Multicellular living organisms and unmodified parts thereof and – Method of introducing a polynucleotide molecule into or... – The polynucleotide confers pathogen or pest resistance
Patent
1997-03-17
2000-10-17
Nelson, Amy J.
Multicellular living organisms and unmodified parts thereof and
Method of introducing a polynucleotide molecule into or...
The polynucleotide confers pathogen or pest resistance
435440, C12N 1582
Patent
active
061335053
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to transgenic plants that are resistant or tolerant to DNA viruses that are pathogenic in plants.
The invention relates more particularly to the seeds from these transgenic plants, which are capable of germinating into plants exhibiting this criterion of resistance or tolerance to phytopathogenic DNA viruses.
The invention also covers the methods of obtaining these plants and seeds.
DESCRIPTION OF THE RELATED ART
Phytopathogenic DNA viruses are essentially represented by single-stranded DNA viruses (ss) and double-stranded DNA viruses (ds).
The double-stranded DNA viruses mainly comprise the Badnaviruses and the Caulimoviruses.
The single-stranded DNA viruses mainly comprise the geminiviruses and other exotic ssDNA viruses.
Among these phytopathogenic DNA viruses, the geminiviruses have received particular study. These are plant viruses which have a considerable impact on agricultural production in many tropical and subtropical regions (Harrison, 1985). They are single-stranded circular DNA viruses, characterized by a structure that is unique in the world of viruses: a capsid in the shape of a double icosahedron (Francki et al., 1980). According to their genomic organization, a distinction is drawn between on the one hand the geminiviruses with a bipartite genome consisting of two DNA molecules A and B, each of about 2.8 kilobases (kb) (as in the case of the African Cassava Mosaic Virus (ACMV) and of the Tomato Golden Mosaic Virus (TGMV)), and on the other hand geminiviruses with a monopartite genome with a single DNA molecule of about 2.8 kb (as in the case of the Maize Streak Virus (MSV), the Wheat Dwarf Virus (WDV) and the Beet Curly Top Virus (BCTV)). Two subgroups have been identified, according to the transmission vector of the virus. Some geminiviruses are transmitted by the whitefly Bemisia tabaci, and until recently were all regarded as having a bipartite genome (ACMV, TGMV). The other geminiviruses are transmitted by leaf-hoppers (Cicadulina sp.) and they all have a monopartite genome (MSV, WDV and BCTV); for a review see Lazarowitz, 1992a.
The tomato yellow leaf curl virus (TYLCV) is an exception to this classification. Thus, although it is transmitted by Bemisia tabaci, its genome is monopartite (Kheyr-Pour et al., 1991; Navot et al., 1991). Only an isolate of TYLCV from Thailand has been described as having a bipartite genome (Rochester et al., 1990).
TYLCV is responsible for considerable damage to tomato crops, with losses of up to 50 to 60% (Allex et al., 1994). In this species, the characteristic symptoms include stunted appearance of the plant, leaf curl and yellowing, a bush-like appearance due to shortening of the internodes and arrest of floral growth. This disease, which already affects numerous regions (Mediterranean basin, Near and Middle East, extreme south of Asia, and Sahelian Africa), is spreading at present (Czosnek et al., 1990). Metropolitan France is spared for the present, but the French Antilles have been affected for two years (Hostachy and Allex, 1993).
Analysis of the viral genome sequence of TYLCV reveals the existence of six open reading frames (ORFs) able to code for products with size greater than 10 kDa. These ORFs are located both on the viral strand (ORFs V1 and V2) and on the complementary strand (ORFs C1, C2, C3 and C4) (Kheyr-Pour et al., 1991); see FIG. 1.
Transcription of the viral genome of the geminiviruses is bidirectional (Hanley-Bowdoin et al., 1988, Accotto et al., 1989). It takes place on either side of the intergenic region (IR), or region common to the two components of DNA of bipartite-genome viruses. The IR of about 200 nucleotides (nt) has a sequence of about 30 nt which could adopt a rod-loop structure. Using mutation analysis, this potential rod-loop structure was shown to be essential to replication of the viral DNA.
Replication of the viral genome passes through a double-stranded intermediate form, in the nuclei of the infected cells (Davies and Stanley, 1989). The presence, at the
REFERENCES:
patent: 5850023 (1998-12-01), Elmer et al.
Von Arnim et al. Inhibition of African cassava mosaic virus systemic infection by a movement protein from the related geminivirus tomato golden mosaic virus. Virology. 187:555-564, Apr. 1992.
Longstaff et al. Extreme resistance to potato virus X infection in plants expressing a modified component of the putative viral replicase. The EMBO Journal. 12(2):379-386, 1993.
Jupin et al. DNA replication specificity of TYLCV geminivirus is mediated by the amino-terminal 116 amino acids of the Rep protein. FEBS Letters. 362:116-120, 1995.
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Centre National de la Recherche Scientifique
Nelson Amy J.
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