Transformation of Plum with the Papaya Ringspot Virus Coat Protein Gene and Reaction of Transgenic Plants to Plum Pox Virus

in Journal of the American Society for Horticultural Science
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  • 1 U.S. Department of Agriculture-Agricultural Research Service, Appalachian Fruit Research Station, 45 Wiltshire Road, Kearneysville, WV 25430
  • 2 U.S. Department of Agriculture Animal and Plant Health Inspection Service-Plant Protection Quarantine, Beltsville Agricultural Research Center-East Building 580, Beltsville, MD 20705
  • 3 U.S. Department of Agriculture-Agricultural Research Service, Foreign Disease-Weed Science Research Unit, Frederick, MD 21702
  • 4 Department of Plant Pathology, Cornell University, Geneva, NY 14456
  • 5 U.S. Department of Agriculture-Agricultural Research Service, Appalachian Fruit Research Station, 45 Wiltshire Road, Kearneysville, WV 25430
  • 6 U.S. Department of Agriculture-Agricultural Research Service, National Germplasm Resources Laboratory, Beltsville, MD 20705
  • 7 Molecular Biology Unit 7242, The Upjohn Company, Kalamazoo, MI 49007
  • 8 Department of Plant Pathology, Cornell University, Geneva, NY 14456

Transgenic plum plants expressing the papaya ringspot virus (PRV) coat protein (CP) were produced by Agrobacterium-mediated transformation of hypocotyl slices. Hypocotyl slices were cocultivated with Agrobacterium tumefaciens strain C58/Z707 containing the plasmid pGA482GG/CPPRV-4. This plasmid carries the PRVCP gene construct and chimeric NPTII and GUS genes. Shoots were regenerated on Murashige and Skoog salts, vitamins, 2% sucrose, 2.5 μm indolebutyric acid, 7.5 μm thidiazuron, and appropriate antibiotics for selection. Integration of the foreign genes was verified through kanamycin resistance, GUS assays, polymerase chain reaction (PCR), and Southern blot analyses. Four transgenic clones were identified. Three were vegetatively propagated and graft-inoculated with plum pox virus (PPV)-infected budwood in a quarantine, containment greenhouse. PPV infection was evaluated over a 2- to 4-year period through visual symptoms, enzyme-linked immunosorbent assay, and reverse transcriptase PCR assays. While most plants showed signs of infection and systemic spread of PPV within l-6 months, one plant appeared to delay the spread of virus and the appearance of disease symptoms. Virus spread was limited to basal portions of this plant up to 19 months postinoculation, but, after 32 months symptoms were evident and virus was detected throughout the plant. Our results suggest that heterologous protection with PRVCP, while having the potential to delay PPV symptoms and spread throughout plum plants, may not provide an adequate level of long-term resistance.

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