VIRUS RESISTANT PAPAYA PLANTS DERIVED FROM TISSUES BOMBARDED WITH THE COAT PROTEIN GENE OF PAPAYA RINGSPOT VIRUS

Papaya ringspot virus (PRV) is a serious disease of papaya (Carica papaya L.) that has only been partially controlled by conventional methods. An alternative control method is coat protein-mediated protection (CPMP) through the transfer and expression of the PRV coat protein (cp) gene in papaya. We report an efficient gene transfer system utilizing microprojectile-mediated transformation of 2,4-D-treated immature zygotic embryos with a plasmid construction that contains the neomycin phosphotransferase H (NPTII) and beta-glucuronidase (GUS) genes flanking a PRV cp gene expression cassette. Putative transgenic R(o) papaya plants, regenerated on kanamycin-containing medium, were assayed for GUS and PRV coat protein expression, for the presence of NPTH and PRV cp genes [with the polymerase chain reaction (PCR) and genomic blot hybridization analysis], and for PRV cp gene transcripts by Northern analysis. Four R(o) transgenic plant lines that contained the PRV cp gene showed varying degrees of resistance to PRV, and one line appeared to be completely resistant. These results represent the first demonstration that CPMP can be extended to a tree species such as papaya.