HERBICIDE-RESISTANT TRANSGENIC PAPAYA PLANTS PRODUCED BY AN EFFICIENTPARTICLE BOMBARDMENT TRANSFORMATION METHOD

A system for the production of transgenic papaya (Carica papaya L.) pl ants using zygotic embryos and embryogenic callus as target cells for particle bombardment is described. Phosphinothricin (bar) and kanamyci n (npt II) resistance genes were used as selectable markers, and the g us gene (uidA) as a reporter gene. Selection with 100 mg/l kanamycin a nd 4 mg/l phosphinothricin (PPT) yielded a total of over 90 resistant embryogenic colonies from three independent experiments using embryoge nic callus as a target tissue. This represents an efficiency of 60 tra nsgenic clones per gram of fresh weight callus bombarded. The efficien cy of genetic transformation using zygotic embryos was lower, as only 8 independent resistant clones were recovered out of 645 bombarded zyg otic embryos, giving a efficiency of 1.24%. Subsequent subculture of t ransgenic somatic embryos both from zygotic embryos and embryogenic ca llus led to the development of plants with apparently normal morpholog y. Histological, fluorimetric assay for GUS, NPT II assay and DNA anal ysis (Southern hybridization) showed that kanamycin /PPT resistant pla nts carried and expressed the transgenes.