putative replicase. RSPaV-1 has no relation to grape viruses whose genomes have been sequenced so far. The closest possibilities, GVA (Minafra et al., “Grapevine virus A: Nucleotide Sequence, Genome Organization, and Relationship in the Trichovirus Genus,” Arch. Virology 142:417-23 (1997), which is hereby incorporated by reference) and GVB (Saldarelli et al., “The Nucleotide Sequence and Genomic Organization of Grapevine Virus B,” J. General Virology 77:2645-52 (1996), which is hereby incorporated by reference), have different genome structures than RSPaV-1.
Among the 138 grapevine entries collected, 25 indexed negatively and 93 indexed positively for RSP on St. George, while the others were not indexed (see Tables 3-7 below). Symptoms induced by RSP on the woody cylinder of St. George after graft inoculation with chip-buds can be divided into two types. The first type is called “specific”, that is, pits and/or grooves being restricted to the area on the woody cylinder below the inoculation sites. The other is called “nonspecific”, that is, pits and/or grooves being present above, around, and below the inoculation sites.
Symbols:
V., Vitis vinefera;
R., Vitis riparia;
H., hybrid;
C., Canada;
I., Italy;
U., USA;
P., Portugal;
a, tested by RSP149F1/R1 and 95F1/R1 and results agree to each other;
b, tested by 95F1/R1 only
Symbols:
V., Vitis vinefera;
R., Vitis riparia;
H., hybrid;
C., Canada;
I., Italy;
U., USA;
P., Portugal;
a, tested by RSP149F1/R1 and 95F1/R1 and results agree to each other;
b, tested by 95F1/R1 only
Symbols:
V., Vitis vinefera;
R., Vitis riparia;
H., hybrid;
C., Canada;
I., Italy;
U., USA;
P., Portugal;
a, tested by RSP149F1/R1 and 95F1/R1 and results agree to each other;
b, tested by 95F1/R1 only.
Symbols:
V., Vitis vinefera;
R., Vitis riparia;
H., hybrid;
NI, not indexed;
C., Canada;
I., Italy;
U., USA;
P., Portugal;
a, tested by RSP149F1/R1 and 95F1/R1 and results agree to each other;
b, tested by 95F1/R1 only
V. acerifolia
V. acerifolia
V. cinerea
V. monticola
V. riparia
V. sp. yenshanesis
Symbols:
V., Vitis vinefera;
R., Vitis riparia;
H., hybrid;
NI, not indexed;
C., Canada;
I., Italy;
U., USA;
P., Portugal;
a, tested by RSP149F1/R1 and 95F1/R1 and results agree to each other;
b, tested by 95F1/R1 only
Among the 93 RSP-infected grapevines, 79 (85%) produced cDNA fragments of expected sizes in repeated RT-PCR using RSP149F1/R1 primers (SEQ. ID. Nos. 49 and 50) and/or RSP95F1/R1 primers (SEQ. ID. Nos. 47 and 48), while the other 14 were negative (see Tables 5 and 6). Interestingly, 12 of 14 (85.7%) grapevine accessions which were not indexed for RSP also produced cDNA fragments of expected size in RT-PCR (see Table 6). Sauvignon blanc healthy control) was negative in repeated RT-PCR (see Table 3).
Results of RT-PCR for grapevines indexed negatively for RSP were surprising (see Tables 3 and 4). While 11 were negative in RT-PCR tests (excluding Sauvignon blanc healthy control), the other 13 produced cDNA fragments of expected sizes.
Since RSPaV-1 was detected not only from grapevines which indexed positively for RSP but also from some of the grapevines indexed negatively for RSP, a search for more healthy materials for RT-PCR tests became necessary. As the majority of plant viruses do not pass on through seeds, grapevine seedlings are probably free of RSPaV-1. Based on this assumption, six seedlings from five Vitis species were included in RT-PCR (see Table 7). None of them produce cDNA of expected size in RT-PCR using RSP149R1/F1 primers (SEQ. ID. Nos. 49 and 50).
The data described above (and shown in Tables 3-7) indicate that RSPaV-1 is closely associated with RSP and that it is likely the causal agent of RSP. RT-PCR detected RSPaV-1 specific sequences from most of the RSP-infected grapevines collected from a wide range of viticultural regions of the world. Among the 93 grapevine accessions indexed positively for RSP on St. George, 85% were positive in RT-PCR (see Table 5). The data also suggests that RT-PCR has the potential to be used as a standard method for diagnosing RSP. This method is advantageous over the biological indexing on indicator St. George, because it is simpler, quicker, and more sensitive.
RT-PCR did not detect RSPaV-1 sequences from 14 of the grapevine accessions indexed positively for RSP (see Table 6). The discrepancy between RT-PCR and indicator indexing can be attributed to the existence in grapevines of different viruses or strains of the same virus which may all induce similar pitting and/or grooving symptoms on St. George upon graft-inoculation. It is believed these agents are only slightly different from RSPaV-1 at the level of their nucleotide sequences, but significant enough to hinder them from being detected by RT-PCR using RSPaV-1 specific primers.
It is likely that many RSPaV strains have genomes with nucleotide sequences that are highly similar to the nucleotide sequence of the RSPaV-1 genome. Evidence that supports this hypothesis includes the finding of a highly conserved region of ca. 600 bps among the nucleotide sequences of RSPaV-1 (type strain) and seven other cDNA clones, as shown in
BM98-3R has a nucleotide sequence corresponding to SEQ. ID. No. 52 as follows:
Primers BM98-3F/BM98-3R can be used in RT-PCR to test further some of the grapevine samples which were negative for RSPaV in RT-PCR using RSP95F1/RSP95R1 primers (SEQ. ID. Nos. 47 and 48, respectively) or RSP149F1/RSP149R1 primers (SEQ. ID. Nos. 49 and 50, respectively). Results show that 6 of the 9 samples included were positive for RSPaV in RT-PCR using BM98-3F/BM98-3R primers. This indicates that these universal primers can be used to achieve even higher detection rates.
Another pair of primers (BM98-1F/BM98-1R) can be designed in a way that they can amplify DNA of 760 bps from RSPaV-1, RSP47-4, and RSP158. BM98-1F has a nucleotide sequence corresponding to SEQ. ID. No. 53 as follows:
BM98-1R has a nucleotide sequence corresponding to SEQ. ID. No. 54 as follows:
Other “universal primers” can be designed manually or with computer programs (such as PrimerSelect) in the same way so that they contain conserved regions of nucleotide sequences for different strains of RSPaV-1.
RT-PCR detected RSPaV-1 sequences from 54% of grapevines negative for RSP as judged by indexing on St. George (see Tables 3 and 4). Several possibilities may account for this discrepancy. First, RT-PCR is much more sensitive than indicator indexing. Virus(es) of extremely low concentration may not induce visible symptoms on St. George within the standard indexing period, while they can be detected by RT-PCR. Second, judging indexing results can, in some cases, be very subjective. For example, it is very difficult to reach a conclusion on whether a grapevine is infected with RSP when only one or a few small pits are present on the woody cylinder of St. George. Third, uneven distribution of virus(es) within grapevines and the relatively limited number of replicates of St. George indicators may result in the failure to detect RSP-infection.
RSP seems to be widespread in different types of grapevines including V. vinifera, hybrids, V. riparia, and rootstocks. It occurs in a wide range of geographic regions including North America, Europe, Australia, and possibly many other countries as well. Testing grapevines from other areas of the world using RSPaV-1 specific primers will provide definitive information on the exact distribution of RSP throughout the world. It is also interesting to investigate whether RSP is transmitted by any vectors in nature.
RSP is a disease under quarantine in Washington and New York of the USA. Since this work and the work of others (Golino and Butler, “A Preliminary Analysis of Grapevine Indexing Records at Davis, California,” in Proceedings of the 10th Meeting of the ICVG, pp. 369-72, Rumbos et al., eds., Volos, Greece (1990); Azzam and Gonsalves, “Detection of dsRNA in Grapevines Showing Symptoms of Rupestris Stem Pitting Disease and the Variabilities Encountered,” Plant Disease, 75:96-964 (1991); Garau, “Kober Stem Grooving and Grapevine Virus A: A Possible Relationship,” in Extended Abstracts of the 11th Meeting of the International Council for the Study of Viruses and Virus Diseases of the Grapevine, p. 54, Montreux, Switzerland (1993); Credi, “Characterization of Grapevine Rugose Wood Sources from Italy,” Plant Disease, 82:1288-92 (1997), all of which are hereby incorporated by reference) showed that RSP is so wide-spread, it is questionable whether or not RSP should be kept under plant quarantine any longer. The devlopment and advance of rapid diagnostic methods will also allow us to investigate on the economic damage caused by RSP.
According to Goheen (“Rupestris Stem Pitting,” in Compendium of Grape Diseases, p. 53, Pearson and Goheen, eds., American Phytopathological Society Press, St. Paul, Minn., USA (1988), which is hereby incorporated by reference), RSP is a disease which induces, after graft-inoculation with a chip bud from an infected grapevine, a row of small pits on the woody cylinder of St. George below the point of inoculation. This definition may not be comprehensive. Indexing record indicated that two types of stem pitting (specific vs. nonspecific) were often observed on the woody cylinder of St. George upon graft inoculation with chip buds. For example, among 16 RSP-positive grapevines collected from Canada in 1995, eight developed specific type symptoms, while the others produced nonspecific symptoms. Credi (“Characterization of Grapevine Rugose Wood Sources from Italy,” Plant Disease, 82:1288-92 (1997), which is hereby incorporated by reference) also observed these two types of stem pitting in his indexing work. However, from the primers used in RT-PCR, as described above, RSPaV-1 was detected in grapevines showing both types of symptoms on St. George.
Thus, RT-PCR detected RSPaV-1 sequences from a wide range of grapevines collected from a number of major grapevine growing countries. The data clearly suggest that RSPaV-1 is closely associated with Rupestris stem pitting of grapevines and that it is likely the causal virus of RSP. Use of “universal” primers which can detect multiple agents which are highly similar to RSPaV-1 in nucleotide sequences would improve the detection rate by RT-PCR In addition, antibodies produced against bacteria-expressed coat proteins of RSPaV-1 will help in finding the viral particles from RSP infected grapevines and in rapid detection of RSP.
To confirm the specificity of the RT-PCR products to RSPaV-1, Southern blot hybridization was conducted using 32P labeled probe specific to RSPaV-1. As shown in
The coat protein gene (SEQ. ID. No. 10) of RSPaV-1 was cloned into the EcoRI and HindIII sites of the polylinker region of a protein expression vector pMAL-c2 which, upon induction by inducer IPTG, produces a fusion protein containing maltose binding protein (MBP) and the coat protein of RSPaV-1. The fusion protein of expected size (ca. 71 KDa) was produced in E. coli bacteria after induction with IPTG. This fusion protein was purified through affinity chromatography using an amylose column. Purified fusion protein was used as an antigen to immunize a rabbit (by subcutaneous injection along the back) with the following scheme:
The antibodies produced against the expressed RSPaV-1 coat protein, therefore, are useful in the identification of the particles associated with RSP disease of grapevines, in the purification of the particles of RSPaV-1, and in the development of a serological diagnosis for RSP in grapevine. The use of the antibodies is suitable for detecting different strains of RSPaV-1. Because the coat proteins for strains RSP47-4 and RSP158 have high amino acid identities with the coat protein of RSPaV-1, it is very likely that the antibodies raised against RSPaV-1 coat protein will also detect other strains. Antibodies can be used in an ELISA to assay rapidly a large number of samples, thus making commercial development and utilization of diagnostic kits possible.
The DNA molecule coding for the RSPaV-1 coat protein (e.g., SEQ. ID. No. 10) was cloned into a pEPT8 plant expression vector that contains the double 35S enhancer at restriction sites SalI and BamHI. The resulting recombinant plasmid, designated pEPT8/RSPaV-1 coat protein, was then cloned into the plant transformation vector pGA482G, which has resistance genes to gentamycin and tetracycline as selection markers. The resultant pGA482G containing pEPT8/RSPaV-1 CP was used to transform grapevines using the Agrobacterium method.
The rootstock Vitis rupestris Scheele St. George was used in genetic transformation. Anthers were excised aseptically from flower buds. The pollen was crushed on a microscope slide with acetocarmine to observe the cytological stage (Bouquet et al., “Influence du Gentype sur la Production de cals: Dembryoides et Plantes Entieres par Culture Danthers in vitro dans le Genre Vitis,” C. R. Acad. Sci. Paris III 295:560-74 (1982), which is hereby incorporated by reference). This was done to determine which stage was most favorable for callus induction.
Anthers were plated under aseptic condition at a density of 40 to 50 per 9 cm diameter Petri dish containing MSE. Plates were cultured at 28° C. in the dark. After 60 days, embryos were induced and transferred to hormone-free medium (HMG) for differentiation. Torpedo stage embryos were transferred to MGC medium yo promote embryo germination. Cultures were maintained in the dark at 26-28° C. and transferred to fresh medium at 3-4 week intervals. Elongated embryos were transferred to rooting medium (5-8 embryos per jar). The embryos were grown in a tissue culture room at 25° C. with a daily 16 h photoperiod (76 μmol. s) to induce shoot and root formation. After plants developed roots, they were transplanted to soil in the greenhouse.
The protocols used for transformation were modified from those described by Scorza et al., “Transformation of Grape (Vitis vinifera L.) Zygotic-Derived Somatic Embryos and Regeneration of Transgenic Plants,” Plant Cell Rpt. 14:589-92 (1995), which is hereby incorporated by reference. Overnight cultures of Agrobacterium strain C58Z707 or LBA4404 were grown in LB medium at 28° C. in a shaking incubator. Bacteria were centrifuged for 5 minutes at 3000-5000 rpm and re-suspended in MS liquid medium (OD 1.0 at A600 nm). Calli with embryos were immersed in the bacterial suspension for 15-30 minutes, blotted dry, and transferred to HMG medium with or without acetosyringone (100 μM). Embryogenic calli were co-cultivated with the bacteria for 48 h in the dark at 28° C. The plant material was then washed in MS liquid plus cefotaxime (300 mg/ml) and carbenicillin (200 mg/ml) 2-3 times. To select transgenic embryos, the material was transferred to HMG medium containing either 20 or 40 mg/L kanamycin, 300 mg/L cefotaxime, and 200 mg/L carbenicillin. Alternatively, after co-cultivation, embryogenic calli were transferred to initiation MSE medium containing 25 mg/l kanamycin plus the same antibiotics listed above. All plant materials were incubated in continuous darkness at 28° C. After growth on selection medium for 3 months, embryos were transferred to HMG or MGC without kanamycin to promote elongation of embryos. They were then transferred to rooting medium without antibiotics. Non-transformed calli were grown on the same media with and without kanamycin to verify the efficiency of the kanamycin selection process.
The X-gluc (5-bromo-4-chloro-3-indoyl-β-glucuronidase) histochemical assay was used to detect GUS (β-glucuronidase) activity in embryos and plants that were transformed with constructs containing the GUS gene that survived kanamycin selection. All propagated plants were screened using an enzyme linked immunoabsorbent assay (ELISA) system (5 Prime-3 Prime, Boulder, Co.) to detect the NPTII (neomycin phosphotransferase II) protein in leaf extracts. ELISA tests with respective coat protein (CP)-specific antibodies were used to assay for CP. ELISA results were read on an SLT Spectra ELISA reader (Tecan U.S. Inc., Research Triangle Park, N.C.) 15-60 minutes after the substrate was added.
PCR analysis was carried out to detect the presence of transgene sequences in grape plants. Genomic DNA was isolated from transformed and non-transformed grape plants according to the method of Lodhi et al., “A Simple and Efficient Method for DNA Extraction from Grapevine Cultivars and Vitis Species,” Plant Mol. Biol. Rpt. 12:6-13 (1994), which is hereby incorporated by reference. Primer sets included those of specific primers to the transgene. DNA was initially denatured at 94° C. for 3 minutes, then amplified by 35 cycles of 1 minute at 94° C. (denaturing), 1 minute at 52° C. (annealing), and 2 minutes at 72° C. (polymerizing). Reaction samples were directly loaded and electrophoresed in 1.5% agarose gels.
Southern analysis of transformants was accomplished by extracting genomic DNA from young leaves of transformed and non-transformed plants (3309C) as described above. DNA (10 μg) was digested with the restriction enzyme Bgl II, electrophoresed on a 0.8% agarose gel in TAE buffer and transferred to a Genescreen Plus membrane by capillary in 10×SSC. A probe was prepared by random primer labeling of a PCR amplified gene coding sequence with radioisotope 32P-dATP (Dupont, NEN). Pre-hybridization and hybridization steps were carried out at 65° C. following the manufacturer's instruction. The autoradiograph was developed after overnight exposure.
Although the invention has been described in detail for the purposes of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention which is defined by the following claims.
This application claims the benefit of U.S. Provisional Patent Applications Ser. No. 60/047,147, filed May 20, 1997, and 60/069,902, filed Dec. 17, 1997.
This work was supported by the U.S. Department of Agriculture Clonal Repository—Geneva, Grant Nos. 58-2349-9-01 and 58-2349-9 and U.S. Department of Agriculture Cooperative Agreement Grant Nos. 58-1908-4-023, 58-3615-5-036, and 58-3615-7-060. The U.S. Government may have certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60047147 | May 1997 | US | |
| 60069902 | Dec 1997 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 09568189 | May 2000 | US |
| Child | 10803063 | Mar 2004 | US |
| Parent | 09081320 | May 1998 | US |
| Child | 09568189 | May 2000 | US |
