BIOLOGICAL CONTROL OF PLANT VIRUSES

Abstract

The present disclosure provides new attenuated Pepino mosaic viruses useful in the control of plant disease. Compositions for biological control of plant disease are also provided as well as methods for producing Pepino mosaic virus resistant plants.

Claims

1. An attenuated Pepino mosaic virus comprising a nucleic acid molecule with a nucleic acid sequence that encodes phenylalanine at the position corresponding to 1052 of SEQ ID NO:2.

2. The virus of claim 1, wherein the nucleic acid sequence further encodes arginine at the position corresponding to 868 of SEQ ID NO:2.

3. An attenuated Pepino mosaic virus comprising a nucleic acid molecule with a nucleic acid sequence that encodes arginine at the position corresponding to 868 of SEQ ID NO:2.

4. The virus according to claim 1, wherein the nucleic acid sequence is at least 80% identical to SEQ ID NO:1.

5. The virus according to claim 1, wherein the nucleic acid sequence is at least 80% identical to SEQ ID NO:8.

6. An isolated nucleic acid molecule encoding an amino acid sequence having at least 95% identity to any one of the amino acid sequences depicted in FIG. 6, wherein the nucleic acid sequence encodes arginine at position 887 of FIG. 6 and/or the nucleic acid sequence encodes phenylalanine at position 1071 of FIG. 6.

7. An isolated nucleic acid molecule encoding an amino acid sequence having at least 95% identity to SEQ ID NO:9.

8. A vector, comprising the nucleic acid molecule according to claim 6.

9. An isolated polypeptide encoded by a nucleic acid molecule of claim 6.

10. A composition for biological control of plant disease comprising the virus of claim 1, and an agriculturally acceptable carrier.

11. A method for the detection of a pepino mosaic virus (PepMV) comprising providing a sample suspected of containing PepMV and detecting in said sample the virus of claim 1.

12. A method for producing a pepino mosaic virus (PepMV)-resistant plant, comprising exposing a plant or plant part to the virus of claim 1.

13. A PepMV-resistant plant comprising a virus according to claim 1.

14. A composition for biological control of plant disease comprising the nucleic acid molecule of claim 6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG. 1. Inoculation of tomato plants with CHD alone resulted in strong necrosis of the leaves and stems, from 3 weeks after inoculation of CHD (FIG. 1A). Inoculation of tomato plants with VCA, followed by CHD, protected plants from necrosis (FIG. 1B).

[0027] FIG. 2. Thirty-nine days after inoculation of tomato plants with VC1 (FIG. 2A) or VCA (FIG. 2B).

[0028] FIG. 3. Development of mild symptoms in infected plants; no treatment (FIG. 3A); VCA treatment (FIG. 3B); VC1 treatment (FIG. 3C).

[0029] FIG. 4. Comparison of symptoms in plants grown under optimal conditions (top row) versus sub-optimal conditions (bottom row); no treatment (FIG. 4A); VC1 treatment (FIG. 4B); VCA treatment (FIG. 4C).

[0030] FIG. 5. An alignment of the sequence of VCA with closely related sequences identified from BLAST (Basic local alignment search tool) from NCBI. The sequence with the highest identity in the BLAST search was 1906, having 99.6% identity. The nomenclature listed in FIG. 5 corresponds to the annotations of NCBI as follows: 1906: Pepino mosaic virus isolate 1906 replicase, triple gene block protein 1 (TGBp1), triple geneblock protein 2 (TGBp2), triple gene block protein 3 (TGBp3), and coat protein genes, complete cds. [0031] DQ000985: Pepino mosaic virus isolate Ch2, complete genome. [0032] FJ212288: Pepino mosaic virus, complete genome. [0033] Pa: Pepino mosaic virus isolate PepMV-Pa, complete genome. [0034] PK: Pepino mosaic virus isolate PepMV-PK, complete genome. [0035] 220606A1: Pepino mosaic virus isolate 220606A1. [0036] VFBC12-04: Pepino mosaic virus isolate VFBC12-04. [0037] VFBC12-08: Pepino mosaic virus isolate VFBC12-08. [0038] P5: Pepino mosaic virus isolate PepMV-P5, complete genome. [0039] PCH06/104: Pepino mosaic virus isolate PCH 06/104 replicase, triple gene block protein 1 (TGBp1), triple gene block protein 2 (TGBp2), triple gene block protein 3 (TGBp3), and coat protein genes, complete cds

[0040] FIG. 6. An alignment of the amino acid sequence of RNA-dependent RNA polymerase from VCA and other PepMV viruses. [0041] LE-2002, AJ438767, and Sp-13 are EU isolates. LP-2001 is an LP isolate. US1 is a US isolate.

[0042] FIG. 7. Sequence listing

[0043] FIG. 8. Sequence listing

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

[0044] Cross-protection is the phenomenon of protecting crops against virulent isolates of viruses by pre-treatment with closely related attenuated isolates of the virus. In the 1970s, it was first applied successfully against infection of tomato with Tobacco mosaic virus in several countries (Burgy?n & G?borj?nyi, 1984). Attenuated isolates may be selected among naturally occurring or be developed by the introduction of mutations into such isolates, for example using random mutagenesis. A strategy in which attenuated isolates are applied to plants relies on the identification of an isolate that has as little impact on total yield and fruit quality as possible, and effectively protects against more virulent isolates at the same time.

[0045] While not wishing to be bound by theory, cross-protection may be due to RNA silencing activity induced by the protective isolate (Ratcliff et al., 1999; Valkonen et al., 2002). The role of post-transciptional gene silencing (PTGS) in cross-protection was demonstrated by the observation that two viral constructs derived from different viruses, but sharing a common sequence, could suppress each other when co-inoculated in plants (Ratcliff et al., 1999). PTGS is an antiviral defense mechanism in plants, which targets double stranded RNA (dsRNA) for degradation in a sequence-specific manner. In cross-protection, it is thought that the mild strain primes the defense system of the plant so that it operates against subsequent infection by severe strains.

[0046] In the study of Schenk et al. (2010), attenuated isolates of PepMV were tested (EU-Att1 and PE-Att1). The attenuated isolates effectively reduced the effects of isolates of PepMV with aggressive symptoms (namely, EU-Ch11 and EU-Nec1). Total virus accumulation, symptom severity and yield losses were significantly reduced in cross-protected plants compared to the single infections by the aggressive isolates. The yields of the cross-protected plants were on a similar level as those of uninfected plants. Although plants cross-protected by the attenuated isolates reduced symptoms, infection by the attenuated isolates alone also produced symptoms (Table 2 of Schenk et al.) The attenuated isolates caused symptoms shortly after inoculation, a pattern which has also been observed in other trials (Spence et al., 2006). Overall, the symptom severity correlated to virus accumulation, but accumulation alone did not explain all differences in symptom severity. In turn, symptom severity was negatively correlated to yield. The two symptoms that had the largest effect on yield i.e. leaf deformation and leaf necrosis, affected the leaf area of the plants, which would explain the observed yield losses. One aspect of the present invention is the provision of an attenuated virus that cross-protects plants from further PepMV infection while causing minimal symptoms from exposure to the attenuated virus alone.

[0047] Accordingly, one aspect of the disclosure provides Pepino mosaic viruses, in particular attenuated viruses. As is known to a skilled person, an attenuated virus is a virus that has been modified from a wild-type pathogenic virus. An attenuated virus has reduced pathogenicity as compared to the wild-type virus. In addition, an attenuated virus disclosed herein can be used to cross-protect plants against infection from virulent PepMV isolates.

[0048] The disclosure identifies several nucleotide positions in PepMV which play a role in the symptoms induced by PepMV infection. Specifically, the disclosure provides PepMV viruses and nucleic acid molecules, wherein the nucleic acid sequence encodes arginine at the position corresponding to 868 of SEQ ID NO:2 (corresponding to position 886 of SEQ ID NO:9) and/or encodes phenylalanine at the position corresponding to 1052 of SEQ ID NO:2 (corresponding to position 1070 of SEQ ID NO:9).

[0049] The disclosure provides that the nucleotides at positions 2605 and 3156 of SEQ ID NO: 1 (corresponding to positions 2675 and 3226 of SEQ ID NO: 8), and consequently the amino acids encoded (in part) by these nucleotides, play a role in the pathogenic symptoms. Specifically, an amino acid change from lysine to arginine at position 868 of SEQ ID NO:2 (corresponding to position 886 of SEQ ID NO:9) and an amino acid change from leucine to phenylalanine at position 1052 of SEQ ID NO: 2 (corresponding to position 1070 of SEQ ID NO:9) results in a PepMV attenuated virus. In the pathogenic viruses depicted in FIG. 6, as well as the attenuated VC1 virus, the amino acids corresponding to 868 and 1052 of SEQ ID NO:2 (and 886 and 1070 of SEQ ID NO:9) are lysine and leucine, respectively. While not wishing to be bound by theory, these amino acid changes are believed to provide attenuated viruses which demonstrate milder symptoms that the VC1 virus (see Examples).

[0050] The disclosure also provides that additional nucleotidesand the amino acids which they encodealso play a role in pathogenic symptoms. Accordingly, in some embodiments the viruses and nucleic acid molecules disclosed herein contain one or more of the following: a C at the nucleotide position corresponding to 191 of SEQ ID NO: 1 (position 261 of SEQ ID NO: 8); a C at the nucleotide position corresponding to 2354 of SEQ ID NO: (position 2424 of SEQ ID NO: 8); a T at the nucleotide position corresponding to 2768 of SEQ ID NO: 1(position 2838 of SEQ ID NO: 8); a T at position corresponding to 2868 of SEQ ID NO:1 (position 2938 of SEQ ID NO: 8); a G at the nucleotide position corresponding to 3422 of SEQ ID NO: 1 (position 3492 of SEQ ID NO: 8); and/or have an A at the nucleotide position corresponding to 3975 of SEQ ID NO: 1 (position 4045 of SEQ ID NO: 8). In some embodiments the viruses or nucleic acid molecules disclosed herein contain at least two, at least three, at least four, at least five, or all 6 of the nucleotides listed above. These six nucleotides are unique to both the VCA attenuated virus and the VC1 attenuated virus as compared to the virulent CH2 strains depicted in FIG. 5. Preferably, the viruses and nucleic acid molecules disclosed herein, in addition to encoding arginine at the position corresponding to 868 of SEQ ID NO:2 (and corresponding to position 886 of SEQ ID NO:9) and/or phenylalanine at the position corresponding to 1052 of SEQ ID NO:2 (and corresponding to position 1070 of SEQ ID NO:9), also encode a phenylalanine at the position corresponding to 956 of SEQ ID NO:2 (and corresponding to position 974 of SEQ ID NO:9) and/or an asparagine at the position corresponding to 1325 of SEQ ID NO:2 (and corresponding to position 1343 of SEQ ID NO:9). As depicted in FIG. 6, the wild-type pathogenic viruses encode a leucine and an aspartic acid at these positions. While not wishing to be bound by theory, these amino acids are believed to play a role in reducing the virulence of the viruses. SEQ ID NO: 1 (herein referred to as the VCA virus) was isolated as an attenuated virus of the CH2 strain. The Examples demonstrate the ability of the VCA virus to cross-protect against wild-type PepMV strains and the reduction of symptoms as compared to another attenuated virus VC1. SEQ ID NO: 1 depicts a partial sequence of the RNA-dependent RNA-polymerase of the VCA virus. SEQ ID NO: 8 depicts the nucleotide sequence of the RNA-dependent RNA-polymerase of the VCA virus, including the complete coding sequence.

[0051] See FIGS. 7 and 8 for the sequence listing. As known to a skilled person, Y indicates a C or T, R indicates A or G; and S indicates G or C. In some embodiments, R is G. In some embodiments, Y1 is C. In some embodiments, Y2 is C. In some embodiments, Y3 is T. In some embodiments, Y4 is T. In some embodiments, S is C. In some embodiments, Y5 is T. In some embodiments, Y6 is T. Viruses having the nucleic acid sequence of SEQ ID NO:1 or SEQ ID NO:8 include a single homogenous virus (i.e., having one sequence; for example SEQ ID NO:1 or SEQ ID NO:8 wherein R is G; Y1 is C; Y2 is C; Y3 is T; Y4 is T; S is C; Y5 is T; Y6 is T) as well as mixtures of viruses each having SEQ ID NO:1 or SEQ ID NO:8.

[0052] The VCA virus was found to have nucleotide substitutions resulting in amino acid changes in the RNA-dependent RNA polymerase gene of the virus. SEQ ID NO:2 depicts the partial amino acid sequence of the RNA-dependent RNA polymerase from VCA. SEQ ID NO:9 depicts the complete amino acid sequence of the RNA-dependent RNA polymerase from VCA

[0053] VCA (SEQ ID NO:1/SEQ ID NO:8) is an exemplary attenuated virus of the CH2 strain. The disclosure also provides attenuated viruses from other PepMV strains. Four amino acids in SEQ ID NO:2 were found to be unique when compared to wild-type EU, LP, CH2, and US1 isolates. Arginine at position 868 of SEQ ID NO:2 (886 of SEQ ID NO:9) corresponds to position 887 in the alignment shown in FIG. 6. Phenylalanine at position 956 of SEQ ID NO:2 (974 of SEQ ID NO:9) corresponds to position 975 in the alignment shown in FIG. 6. Phenylalanine at position 1052 of SEQ ID NO:2 (1070 of SEQ ID NO:9) corresponds to position 1071 in the alignment shown in FIG. 6. Asparagine at position 1325 of SEQ ID NO:2 (1343 of SEQ ID NO:9) corresponds to position 1344 in the alignment shown in FIG. 6. It is clear to a skilled person that attenuated viruses from any PepMV isolate can be prepared based on these amino acids.

[0054] In some embodiments, the virus is an attenuated virus of a EU strain. Exemplary wild-type EU viral sequences are depicted in SEQ ID Nos:3-5.In some embodiments, the virus is an attenuated virus of a US1 strain. An exemplary wild-type US1 viral sequence is depicted in SEQ ID NO:6. In some embodiments, the virus is an attenuated virus of an LP strain. An exemplary wild-type LP viral sequence is depicted in SEQ ID NO:7.

[0055] PepMV viruses have, on the average, around 80% nucleic acid sequence identity. Accordingly, in preferred embodiments the PepMV viruses have a nucleic acid sequence at least 80% identical to SEQ ID NO:1, wherein the nucleic acid sequence encodes arginine at the position corresponding to 868 of SEQ ID NO:2 and/or encodes phenylalanine at the position corresponding to 1052 of SEQ ID NO:2 (or rather, encodes arginine at position 887 of FIG. 6 and/or the nucleic acid sequence encodes phenylalanine at position 1071 of FIG. 6). In preferred embodiments, the PepMV viruses have a nucleic acid sequence at least 80% identical to SEQ ID NO:8, wherein the nucleic acid sequence encodes arginine at the position corresponding to 886 of SEQ ID NO:9 and/or encodes phenylalanine at the position corresponding to 1070 of SEQ ID NO:9. In a preferred embodiment, the attenuated viruses disclosed herein have a nucleic acid sequence at least 80%, at least 90%, preferably at least 95%, more preferably at least 98%, and most preferably at least 99% identical to SEQ ID NO:1, SEQ ID NO:8, SEQ ID NO: 3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, or SEQ ID NO: 7. The sequences provided herein refer to the bases A, T, C, and G. However, it is clear to a skilled person that when referring to a PepMV virus (an RNA virus), uracil is present instead of thymine.

[0056] The disclosure also provides an isolated nucleic acid molecule comprising a nucleic acid sequence at least 80%, at least 90%, preferably at least 95%, more preferably at least 98%, and most preferably at least 99% identical to SEQ ID NO:1, SEQ ID NO:8, SEQ ID NO: 3, SEQ ID NO:4, SEQ ID NO:5, SEQ ID NO:6, or SEQ ID NO: 7, wherein the nucleic acid sequence encodes arginine at the position corresponding to 868 of SEQ ID NO:2 and/or encodes phenylalanine at the position corresponding to 1052 of SEQ ID NO:2 (or rather, encodes arginine at position 887 of FIG. 6 and/or the nucleic acid sequence encodes phenylalanine at position 1071 of FIG. 6; or rather encodes arginine at position 886 of SEQ ID NO:9 and/or the nucleic acid sequence encodes phenylalanine at position 1070 of SEQ ID NO:9).

[0057] In some embodiments, the nucleotide at the position corresponding to 2605 of SEQ ID NO:1 (2675 of SEQ ID NO:8) is G; the nucleotide at the position corresponding to 3156 of SEQ ID NO: 1 (3226 of SEQ ID NO:8) is T and/or the nucleotide at the position corresponding to 3422 SEQ ID NO: 1 (3492 of SEQ ID NO:8) is G. In preferred embodiments, the nucleotide at the position corresponding to 2605 of SEQ ID NO:1 (2675of SEQ ID NO:8) is G and/or the nucleotide at the position corresponding to 3156 of SEQ ID NO: 1 (3226 of SEQ ID NO:8) is T. In preferred embodiments, the nucleic acid molecules comprise one or more of the following: a C at the nucleotide position corresponding to 191 of SEQ ID NO: 1 (position 261 of SEQ ID NO: 8); a C at the nucleotide position corresponding to 2354 of SEQ ID NO: 1 (position 2424 of SEQ ID NO: 8); a T at the nucleotide position corresponding to 2768 of SEQ ID NO: 1 (position 2838 of SEQ ID NO: 8); a T at position corresponding to 2868 of SEQ ID NO:1 (position 2938 of SEQ ID NO: 8); and/or have an A at the nucleotide position corresponding to 3975 of SEQ ID NO: 1 (position 4045 of SEQ ID NO: 8). Such nucleic acid molecules are useful, for example, for producing the viruses disclosed herein.

[0058] As used herein, the term isolated refers to a protein, peptide or nucleic acid molecule which is substantially separated from other (sub)cellular components. The term includes a nucleic acid molecule or protein which has been removed from its naturally occurring environment, as well as recombinant or cloned DNA isolates and chemically synthesized analogues or analogues biologically synthesized by heterologous systems.

[0059] A further aspect of the disclosure provides vectors and expression vectors comprising the nucleic acid molecules and viruses disclosed herein. Expression vectors useful in the present disclosure include vaccinia virus, retroviruses, and baculovirus. The expression vector may comprise the nucleic acid sequences disclosed herein or a fragment thereof that is under control of or operatively linked to a regulatory element, such as a promoter. The segment of DNA referred to as the promoter is responsible for the regulation of the transcription of DNA into mRNA. The expression vector may comprise one or more promoters suitable for the expression of the gene in, e.g., plant cells, fungal cells, bacterial cells, yeast cells, insect cells or other eukaryotic cells.

[0060] The viruses and nucleic acid molecules disclosed herein can be made by any method known to one of skill in the art. Methods of generating full length cDNA clones of the RNA genome of PepMV have been described, see, e.g., Hasiow-Jaroszewsk et al. Arch Virol (2009) 154:853-856. In addition, the cloning of both EU and CH2 PepMV clones has also been described in Duff-Farrier et al., Molecular Plant Pathology (2015) 16:308-315. Duff-Farrier et al. describes the construction of cDNA from PepMV EU and CH2 isolates and well as the introduction of chimeric sequences into the cDNA. Infectious RNA was synthesized in vitro, which was used to infect plants. Similar methods can be used to generate the viruses and nucleic acid molecules with sequences described herein.

[0061] The viruses and nucleic acid molecules discloses herein are useful for producing plants with increased resistance to PepMV, in particular to disease causing strains of PepMV such as the Peruvian (LP) strain, the European (EU) strain, the CH2 strain, first identified in Chile, and the US1 strain, identified in the United States. Accordingly, the disclosure provides attenuated viruses and nucleic acid molecules for controlling PepMV infection and/or PepMV disease in a plant. As used herein, controlling PepMV infection includes the reduction, prevention, or delay of PepMV accumulation in a plant. As used herein, controlling PepMV disease includes the reduction, prevention, or delay of PepMV symptoms.

[0062] The nucleic acid molecules disclosed herein, the polypetides encoded by said nucleic acid molecules, as well as antibodies recognizing said polypeptides are all useful for, e.g., detecting infection by the attenuated virus and thereby detecting plants with increased resistance to PepMV.

[0063] The viruses and nucleic acid molecules disclosed herein may be provided in compositions comprising an agriculturally acceptable carrier. Such compositions can be used for the biological control of plant disease. Preferably, the composition comprises and anti-oxidant, a phosphate buffer and/or a sulphite (sulphite can help prevent rotting). Preferably, the compositions have a pH range of 6-8.5, more preferably a pH of 7.7?0.5. Preferably the compositions comprise one or more of the following: mono-basic potassium phosphate, di-basic sodium phosphate dodecahydrate, and/or sodium sulphite. More preferably, the compositions comprises 0.4-1.6 g of mono-basic potassium phosphate per liter, more preferably around 0.8 g/L; 15-60 g of di-basic sodium phosphate dodecahydrate per liter, more preferably around 30 g/L; and 1-4 g sodium sulphite per liter, more preferably around 2 g/L.

[0064] The viruses may be propagated in a suitable plant host. The tissue from infected plants is ground and the homogenate (the sap) can be used to prepare the compositions disclosed herein. Alternatively, the nucleic acid molecules disclosed herein may be cloned into a vector for replication in another host.

[0065] The host range of PepMV is mainly restricted to plant species of the Solanaceae family Tomato (Solanum lycopersicum) is one of the most economically important natural host of PepMV. Pepino plant (S. muricatum) is a host in Peru and China (Jones et al., 1980; Soler et al., 2002; Zhang et al., 2003). In surveys in Peru, PepMV has been found to be naturally present in wild Solanum species (S. chilense, S. chmielewskii, S. parviflorum and S. peruvianum).

[0066] Infections, symptomless or with mild symptoms have also been observed in weed species which are member of families of Amaranthaceae, Asteraceae, Boraginaceae, Brassicaceae, Chenopodiaceae, Compositae, Convolvulaceae, Malvaceae, Plantaginaceae, Polygonaceae and Solanaceae. (C?rdoba et al., 2004; Jord? et al., 2001; Kazinczi et al., 2005, Papayiannis et al., 2012; Salomone & Roggero 2002; Soler et al., 2002; Stobbs et al., 2009). Most of these infections were found in the vicinity of tomato greenhouses. PepMV has also been detected in a few potato cultivars (e.g., Solanum tuberosum cv. Yungay).

[0067] Several species have been found to be experimentally-susceptible to infection by PepMV following artificial inoculation, including eggplant (Solanum melongena) which was found to be infected by PepMV by mechanical inoculation (Salomone & Roggero, 2002; Verhoeven et al., 2003). Some cultivars of potato (S. tuberosum) can also be experimentally infected by PepMV (Jones et al., 1980). PepMV can infect Datura metel, D. stramonium, Nicotiana debneyi, N. benthamiana systemically (Jones et al., 1980; Verhoeven et al., 2003). Some PepMV isolates can infect N. glutinosa and N. tabacum (LP and some EU isolates; Verhoeven et al., 2003).

[0068] Preferably, the term plant refers to any plant which is capable of being infected with PepMV. In some embodiments, the plant belongs to the Solanaceae family, in particular the genus Solanum or Lycopersicon. As is known to the skilled person, the nomenclature for tomato plants has recently changed. For example, Solanum juglandifolium is now referred to as Lycopersicon juglandifolium. A preferred plant is a tomato plant.

[0069] As used herein, the term plant part includes, for example, single cells and tissues from pollen, ovules, leaves, embryos, roots, root tips, anthers, flowers, fruits, stems shoots, and seeds; as well as pollen, ovules, leaves, embryos, roots, root tips, anthers, flowers, fruits, stems, shoots, scions, rootstocks, seeds, protoplasts, calli, and the like.

[0070] PepMV induces a wide range of symptoms on tomato, such as yellow mosaic, leaf distortion, leaf blistering or bubbling, nettle-like heads, single yellow spots, inter-veinal chlorosis, severe leaf mosaics, leaf or stem necrosis and [0071] fruit discolouration (Van der Vlugt et al., 2000; Jorda et al., 2001; Roggero et al., 2001; Spence et al., 2006; Hasi?w et al., 2008; Hasi?w-Jaroszewska et al., 2009a; Hanssen et al., 2009). Tomato plants display symptoms shortly after infection with PepMV and, in general, symptoms subsequently subside (Van der Vlugt & Stijger, 2008). However, symptoms may return later during the growing season.

[0072] Expression of symptoms may depend on environmental conditions, such as temperature and light intensity. Low environmental temperatures and low light intensity result in more severe damage (Jorda et al., 2001; Van der Vlugt & Stijger, 2008). PepMV is sometimes suggested to cause yield losses in tomato, but the highest economic losses are attributed to symptoms that affect the commercial value of tomato fruits, such as flaming, marbling, blotchy ripening and fruit size reduction (Soler et al., 2000; Spence et al., 2006; Hanssen & Thomma, 2010). In addition, the so-called tomato collapse, a sudden and progressive wilt of tomato which can lead to plant death is probably caused by PepMV accumulation in the vascular system (Soler-Aleixandre et al., 2005). Striking differences in the severity of symptomatology have been reported (Verhoeven et al., 2003; Hanssen et al., 2008) and not all isolates cause typical PepMV symptoms such as marbled and flamed fruits (Hanssen et al., 2009).

[0073] Symptoms in plants can be characterized either qualitatively or quantitatively.

[0074] The viruses disclosed herein are also useful for inducing resistance in tolerant plants, i.e., plants which may become infected with the virus and further its spread but remain symptomless or will have mild symptoms.

[0075] Several methods have been developed to detect PepMV. A robust method to detect PepMV in plants is DAS-ELISA (Van der Vlugt et al., 2002). Commercially available polyclonal antibodies can be purchased at Prime Diagnostics (Wageningen, The Netherlands). Different PCR-assays have been described to detect PepMV: a general potexvirus detection method (Van der Vlugt & Berendsen, 2002), a real-time immunocapture RT-PCR (Mansilla et al., 2003; Mat?nez-Culebras et al., 2002; Ling, 2005; Ling et al., 2007) and sensitive real-time PCR assays (Alfaro-Fern?ndez et al., 2009; Johnson & Walcott, 2012; Guti?rrez-Aguirre et al., 2009). Simultaneous detection of multiple plant viruses including PepMV can be performed by using micro-arrays (Boonham et al., 2007) and deep sequencing (Li et al., 2012). Preferably, the accumulation of PepMV in a plant is determined using a quantitative detection method (e.g. an ELISA method or a quantitative reverse transcriptase-polymerase chain reaction [RT-PCR]).

[0076] A further aspect of the disclosure provides isolated polypeptides expressed by the viruses. In some embodiments the polypeptide is a RNA-dependent polymerase (RdRp) or a coat protein (CP). Preferably, the polypeptide is RdRp.

[0077] A further aspect of the disclosure provides antibodies specific for the polypeptides disclosed herein, preferably RdRp. In preferred embodiments, the antibody recognizes an antigen specific to VCA, but does not recognize the CH2, the US-1, the EU, or the LP strains. Preferably the antigen comprises the arginine at the position corresponding to 868 of SEQ ID NO:2 and/or the phenylalanine at the position corresponding to 1052 of SEQ ID NO:2 (or rather, the arginine at the position corresponding to 886 of SEQ ID NO:9 and/or the phenylalanine at the position corresponding to 1070 of SEQ ID NO:9).

[0078] A further aspect of the disclosure provides a method for producing said antibodies comprising immunizing a host (such as a mouse) with the attenuated virus, or a protein or peptide fragment thereof; harvesting from blood (including serum) or splenocytes of said host antibodies against said virus, protein or peptide fragment. In a preferred embodiment, the method further comprises selecting one antibody-producing splenocyte, fusing said splenocyte to an immortalized hybridoma cell line and allowing said hybridoma fusion to produce monoclonal antibodies. Preferably, the antigen is in part encoded by a nucleic acid sequence wherein the nucleotide at the position corresponding to 2605 of SEQ ID NO:1 (2675 of SEQ ID NO:8) is G; the nucleotide at the position corresponding to 3156 of SEQ ID NO: 1 (3226 of SEQ ID NO:8) is T and/or the nucleotide at the position corresponding to 3422 SEQ ID NO: 1 (3492 of SEQ ID NO:8) is G. More preferably, the antigen is in part encoded by a nucleic acid sequence wherein the nucleotide at the position corresponding to 2605 of SEQ ID NO:1 (2675 of SEQ ID NO:8) is G and/or the nucleotide at the position corresponding to 3156 of SEQ ID NO: 1 (3226 of SEQ ID NO:8) is T.

[0079] A further aspect of the disclosure provides a method for detecting the presence of the attenuated virus in a plant sample comprising reacting said sample with an antibody according to the disclosure. Suitable methods for performing immunoassays are well-known to a skilled person and include, e.g., radio-immunoassay (RIA), immunogold labeling, immunosorbent electron microscopy (ISEM), enzyme-linked immunosorbent assay (ELISA), Western blotting and immunoblotting.

[0080] A further aspect of the disclosure provides a method for identifying a pepino mosaic virus (PepMV)-resistant plant, comprising [0081] a) exposing a plant or plant part to an infective dosage of the attenuated viruses or nucleic acid molecules disclosed herein, [0082] b) exposing the plant or plant part to an infective dosage of PepMV, and [0083] c) identifying said plant as PepMV-resistant plant when, after exposure to PepMV, disease-symptoms in said plant or plant part are reduced or delayed and/or PepMV accumulation in said plant or plant parts is reduced in comparison to a control plant.

[0084] It is clear to a skilled person that step a) includes an incubation period of sufficient duration to allow establishment of the attenuated virus. Preferably, such incubation period is at least one week, more preferably at least 5 weeks. In some embodiments, the presence of virus in the plant can be confirmed by one of the methods disclosed herein. It is also clear to a skilled person that step b) includes an incubation period of sufficient duration to allow establishment of the PepMV virus and detectable symptoms in control plants. Preferably, such incubation period is at least one week, more preferably at least 5 weeks.

[0085] As used herein, resistant refers to a reduction in multiplication of PepMV, a reduction of movement/spread of the virus to other cells, and/or a reduction or delay in the development of disease symptoms after infection with PepMV. Resistance can be determined by comparing a PepMV infected plant with a plant exposed to VCA and PepMV. Preferably, the PepMV referred to above is a CH2, US-1, EU, or LP strains, however, it also includes other disease causing PepMV strains.

[0086] Preferably, the accumulation of PepMV in a plant is determined using a quantitative detection method (e.g. an ELISA method or PCR, such as a quantitative reverse transcriptase-polymerase chain reaction [RT-PCR]).

[0087] As used herein, an infective dosage refers to the dosage of viral particles or viral nucleic acid molecule capable of infecting a plant. As is clear to as skilled person, the dosage may vary between plant species.

[0088] Methods of exposing a plant or a plant part to virus are well-known in the art and include dusting, coating, injecting, rubbing, rolling, dipping, spraying, or brushing. Exemplary methods include mechanical innoculation (e.g., rubbing plants or plant parts with infected plant material) and spraying plants with a solution containing virus particles or viral nucleic acid (see Example 1). The attenuated virus may be isolated from infected plants or other sources by any method known to one of the art.

[0089] As is known to a skilled person, cross protection may not lead to resistance in 100% of plants of the same species. Typically, cross protection protects more that 50% of the plants, preferably more than 80% of the plants.

[0090] A further aspect of the disclosure provides a method for producing a pepino mosaic virus (PepMV)-resistant plant using the attenuated viruses or nucleic acid molecules disclosed herein for cross-protection. Also provided are methods for controlling or preventing plant disease, in particular PepMV causing disease. Also provided are methods for controlling or preventing infection by PepMV. The methods comprise exposing a plant or plant part to an infective dosage of the attenuated virus, the nucleic acid molecules disclosed herein, or the compositions disclosed herein. In some embodiments, the methods further comprise detecting the attenuated virus in said plants or plant parts, such as by a method disclosed herein.

[0091] The disclosure also provides for PepMV-resistant plants comprising the attenuated virus or the nucleic acid sequences disclosed herein. Such plants may have been infected by the attenuated virus or are the progeny of a plant infected by the virus. The plants may also have been transformed by the nucleic acid molecules disclosed herein or a vector comprising the nucleic acid molecule. Progeny of said plants are also encompassed by the invention. Such plants are obtainable by the methods described herein.

[0092] PepMV is an RNA virus. As such it is preferred that the nucleic acid molecule that is comprised in the virion is RNA. Sequences indicated herein contain a T and as such refer to DNA. Wherein herein reference is made to a virus comprising a nucleic acid molecule with a certain nucleic acid sequence and reference is made to a DNA sequence in the context of a virus, it is of course clear to the person skilled in the art that the corresponding RNA sequence is intended. In other words that the reference is to the SEQ ID wherein the T is replaced by a U. Vectors and other compositions that do not refer to a virus or virus particle can have the referenced DNA, an RNA with the same sequence or a combination thereof.

Definitions

[0093] As used herein, to comprise and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition the verb to consist may be replaced by to consist essentially of meaning that a compound or adjunct compound as defined herein may comprise additional component(s) than the ones specifically identified, said additional component(s) not altering the unique characteristic of the invention.

[0094] The articles a and an are used herein to refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, an element means one element or more than one element.

[0095] The word approximately or about when used in association with a numerical value (approximately 10, about 10) preferably means that the value may be the given value of 10 more or less 1% of the value.

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[0216] The invention is further explained in the following examples. These examples do not limit the scope of the invention, but merely serve to clarify the invention.

EXAMPLES

Example 1

Cross-protection Experiments with New Mild Isolates of the CH2 Strain of PepMV

[0217] VC1 is a mild isolate of the CH2 strain of pepino mosaic virus (PepMV). During wintertime, VC1 infection can produce unwanted symptoms in inoculated plants, namely, nettle-heads and growth retardation. New variants of the CH2 strain were produced in order to identify viruses that would offer cross-protection but with reduced unwanted symptoms. In this trial, the new mild isolate VCA is compared with VC1 for symptoms and their cross-protection effectivity. The RNA-dependent RNA-polymerase (RdRp) of VCA was sequenced and was found to comprise a mixture of closely related viruses having the sequence of SEQ ID NO:1. Additional sequencing was performed to determine the complete coding sequence of the RdRp which is depicted in SEQ ID NO:8. The overlapping sequences of SEQ ID NO:1 and 8 are identical with the exception of position 6290 of SEQ ID NO:8. AC is present at this position in SEQ ID NO:8 instead of a T in the SEQ ID NO:1. This may reflect a mutation, but does not lead to an amino acid change.

[0218] A sequence alignment of VCA with known PepMV viruses is depicted in FIG. 5. Three of the nucleotides in SEQ ID NO:1 (corresponding to positions 2605, 3156 and 3422 of SEQ ID NO:1) are unique to VCA in comparison to not only the known PepMV viruses, but also to the attenuated strain VC1. While not wishing to be bound by theory, it is believed that these two nucleotide changes alter the amino acid sequence, which in turn results in milder symptoms.

Set-up:

[0219] Tomato plants of the cultivar Merlice (on rootstock) were used. Each row of 12 plants was a different treatment. The plants were grown in two greenhouse compartments. The set temperatures were 20? C. at daytime and 18? C. at nighttime. The trial lasted 3 months. Inoculations were carried out by the rubbing protocol (see below).

[0220] Plants were innoculated first with mild isolates (VC1 or VCA) and tested with ELISA to determine infection. The results of the ELISA are shown below.

TABLE-US-00001 VC1 4/4+ VCA 4/4+ Negative control 0/4+

[0221] Approximately six weeks (39 days) after the first inoculation the plants were innoculated with the virulent isolate (CHD).

Results

[0222] Infection with the mild isolates VCA and VC1 resulted in very mild symptoms, namely, light bubbling on the young leaves and minor nettle-heads (FIG. 2). Infection with the virulent CH2 isolate CHD alone showed strong necrosis of the leaves and stems, from 3 weeks after inoculation of CHD (FIG. 1A). Treatment with VCA or VC1 protected plants from necrosis (see, e.g., FIG. 1B)

Conclusions

[0223] VCA is as mild as VC1 and maybe even milder. [0224] Both VCA and VC1 prevented symptoms of the virulent CH2 isolate CHD.

Example 2

Symptoms Observed from Treatment with PepMV Variants

[0225] VC1 infection can produce unwanted symptoms in inoculated plants, namely, nettle-heads and growth retardation. In this trial, the new mild isolate VCA is compared with VC1 for the induction of symptoms in treated plants.

[0226] Tomato plants of the cultivar Komeett were used. Inoculations were carried out by the rubbing protocol (see below). Plants were innoculated with mild isolates (VC1 or VCA) and tested two weeks later with ELISA to determine infection. It was found on average 95% of the virus inoculated plants had been infected. The virus-free plants remained free until the end of the test. Treatment with either VCA or VC1 resulted in the development of light symptoms, such as leaf misformation. However, plants treated with VCA (FIG. 3B) had more leaf volume and grew better than those treated with VC1 (FIG. 3C).

Example 3

Comparison of Symptoms in Plants Grown Under Optimal Conditions Versus Sub-Optimal Conditions

[0227] FIG. 4 depicts plants grown under optimal conditions versus sub-optimal conditions. In optimal growing conditions, plants treated with VC1 and VCA show a comparable level of very mild symptoms. However, in sub-optimal growing conditions, VC1 treated plants show much more severe symptoms than VCA treated plants. While not wishing to be bound by theory, it is believed that the nucleotide differences at position 2605, and 3156 of SEQ ID NO:1 result in an amino acid alteration as compared to VC1 and that one or both of these amino acid alterations is responsible for the milder symptoms.

Material and Methods:

Rubbing Protocol:

[0228] Knead frozen or fresh infected plant material. Take 7.5-10 ml of extracted plant sap or 7.5-10 ml virus suspension of virus product. [0229] Put the 7.5-10 ml in a plastic tray [0230] Dilute virus suspension 10-times with PBS [0231] Add 1-2% (w/v) carborundum [0232] Mix suspension well. [0233] Put disposable gloves on your hands. [0234] Stir with your fingers and thumb in the suspension. [0235] Inoculate two leaves on each plant in upper half on a leaflet by rubbing 5-times leaflet between thumb and index finger. Leaves should be damaged a little bit. (light discolouration, without holes). [0236] Dip for each plant your finger and inoculate the plant [0237] After inoculation, collect all residual material and put this in a garbage bin or waste container. The residual material should be disinfected by 100-200 ppm hypochlorite and after that it can be processed as regular waste. [0238] Test after 14 (?2) days the percentage of infected plants. This can be determined by the method ELISA.
High pressure spraying protocol: [0239] Usage of spraying liquid: 0.5 L/ m. [0240] Measure the needed amount of cold tap water and put this in the tank of the spraying cart. [0241] Prepare virus solution [0242] Add carborundum 800 gram/100 L to spraying liquid. [0243] Mix carborundum well in spray cart, by hand, cover your fore-arm in a disposable overboot, circulate to contents of the tank [0244] Pressure on nozzles in spraying arm: 12-15 bar [0245] Spraying width: 1.20 m, 6 nozzles [0246] Spraying height: 10-15 cm above the plants. [0247] Check the nozzles for blockages and evenness of spray. [0248] After inoculation, collect all residual material and put this in a garbage bin or waste container. The residual material should be disinfected by 100-200 ppm hypochlorite and after that it can be processed as regular waste. [0249] Test after 14 (?2) days the percentage of infected plants. This can be determined by the ELISA method.

ELISA for Measuring PepMV in Sample

[0250] Reagents for performing DAS-ELISA were obtained from PRIME Diagnostics, Wageningen, The Netherlands. The ELISAs were carried out according to the manufacturer's instructions.