TRANSFORMATION OF PLUM WITH THE PAPAYA RINGSPOT VIRUS COAT PROTEIN GENE AND REACTION OF TRANSGENIC PLANTS TO PLUM POX VIRUS

Transgenic plum plants expressing the papaya ringspot virus (PRV) coat protein (CP) were produced by Agrobacterium-mediated transformation o f hypocotyl slices. Hypocotyl slices were cocultivated with Agrobacter ium tumefaciens strain C58/Z707 containing the plasmid pGA482GG/CPPRV- 4. This plasmid carries the PRVCP gene construct and chimeric NPTII an d GUS genes. Shoots were regenerated on Murashige and Skoog salts, vit amins, 2% sucrose, 2.5 mu M indolebutyric acid, 7.5 mu M thidiazuron, and appropriate antibiotics for selection. Integration of the foreign genes was verified through kanamycin resistance, GUS assays, polymeras e chain reaction (PCR), and Southern blot analyses. Four transgenic cl ones were identified. Three were vegetatively propagated and graft-ino culated with plum pox virus (PPV)-infected budwood in a quarantine, co ntainment greenhouse. PPV infection was evaluated over a 2- to ii-year period through visual symptoms, enzyme-linked immunosorbent assay, an d reverse transcriptase PCR assays. While most plants showed signs of infection and systemic spread of PPV within la months, one plant appea red to delay the spread of virus and the appearance of disease symptom s. Virus spread was limited to basal portions of this plant up to 19 m onths postinoculation, but, after 32 months symptoms were evident and virus was detected throughout the plant. Our results suggest that hete rologous protection with PRVCP, while having the potential to delay PP V symptoms and spread throughout plum plants, may not provide an adequ ate level of long-term resistance.